JP2006009099A - Film thickness control method and apparatus, and optical multilayer film manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease noise in a transmitted light quantity caused by interference of light on a substrate and to control the film thickness with high accuracy. <P>SOLUTION: A carousel type sputtering apparatus which gives preferable uniformity in the film thickness without autorotation of a substrate during film formation is used, as well as a substrate 18 having the back face 18B inclined at a predetermined angle with respect to the film formation face 18A of the substrate is used. The inclination angle θ of the back face 18B with respect to the film formation face 18A is preferably in a range of 0°<θ≤2°. The substrate is fixed so that the thickest part or the thinnest part of the substrate 18 is aligned in the vertical direction of a substrate holder. The optical axis is preferably adjusted in such a manner that the light outputted from a projecting unit is perpendicular to the film formation surface 18A on the film formation surface 18A. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film thickness control method and apparatus for producing a thin film using a sputtering apparatus, and an optical multilayer film manufacturing method, and more particularly to a WDM filter used in WDM (Wavelength Division Multiplexing) technology. The present invention relates to a film thickness control method and apparatus suitable for manufacturing the optical multilayer film, and an optical multilayer film manufacturing method.

  A WDM filter used in the WDM technology is formed by combining a low refractive index material and a high refractive index material and laminating an extremely large number of layers (for example, about 100 layers) on a glass substrate. In the production of such an optical multilayer film, it is extremely important to accurately form the film thickness of each layer as designed, and for this reason, the film thickness monitoring system provided in the thin film forming apparatus is used for film formation or formation. It is necessary to precisely control the film thickness by monitoring the transmitted light amount (or transmittance) of the monitoring light of the glass substrate after film formation (see Patent Documents 1 to 3).

Conventional film thickness monitoring systems use a laser light source or ASE (Amplified Spontaneous Emission) light source that has a large received light quantity (excellent S / N ratio) and excellent wavelength monochromaticity for the light projecting unit. It has been. In the case of a transmission type film thickness monitoring system using a laser light source having a long coherent length as a light projecting unit, in order to reduce the noise of the transmitted light amount generated by light interference on the glass substrate, the optical film is formed in advance. It is necessary to form a high-performance low-reflection film on the back surface (the surface opposite to the film formation surface) of the glass substrate.
International Publication No. 02/063064 Pamphlet JP 2002-340523 A JP 2003-121118 A

  However, it is extremely difficult to produce a high-performance low-reflection film, and it is one of the factors that increase the product cost.

  The present invention has been made in view of such circumstances, and it is possible to easily reduce the noise of the transmitted light amount and control the film thickness with high accuracy without requiring a high-performance low-reflection film. It is an object of the present invention to provide a control method and apparatus, and an optical multilayer film manufacturing method using the same.

  In order to achieve the above object, an invention according to claim 1 is a film thickness control method for controlling a film thickness of a film formed on a substrate, wherein the substrate back surface opposite to the film formation surface of the substrate is formed on the substrate back surface. A substrate having a shape inclined at a predetermined angle with respect to the film surface is fixed to a substrate holder of a sputtering apparatus, and film formation is performed by the sputtering apparatus, and light is emitted from a light projecting unit toward the substrate on the substrate holder. Irradiate the received light by the light receiving unit located on the opposite side of the light projecting unit across the substrate, measure the transmitted light amount according to the received light amount, and transmit the transmitted light amount data of the film-coated substrate based on the transmitted light amount And obtaining a desired film thickness by controlling a parameter that affects the amount of film formation based on the measurement result.

  According to the present invention, since the back surface of the substrate used for film formation has a shape (substantially wedge shape) inclined at a predetermined angle with respect to the film formation surface, light having a long coherent length is emitted from the light projecting unit. Even in this case, optical interference on the substrate (interference between light reflected in the substrate) hardly occurs, and noise components due to optical interference on the substrate itself can be greatly reduced. This eliminates the need for the formation of a high-performance low-reflection film on the back surface of the substrate, which has been conventionally required, and realizes highly accurate film thickness control.

  When the film thickness is monitored during film formation, and the information is fed back to the control system to control the film formation, for example, the power control of the sputtering power supply, the substrate holder (drum) can be controlled as parameters that affect the film formation amount. The rotation speed, film formation time, shutter opening / closing degree, sputtering pressure, etc. are controlled. The film formation amount is controlled by controlling at least one of various parameters represented by these.

  In addition, in the conventional apparatuses disclosed in Patent Documents 2 and 3, it is necessary to rotate the substrate during film formation in order to improve mass productivity (film thickness distribution). The sputtering apparatus has a feature that practically sufficient film thickness uniformity can be obtained without rotating the substrate during film formation.

  If the transmitted light amount is measured while rotating the back-tilted substrate used in the present invention, the transmitted light emission direction of the substrate changes according to the rotation position of the substrate, so that the transmitted light amount can be measured accurately. Instead, it may be a factor that increases noise.

  Therefore, in the present invention, by using a carousel type sputtering apparatus that does not require the rotation of the substrate, the noise of the transmitted light amount is reduced in combination with the inclined structure on the back surface of the substrate.

