JP2002342974A - Laser exposure device, laser exposure method, master disk producing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser exposure device which can accurately detect a focus error when a master disk exposure is carried out by using a ultraviolet laser. SOLUTION: The laser exposure device is provided with an objective lens 11 and a focus control means. The objective lens 11 passes and condenses a ultraviolet laser beam 2 and focus error detection light 12, the glass master disk 14 is irradiated with the detection light 12 condensed by passing through a correcting lens 21 and the objective lens 11, and focus error detection light 13 reflected from the glass master disk 14 is supplied to a bisecting photodetector 23 after passing through the objective lens 11 again. The focus control means does not control the position of the objective lens 11 in the direction of the focus when the detection result of the detector 23 is 'focused', and controls the position of the objective lens 11 in the direction of the focus until the detection result of the detector 23 becomes 'focused' when the detection result is 'unfocused'. The detection light 12 is set so as to be introduced in almost parallel to the optical axis (a) of the objective lens 11 through to correcting lens 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser exposure apparatus, a laser exposure method, and a disk master using a visible light laser as a light source for detecting a focus error during exposure while using an ultraviolet laser as a light source for exposure. It concerns the device.

[0002]

2. Description of the Related Art Hereinafter, a description will be given of a master recording machine for an optical disk as an example. Here, the master recording machine for optical disks is
This refers to a disc master making device that creates a master disc that is the basis for creating a disc substrate that constitutes a recording-only (ROM) optical disc, a write-once (R) optical disc, and a repetitive recording (RW, RAM) optical disc. is there.

[0003] The master disc uses a photoresist as a photosensitive agent applied to the entire surface of the disc-shaped glass substrate. This photoresist has a characteristic that a photosensitive action is developed according to the intensity of an electric field of light which is an electromagnetic wave. This is usually called recording in the photon mode. For this reason, if a focus error is detected using an exposure laser used for exposure, a problem occurs in actual work (for example, when the focus servo is applied, the objective lens is moved to an arbitrary radius on the master disk). Therefore, it is difficult to form an exposure light spot by irradiating an exposure laser at an arbitrary position in the radial direction of the master disc, and to start exposure from this position.

Therefore, focus error detection is performed by using a visible light laser having a wavelength to which the photoresist is not exposed as a focus error detection laser for focus error detection. As a focus error detection laser, typically, a 633 nm wavelength helium-neon laser or 630 nm to 690 nm is used.
A semiconductor laser having a wavelength of m is used.

[0005]

The above-mentioned master recording machine for an optical disk has been developed in accordance with an increase in the recording capacity of the optical disk.
It is required to form (engrave) finer pits or grooves on a master disk, and therefore, high-resolution exposure is required. This resolution is determined by the size (diameter) of the exposure light spot irradiated and formed on the master disc. The smaller the diameter of the exposure light spot at the time of focusing (just focus) on the master disc, the higher the resolution.

The size of the exposure light spot is defined by the wavelength of the exposure laser and the numerical aperture of the objective lens.
Since the numerical aperture of the objective lens is practically close to the upper limit,
It is necessary to gradually shorten the wavelength of the exposure laser with each generation change of the master disk recorder (with an increase in the recording capacity of the optical disk). As an exposure laser, a compact disk (CD) compatible master recording device is 458 nm.
The laser having a wavelength of is often used and has a sufficient resolution as a CD. However, in a master recording device corresponding to a digital versatile disk (hereinafter referred to as a DVD), 413n
It is essential to use a laser having a wavelength of m to 351 nm.

In recent years, with the rapid development of information communication and image processing technologies, it has been desired to increase the recording capacity of optical discs. Existing external dimensions (diameter 1
In order to increase the capacity of the optical disk while maintaining the thickness of the optical disk at 20 mm, it is necessary to further reduce the pit or groove pattern to improve the recording density. DVD mentioned above
Exposure lasers used when producing a master disc corresponding to the next generation of high-density optical discs are DV lasers.
Since a laser having a wavelength of 351 nm used for D cannot provide a sufficient resolution, it is necessary to use an exposure laser having a shorter wavelength than this. For this reason, master recording devices using deep ultraviolet light having a wavelength of 300 nm to 200 nm as an exposure laser have been developed.
The term “ultraviolet light” is a general term for light having a wavelength of 400 nm or less, and is called by being subdivided according to the wavelength. For example,
Light of 200 nm to 300 nm is called deep ultraviolet light,
200 nm that cannot be handled in air because it is absorbed by air
The following light is called vacuum ultraviolet light.

