JP2009198460A - Film thickness measurement method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film thickness measuring device and a film thickness measurement method capable of easily measuring the thickness of a thin film, such as a reflection prevention film, without being affected by reflected light even if reflectance varies by a crystal pattern. <P>SOLUTION: The film thickness measurement method has coaxially arranged light projection/reception sections and measures the thickness of a film formed on the surface of a planar object by the light interference type film thickness measuring device. The film thickness measurement method includes: a process S21 for holding the planar object in a state where a surface in which the film is formed is inclined from a surface vertical to the light axis of the light projection/reception sections; a process for applying measurement light from the light projection/reception sections to the surface of the planar object and inputting reflected light from the planar object to the light projection/reception section; and a process S25 for measuring the thickness of the film formed on the surface of the planar object based on the input reflected light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a film thickness measuring method and a film thickness measuring apparatus, and in particular, a film thickness measuring method and a film thickness measurement for measuring a transparent film such as an antireflection film on a polycrystalline silicon substrate used in a solar cell by an optical interference method. Relates to the device.

  A conventional optical interference type film thickness measuring device is described in, for example, Japanese Patent No. 3944693 (Patent Document 1). FIG. 10 is a diagram showing a main part of the film thickness measuring apparatus 100 disclosed in Patent Document 1. As shown in FIG. FIG. 10A is a block diagram illustrating an electrical configuration of the film thickness measuring apparatus 100, and FIG. 10B is a diagram illustrating a configuration of an optical system and the like in the sensor head 120 of the film thickness measuring apparatus 100.

  Referring to FIG. 10, film thickness measuring apparatus 100 is provided in a small sensor head 120 that can be attached close to measurement object 30, and in an internal slot of computer 140 that is installed separately from measurement object 30. And a PCI (Peripheral Component Interconnect) board 130 that can be mounted. Here, the measurement object 30 is placed on the stage 129, and light from the sensor head 120 enters the measurement object 30 perpendicularly.

  The sensor head 120 and the PCI board 130 are connected by a cable (electric wire) 123a. A PCI bus 135 is connected between the PCI board 130 and a CPU (Central Processing Unit, not shown) serving as a control unit of the computer 140. The PCI board 130 receives an A / D converter 131 that converts an analog signal from the light receiver 125 into a digital signal, a signal processor 132 having predetermined firmware 133, and a signal from the signal processor 132. And a light projecting / receiving control unit 134 for controlling the light receiving unit 125.

  The computer 140 includes software 141 for measuring the film thickness. Further, the computer 140 outputs film thickness measurement data and film thickness determination output to an external device (not shown) via an external interface (I / F) 142, and inputs various digital command signals from the outside.

  The sensor head 120 includes a light projecting unit 121 and a light receiving unit 125. The light projecting unit 121 includes an infrared light LED 122 that emits infrared light, and a light projecting side optical system 120 a that emits the infrared light emitted from the infrared light LED 122 toward the measurement object 30. The light projecting side optical system 120 a is projected with a half mirror 123 that reflects the infrared light from the infrared light LED 122 and projects it onto the measurement object 30 and transmits the reflected light from the measurement object 30. It includes a lens 124 that causes infrared light to enter a predetermined position on the measurement object 30 and sends the reflected light to the spectroscopic element. The light receiving unit 125 receives a reflected light from the measurement object 30, a spectroscopic element 126 that splits the reflected light received by the light receiving side optical system, and a series of component light obtained from the spectroscopic element 126. And a CCD (Charge Coupled Device) 127 that performs photoelectric conversion separately and appropriately. In this example, the light projecting side optical system 120a also operates as a light receiving side optical system. That is, the film thickness measuring apparatus 100 has an equal light receiving portion arranged coaxially.

  The analog signal from the CCD 127 is output to the A / D converter 131 via the cable 123a. Further, the light projecting / receiving control unit 134 outputs a control signal for controlling the light projecting unit 121 and the light receiving unit 125 to the sensor head 120.

