JP2003091839A - Focal error detector and optical information recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focal error detector to reduce offset of a focal error signal due to chromatic aberration on an axis of an objective lens and to enable stable focal control. SOLUTION: The focal error detector is provided with the objective lens 113 with different focal distance between light source wavelength for exposure and light source wavelength for focal control, an optical member 105 that divides a light flux from a light source for the focal control into a plurality of light fluxes, optical systems 109 to 112 that is made incident on the objective lens by symmetrically making the plurality of light fluxes eccentric to a light axis of the objective lens, a plurality of optical detectors 115, 116 that makes light fluxes reflected from an original disk of the optical disk and transmitted the objective lens incident on and detects positions of the light fluxes by light quantity distribution and an arithmetic circuit that calculates a focal error of the objective lens to the original disk of the optical disk from an output signal of an optical detector and generates the focal error signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an optical disk master exposure apparatus for manufacturing an optical disk master, and in particular, an optical disk master exposure that uses an objective lens having a different focal length between the exposure light source wavelength and the focus control light source wavelength. The present invention relates to a focus error detection device and an optical information recording device used in the device.

[0002]

2. Description of the Related Art In mass production of optical discs, a master coated with a photoresist on a glass substrate is exposed to form recording pits and guide grooves (grooves), and a predetermined die is manufactured from the master to make a stamper. The process of mass production is generally adopted. A focus control laser with a different wavelength from the exposure laser is used to constantly irradiate the master coated with photoresist with the exposure-optimized laser, which is generated by the light returned from the master. The focus of the objective lens is controlled based on the focus error signal. Astigmatism is often used as a focus error detection method. For an explanation of the principle of the astigmatism method, see, for example, Impress Communications Optical Disc Technology.
It is described in ISBN 4-8443-0198-5.

In recent years, DVD (Digital Versatile Disc)
The development of next-generation high-density optical discs with a recording capacity (20 GB / layer grade) several times higher than that of Deep ultraviolet (De UV
ep UV) laser is used, but in the deep ultraviolet wavelength range, the types of glass that can be used for the objective lens are limited, so
If the focal lengths of the exposure laser wavelength and the focus control laser wavelength are made to be the same, the number of lenses inevitably increases, and it is very difficult to manufacture a compact and lightweight high NA objective lens. Therefore, the next-generation high-density optical disc master exposure apparatus has an exposure laser wavelength (for example, 257n).
m) and the focus control laser wavelength (for example, 635 nm) have different focal lengths, that is, an objective lens having axial chromatic aberration is used.

In the case of using an objective lens having axial chromatic aberration, in order to focus the focus control laser on the focus point of the exposure laser which is incident on the objective lens as a parallel light flux, the focus control laser is used as a convergent light flux. It is necessary to enter the objective lens. However, as qualitatively shown in FIG. 1, from the state of FIG. 1B in which the focus points of the exposure laser 20 and the focus control laser 21 coincide with each other, as the position of the master 119 changes,
The position of the objective lens 113 is displaced in the optical axis direction by the voice coil actuator 114, and the position shown in FIGS.
In this state, since the distance between the focus control laser device 101 and the objective lens 113 changes, the focus points of the exposure laser 20 and the focus control laser 21 deviate. The above-mentioned position change of the master includes a position change caused by the thickness difference of the master for each master, a surface fluctuation at the time of exposure (when the master rotates), or a position change caused by uneven thickness of the master.

As a method of solving the light-converging point shift caused by the position change of the master disk due to the master disk thickness variation among the master disks, a focus control laser device and an objective lens are mounted on an elevator table movable in the vertical direction with respect to the master disk. Japanese Patent Laid-Open No. 2000-3
It is disclosed in Japanese Patent No. 48370. This is a method that can easily correct the focal point shift between the exposure laser and the focus control laser in the optical adjustment stage before exposure. However, it is not effective for the light-converging point shift caused by the surface fluctuation or the position change of the master due to the unevenness of the master during exposure (when the master rotates). During exposure (when the master rotates), if the position of the master is changed by about ± 10 μm, the focal points of the exposure laser and the focus control laser are displaced by the focal depth of the objective lens.
Stable focus control cannot be realized.