However, when the wavelength of the exposure laser is shortened to the deep ultraviolet region, the glass material applicable to the objective lens is limited accordingly. For example, when a deep ultraviolet laser having a wavelength of about 250 nm is used as an exposure laser, the glass material applicable to the objective lens is limited to quartz glass or fluorite. In practice, it is extremely difficult to produce a uniform lens of a sufficient size as an objective lens using fluorite, so that the objective lens is produced from a single glass material made of only quartz glass.

FIG. 6 shows an example of such an objective lens.
FIG. 6 is a diagram showing the structure of seven objective lenses in seven groups. In FIG. 6, a is the optical axis. This objective lens has a seven-group, seven-element structure in which all glass materials are made of quartz glass. This objective lens is designed to be able to collect light without aberration when a deep ultraviolet laser is incident as an exposure laser. When a visible light laser is passed through this objective lens as a laser for focus error detection, since the focal length of the visible light laser is different from that of the deep ultraviolet laser because it is made of a single glass material, the visible light laser Does not match the focal plane for the deep UV laser. Optically,
This is called axial chromatic aberration. Here, the axial chromatic aberration between the deep ultraviolet laser and the focus error detecting laser is called chromatic aberration.

In other words, as a result of such a wavelength difference, both the exposure laser and the focus error detection laser pass through this objective lens, and the exposure light spot and the focus error detection light spot are formed on the surface of the master disc. When both are formed by irradiation, there is a problem that the focal plane of the focus detection laser and the focal plane of the exposure laser largely deviate due to the chromatic aberration of the focus error detection light spot. In the example of the lens of FIG. 6, there is a great difference such that the focal length of the objective lens differs by 15% due to chromatic aberration.

As one method for removing the chromatic aberration generated in such an objective lens having a multi-group, multi-lens configuration, Japanese Patent Application No.
There is one described in JP-A-00-33487.
That is, in the outward optical path until the focus error detection laser is incident on the objective lens, optical characteristics such that the chromatic aberration generated by the focus error detection laser passing through the objective lens can be offset (actually, (The compensation lens is an optical characteristic of a convex lens to compensate for the increase in the focal length of the objective lens due to the longer wavelength.)
Is provided. If this correction lens is not provided in the forward optical path of the focus detection light, even if the exposure light spot is in focus on the disc master surface (light spot is point-like), a focus error detection light spot having chromatic aberration Is no longer in focus (the light spot is circular), resulting in inaccurate focus error detection, which prevents high-resolution exposure.

As described above, by providing the correction lens in the outward optical path of the focus error detection laser, the exposure laser and the focus error detection laser having the wavelength difference are both incident on the objective lens. Even when the light is condensed, the focus error detection light spot irradiated and formed on the surface of the disk master does not have the chromatic aberration described above, which enables accurate focus error detection. Can be expected.

What has been described so far is based on the premise that the surface of the master disc on which the exposure light spot and the focus error detection light spot are formed is ideally flat. However, in reality, the surface of the disk master is not always flat, and when the disk master is rotated during exposure, the disk master may run out, or the disk master may be exposed from the inner circumference to the outer circumference. In this case, a slight change in the height position occurs on the surface in the radial direction (the surface of the disk master is microscopically convex or concave with respect to an ideal flat surface). When exposing the surface of the disk master, the objective lens is finely moved (position controlled) in the focus direction according to the state of a minute change in the height position of the surface to irradiate the surface of the disk master. It is necessary to perform focus control so that the exposure light spot is always in focus.