  In the conventional example shown in FIG. 10, infrared light is used. More generally, measurement is obtained by irradiating a measurement object with a film such as a halogen lamp or a white LED and spectrally analyzing the reflected light. It is preferable to measure the film thickness by curve fitting the reflection spectrum (optical interference waveform) and the theoretical optical interference waveform derived from the optical interference theory of the thin film.

  Next, measurement of the film thickness of an antireflection film formed on a polycrystalline silicon solar cell using a conventional film thickness measuring device will be described. A device for generating electricity with sunlight is a solar cell. There are several types of solar cells, but the current mainstream is polycrystalline silicon solar cells. FIG. 11 is a view showing the structure of a typical polycrystalline silicon solar cell wafer 200. A semiconductor circuit such as an IC or LSI uses a single crystal wafer made by slicing a single crystal ingot of silicon, but a solar cell often uses a polycrystalline silicon wafer that can be manufactured at a lower cost.

Referring to FIG. 11, solar cell wafer 200 includes p-type polycrystalline silicon wafer 201, n-type layer 202 provided above and below p-type polycrystalline silicon wafer 201, p ⁺ layer 203, n An antireflection film 204 formed on the mold layer 202, a surface electrode 206 connected to the n-type layer 202 and provided at a predetermined position on the antireflection film 204, and provided below the p ⁺ layer 203. Back surface electrode 207. Sunlight 208 enters through the antireflection film 204 to generate electric power.

  FIG. 12 is a view showing an example of the surface of the p-type polycrystalline silicon wafer shown in FIG. 12A is a diagram showing a part of the surface, FIG. 12B is an enlarged view of a portion that looks dark in FIG. 12A, and FIG. 12C is bright in FIG. 12A. It is an enlarged view of the part which can be seen.

  Referring to FIG. 12, an atypical pattern of about 0.2 to 1 square cm is observed on the surface of the polycrystalline wafer. The reason for this seems to be that in a polycrystalline ingot, the crystals grow atypically in various directions. Further, when the ingot is sliced into a wafer and then alkali etched, there is a difference that it is difficult to be etched by the crystal orientation plane, so that only a certain crystal orientation is likely to remain selectively. As a result, as shown in FIG. 12, fine pyramidal irregularities having a size of about 10 μm are generated, and a pattern in which the height and direction of the pyramid are atypical is formed.

  By forming such a shape, even if the silicon surface is directed in the direction of the sun as a whole, sunlight will be incident obliquely on the silicon surface, and light once incident on the oblique surface will be The probability of reflection and irradiation to the adjacent pyramid increases, and as a result, more light energy is absorbed by silicon than in the case where the surface is flat, and the power generation efficiency is further increased.

Furthermore, an antireflection film 204 such as SiN (Silicon Nitride) is formed with a thickness of about 80 nm for the purpose of increasing the energy absorption efficiency by reducing the light reflected off the silicon surface to the outside. . Since the antireflection effect of the antireflection film 204 is determined by the film thickness, it is important to measure and manage the film thickness.
Japanese Patent No. 3944693 (FIGS. 2 and 3 and related descriptions)

  As described above, in order to measure the film thickness of the antireflection film 204 of the product completed as the solar cell wafer 200 in a nondestructive manner, it is necessary to measure the film thickness with an optical film thickness measuring device.

  However, a polycrystalline silicon solar cell wafer is usually composed of a large number of atypical crystal patterns with different crystal directions and sizes as shown in FIG. 12, and the reflectivity varies greatly from pattern to pattern. .

  The reason why the reflectivity varies greatly from pattern to pattern is that the size of crystal grains varies when a polycrystalline silicon ingot is manufactured as shown in FIG. For example, when the size of the crystal grain is small (the portion shown as 10 μm in FIG. 12B), the inclination of the side surface of the pyramidal grain is close to the wafer surface, and the light incident on the wafer surface is Since the light is reflected in the side direction, it appears darker than the surroundings, that is, it is assumed that the reflectance is low.