[0006]

As described above, in the optical disc master exposure apparatus using the objective lens having the axial chromatic aberration, the position of the master caused by the surface wobbling or the thickness unevenness of the master during exposure (when the master rotates). Due to the change, the focal points of the exposure laser and the focus control laser deviate from each other. As a result, in the conventional focus error detection method (astigmatism method) in which the focus control laser is focused on the focus point of the exposure laser to detect the focus error,
Stable focus control was difficult.

It is an object of the present invention to provide a focus error detection device capable of reducing the offset of the focus error signal due to the axial chromatic aberration of the objective lens and performing stable focus control.

[0008]

According to the present invention, there is provided a focus control light source, an objective lens, and the focus control light source which is symmetrically decentered with respect to the optical axis of the objective lens and enters the objective lens. A light beam dividing means for dividing a light beam from the light source into a plurality of light beams, and a plurality of light beam position detecting means for detecting the position of the light beam by the light amount distribution of the light beam reflected by the focusing object facing the objective lens and transmitted through the objective lens. A focus error detection device comprising: a photodetector; and a calculation unit that calculates a focus error of the objective lens with respect to the focusing target from an output signal of the photodetector to generate a focus error signal. provide.

In the focus error detecting apparatus according to the present invention, a plurality of focus control lasers which are symmetrically decentered from the optical axis of the objective lens are made incident on the objective lens, and the optical information recording medium or the observation target which is the focus object. By detecting the focus error signal by the reflected light from the object, the offset to the focus error signal due to the axial chromatic aberration of the objective lens can be reduced, and stable focus control can be realized.

The present invention further comprises an arithmetic circuit for calculating an inclination error of the objective lens with respect to an optical information recording medium or an observation object which is an object to be focused and for producing an inclination error signal. Provided is a focus error detection device which also has a function of detecting a tilt error by receiving a light beam reflected by a medium or an observation object and transmitted through an objective lens by a light detection means.

In the focus error detecting apparatus according to the present invention, a plurality of focus control lasers, which are symmetrically decentered from the optical axis of the objective lens, are incident on the objective lens, and the reflected light from the optical information recording medium or the object to be observed is reflected. By detecting the focus error signal, the offset to the focus error signal due to the axial chromatic aberration of the objective lens can be reduced, and stable focus control can be realized. It is also possible to generate a master tilt error signal.

The present invention provides an exposure light source, a focus control light source having a wavelength longer than that of the exposure light source, an objective lens having a different focal length between the exposure light source wavelength and the focus control light source wavelength, and the objective lens. A light beam splitting unit that splits a light beam from the focus control light source into a plurality of light beams so as to be symmetrically decentered with respect to the optical axis and incident on the objective lens, and a focusing target facing the objective lens. A plurality of photodetectors for detecting the position of the light flux by the light amount distribution of the light flux reflected by the optical information recording medium and transmitted through the objective lens; and the objective for the focusing target from the output signal of the photodetector. An optical information recording apparatus is provided, which comprises: a calculating unit that calculates a focus error of a lens and generates a focus error signal.

According to the present invention, an optical disk master is used as the optical information recording medium, the focus control light source, the light beam splitting means, the objective lens, and the light detecting means are mounted, and the optical disk master is arranged in a radial direction. Provided is an optical disk master exposure apparatus, which is equipped with a slider that moves to the front.

The focus control laser in the optical disk master exposure apparatus according to the present invention is preferably a laser with low coherence.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, an optical disc master exposure device using the focus error detection device according to the present invention will be described. Further, the light beam split by the light beam splitting optical member will be described as two light beams.

(First Embodiment) FIG. 2 shows a main part of an optical configuration of an optical disk master exposure apparatus according to the present invention. The optical disc master exposure apparatus includes an exposure laser device 124 having a wavelength of 257 nm and a focus control laser device 1 having a wavelength of 635 nm.
01, a luminous flux diameter expanding portion 103, a condenser lens 104,
An iris diaphragm 123, a light beam splitting mirror (light beam splitting optical member) 105 including two mirrors, a polarization beam splitter 108, a falling mirror 109, a quarter-wave plate 110, and aberration correction. A parallel plate 111 and a dichroic mirror 112 for combining / separating both laser optical paths.
And an objective lens 113 having a numerical aperture of 0.9 having different focal lengths at both laser wavelengths, that is, having axial chromatic aberration, and a voice coil actuator 114 for driving the objective lens up and down.
, Two-division photodetectors 115 and 116, and arithmetic circuit 117
, Turntable 120, and spindle motor 121
And. The moving optical system 118 is the optical disc master 11.
9 is arranged on a slider 122 which moves in the radial direction.