  The invention according to claim 2 relates to an aspect of the film thickness control method according to claim 1, and the substrate with respect to the film formation surface is considered in consideration of noise reduction of the transmitted light amount due to light interference in the substrate and handling property of the substrate. The predetermined angle θ on the back surface is preferably 0 ° <θ ≦ 2 °, more preferably 0.3 ° ≦ θ ≦ 2 °, and particularly preferably 0.5 ° ≦ θ ≦ 2 °.

  A third aspect of the present invention relates to an aspect of the film thickness control method according to the first or second aspect, wherein the substrate has a thickest portion or a thinnest portion having the inclined surface having the predetermined angle as a substrate holder. It is fixed to the substrate holder so as to be in the vertical direction.

  In the carousel type sputtering apparatus, film formation is performed while the substrate holder attached to the rotating drum rotates, so the substrate is fixed in a posture in which the thickest part or the thinnest part of the substrate is directed in the vertical direction of the substrate holder. It is preferable. By doing so, the thickness of the substrate becomes constant along the rotation direction of the drum (that is, the scanning line of the light emitted from the light projecting unit), and the noise of the transmitted light amount can be further reduced.

  The invention according to a fourth aspect relates to an aspect of the film thickness control method according to the first, second, or third aspect, wherein the optical axis of the light emitted from the light projecting unit is controlling the film thickness of the film formation surface of the substrate. In any of the above, the film is adjusted to be perpendicular to the film formation surface.

  An embodiment in which an optical axis adjustment mechanism is provided so that the optical axis can be finely adjusted according to the inclined shape of the back surface of the substrate is preferable.

  The sputtering apparatus used for the film thickness control method according to any one of claims 1 to 4, as shown in claim 5, is a chamber and is rotatably installed in the chamber, and has a polygonal cross section. It comprises a circular drum, the substrate holder mounted on the outer peripheral surface of the drum, and a magnetron sputtering source disposed inside the chamber wall.

  The invention according to claim 6 provides a film thickness control apparatus for achieving the object. That is, the invention according to claim 6 is a film thickness control device for controlling the film thickness of the film formed on the substrate, wherein the substrate back surface opposite to the film forming surface of the substrate is predetermined with respect to the film forming surface. A substrate holding mechanism for fixing a substrate having a shape inclined at an angle to a substrate holding portion of a sputtering apparatus; a light projecting means for irradiating light toward the substrate held by the substrate holding mechanism; and A light receiving means for receiving the passed light and outputting an electrical signal corresponding to the amount of received light, and measuring the amount of transmitted light according to the amount of received light from the electrical signal output from the light receiving means, and with a film based on the amount of transmitted light Computational processing means for acquiring transmitted light amount data of the substrate, and control means for controlling a parameter that affects the film formation amount based on the transmitted light amount data obtained by the arithmetic processing means.

  According to a seventh aspect of the present invention, the substrate holding mechanism fixes the substrate so that the thickest portion or the thinnest portion of the substrate having the inclined surface having the predetermined angle is in the vertical direction. It is preferable.

  Furthermore, as shown in claim 8, there is provided an optical axis adjusting mechanism for adjusting an optical axis so that light emitted from the light projecting means is perpendicular to the film forming surface of the substrate. A configuration is preferred.

  The invention according to claim 9 provides a method for producing an optical multilayer film for achieving the object. That is, the invention according to claim 9 is a manufacturing method for manufacturing an optical multilayer film formed by alternately laminating two types of thin films having different refractive indexes on a substrate, wherein the substrate is opposite to the film formation surface of the substrate. A magnetron sputter for forming a low refractive index film using a substrate having a shape in which the back surface is inclined at a predetermined angle with respect to the film forming surface and to which a target for forming a relatively low refractive index thin film is attached. And a magnetron sputtering source for forming a high refractive index film to which a target for forming a thin film having a relatively high refractive index is attached, and the substrate is mounted on a substrate holder of the sputtering apparatus. Film is formed, and light is emitted from the light projecting unit toward the substrate on the substrate holder during film formation, and the transmitted light is received by the light receiving unit and the amount of transmitted light corresponding to the amount of light received is measured. And The transmission light amount data of the substrate with film is acquired based on the transmitted light amount, and a thin film having a desired film thickness is formed by controlling a parameter that affects the film formation amount based on the measurement result. . The total number of layers of the optical multilayer film is preferably 2 to 2000, and the total layer thickness is preferably 50 nm to 400 μm.

  According to the method for producing an optical multilayer film according to the present invention, the film thickness can be accurately grasped by a combination of a carousel type sputtering apparatus that does not require rotation of the substrate and a substrate shape that avoids optical interference with the substrate. Thus, the film thickness of each layer can be formed as designed. In addition, it is not necessary to form a high-performance low-reflection film on the back surface of the substrate, which has been conventionally required, and cost reduction can be realized.

  According to the present invention, by using a sputtering apparatus and using a substrate having a shape in which the back surface of the substrate is inclined at a predetermined angle with respect to the film formation surface of the substrate, the amount of transmitted light generated by light interference on the substrate can be reduced. Noise can be greatly reduced, and high-precision film thickness control can be realized.

  Hereinafter, preferred embodiments of a film thickness control method and apparatus and an optical multilayer film manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic plan view showing a configuration of a sputtering apparatus for forming an optical multilayer film to which a film thickness control apparatus according to an embodiment of the present invention is applied. 1 includes a drum (not shown in FIG. 1, reference numeral 17 in FIG. 5) and an outer peripheral surface of the drum 17 in a substantially cylindrical chamber 12 having a height of 2 m and a diameter of 1.5 m. A carousel type sputter having a structure in which each substrate holder 14 constituting a regular dodecagon having a diameter of 1 m is rotatably supported around a central axis 16 of a drum 17. Device.