  On the other hand, when the size of the crystal grain is large (the part shown as 20 μm in FIG. 12C), the inclination of the side face of the pyramidal grain is close to parallel to the wafer surface, The vertically incident light is reflected by the side surfaces of the grains and travels in a direction close to the vertical direction, so that it appears brighter than the surroundings, that is, the reflectance is high.

  Moreover, it is estimated that the part which looks like these intermediate brightness also shows an intermediate value also in a reflectance.

  The reflectance of the surface of the solar cell wafer is different due to such a mechanism.

  For this reason, when trying to measure the film thickness with the optical film thickness meter as in the conventional example shown in FIG. 10, the reflected light amount is too small and the SN (signal / noise) of the interference waveform is significantly deteriorated. However, there is a problem that the light receiving element is saturated due to too much, and stable measurement cannot be performed.

  The present invention has been made in view of the above problems, and can easily measure the thickness of a thin film such as an antireflection film without being affected by variations in reflectivity depending on crystal patterns. An object is to provide a film thickness measuring method and a film thickness measuring apparatus.

  The film thickness measuring method according to the present invention measures the thickness of a film formed on the surface of a plate-like object using an optical interference type film thickness measuring apparatus having a light projecting / receiving unit arranged coaxially. The film thickness measurement method includes a step of holding the plate-like object in a state in which the surface on which the film is formed is inclined from a plane perpendicular to the optical axis of the light projecting / receiving unit, and a measurement light from the light projecting / receiving unit to the plate-like object surface. And the step of inputting the reflected light from the plate-like object to the light projecting / receiving unit and the step of measuring the thickness of the film formed on the surface of the plate-like object based on the inputted reflected light .

  Preferably, the angle at which the plate-like object is inclined from the vertical plane with respect to the light projecting / receiving unit is in the range of 5 degrees to 20 degrees.

  More preferably, the angle at which the plate-like object is inclined from the vertical plane with respect to the light projecting / receiving unit is in the range of 10 degrees to 20 degrees.

The plate-like object has one surface and the other surface, and has a film only on one surface, and positioning the measurement position in a state where the plate-like object is held so that the other surface faces the light projecting / receiving unit. When,
A step of holding the one surface toward the light projecting / receiving unit and positioning the measurement position so that the measurement light is irradiated may be further included.

  The plate-like object may be a polycrystalline silicon substrate.

  In another aspect of the present invention, the film thickness measuring device measures the thickness of the film formed on the surface of the plate-like object using optical interference. The film thickness measuring device irradiates a plate-like object with measurement light and inputs a reflected light from the plate-like object, and a vertical plane with respect to the optical axis of the coaxial light-receiving / receiving unit, And a holding unit that holds the plate-like object in a state where the surface on which the film is formed is inclined.

  Preferably, the holding part is inclined within a range of 5 degrees to 20 degrees from a vertical plane with respect to the optical axis of the coaxial light projecting / receiving part.

  More preferably, the holding part is inclined within a range of 10 degrees to 20 degrees from a plane perpendicular to the optical axis of the coaxial light projecting / receiving part.

  It is preferable to include moving means for arbitrarily changing the relative position of the coaxial light projecting / receiving unit and the holding unit.

  The plate-like object has one surface and the other surface, and has a film only on one surface, and the measurement position determined in a state where the plate-like object is held so that the other surface faces the light projecting / receiving unit. And means for holding the one surface facing the light projecting / receiving unit and positioning the measurement light so that the measurement light is irradiated to the measurement position.

  According to the present invention, it is possible to provide a film thickness measuring method and a film thickness measuring apparatus capable of easily measuring the thickness of a thin film such as an antireflection film by reducing the influence of variation in reflectance due to a difference in crystal pattern.