The structure of the focus error detection system is as follows. A laser beam emitted from the focus control laser device 101 is expanded in the beam diameter by a beam diameter expanding section 103, and the iris diaphragm 1
After setting the desired light beam diameter at 23, the parallel light beam is converted into a convergent light beam by the condenser lens 104. The reason why the parallel light flux is converted into the convergent light flux will be described later.

The condensed light flux is split by the light flux splitting mirror 105 into two light fluxes indicated by a chain double-dashed line 106 and a broken line 107 in the figure. It should be noted that drawing the light beam after the light beam splitting mirror 105 causes the two light beams to be intricate and the figure becomes confusing. Therefore, only the central ray is shown after the light beam splitting mirror 105. The two light beams split by the light beam splitting mirror 105 are transmitted through the polarization beam splitter 108, converted from linearly polarized light to circularly polarized light by the quarter-wave plate 110, and the aberration correcting parallel plate 11 is used.
1. After passing through the dichroic mirror 112, the two light beams enter the objective lens 113 so as to be symmetrically decentered with respect to the optical axis of the objective lens 113.

The aberration-correcting parallel plate 111 is for correcting the aberration generated when the convergent light beam is transmitted through the dichroic mirror 112, and the dichroic mirror 11 is used.
It is a parallel plate having the same material and thickness as those of No. 2. Objective lens 113
The two light fluxes emitted from are reflected by the master 119 which is the focus object to be condensed. After that, the objective lens 113, the dichroic mirror 112, and the aberration correcting parallel plate 111 are transmitted, and the quarter-wave plate 110 converts circularly polarized light into linearly polarized light, and then is reflected by the polarization beam splitter 108.
They are led to the two-divided photodetectors 115 and 116, respectively. The output signals of the two-divided photodetectors 115 and 116 are input to the arithmetic circuit 117, and the focus error signal of the objective lens 113 with respect to the master 119 is generated.

The reason why the parallel light flux is converted into the convergent light flux by the condenser lens 104 is as follows. Objective lens 11
Since the focal length of No. 3 is different between the wavelength of 257 nm and the wavelength of 635 nm, when a parallel light flux of wavelength 635 nm enters the objective lens 113 when the exposure laser is focused, the master disk 119
Thus, the light flux reflected by and emitted from the objective lens 113 is diffused. Therefore, the convergent lens 104 enters the objective lens 113 as a convergent light beam to reduce the light beam diameter on the two-divided photodetector surface, so that sufficient focus error detection sensitivity / detection range can be secured. . still,
The light flux diameters of the two light fluxes entering the objective lens 113 are set to be sufficiently smaller than the objective lens aperture diameter so that the aberration that causes a problem does not occur in the objective lens 113.

Next, referring to FIG. 3, description will be given of the light beam splitting mirror 105 which splits the incident light beam into two light beams which are deviated from each other. The standard distance L1 between the central rays of the two light fluxes is 0.1 m
It is about m to 0.5 mm. When the distance between the central rays of the two light beams is small, for example, as shown in FIG. 3, a mirror 105a (partial reflection mirror) that transmits a part of the light and a mirror 105b (total reflection mirror) that totally reflects the light are used as reflecting surfaces. Composed so that they face each other. A space and parallelism can be secured by fixing the two mirrors with a spacer sandwiched between the mirrors. The partial reflection mirror is used as a back surface mirror, and the total reflection mirror is used as a front surface mirror.

When the mirror interval is L2, the interval L1 = 2
It becomes possible to create two light beams separated by ¹ / 2.L2. Since L1 is determined by the spacer thickness, 0.1 mm
It is possible to easily realize a high degree of accuracy with a high degree of accuracy. L1 is 0.5
In the case of about mm, it is possible to use an element having a partial reflection mirror and a total reflection mirror on the front and back of one glass plate. In this case, since the number of parts is small and no assembly is required, it can be realized at a lower cost. Since it is desirable that the signal levels of the output signals from the two-split photodetectors 115 and 116 are about the same, the beam splitting mirror 10
It is desirable that the optical powers of the two light beams divided by 5 are about the same. In order to realize this, the reflectance R of the partial reflection mirror may be set to about 0.38.