  The chamber 12 serving as a reaction chamber is connected to an exhaust pump (not shown) and can obtain a low pressure necessary for sputtering. Although not shown, the chamber 12 is provided with a gas supply means for introducing a gas necessary for sputtering and a loading door. The inner wall of the chamber 12 has a shape (inner peripheral shape) that faces the drum 17 at a substantially predetermined interval.

  Although details will be described later (FIGS. 4 to 9), a film-forming substrate (for example, a glass substrate) 18 is attached to each substrate holder 14, and the substrate holder 14 is attached to a drum 17 by a rotary drive device (not shown). Along with the rotation, it rotates at a constant rotation speed (for example, 6 rpm). As the drum 17 rotates, for example, a low refractive index film or a high refractive index film is formed on the substrate 18 mounted on the substrate holder 14. An optical multilayer film is formed by stacking a combination of a high refractive index film and a low refractive index film.

  As shown in FIG. 1, an AC magnetron 20 for forming a low refractive index film and an AC magnetron 30 for forming a high refractive index film are installed inside the chamber 12.

  The AC magnetron 20 for forming a low refractive index film is an AC magnetron sputtering source in which one AC power source 26 is connected to the two magnetron portions 22 and 23 and the anode / cathode relationship is alternately switched at a predetermined frequency. .

  Similarly, in the AC magnetron 30 for forming a high refractive index film, one AC power source 36 is connected to the two magnetron portions 32 and 33, and the AC magnetron sputtering is used to alternately switch the anode / cathode relationship at a predetermined frequency. Is the source.

  The operating principles of the AC magnetrons 20 and 30 are disclosed in JP-A-5-222530, JP-A-5-222231, JP-A-6-212421, and JP-A-10-130830. In general, an AC magnetron is a magnetron device in which two targets are arranged side by side, and when one target is a cathode, the other is an anode, and the cathode and anode are switched at a frequency of several tens of kHz. By performing the above, an oxide film, a nitride film, or the like can be formed stably and at high speed.

  Shutters 28 and 38 that can be opened and closed are provided between the AC magnetrons 20 and 30 and the substrate 18, respectively. Although FIG. 1 shows a state in which both shutters 28 and 38 are opened, only the shutter 28 or 38 of one sputtering source used for film formation is selectively opened, and the other sputtering not used for film formation is performed. By closing the source shutter 38 or 28, the target can be prevented from deteriorating. By closing the shutter 28 or 38 when a desired film thickness is obtained by the reactive sputtering process, the film formation reaction can be reliably stopped.

  The sputtering apparatus 10 is a means for measuring the film thickness during film formation (film thickness monitoring system). The light source 40, the optical fiber 42, the light projecting unit 44, the light receiving unit 46, the light receiving processing unit 48, and a personal computer (hereinafter “ A variable wavelength laser is suitably used for the light source 40 provided with 50. The light emitted from the light source 40 is guided to the light projecting unit 44 through the optical fiber 42. The light projecting unit 44 is installed inside the substrate holder 14 (inside the drum 17), and light is emitted from the light projecting unit 44 toward the rotating substrate 18.

  A light receiving unit 46 is installed outside the chamber 12, and a window (not shown) for guiding light to the light receiving unit 46 is provided on the outer wall of the chamber 12. The light transmitted through the substrate 18 is received by the light receiving unit 46, converted into an electrical signal corresponding to the amount of received light, and then sent to the light receiving processing unit 48. The light reception processing unit 48 performs predetermined signal processing on the received signal and converts the received signal into an electrical signal called a transmitted light amount corresponding to the amount of received light. The transmitted light amount processed by the light receiving processing unit 48 is sent to the personal computer 50.

  The personal computer 50 includes a central processing unit (CPU), functions as an arithmetic processing unit, and acquires transmitted light amount data of the film-coated substrate based on the transmitted light amount. The amount of transmitted light is measured as follows. FIG. 2 is a schematic diagram showing how the amount of transmitted light is measured. 2A to 2C, the drum 17 to which the substrate 18 is attached rotates counterclockwise in the drawing, and the monochromatic laser light 44A emitted from the light projecting unit 44 passes through the substrate 18. The light receiving unit 46 receives the light. The wavelength of the monochromatic laser beam 44A is not particularly limited, but is preferably 350 to 2000 nm from the viewpoint of glass absorbability.

  As shown in FIGS. 2A to 2C, when monitoring the film thickness during film formation, the incident angle of the monochromatic laser beam 44 </ b> A with respect to the film formation surface 18 </ b> A of the substrate 18 sometimes varies with the rotation of the drum 17. It changes every moment. For this reason, the amount of received light measured through the substrate during film formation (drum rotation) can change from moment to moment depending on the incident angle. The amount of light received continuously from the light receiving unit 46 during the rotation of the drum 17 is converted into an electrical signal called transmitted light amount. That is, if the amount of received light is continuously obtained from the light receiving unit 46 while the drum 17 is rotating, the amount of transmitted light at the incident angle corresponding to the position of the substrate (substrate with film) 18 can be obtained.