  The present invention is based on the fact that the inventors have discovered a phenomenon in which polycrystalline silicon solar cells have regions having different reflectivities, and the direction in which light is reflected differs in each region. By tilting, it is possible to measure the film thickness of a thin film such as an antireflection film on the substrate with little influence of reflectance.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a main part of a film thickness measuring apparatus 10 according to an embodiment of the present invention. Here, the case where the above-described polycrystalline silicon solar cell wafer is measured as the measurement object 30 will be described. Referring to FIG. 1, film thickness measuring apparatus 10 projects and reflects a stage 20 that holds a measurement object 30 such as a solar battery wafer, and a solar battery wafer 31 that is placed on stage 20. It includes a fiber head 12 that receives light, a PCI board 130 connected to the fiber head 12, and the like. The fiber head 12 is connected to the PCI board 130 via the light projecting fiber 13 and the light receiving fiber 14. 1 corresponds to FIG. 10, but only the fiber head 12 and the PCI board 130 are shown in FIG. 1. In this embodiment, the light projecting unit and the light receiving unit in the sensor head 120 of FIG. 10 are built in the PCI board and are configured to project and receive light from the fiber head 12 via an optical fiber. In this embodiment, the stage 20 can be tilted unlike the conventional case. Since the other parts are the same as those of the conventional example shown in FIG. 10, their description is omitted except for the different parts.

  Therefore, the fiber head 12 projects the light from the light projecting unit 121 onto the solar cell wafer 31 that is the measurement object 30 on the stage 20, receives the reflected light at the light receiving unit 125, and inputs the light to the CCD. The data is sent to the conversion unit 131.

  The film thickness measuring apparatus 10 according to this embodiment has such a tiltable stage 20, so that even if the measurement object 30 is a polycrystalline silicon solar cell wafer 31, a polycrystalline silicon substrate. The reflected light from the side surface of the fine pyramidal crystal can be received as an appropriate amount of received light by adjusting the tilt angle. Therefore, the conventional film thickness measuring apparatus 100 in which the stage is perpendicularly opposed to the optical axis can stably measure even a crystal pattern in which sufficient reflected light cannot be obtained. The inclination angle of the stage 20 may be fixed.

  The inclination angle θ of the stage 20 from the horizontal plane is preferably in the range of about 5 degrees to 20 degrees. The reason for this will be described later. Further, the inclination of the stage 20 can be realized by any known mechanical configuration, and may be inclined manually or automatically.

  FIG. 2 is a diagram showing a surface (A) on which a SiN film of a polycrystalline silicon solar cell is formed and a back surface (B) on which no film is formed. Referring to FIG. 2, a portion showing a crystal pattern with low reflectivity on the front surface shows low reflectivity also on the back surface, and a portion showing a crystal pattern with high reflectivity on the front surface shows high reflectivity on the back surface. The polycrystalline silicon substrate constituting the solar cell is very thin, about 200 μm, and one crystal region penetrates from the front surface to the back surface of the substrate. Therefore, as shown in FIG. Corresponds like a mirror surface.

  Therefore, when it is desired to measure the film thickness of a pattern having a low reflectance, a reference is acquired with a pattern corresponding to the position on the back surface. Similarly, when it is desired to measure the film thickness in a pattern having a high reflectance, a reference is obtained with a pattern corresponding to the position on the back surface. The reference will be described later.

  By doing so, the ratio of “reflectance with film / reflectivity without film” becomes almost constant, so that the amount of received light can be too small or too large depending on the pattern as before. The problem of being able to or cannot be made less likely to occur.

  Next, a specific configuration of the stage 20 of the film thickness measuring apparatus 10 having the tiltable stage 20 as shown in FIG. 1 will be described. FIG. 3 is a view showing a main part of the film thickness measuring apparatus 10 having the tiltable stage 20. 3A is a side view of the film thickness measuring device 10 (an arrow view from the X direction), and FIG. 3B is an arrow view indicated by arrows BB in FIG. 3A.