Next, the principle of the focus error detecting method according to the present invention will be described with reference to FIG. FIG. 4A shows a master 119.
4 (b) is located closer to the objective lens 113 than the focus of 257 nm light, FIG. 4 (b) shows that the master 119 is located at the focus of 257 nm light, that is, when focusing, and FIG. This is the case in which it is located far from the focal point of 257 nm light. In addition, from the objective lens 113 to the two-split photodetector 1
The optical elements between 15 and 116 are omitted because they are not essential in the explanation of the principle of the focus error detection method according to the present invention.

The chain double-dashed line 70 in the figure represents the focal plane of the objective lens at a wavelength of 257 nm. The two light beams 106 and 107 from the laser device for focus control (not shown) are passed through the objective lens 113.
Are symmetrically deviated by distances Δx and −Δx with respect to the optical axis of the light beam and enter the objective lens 113. Objective lens 1
The two light fluxes that have passed through 13 are reflected by the master 119, then emitted from the objective lens 113, and guided to the two-split photodetectors 115 and 116, respectively, and the two-split photodetectors 115 and 116.
The output signal from is input to the arithmetic circuit 117. Since the focal length of the objective lens 113 is different between the wavelength of 257 nm and the wavelength of 635 nm, the emitted light (center ray) from the objective lens 113 is not parallel to the optical axis of the objective lens as shown.

Light receiving surfaces 115a, 115 of the two-division photodetector
The output signals from b, 116a, and 116b are respectively D
Assuming 1, D2, D3 and D4, the focus error signal Sf is
It is generated by the operation circuit 117 performing the operation of the following expression (1).

Sf = (D1−D2) − (D3−D4) (1) As the focus between the objective lens 113 and the master 119 shifts, the direction of the light emitted from the objective lens 113 changes as shown in the drawing, and the light is divided into two. Since the positions of the light beams on the surfaces of the photodetectors 115 and 116 change, the focus error signal S is calculated by the above equation (1).
f can be generated. The focus error detection method using one light beam decentered from the optical axis of the objective lens is known as the skew beam method (for example, Shokodo Applied Optical Electronics Handbook ISBN4-7856-9031-3). The novel point of the present invention is to use a plurality of light beams symmetrically decentered from the optical axis.

Next, (i) the offset to the focus error signal due to the displacement of the objective lens in the optical disc master exposure apparatus according to the present invention, and (ii) the reason why two light fluxes are used in the optical disc master exposure apparatus according to the present invention. Will be described.

(I) Offset to Focus Error Signal In the optical disc master exposure apparatus according to the present invention, the fact that the offset to the focus error signal due to the displacement of the objective lens is sufficiently small means that on the two-divided photodetector surface with respect to defocus. This will be described by comparing the positional displacement amount of the light flux with the positional displacement amount of the light flux on the two-division photodetector surface due to the displacement of the objective lens.

As shown in FIG. 4, the eccentric amount of the incident light beam from the optical axis of the objective lens is Δx, the objective lens focal length at the focus control laser wavelength is f ₆₃₅ , and the defocus amount is Δ.
d, the distance from the principal plane of the objective lens to the two-division photodetector is D (negative value). Also, the distance (F ₆₃₅ −F ₂₃₇ ) between the objective lens focus position F _{257 at} the exposure laser wavelength and the objective lens focus position F ₆₃₅ at the focus control laser wavelength is Δ.
Let it be F. The light beam position h (distance from the optical axis of the objective lens) on the two-divided photodetector surface is given by the following equation (2) as a function of Δx, Δd and D by paraxial calculation.

[0030]

[Equation 1]

Therefore, the positional displacement of the light beam on the photodetector surface due to the defocus Δd from the in-focus position is given by the following equation (3).

[0032]

[Equation 2]

Next, as shown in FIG. 5, let us consider a case where the objective lens is displaced by Δz in the optical axis direction while maintaining the in-focus state. The positional displacement amount h of the light flux on the two-divided photodetector surface is given by the following equation (4) from the above equation (2). Due to this positional displacement of the light flux, the focus error signal does not become zero but becomes an offset regardless of the in-focus state.