  FIG. 2B is a diagram when the incident angle is 0 °, and at this time, the monochromatic laser light 44 </ b> A passes through the center of the substrate 18. 2A is a negative incident angle state, and FIG. 2C is a positive incident angle state with the incident angle of light on the film formation surface of FIG. Shall.

  An example of the spectrum of the transmitted light amount obtained by the method as described above is shown in FIG. In FIG. 3, the horizontal axis represents the incident angle of light on the film formation surface, and the vertical axis represents the amount of transmitted light at this angle. In FIG. 3, the region where a transmitted light amount of about 0.63 V is obtained is when the laser light passes through the substrate.

  Next, the transmitted light amount data in a certain part of the film-coated substrate is acquired from the transmitted light amount at each incident angle. The portion with the film-coated substrate is not particularly limited as long as it is one point within the range where the film-coated substrate is formed, but from the point of film thickness control, it is the center point of the film-coated substrate. Is preferred. In addition, in order to acquire transmitted light amount data useful for control, other processing (moving average processing for noise reduction, soft processing for acquiring data of one point of the substrate with film, etc.) is performed on the transmitted light amount. May be.

  The personal computer 50 shown in FIG. 1 also functions as a control device that controls each sputtering power source (26, 36). Further, the personal computer 50 can perform light emission control (including light amount control) of the light source 40, rotation control of the substrate holder 14, pressure control of the chamber 12, supply control of introduced gas, and opening / closing control of the shutters 52 and 54. . For each substrate 18 attached to the drum 17, the transmitted light amount data of a certain portion of the film-coated substrate is calculated for each drum rotation, and the film formation amount is calculated based on the calculated transmitted light amount data of the film-coated substrate for each drum rotation. While controlling the sputter power control, the rotation speed of the substrate holder, the film formation time, the shutter opening / closing degree, and the sputter control, which are influential parameters, the film formation is stopped when the transmitted light amount data reaches a desired value. The personal computer 50 incorporates programs and various data necessary for each control.

  In the film thickness monitoring system of the present embodiment, for example, the light source 40 may be a wavelength tunable laser module 8168B built in a light wave measurement system 8164B manufactured by Agilent Technologies. An optical head 81624B manufactured by Agilent Technologies is used for the light receiving unit 46, and a glass substrate WMS02, WMS13, or WMS15 manufactured by OHARA can be preferably used for the substrate 18. Note that the light wave measurement system 8164B has a function of receiving an electrical signal from the light receiving unit and processing the data.

  In order to eliminate the noise of the transmitted light amount due to the light interference at the substrate 18 during the film thickness monitoring, the substrate 18 of the present embodiment has a surface opposite to the film forming surface 18A as shown in FIG. (Referred to as “back surface of substrate”) 18B is used in a shape that is inclined at a predetermined angle θ, for example, polished so as to have a shape that is inclined at θ = 1 °. In FIG. 4, the right view is a view of the substrate 18 as viewed from the rotation direction, and the left view is a view of the substrate 18 as viewed from the direction of the rotation axis 16. The predetermined angle (here, the polishing angle) θ does not necessarily have to be 1 °, and it is sufficient if it is larger than 0 °.

  However, the arrangement and performance of the optical system such as the distance between the light projecting unit 44 and the substrate 18 and the tilt angle that can be adjusted by the light projecting unit optical axis adjusting member (described later), and the size and thickness t of the substrate 18 In consideration, the predetermined angle θ is preferably greater than 0 ° and 2 ° or less (that is, 0 ° <θ ≦ 2 °), and 0.3 ° ≦ θ ≦ 2 °, 0.5 ° ≦ θ ≦. 2 ° is particularly preferable. If the predetermined angle θ exceeds 2 °, the processing time of the substrate 18 becomes long, which is problematic in terms of productivity.

  The thickness t of the substrate 18 is not particularly limited, and a standard value is about t = 6 mm. Although the circular substrate 18 is illustrated in this example, the planar shape of the substrate 18 is not particularly limited when the present invention is implemented, and may have various shapes such as a polygon and an ellipse.

  By configuring the substrate 18 as described above, even when light having a long coherent length from the light projecting unit 44 is irradiated, optical interference on the substrate 18 hardly occurs and is caused by optical interference of the substrate itself. The noise of the transmitted light amount can be greatly reduced. Also, with this configuration, it is not necessary to form a high-performance low-reflection film that has been conventionally required, and high-precision film thickness control can be realized.

  Here, the structure of the substrate holder 14 will be described.

  FIG. 5 is a perspective view of the substrate holder 14 attached to the drum 17. As shown in the figure, the rectangular substrate holder 14 is attached to the outer peripheral surface of a cylindrical drum 17 and rotates integrally with the drum 17 installed rotatably. In addition, the shape of the drum 17 is not limited to a cylindrical shape, and may be a polygonal cylindrical shape (a cross section is a polygonal shape) or the like.

  A light passage opening (hereinafter referred to as “measuring hole”) 14A for film thickness measurement is formed at a substantially central portion in the vertical direction of the substrate holder 14, and the substrate 18 (FIG. 5) is formed through the measuring hole 14A. Light is irradiated to the middle (not shown).