  Referring to FIG. 3, stage 20 is provided on moving table 21. The moving table 21 is provided below the fiber head 12 and can move in an arbitrary direction on the XY plane orthogonal to the moving direction (Z direction) of the fiber head 12. It has an arcuate portion 21 a that forms a recess, and operates as a stage holding means for holding the stage 20. Further, the movement of the movable table 21 on the XY plane can be performed using any known configuration.

  On the other hand, the stage 20 has a holding part 20a having a rectangular plane for holding the measurement object 30, and a bowl-like bottom part that protrudes along the arcuate part 21a of the moving base 21 and extends in the X direction. 20b, and a side wall portion 20c that connects the holding portion 20a and the bottom portion 20b with four rectangular sides.

  The stage 20 is held at an arbitrary inclination angle θ in the range of 0 degrees to 30 degrees on the moving table 21, and the measurement object 30 such as a solar cell wafer is placed on the stage 20 in an arbitrary state on the XY plane. It is possible to move to the position.

  The initial position of the moving base 21 is a position where the center is located at the origin on the XY plane, and the fiber head 12 moves on the origin in a direction (Z direction) orthogonal to the XY plane. Further, the stage 20 is horizontal at the initial position.

  The solar cell wafer 31 that is the measurement object 30 is, for example, a square of 12.5 cm on each side so that it can be reliably positioned and fixed on the stage 20 using means such as the guide pins 23 shown in FIG. Mechanism. In the example shown in FIG. 3C, the guide pins 23b are fixed so as to contact two adjacent sides of the solar cell wafer 31, and the guide pins 23a are slidable in the direction indicated by the arrows in the figure. The spring is biased in the right direction where the opposing guide pin 23b is located.

  Next, an actual measurement procedure will be described. FIG. 4 is a block diagram showing the overall configuration of the film thickness measuring apparatus 10 in this embodiment, which corresponds to the conventional FIG.

  Referring to FIG. 4, the overall configuration of film thickness measuring apparatus 10 is basically the same as that shown in FIG. 10A, and tiltable stage 20 on which measurement object 30 is placed, and fiber head. 12, a PCI board 130 that is a film thickness measurement hardware connected to the fiber head 12, and a computer 140 connected to the PCI board 130 via a PCI bus. The computer 140 is provided with a control unit (CPU) 141.

  In this embodiment, as described above, the stage 20 on which the measurement object 30 is placed can move on the XY plane and can be tilted. Further, the fiber head 12 can move in the Z direction perpendicular to the XY plane with respect to the measurement object 30.

  The fiber head 12 is held and moved by a Z stage 15 provided so as to be movable in the Z direction. Accordingly, the Z stage 15 operates as a moving unit that arbitrarily changes the relative position of the coaxial light projecting / receiving unit and the holding unit.

  The film thickness measurement software 145 loaded on the computer 140 moves the moving table 21 in the XY directions, tilts the stage 20 by a desired angle θ, and moves the fiber head 12 in the Z-axis direction. Each driver software to be moved to is included. That is, the software 145 includes a Z stage driver 146 that moves the Z stage 15 that moves the fiber head 12 in the Z-axis direction, and X and Y stage drivers 147 and 148 that move the stage 20 on the XY plane. And a θ stage driver 149 for inclining the measuring object 30 on the stage 20 by an angle θ.

  An encoder (not shown) is provided on the stage 20 and the movable table 21 for positioning the movable table 21 and detecting the tilt angle of the stage 20.

  On the Z stage 15 that moves the fiber head 12 in the Z-axis direction, a focus detection unit 16 that detects whether or not the measurement light from the fiber head 12 is focused on the measurement object 30 has an X with respect to the fiber head 12. It is provided in the axial direction.

  In addition, a display 150 is connected to the computer 140. The display 150 automatically measures a film thickness of a thin film provided on a measurement object and a “reference” button 151 for instructing a reference process described later. A “measurement” button 152 for giving an instruction is displayed. When the “reference” button 151 is pressed, the reference is started. The reference is a function of adjusting the gain of the CCD 127 so that the amount of reflected light from the measurement object is optimized according to the reflectance of the measurement object.