[0034]

[Equation 3]

The positional displacement amount h of the light beam on the two-divided photodetector surface will be calculated below using specific numerical values. The objective lens focal length f ₂₅₇ at the exposure laser wavelength 257 nm is 2.0 mm, and the objective lens focal length f ₆₃₅ at the focus control laser wavelength 635 nm is 2.4 mm. Wavelength 25
The positions of the principal points of the objective lens of 7 nm and the wavelength of 635 nm are generally different, but the distance between them is considered to be 0.1 mm or less, so ΔF≈f ₆₃₅ −f ₂₅₇ = 0.4 mm. These numerical values are described in Japanese Patent Laid-Open No. 2000-348370. Also, the amount of eccentricity Δx of the incident light beam from the optical axis of the objective lens is 0.3 mm, which is 2 from the main plane of the objective lens.
The distance D to the split photodetector is -400 mm. FIG. 6 shows the amount of positional displacement of the light beam on the two-divided photodetector surface due to defocus Δd. Further, FIG. 7 shows the positional displacement amount h of the light beam on the two-divided photodetector surface due to the displacement Δz of the objective lens.

The objective lens focal depth is λ at the laser wavelength,
If the numerical aperture of the objective lens is NA, then ± λ / (2NA ² )
Is given by, and the wavelength is 257 nm, NA is ± 0.1
It is 59 μm. The positional displacement of the light beam on the two-divided photodetector surface with respect to the defocus of ± 0.159 μm (depth of focus) is ± 6.59 μm, whereas the displacement of the objective lens is ± 1.
The positional displacement of the light flux on the two-division photodetector surface due to 0 μm is ± 0.42 μm. By using the optical disk master exposure apparatus according to the present invention, the offset to the focus error signal due to the displacement of the objective lens can be made sufficiently smaller than the depth of focus of the objective lens.

(Ii) Reason for using two light fluxes In the optical disk master exposure apparatus according to the present invention, two light fluxes symmetrically decentered with respect to the optical axis of the objective lens are used because of the focus caused by the tilt of the master. This is to reduce the offset to the error signal. FIG. 8 shows the position of the light beam on the two-division photodetector surface when the master disc is tilted during focusing. Figure 8
FIG. 8A shows the case where there is an inclination around the rotation axis parallel to the paper surface, while FIG. 8B shows the case where there is an inclination around the rotation axis perpendicular to the paper surface. In the case of FIG. 8A in which there is an inclination around the rotation axis parallel to the paper surface, the light flux on the two-division photodetector surface is displaced in the division line direction of the two-division photodetectors 115 and 116, so the inclination of the master disc The offset of the focus error signal due to the above does not occur. On the other hand, in the case of FIG. 8B in which there is an inclination around the rotation axis perpendicular to the paper surface, the positions of the two light beams on the two-division photodetector surface are orthogonal to the division line of the two-division photodetectors 115 and 116. Displace in the direction.

FIG. 9 shows the focus error signals S1 = (D1-D2) and S2 = (D3-D4) generated using only one light beam.
9A and 9B, the focus error signal Sf = (D1-D2)-(D3-D4) generated using two light fluxes is shown in FIG.
It shows in (c). In the figure, the horizontal axis is the objective lens 113 and the master 1.
19, the broken line 130 is the focus error signal when the master 119 is not tilted, and the solid line 131 is the master 119.
This is the focus error signal when there is an inclination in. As shown, when the focus error signal is generated using only one light flux,
The tilt of the master 119 causes an offset to the focus error signal. However, by using two light fluxes that are symmetrically decentered from the optical axis of the objective lens, (D1-D2)-(D3-
If the focus error signal is generated by the calculation of D4), the offset to the focus error signal due to the inclination of the master 119 can be reduced as shown in the figure, and stable focus control can be performed. Incidentally, the warp of the master 119 or the offset to the focus error signal due to the waviness of the master surface can be similarly reduced, and stable focus control can be performed.