The above-mentioned Japanese Patent Application No. 2000-33487 describes an optical system having a structure in which a laser for focus error detection, which has passed through the above-mentioned correction lens, enters the optical axis of the objective lens at a slight angle. (FIG. 5 (a)). In this case, when the focus control for controlling the position of the objective lens in the focus direction is performed, the distance between the objective lens and the correction lens fixed at a predetermined position changes.
(Small contraction, small extension).

Due to the change in the distance, the focus error detecting laser, which is slightly obliquely incident on the optical axis of the objective lens, is reflected on the surface of the master disc and returns through the objective lens and exits. The optical path of the light (the return optical path of the focus error detection light) is set to the normal optical path of the return light (a predetermined distance is set between the correction lens and the objective lens, which is set when the surface of the disk master is ideally flat. (The return optical path of the focus error detection light) obtained by the above operation.

A focus error detector is provided at the end of the optical path of the normal return light. The focus error detector is located at a position for detecting and outputting no focus error (in-focus state) when receiving return light on the optical path of the normal return light. On the other hand, when the return light deviating from the optical path of the normal return light is received, the focus error detector detects and outputs a focus error (out-of-focus state).

In other words, when the focus error detecting laser beam that has passed through the correction lens is slightly obliquely incident on the optical axis of the objective lens, the objective lens as described above is placed on the glass substrate. When focus control for following the surface of the state is performed, when the light spot of the exposure laser (deep ultraviolet laser) is in focus on the disc master, the return light of the focus error detection laser is the regular light as described above. The light enters the focus error detector in a state shifted from the optical path of the return light.

For this reason, when the servo operation is performed, the distance between the objective lens and the master disc is adjusted so that the error on the focus error detector is eliminated, and as a result, defocus occurs in the deep ultraviolet spot. . As a result, there is a problem that it is extremely difficult to perform high-resolution exposure.

As one method for solving this problem, it is conceivable that both the objective lens and the correction lens are incorporated in a focus actuator, and a focus error detection operation is performed integrally with both. However, in such a case, since the ultraviolet light as the exposure laser beam passes through the correction lens, inconvenience is included in the exposure light spot, and chromatic aberration is included. It was inappropriate.

Therefore, the present invention has been made in view of the above problem, and in particular, the laser for focus error detection via the correction lens enters substantially parallel to the optical axis of the objective lens. When the objective lens is moved in the focus direction by the above-described focus control operation, for example, when the surface of the medium to be exposed, which is the master disc, changes minutely due to surface runout or the like. Accordingly, even if the distance between the objective lens and the correction lens changes, the incident position where the focus error detection laser enters the objective lens does not change. After passing through the correction lens and the objective lens, the reflected light is reflected on the surface of the medium to be exposed and is transmitted again through the objective lens and emitted therefrom. The change in the optical axis of the return light toward the focus error detecting means (focus error detector) can be suppressed to a small extent (the optical path of the return light is changed according to the ratio of the change in the distance between the objective lens and the correction lens). (Since it is only slightly displaced in parallel translation), this ensures that even when the medium to be exposed whose surface has a minute change in the height position is exposed using an ultraviolet laser, the focus is always stable and highly accurate. It is an object of the present invention to provide a laser exposure apparatus capable of detecting an error and thereby exposing a high-resolution pit or groove.

[0021]