  The focus detection unit 16 can use, for example, a triangulation displacement meter using laser light. The output of the displacement meter is sent to a stage control unit (not shown) provided in the computer 140, and the stage control software incorporated in the software 145 moves the Z-axis stage 15 up and down while monitoring the output of the displacement meter. The Z-axis stage 15 is controlled so that a displacement meter output corresponding to the known just focus (in-focus) can be obtained.

  Next, a procedure for measuring the film thickness of the measurement object using the film thickness measuring apparatus 10 will be described. FIG. 5 is a flowchart showing the processing in this case. FIG. 6 shows a state (A) where the back surface of the solar cell wafer 31 is placed on the stage 20 with the back surface facing the fiber head 12, and the surface on which the thin film is provided is placed facing the fiber head 12 by inverting it. It is a figure which shows a state (B).

  Referring to FIG. 5, first, the measurer places the solar cell wafer on the stage 20 with the back surface thereof facing up (S11). The coordinates at this time are assumed to be the initial position (X, Y, Z) = (0, 0, 0). The stage base 21 is moved manually in the X and Y directions or using the X stage driver 147 and / or the Y stage driver 148 so that the measurement light spot hits the desired measurement pattern from the initial position.

  Subsequently, when the Z stage 15 holding the fiber head 12 is moved so that the measurement spot is just focused, and the measurer presses the reference button 151 on the display 150, the control unit 141 of the computer 140 causes the film thickness to be adjusted. Reference processing is performed in accordance with an instruction from the measurement software (software 145) (S13), and the stage control software stores coordinates (X, Y, Z) = (x1, y1, z1) at the time of reference (S14). ). This may be recorded on paper or the like by the measurer, or the control unit 141 of the computer 140 may store the movement amount by each driver 146 to 149 in a memory (storage means) not shown. Good. Next, a reference completion flag is held in the film thickness measurement software 145, and “reference completion” is displayed on the display 150 (S15). The X, Y, Z coordinates and the inclination angle θ of the stage 20 can always be detected by the absolute coordinate detection type linear encoder or the like, and the origin position and current position information of the stage coordinates disappear even when the apparatus is turned off. There shall be no such thing. As described above, the control unit 141 of the computer 140 operates as a positioning unit.

  Referring to FIG. 7, next, the measurer reverses the solar cell wafer 31 in the X-axis direction and places it on the stage with the front side on which the thin film is provided facing up (S 21), and on the display 150. The measurement button 152 is pressed (S22).

  The control unit 141 of the computer 140 performs the following operation in response to an instruction from the software 145. First, it is determined whether or not the above-referenced flag is held (S23). If the referenced flag is held, the stage control software included in the software 145 moves the stage 20 to the coordinates (−x1, y1, z1) (S24). That is, the stage 20 is driven in the direction opposite to the X axis with the origin at the center based on the coordinates stored during the reference processing. Y and Z are not changed. Thereafter, the film-coated surface is irradiated with light from the fiber head 12, the reflection spectrum is measured, and the film thickness measurement process is executed (S25).

  On the other hand, if the measurement software does not have a reference flag in S23, an error for which reference is not acquired is displayed on the display 150 (S26).

  As described above, the control unit 141 of the computer 140 automatically measures the film thickness after the measurer places and inverts the measurement object. Further, the measurement object 30 may be reversed automatically.

  Next, the relationship between the actually measured waveform obtained by the film thickness measuring apparatus and the theoretical waveform obtained by calculation when the tilt angle of the stage 20 is changed will be described. This will be described separately for cases where the reflectance of the crystal pattern is low and high.

  The measurement of the thin film is performed by fitting (curve fitting) between the measured value and the theoretical value. Specifically, the least square method or the like is used. This is a method of determining the theoretical value that minimizes the sum of the squares of the difference between the measured value and the theoretical value (fitting level) as the film thickness value (Patent Literature). 1). It can be said that the film thickness value output as the measurement result is more reliable as the fitting level is smaller because the measured waveform is closer to the theoretical value. There is no reference value indicating that the fitting level may be any value or less as an absolute value, and the fitting level is used as a relative evaluation value.