Next, the focus control laser will be described. Objective lens 1 used in optical disc master exposure device
Reference numeral 13 is composed of a large number of lenses, and each surface of the lenses is antireflection against the exposure laser wavelength.
However, when the exposure laser wavelength is in the deep ultraviolet wavelength range, it becomes difficult to simultaneously satisfy the antireflection condition for other wavelengths. Therefore, when the focus control laser enters the objective lens 113, the reflected light on each surface of the lens becomes stray light. There is a problem if these stray lights interfere with each other or the stray lights interfere with the return light from the master 119. That is, as the distance between the focus control laser device and the objective lens changes due to the displacement of the objective lens, the interference state changes and ripple noise is superimposed on the focus error signal. Further, when the exposure laser in the deep ultraviolet wavelength range is used, the depth of focus is shallower than that in the case where an ultraviolet laser having a wavelength of 351 nm which has been conventionally used is used. Therefore, even a slight noise may greatly affect the recording state. .

Therefore, as the focus control laser device,
Semiconductor laser with low coherence driven by high frequency superposition, or SLD (Super Luminescent Diode) with low coherence
e) and the like are preferable.

(Second Embodiment) A second embodiment in which the light beam splitting mirror 105 of the first embodiment is formed of another optical member will be described. The light beam splitting mirror 105 shown in FIG.
Although the structure is simple, the influence of the inclination of the master 119 cannot be completely removed. This is because an optical path difference is generated between the two divided light beams 106 and 107. A light beam splitting mirror unit 211 that avoids this problem is shown in FIG. The light beam splitting mirror unit 211 includes a first light beam splitting mirror 202, a half-wave plate 203, and a second light beam splitting mirror 204. The light beam splitting mirror unit 211 is the light beam splitting mirror 105 shown in FIG.
Corresponding to. According to this, the polarization beam splitter 202a has a function of splitting the light flux, and the first light flux splitting mirror 202 and the second light flux splitting mirror 204 have the function of shifting the split light flux. Is lost.

The light beam which passes through the condenser lens 104, is reflected by the mirror 201, and is incident on the light beam splitting mirror 211 is p.
It is assumed to have both polarized light and s-polarized light components. Figure 10
Shows an example of tilted linearly polarized light, but circularly polarized light may also be used. This incident light enters the first light beam splitting mirror 202. The s-polarized component of the light beam incident on the mirror 202 is reflected by the polarization beam splitter 202a. On the other hand, the p-polarized light component passes through the polarization beam splitter 202a, is reflected by the mirror 202b, and passes through the polarization beam splitter 202a again.

The incident light beam is thus split into two deviated light beams. After that, the two luminous fluxes are both halved
The polarization direction is rotated 90 degrees by the wave plate 203, and the second
Is incident on the light beam splitting mirror 204. The second light beam splitting mirror 204 is an element having the same specifications as the first light beam splitting mirror 202. The s-polarized component (light flux reflected by the mirror 202b) that has entered the second light flux splitting mirror 204 is reflected by the polarization beam splitter 204a. On the other hand, the p-polarized component (light flux reflected by 202a) passes through the polarization beam splitter 204a and is reflected by the mirror 204b,
It again passes through the polarization beam splitter 204a. As a result, the optical path lengths of the two light beams 206 and 207 are determined by a plane perpendicular to the optical axis after passing through the polarization beam splitter 204a, for example,
It becomes the same at the position of the non-polarizing beam splitter 212. After that, the light beam reflected by the master and returned is guided to the photodetectors 115 and 116 by the non-polarizing beam splitter 212.

(Third Embodiment) A third embodiment in which the light beam splitting mirror 105 of the first embodiment is constituted by another optical member will be described. FIG. 11 shows a light beam splitting mirror unit 210 of this embodiment. In the third embodiment, a wave plate 206 is arranged after the second light beam splitting mirror 204,
A polarization beam splitter 108 is arranged behind the light beam splitting mirror unit 210. The wave plate 205 is
Either a half wave plate or a quarter wave plate may be used.

After the transmission, the polarization directions of the two light beams rotate by 45 ° and 135 °, respectively, that is, the polarization direction of one light beam and the optical axis direction of the wave plate form an angle of 22.5 °. Install a half-wave plate. In the case of the quarter-wave plate, both of the two light fluxes after transmission are circularly polarized, that is, the polarization direction of one light flux and the crystal optical axis direction of the wavelength plate form an angle of 45 degrees. To place. By doing so, the two light fluxes can be transmitted through the polarization beam splitter 108 with a transmittance of 50%, and the light can be efficiently used.