  6 is a front view of the base plate 60 constituting the substrate holder 14, FIG. 7 is a front view of the substrate holding unit 62 attached to the dotted line portion of the base plate 60 shown in FIG. 6, and FIG. 8 is the substrate holding unit of FIG. FIG. 9 is a view when 62 is viewed from the direction of arrow A, and FIG. 9 is a view when viewed from the direction of arrow B in FIG.

  As shown in FIG. 6, the base plate 60 has the measurement hole 14A, and the base plate 60 is fixed to the outer peripheral surface of the drum 17 as described in FIG. Reference numeral 61 in FIG. 6 denotes a bolt through hole for passing a fixing bolt (not shown). The substrate holding unit 62 shown in FIGS. 7 to 9 is attached to the portion indicated by the dotted line in FIG.

  As shown in FIG. 7, the substrate holding unit 62 has a structure in which the substrate 18 is sandwiched between the holding frame plate 64 and the pressing plate 65. The opening 65A of the pressing plate 65 has a diameter smaller than the diameter of the substrate 18, and a thin film is formed on the substrate surface exposed from the opening 65A.

  In FIG. 7, reference numeral 66 denotes a bolt for fixing the presser plate 65 to the holding frame plate 64, and reference numeral 67 denotes a bolt for fixing the holding frame plate 64 to the base plate.

  In the holding frame plate 64, the through holes 68 of the bolts 67 are formed in an elongated hole shape that is long in the left-right direction so that the attachment position can be finely adjusted in the left-right direction in FIG. A guide member 69 is provided along the upper and lower sides of the holding frame plate 64, and the holding frame plate 64 can be slid along the guide member 69.

  As shown in FIG. 9, the holding frame plate 64 has a substrate support surface 64 </ b> A that stably supports the substrate 18 in accordance with the back surface inclination angle (the predetermined angle θ described in FIG. 4) of the substrate 18. (See FIG. 9) The film forming surface 18A of the substrate 18 is held together with the presser plate 65 in a state substantially parallel to the vertical direction.

  The posture of the substrate 18 (the angle of the film forming surface 18A) can be adjusted by replacing the substrate support surface 64A with another holding frame plate having a different slope angle. Of course, a mechanism capable of finely adjusting the posture of the substrate 18 may be provided.

  With the above configuration, the angle can be adjusted for each substrate holder 14 installed on each surface of the drum 17.

  In order not to impede characteristics other than the noise reduction or disappearance of the transmitted light amount in the film thickness monitoring, the substrate 18 has a thickest portion or a thin portion having an inclined surface with a predetermined angle θ in the vertical direction of the substrate holder 14. Fix to the substrate holder 14. In FIG. 9, the thickest portion is fixed so as to be below the substrate holder.

  The position of the substrate 18 in the substrate holder is not limited to the vicinity of the center of the substrate holder 14, and a plurality of substrates may be fixed. For example, each substrate holder 14 can be mounted with nine circular substrates each having a thickness (thickest portion) of 6 mm and a diameter of 10 cm arranged in the vertical direction.

  Next, the optical axis adjustment mechanism of the light projecting unit will be described.

  10 is a side view of the optical axis adjusting member that supports the light projecting unit 44 described in FIG. 1, FIG. 11 is a plan view, and FIG. 12 is a view as seen from the direction of arrow C in FIG.

  As shown in these drawings, the optical axis adjusting member 70 includes a tapered base 71 and a fixing member 72 having an inclined surface for holding the light projecting portion 44 at a predetermined turning angle ψ. Reference numeral 74 is a support plate, and reference numeral 75 is a through hole for a fixing bolt. The optical axis adjusting member 70 is attached to a fixing base (not shown) using a fixing bolt.

  Grooves 71A and 72A for sandwiching the light projecting portion 44 are formed on the taper base 71 and the fixing member 72, respectively, and the space between the grooves (light projection indicated by reference numeral 77 in FIGS. 11 and 12). The light projecting portion 44 (not shown in FIGS. 10 to 12) is sandwiched in the portion holding hole) and fixed with a bolt (not shown). In FIG. 12, reference numeral 78 denotes a hole (a female screw on the support plate 74 side) into which a bolt (not shown) for fixing the taper base 71 to the support plate is inserted, and reference numeral 79 fixes the fixing member 72 to the taper base 71. This is a hole (a taper base 71 side is a female screw) into which a bolt (not shown) is inserted.

  When changing the turning angle ψ, the angle is replaced with a taper base having an inclined surface of another angle. Of course, a mechanism that can freely finely adjust the direction of the optical axis may be used.

  Using this optical axis adjusting member 70, the optical axis is adjusted by adjusting the turning angle ψ so that the light emitted from the light projecting unit 44 is perpendicular to the film forming surface 18A on the film forming surface 18A. Alternatively, instead of or in combination with the optical axis adjustment by the optical axis adjustment member 70, the angle and position of the substrate holder optical axis adjustment member described in FIG. 7 are finely adjusted.

The light axis adjusting member 70 of the light projecting unit may have a function capable of adjusting the angle not only in the turning direction but also in the carousel rotation direction. In addition, the light emitted from the light projecting unit 44 does not necessarily have to be perpendicular to the film forming surface 18A on the film forming surface 18A, and may have an arbitrary angle. Examples of the low refractive index film used in the present invention include SiO ₂ , and examples of the high refractive index film include Nb ₂ O ₅ , TiO ₂ , and Ta ₂ O ₅ .