(1) Stage tilt angle and interference waveform in crystal pattern with low reflectivity FIG. 8 is a graph showing the relationship between wavelength and absolute reflectivity for each tilt angle in this case. FIG. 8A to FIG. 8G are graphs showing measured waveforms and theoretical waveforms when the inclination angles are varied from 0 degrees to 30 degrees at intervals of 5 degrees, respectively. The numerical value on the right side of the angle represents the fitting level at that time.

  Referring to FIG. 8, when the inclination is 0 degree, the fitting level is relatively large as compared with the case of other inclinations. This shows that the reliability of the output film thickness is not good. This is because the amount of reflected light is too small to ensure the linearity of the spectroscopic element 126, and as a result, the interference waveform is distorted. As the slope increases, the fitting level decreases and the reliability of the measured value improves. From this, it can be determined that the reliability of the output film thickness is high. If the allowable value of the film thickness measurement value is within ± 5% of the design value (for example, 80 nm), the oblique angle is preferably 0 to 20 degrees. Further, if the allowable value of the fitting level is 0.02, the optimum angle is about 10 degrees to 20 degrees.

(2) Stage tilt angle and interference waveform in crystal pattern with high reflectivity FIG. 9 is a graph showing the relationship between wavelength and absolute reflectivity for each tilt angle in this case. FIG. 9A to FIG. 9G are graphs showing measured waveforms and theoretical waveforms when the inclination angles are varied from 0 degrees to 30 degrees at intervals of 5 degrees, respectively.

  In this case, it can be seen that the measured waveform does not change so much when the inclination is 5 degrees to 25 degrees. The reason is considered that a sufficient amount of light returns in the direction of the fiber head 12 of the film thickness measuring device 10 because the inclination of the pyramidal crystal is small.

  The reason why the film thickness is about 10 nm thicker than the result when the reflectance is low is due to the film thickness unevenness in the substrate.

  In this case, if the allowable value of the film thickness measurement value is within ± 5% of the design value (for example, 90 nm), the inclination angle of the stage 20 is preferably 5 degrees to 25 degrees. In this case, even if the allowable value of the fitting level is 0.02, the optimum angle is about 5 to 25 degrees.

  From the above, the tilt angle of the stage 20 capable of highly reliable measurement irrespective of the reflectance is preferably 5 degrees to 20 degrees in consideration of only the film thickness value, and is optimal in consideration of the fitting level. The angle is about 10 degrees to 20 degrees.

  In the above embodiment, an example has been described in which the stage is provided on the moving table and the stage can be moved in any direction on the XY plane. It may be movable in the direction. The example in which the fiber head can be moved toward the stage in the Z direction has been described. However, the present invention is not limited to this, and it is only necessary that both can move relatively. Regarding the tilt, the example has been described in which the stage can be tilted at a desired angle with respect to the direction in which the light from the fiber head is incident, but the fiber head may be tilted with respect to the stage.

  Moreover, in the said embodiment, although demonstrated with the structure which makes an inclination angle variable, it is good also as a structure which fixed the inclination angle to the predetermined angle.

  A robot hand capable of multi-axis control may be used as means for holding, reversing, moving and tilting the substrate.

  Further, if the measurement object can be held on the stage, the light from the fiber head may be irradiated from the lower surface of the stage.