(Fourth Embodiment) In the fourth embodiment of the present invention, as shown in FIG. 12, the tilt error signal St of the master 119 is output to the arithmetic circuit 117 shown in the first embodiment. The arithmetic circuit 125 is added. The components of the fourth embodiment other than the arithmetic circuit 125 are the same as those of the first embodiment, and thus the description thereof will be omitted. Focus error signal Sf,
And the tilt error signal St of the master 119 is calculated by the arithmetic circuit 11
It is generated by performing the operations of the following equations (5) and (6) using Nos. 7 and 125.

Sf = (D1-D2)-(D3-D4) (5) St = (D1-D2) + (D3-D4) (6) Based on the focus error signal generated by the calculation of the above formula (5). When the master disc 119 has no inclination when the focus control is performed by the focus control, the signal St of the above equation (6) outputs a signal of zero. On the other hand, when the master disk 119 has a tilt, as is apparent from FIG. 8B, a signal in which St is non-zero is output. That is, the tilt error signal of the master can be generated by the calculation of (6).

The embodiments of the present invention have been described above with reference to specific examples. In the description of the embodiment,
Although the photodetector is a two-division photodetector, a PSD (position detection element) that detects the barycentric position of the light amount distribution may be used instead of the two-division photodetector. Also, in the above-described embodiment,
Although the description has been made assuming that the number of light beams split by the light beam splitting mirror is two, the number of light beams is not limited to this, and a plurality of more light beams may be used. Further, in the above description, the present invention is applied to the optical disk master exposure apparatus, but it can be applied to a mask inspection apparatus or mask positioning in semiconductor manufacturing.

The present invention is not limited to the above embodiment, and can be variously modified at the stage of implementation without departing from the spirit of the invention. Furthermore, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some of the constituent elements are deleted from all the constituent elements shown in the embodiment, at least one of the problems described in the section of the problem to be solved by the invention can be solved and described in the section of the effect of the invention. When at least one of the effects described above is obtained, a configuration in which this constituent element is deleted can be extracted as an invention.

[0050]

As described above, according to the present invention,
When using an objective lens with different focal lengths for the exposure laser wavelength and the focus control laser wavelength, use multiple light beams that are symmetrically incident with respect to the optical axis of the objective lens, and It is possible to provide an optical disc master exposure apparatus that can reduce the offset to the focus error signal that occurs with it and can perform stable focus control. Further, stable focus control can be realized by a focus control laser having a wavelength different from that of the exposure laser, so that it can be applied to optical disks of various formats such as ROM and RAM. Further, not only the focus error signal but also the tilt error signal of the master can be generated. Further, according to the present invention, it is possible to provide an inexpensive optical disk master exposure apparatus in which the actuator part has a simpler structure and is cheaper than the case where an objective lens which is expensive and has a corrected axial chromatic aberration is used.

[Brief description of drawings]

FIG. 1 is a diagram showing a focusing state of an exposure laser and a focus control laser according to displacement of an objective lens.

FIG. 2 is a diagram showing a main optical system of the optical disk master exposure apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a light beam splitting mirror configured by a partial transmission mirror and a total reflection mirror.

FIG. 4 is a diagram showing the principle of focus error detection according to the present invention.

FIG. 5 is a diagram showing positional displacement of a light beam on a photodetector surface due to displacement of an objective lens.

FIG. 6 is a diagram showing a positional displacement amount of a light beam on a photodetector surface with respect to defocus.

FIG. 7 is a diagram showing a positional displacement amount of a light beam on a photodetector surface with respect to displacement of an objective lens.

FIG. 8 is a diagram showing the position of a light beam on the photodetector surface when the master disc is tilted.

FIG. 9 is a diagram showing a focus error signal when the master disc is tilted.

FIG. 10 is a view showing a light beam splitting mirror unit used in an optical disk master exposure apparatus according to the second embodiment of the present invention.

FIG. 11 is a diagram showing a light beam splitting mirror unit used in an optical disk master exposure apparatus according to a third embodiment of the present invention.