Next, a method for producing a band-pass filter using the sputtering apparatus 10 and the film thickness monitoring system (control apparatus) configured as described above will be described. Here, an example will be described in which SiO ₂ is formed as a low refractive index film and Nb ₂ O ₅ is formed as a high refractive index film by reactive sputtering to form a bandpass filter.

  The film configuration of the bandpass filter to be manufactured is, for example, the 26-layer film shown below.

Glass substrate / (H / L) × 6 / H × 2 / (L / H) × 6 / L (1)
H and L in the film configuration shown in (1) above mean that the optical film thickness is λ / 4 for the high refractive index film and the low refractive index film (where λ = 1550 nm and At this time, the physical film thickness of H is 174.5 nm, and the physical film thickness of L is 264.5 nm.

4 to 9, the substrate 18 is set on the substrate holder 14 with the thickest part at the bottom and the thinnest part at the top, and the optical axis adjusting member 70 in FIGS. The optical axis is adjusted, and then the chamber 12 is roughly evacuated to 5 Pa with a rotary pump and then evacuated to 1 × 10 ⁻³ Pa with a cryopump.

  Next, 100 sccm of argon gas and 30 sccm of oxygen gas are introduced into the chamber through a mass flow controller. The gas pressure at this time is 0.4 Pa.

In order to form the Nb ₂ O ₅ film, AC power of 20 kW is supplied to the AC magnetron 30 to which the Nb target is attached, respectively, and the shutter 38 disposed between the target and the substrate is closed to perform a preliminary discharge for 5 minutes. Then, the shutter 38 is opened and film formation is started.

  The amount of transmitted light during film formation is measured by the following method using a film thickness monitoring system. A monochromatic laser beam of 1550 nm is emitted from the light source 40, and this light passes through the substrate 18 attached to the rotating drum 17 and enters the light receiving unit 46. The received light amount of the laser light incident on the light receiving unit 46 is converted into an electrical signal called transmitted light amount, and then taken into the personal computer 50 as transmitted light amount data.

  As described above with reference to FIG. 2, the transmitted light amount is acquired for each substrate 18 attached to the drum 17, and the transmitted light amount data of the film-coated substrate is calculated based on the transmitted light amount for each drum rotation at the center of the substrate 18. To do. Based on the calculated transmitted light amount data of the film-coated substrate for each drum rotation, the film formation is stopped when the transmitted light amount data reaches a desired value.

Next, in order to form the SiO ₂ film, AC power of 20 kW is supplied to the AC magnetron 20 to which the Si target is attached, respectively, and a preliminary discharge is performed for 5 minutes, and then the shutter 28 is opened to start the film formation. To do.

The measurement of the amount of transmitted light at the time of film formation and the calculation of the amount of transmitted light data of the substrate with the film are the same as the measurement method at the time of forming the Nb ₂ O ₅ film. Thus, the film formation is stopped when the transmitted light amount data of the film-coated substrate 18 reaches a desired value.

The target optical multilayer film is formed by alternately repeating the film formation process of the high refractive index material (Nb ₂ O ₅ ) and the film formation process of the low refractive index material (SiO ₂ ).

  FIG. 3 described above is an example of the transmitted light amount (voltage value) acquired by the above-described method and apparatus when the first layer of the bandpass filter is formed (carousel rotation speed: 100th rotation). In FIG. 3, the horizontal axis indicates the incident angle of light on the film formation surface, and the vertical axis indicates the amount of transmitted light obtained from the light receiving unit 46.

  In the illustrated transmitted light amount, the ratio of noise to light amount is as small as 0.01 or less, and the transmitted light amount at the center of the substrate can be accurately measured. Note that the “noise” is a graph that swings up and down in a state where light enters the film formation surface (incident angle in the range of −5 ° to 5 ° in FIG. 14). The “light quantity” means the average value of the transmitted light quantity (about 0.61 in FIG. 14) in a state where light enters the film formation surface in FIG. To do.

When the present invention is applied to control the film thickness, the amount of transmitted light noise is very small as shown in FIG. Therefore, the film formation progress of the transmittance calculated based on such low-noise transmitted light amount data shows a transmittance change that closely matches the theoretical value as shown in FIG. FIG. 13 is a graph showing the theoretical value and the actual measurement result of the transmittance change for each drum rotation at the center of the substrate 18 when forming the first Nb ₂ O ₅ film. The reason why the vertical axis in FIG. 13 is standardized is to facilitate comparison with FIG. 17 described later, and the transmittance in FIG. 13 is normalized by the transmittance of the glass substrate from the transmitted light amount data. It is a thing.

  According to the embodiment of the present invention, as shown in FIG. 13, the amount of transmitted light can be measured more accurately without impairing other characteristics and without optical interference with the substrate, so a high-performance low-reflection film is required. It is possible to control the film thickness easily and with high accuracy.

[Comparative Example]
For comparison, an example in which an optical multilayer film is formed by a carousel type sputtering apparatus by applying a conventional method of forming a low reflection film on the back surface of a substrate will be described.

  The thickness of the glass substrate used in this conventional method is constant (a predetermined angle of 0 ° on the back surface of the substrate), and a low reflection film having a film thickness configuration shown in (2) below is applied to the back surface, for example. When the low reflection film is coated on both surfaces of the substrate, it has a low reflection performance of about 0.2% near the wavelength of 1550 nm.