In order to solve the above-mentioned problems, the present invention provides a laser exposure apparatus, a laser exposure method, and a disk master making apparatus having the following constitutions (1) to (3). . (1) As shown in FIGS. 1 to 4, an objective lens 1 that focuses an incident ultraviolet laser (ultraviolet laser beam) 2 for exposure and emits it to a medium (glass master) 14 to be exposed.
1 so that a light spot formed on the medium 14 to be exposed by the irradiation of the ultraviolet laser 2 emitted from the objective lens 11 is exposed on the medium 14 as an exposure light spot in a focused state. A focus error detection laser (focus error detection light (going)) 12 that is used for detecting the focus state and is a visible light laser.
Passes through the correction lens 21 having an optical characteristic for correcting chromatic aberration between the ultraviolet laser 2 generated by passing through the objective lens 11 and passes through the objective lens 11 through the focus error detection laser 12. Then, the focus light is irradiated on the medium 14 to be exposed, and the return light (focus error detection light (return)) 13 reflected from the exposed medium irradiated with the focus error detection laser 12 is After passing through the objective lens 11 again, it is supplied to a focus error detecting means (two-split photodetector) 23 for detecting the in-focus state without passing through the correction lens 21 again.
When the detection output of is not in focus, the position of the objective lens 11 is not controlled in the focus direction. When the detection output of the focus error detection means 23 is not in focus, the detection of the focus error detection means 23 is performed. In a laser exposure apparatus (laser cutting apparatus) AA including a series of focus control means for performing a series of focus controls for controlling the position of the objective lens 11 in the focus direction until the output becomes in focus, the correction lens 21 The focus detection laser 12 through the objective lens 11
A laser exposure apparatus which is set so as to be incident substantially parallel to the optical axis a of the laser exposure apparatus. (2) a light spot forming step of forming a light spot on the medium to be exposed by irradiating the medium to be exposed with an ultraviolet laser for exposure by condensing an ultraviolet laser for exposure through an objective lens; Focus error detection, which is used to detect the in-focus state and is a visible light laser, such that the light spot formed on the exposure medium exposes the medium to be exposed as an in-focus exposure light spot. Laser for
After passing through a correction lens having optical characteristics to correct chromatic aberration between the ultraviolet laser and the ultraviolet laser generated by passing through the objective lens, the light is incident substantially parallel to the optical axis of the objective lens and condensed. The return light reflected from the exposed medium irradiated with the focus error detection laser is irradiated onto the exposed medium without passing through the correction lens after passing through the objective lens again. The focus error is supplied to a focus error detecting means for detecting a focus state, and when the detection output of the focus error detecting means is in a focus state, the position of the objective lens is not controlled in a focus direction, and the detection output of the focus error detecting means is not obtained. If the objective lens is not in focus, the objective lens is forged until the detection output of the focus error detection means is in focus. The laser exposure method is characterized in that a focus control step of performing a series of focus control for position control in the scan direction. (3) A disk master (disk-shaped glass master) 14, which is a base for forming a disk substrate (having minute pits and fine grooves formed concentrically or spirally) constituting a disk-shaped recording medium, A disk master making apparatus (laser cutting apparatus) AA to be made, which focuses an incident ultraviolet laser (ultraviolet laser beam) 2 for exposure and has a surface coated with a photosensitive agent on the side of the disk master 14 side. Objective lens 11 for emitting light to the objective lens 1
The light spot formed on the disk master 14 by the irradiation of the ultraviolet laser 2 emitted from the disk master 1 is used as an exposure light spot in a focused state.
A laser for focus error detection (focus error detection light (going)) 12 which is used to detect the in-focus state and is a visible light laser as if the top is exposed, is generated by passing through the objective lens 14. After passing through a correction lens 21 having optical characteristics for correcting chromatic aberration between the ultraviolet laser 2 and the laser beam 2, the focus error detection laser 12 is condensed by passing through the objective lens 11, and the disc master 14 is focused. The return light (focus error detection light (return)) 13 reflected from the disk master 14 irradiated with the focus error detection laser 12 and irradiated by the focus error detection laser 12 passes through the objective lens 11 again, and then the correction lens Focus error detecting means (two-segment photodetector) for detecting the in-focus state without passing through the light-receiving element 21 again
When the detection output of the focus error detection means 23 is in a focused state, the position of the objective lens 11 is not controlled in the focusing direction, and when the detection output of the focus error detection means 23 is not in the focused state. A master disc producing apparatus, comprising: focus control means for performing a series of focus controls for controlling the position of the objective lens 11 in a focus direction until a detection output of the focus error detection means 23 is brought into a focused state. (Laser Cutting Apparatus) In the AA, the focus detection laser 12 through the correction lens 21
An apparatus for producing a master disc, characterized in that it is set so as to be incident substantially parallel to one optical axis a.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser exposure apparatus, a laser exposure method, and a disc master making apparatus according to the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a view for explaining a recording (exposure) optical system of an optical disk master recording machine (laser cutting machine) as an embodiment of the laser exposure apparatus of the present invention, and FIG. 2 is an optical system of focus error detection light. FIG. 3 is a diagram for explaining a focus error detection method, and FIG. 4 is a focus detection laser via a correction lens when a change in the height position occurs on the surface of the disc master in the present invention. FIG. 5 is a diagram for explaining that the optical path of the return light of the laser for focus error detection reflected from the surface of the master disk moves in parallel after the laser beam is incident substantially parallel to the optical axis of the objective lens, and FIG. When the height position changes on the surface of the master disk in the master disk recorder, the focus detection laser through the correction lens enters the optical axis of the objective lens slightly obliquely. The optical path of the focus error detection laser return light reflected from the disc master surface is a diagram for explaining a moving later.