  Furthermore, in the above embodiment, the case where the film thickness of a thin film provided on polycrystalline silicon as a solar cell wafer is measured has been described. However, the present invention is not limited to this, and single crystal silicon, microcrystalline silicon, amorphous silicon, etc. The present invention can also be applied to the solar cell wafer.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

It is a figure which shows the principal part of the film thickness measuring apparatus which concerns on one embodiment of this invention. It is a figure which shows the surface and back surface of the solar cell wafer used as a measuring object. It is a figure which shows the detail of the stage of a film thickness measuring apparatus. It is a block diagram including the control part of the film thickness measuring apparatus which concerns on this embodiment. It is a flowchart which shows the reference process in a film thickness measuring apparatus. It is a figure which shows the positional relationship of the board | substrate at the time of a reference and a measurement. It is a flowchart which shows the measuring method in a film thickness measuring apparatus. It is a graph which shows the fitting condition of the actual measurement waveform and theoretical waveform for every inclination-angle of a stage when a crystal pattern with low reflectance is measured. It is a graph which shows the fitting condition of the actual measurement waveform for every inclination-angle of a stage when a crystal pattern with a high reflectance is measured, and a theoretical waveform. It is a block diagram which shows the structure of the conventional film thickness measuring apparatus. It is a perspective view which shows the whole structure of a solar cell wafer. It is a photograph which shows the surface of a solar cell wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 Film thickness measuring apparatus, 12 Fiber head, 13 Light emitting fiber, 14 Light receiving fiber, 15 Z stage, 16 Focus detection part, 20 Stage, 21 Moving stand, 30 Measurement object, 31 Solar cell wafer, 130 PCI board 135 PCI bus, 140 computer, 141 controller, 145 software.

Claims (10)

A film thickness measuring method for measuring the thickness of a film formed on the surface of a plate-like object using a light interference type film thickness measuring device having a coaxially arranged light emitting and receiving part,
A step of holding the plate-like object in a state in which the surface on which the film is formed is inclined from the plane perpendicular to the optical axis of the light projecting and receiving unit;
Irradiating measurement light from the light projecting / receiving unit to the surface of the plate-like object, and inputting reflected light from the plate-like object to the light projecting / receiving unit;
Measuring the thickness of the film formed on the surface of the plate-like object based on the input reflected light. The film thickness measuring method according to claim 1, wherein the angle at which the plate-like object is inclined from the vertical plane with respect to the light projecting / receiving unit is in the range of 5 degrees to 20 degrees. The film thickness measurement method according to claim 1, wherein an angle at which the plate-like object is inclined from a vertical plane with respect to the light projecting / receiving unit is in a range of 10 degrees to 20 degrees. The plate-like object has one side and the other side, and has a film only on one side,
A step of positioning the measurement position in a state where the plate-like object is held so that the other surface faces the light projecting / receiving unit;
The film thickness measuring method according to claim 1, further comprising a step of holding the one surface toward the light projecting / receiving unit and positioning the measurement position to be irradiated with the measurement light. The film thickness measuring method according to claim 1, wherein the plate-like object is a polycrystalline silicon substrate. A film thickness measuring device that measures the thickness of a film formed on the surface of a plate-like object using optical interference,
A coaxial light emitting and receiving unit that irradiates the plate-like object with measurement light and inputs reflected light from the plate-like object;
A film thickness measuring device comprising: a holding unit that holds the plate-like object in a state where the surface on which the film is formed is inclined from a plane perpendicular to the optical axis of the coaxial light projecting and receiving unit. 7. The film thickness measuring apparatus according to claim 6, wherein the holding part is inclined within a range of 5 degrees to 20 degrees from a vertical plane with respect to the optical axis of the coaxial light projecting / receiving part. The film thickness measuring device according to claim 6, wherein the holding part is inclined in a range of 10 degrees to 20 degrees from a vertical plane with respect to the optical axis of the coaxial light projecting and receiving part. The film thickness measuring apparatus according to claim 6, further comprising a moving unit that arbitrarily changes a relative position between the coaxial light projecting / receiving unit and the holding unit. The plate-like object has one side and the other side, and has a film only on one side,
Storage means for storing a measurement position determined in a state where the plate-like object is held so that the other surface faces the light projecting / receiving unit;
The film thickness measuring device according to claim 9, further comprising positioning means for holding the one surface toward the light projecting / receiving unit and positioning the measurement light so that the stored measurement position is irradiated with the measurement light.