SiO ₂ (film thickness 275 nm) / Nb ₂ O ₅ (film thickness 141 nm) / SiO ₂ (film thickness 78 nm)
/ Nb ₂ O ₅ (film thickness 73 nm) / glass substrate (2)
A substrate having the low-reflection film coated on the back surface is set on a substrate holder. At this time, instead of the substrate holding unit 62 described with reference to FIGS. 5 to 7, a substrate holding unit having a structure suitable for holding a flat plate (constant thickness) substrate is used.

  Next, the turning angle of the light projecting portion optical axis adjusting member is adjusted so that the light emitted from the light projecting portion is perpendicular to the film forming surface on the film forming surface of the substrate. Alternatively, the angle and position of the substrate holder optical axis adjusting member are finely adjusted in place of or in combination with the turning angle.

After evacuating the chamber, film formation is started under the same conditions as those in the above-described embodiment, and while monitoring the film thickness, the film formation process of the high refractive index material (Nb ₂ O ₅ ) and low refraction are performed. The target optical multilayer film is formed by alternately repeating the film forming step of the refractive index material (SiO ₂ ).

  FIG. 14 to FIG. 16 show the amount of transmitted light acquired at the time of forming the first layer of the created bandpass filter.

14 to 16 show the amounts of transmitted light when the carousel rotation speed is 10th rotation (FIG. 14), 100th rotation (FIG. 15), and 150th rotation (FIG. 15), respectively, at the time of forming the first Nb ₂ O ₅ film. It is. As shown in these drawings, in the conventional method, the ratio of noise to light quantity is as large as 0.03 or more. The noise / light quantity ratio is preferably 0.02 or less from the viewpoint of improving the reflectance.

  In addition, since the low reflection film formed on the back surface of the substrate cannot completely prevent the reflection of light on the back surface of the substrate, the amount of transmitted light that fluctuates in a wavy manner with the rotation of the drum due to light interference on the substrate. can get. Since this wave-like transmitted light amount changes as shown in FIGS. 14 to 16 with the progress of film formation, film formation of transmittance at the center of the substrate (incidence angle 0 °) calculated based on this transmitted light amount. The progress (first band-pass filter layer) shows a wavy change in transmittance as shown in FIG.

  With this wavy transmittance change, the transmittance does not become an extreme value at a desired film thickness that should originally stop film formation, or the extreme value that should originally stop film formation is determined because there are a plurality of extreme values. Is extremely difficult.

  It is understood that this wavy change in transmittance can be almost eliminated by applying an extremely high performance low reflection film of 0.003% or less on the back surface of the substrate. It is extremely difficult to obtain a film with good reproducibility.

  Therefore, when film thickness control is performed by applying a conventional method, it is extremely difficult to stop film formation at a desired transmittance that should originally be stopped and control the film thickness with high accuracy.

[Other Embodiments Regarding Polishing Angle of Substrate Back Side]
In the above-described embodiment, the case where the predetermined angle θ of the back surface of the substrate is 1 ° has been exemplified. However, for the implementation of the present invention, the predetermined angle θ is appropriately designed from the viewpoint of preventing optical interference on the substrate. FIG. 18 shows an example of the transmitted light amount (voltage value) acquired when the first layer of the bandpass filter is formed (carousel rotation speed: 10th rotation) when a substrate having a predetermined angle of 0.5 ° is used. It is. The film forming conditions other than the inclination angle of the back surface of the substrate are the same as in the case of FIG.

  As shown in FIG. 18, even when a substrate having a predetermined angle (inclination angle of the back surface with respect to the film formation surface) of 0.5 ° is used, noise and light intensity are used as in FIG. 3 (predetermined angle = 1 °). Is as small as 0.01 or less, and the transmittance at the center of the substrate can be measured more accurately.