FIG. 12 is a diagram showing an arithmetic circuit of an optical disc master exposure apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

20 ... Laser for exposure 21 ... Laser for focus control 70 ... Objective lens focal plane at wavelength 257 nm 101 ... Laser device for focus control 102 ... 45 degree mirror 103 ... Enlarged part of luminous flux diameter 104 ... Condensing lens 105 ... Beam splitting mirror 106, 107 ... Focus control laser 108 ... Polarizing beam splitter 109 ... Falling mirror 110 ... Quarter wave plate 111 ... Parallel plate for aberration correction 112 ... Dichroic mirror 113 ... Objective lens 114 ... Voice coil actuator 115, 116 ... 2-split photodetector 117 ... Focus error calculation circuit 118 ... Moving optical system 119 ... Master 120 ... turntable 121 ... Spindle motor 122 ... slider 123 ... Iris diaphragm 124 ... Laser device for exposure 125 ... Inclination error calculation circuit 130 ... Focus error signal when the master disc is tilted 131 ... Focus error signal when the master does not tilt 201 ... Mirror 202 ... First light beam splitting mirror 203 ... Half wave plate 204 ... Second beam splitting mirror 205 ... Half wave plate or quarter wave plate 206 ... Focus control laser 207 ... Laser for focus control 210 ... Luminous flux splitting mirror unit 211 ... Luminous flux splitting mirror unit 212 ... Non-polarizing beam splitter

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D118 AA01 AA03 AA18 BA01 BB09                       BF03 CA11 CC04 CC12 CD02                       CF03 CG03 CG07 CG17 CG26                       DA19 DA33                 5D119 AA01 AA20 AA29 BA01 BB09                       CA05 DA01 EA03 EB12 EC26                       EC40 FA05 JA21 JA32 JA43                       JB01 KA10 KA17                 5D121 BB21 BB38                 5D789 AA01 AA20 AA29 BA01 BB09                       CA05 DA01 EA03 EB12 EC26                       EC40 FA05 JA21 JA32 JA43                       JB01 KA10 KA17

Claims (8)

[Claims] 1. A light source for focus control, an objective lens, and a plurality of light fluxes from the light source for focus control so as to be symmetrically decentered with respect to the optical axis of the objective lens and enter the objective lens. A light beam splitting means for splitting the light beam into a plurality of light detectors, a plurality of light detectors for detecting the position of the light beam by the light amount distribution of the light beam reflected by the focusing object facing the objective lens and transmitted through the objective lens, and the light detection. Error detecting apparatus for calculating a focus error of the objective lens with respect to the focusing object from an output signal of the instrument and generating a focus error signal. 2. An exposure light source, a focus control light source having a wavelength longer than that of the exposure light source, an objective lens having a different focal length depending on the wavelength of the exposure light source and the wavelength of the focus control light source, and the optical axis of the objective lens. A beam splitting means for splitting the light beam from the focus control light source into a plurality of light beams so as to be symmetrically decentered and incident on the objective lens; and a focus object facing the objective lens. A plurality of photodetectors for detecting the position of the light flux by the light amount distribution of the light flux reflected by the optical information recording medium and transmitted through the objective lens, and the objective lens for the focusing target from the output signal of the photodetector. An optical information recording device, comprising: a calculating unit that calculates a focus error and generates a focus error signal. 3. The apparatus according to claim 1, wherein the light beam splitting means comprises a partial transmission mirror and a total reflection mirror which are arranged with a predetermined distance therebetween. 4. The light beam splitting means is provided with a plurality of optical elements, which are arranged at a predetermined distance apart and are composed of a polarization beam splitter functioning as a partial transmission mirror and a total reflection mirror, and between these optical elements. An apparatus according to claim 1 or 2, further comprising: a half-wave plate disposed on the. 5. The light beam splitting means is provided with a plurality of optical elements, which are arranged at a predetermined distance from each other and are composed of a polarization beam splitter functioning as a partial transmission mirror and a total reflection mirror, and between these optical elements. The apparatus according to claim 1 or 2, further comprising: a half-wave plate disposed on the output side and a quarter-wave plate disposed on the emission side. 6. A calculation means for calculating a tilt error of the objective lens with respect to the focusing object to generate a tilt error signal, further comprising: a light beam reflected by the focusing object and transmitted through the objective lens. The apparatus according to claim 1, further comprising a function of detecting light by a detector to detect an inclination error. 7. The optical information recording device according to claim 2, wherein an optical disk master is used as the optical information recording medium, the focus control light source, the light beam splitting means, the objective lens, and the light. An optical disk master exposure apparatus, comprising: a detection unit and a slider that moves in a radial direction of the optical disk master. 8. The optical disk master exposure device according to claim 7, wherein the optical information recording device is provided with a tilt detecting beam function.