1 is a schematic plan view of an aspect showing a configuration of a sputtering apparatus for forming an optical multilayer film to which a film thickness control apparatus according to an embodiment of the present invention is applied. Schematic diagram of one mode showing how to measure the amount of transmitted light The figure which shows the example of the transmitted light amount (voltage value) acquired at the time of film-forming (carousel rotation speed: 100th rotation) in the 1st layer of a band pass filter in this embodiment. Schematic diagram of one embodiment showing the shape of the substrate The perspective view of the one aspect | mode of the substrate holder used with the sputtering device of FIG. Front view of one embodiment of base plate of substrate holder Front view of one mode of substrate holding unit attached to base plate The figure which looked at the board | substrate holding unit of FIG. 7 from the arrow A direction The figure which looked at the board | substrate holding unit of FIG. 7 from the arrow B direction Side view of one aspect of optical axis adjusting member for supporting light projecting unit Plan view of the optical axis adjusting member shown in FIG. The figure which looked at the optical-axis adjustment member of FIG. 10 from the arrow C direction The graph which shows an example of the change of the transmittance | permeability of the 1st layer of the band pass filter obtained by embodiment of this invention, and a theoretical film-forming progress Reference diagram showing the amount of transmitted light obtained when the first layer of the bandpass filter prepared by the conventional method is formed (carousel rotation speed: 10th rotation) Reference diagram showing the amount of transmitted light obtained when the first layer of the bandpass filter prepared by the conventional method is formed (carousel rotation speed: 100th rotation) Reference diagram showing the amount of transmitted light obtained when the first layer of the bandpass filter prepared by the conventional method is formed (carousel rotation speed: 150th rotation) The graph which shows the change of the transmittance | permeability of the 1st layer of the band pass filter obtained by the conventional method The figure which shows the example of the transmitted light amount acquired at the time of film-forming (carousel rotation speed: 10th rotation) using the board | substrate with the back surface grinding | polishing angle of 0.5 degree | times.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Sputtering device, 12 ... Chamber, 14 ... Substrate holder, 14A ... Measurement hole, 16 ... Center axis, 17 ... Drum, 18 ... Substrate, 18A ... Deposition surface, 18B ... Substrate back surface, 20 ... AC magnetron, 22 , 23 ... Magnetron unit, 26 ... AC power source, 28 ... Shutter, 30 ... AC magnetron, 32, 33 ... Magnetron unit, 36 ... AC power source, 38 ... Shutter, 40 ... Light source, 42 ... Optical fiber, 44 ... Projection unit, 46: light receiving unit, 48: light receiving processing unit, 50: personal computer, 52, 53, 54, 55 ... shutter, 60 ... base plate, 61 ... bolt, 62 ... substrate holding unit, 64 ... holding frame plate, 64A ... substrate support surface 65, presser plate, 66, 67, bolt, 68, through hole, 69, guide member, 70, optical axis adjusting member, 71, taper base, 7 A ... groove, 72 ... fixing member, 72A ... groove, 74 ... support plate, 75 ... through hole, 78, 79 ... bolt insertion hole

Claims (9)

A film thickness control method for controlling the film thickness of a film formed on a substrate,
A substrate having a shape in which a substrate back surface opposite to a film formation surface of the substrate is inclined at a predetermined angle with respect to the film formation surface is fixed to a substrate holder of a sputtering apparatus, and film formation is performed by the sputtering apparatus.
Irradiate light from the light projecting unit toward the substrate on the substrate holder,
The irradiated light is received by the light receiving unit located on the opposite side of the light projecting unit across the substrate, the transmitted light amount is measured according to the received light amount, and the transmitted light amount data of the film-coated substrate is obtained based on the transmitted light amount. ,
A film thickness control method characterized in that a desired film thickness is obtained by controlling a parameter that affects a film formation amount based on the measurement result.   The film thickness control method according to claim 1, wherein the predetermined angle is greater than 0 ° and 2 ° or less.   The said board | substrate is fixed to the said board | substrate holder so that the thickest part or the thinnest part of the shape which has the inclined surface of the said predetermined angle may become the up-down direction of a board | substrate holder. Film thickness control method.   The optical axis of the light emitted from the light projecting unit is adjusted to be perpendicular to the film formation surface at any one point during the control of the film formation surface film thickness of the substrate. The film thickness control method according to 1, 2 or 3. The sputtering apparatus is
A chamber;
A drum that is rotatably installed in the chamber and has a polygonal or circular cross section;
The substrate holder mounted on the outer peripheral surface of the drum;
A magnetron sputter source disposed inside the chamber wall;
The film thickness control method according to any one of claims 1 to 4, wherein A film thickness control device for controlling the film thickness of a film formed on a substrate,
A substrate holding mechanism for fixing a substrate having a shape in which a substrate back surface opposite to a film forming surface of the substrate is inclined at a predetermined angle with respect to the film forming surface to a substrate holding portion of a sputtering apparatus;
A light projecting means for irradiating light toward the substrate held by the substrate holding mechanism;
A light receiving means for receiving light that has passed through the substrate and outputting an electrical signal corresponding to the amount of light received;
An arithmetic processing unit that measures a transmitted light amount according to a received light amount from an electrical signal output from the light receiving unit, and obtains transmitted light amount data of the film-coated substrate based on the transmitted light amount;
Control means for controlling a parameter affecting the film formation amount based on the transmitted light amount data obtained by the arithmetic processing means;
A film thickness control apparatus comprising:   The film according to claim 6, wherein the substrate holding mechanism fixes the substrate so that a thickest portion or a thinnest portion of the substrate having the inclined surface having the predetermined angle is in the vertical direction. Thickness control device.   8. An optical axis adjustment mechanism for adjusting an optical axis so that light emitted from the light projecting unit is perpendicular to the film formation surface of the substrate. Film thickness control device. A manufacturing method for manufacturing an optical multilayer film formed by alternately laminating two types of thin films having different refractive indexes on a substrate,
While using a substrate having a shape in which the substrate back surface opposite to the film formation surface of the substrate is inclined at a predetermined angle with respect to the film formation surface,
Magnetron sputtering source for forming a low refractive index film with a target for forming a relatively low refractive index thin film, and high refraction with a target for forming a relatively high refractive index thin film Using a sputtering apparatus provided with a magnetron sputtering source for forming an index film,
The substrate is fixed to the substrate holder of the sputtering apparatus to form a film,
Irradiate light from the light projecting unit toward the substrate on the substrate holder during film formation,
The irradiated light is received by the light receiving unit, the transmitted light amount is measured according to the received light amount, and the transmitted light amount data of the film-coated substrate is obtained based on the transmitted light amount,
A method for producing an optical multilayer film, comprising: forming a thin film having a desired film thickness by controlling a parameter that affects a film formation amount based on the measurement result.

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