A laser cutting machine (disk master making apparatus), which is an embodiment of the laser exposure apparatus of the present invention, comprises:
200nm wavelength for recording laser (exposure laser)
~ 400nm UV laser, especially 200nm ~ 3
A deep ultraviolet laser having a wavelength of 00 nm, for example, a YAG fourth harmonic laser which is an ultraviolet laser having a wavelength of 266 nm is used.

The laser cutting apparatus AA shown in FIG.
A description will be given of a focus detection system to be described later (when a change in the height position occurs on the surface of the glass master (disc master) 14, focus error detection light (focus detection laser) 12 The purpose is to explain that the optical path of the focus error detection light 12 (return light) 13 of the focus error detection light 12 reflected from the surface of the glass master 14 after being incident substantially parallel to the optical axis a) moves in parallel. The description of the recording optical system using the ultraviolet laser will be minimized.

The ultraviolet laser beam 2 emitted from the ultraviolet laser light source 1 of the above-described ultraviolet laser is supplied to a light modulator 3, where the exposure amount of the ultraviolet laser is adjusted. The optical modulator 3 is an EO using an electro-optical element.
A modulator or an acousto-optic modulator is used. The ultraviolet laser beam 2 whose exposure amount has been adjusted by the optical modulator 3 is input to an optical deflector 5 after its optical path is deflected at right angles by a mirror 4. This optical deflector 5 is an EO using an electro-optical element.
A deflector or an acousto-optic deflector is used. When exposing the recording pit row or groove in a meandering (wobble) manner, the beam is deflected by the optical deflector 5. In addition,
Although not shown in FIG. 1, the above-mentioned exposure amount, deflection amount and the like are optimally controlled based on a signal detected by a photodetector appropriately arranged on the optical path of the ultraviolet laser beam 2.

The ultraviolet laser beam 2 deflected by the light deflector 5 is supplied to a beam expanding optical system 7 composed of lenses 7a and 7b after its optical path is further deflected by a mirror 5 at a right angle. You. The ultraviolet laser beam 2 whose optical path is deflected by the mirror 4 passes through the beam expanding optical system 7 and is converted into a light beam diameter larger than the entrance pupil diameter of the objective lens 11. Thereafter, the optical path of the ultraviolet laser beam 2 emitted from the beam expanding optical system 7 is further deflected at a right angle by a mirror 8, passed through a dichroic mirror 9, guided to an objective lens 11, and focused there. Irradiation is performed on an exposure position to be exposed on the glass master 14 whose surface is coated with a photosensitive material. In this way, the exposure position is exposed to light by irradiating the exposure position with the light spot for exposure. A focus actuator 10 is provided around the objective lens 11, and the position of the objective lens 11 is controlled in the focus direction by a drive control signal applied to the focus actuator 10.

Here, the dichroic mirror 9 provided on the incident side of the objective lens 11 transmits all of the ultraviolet laser beam 2 incident from the mirror 8 side, but from the optical system of the focus error detection light (FIG. 2). Spectral characteristics (wavelength selectivity) are imparted such that all the incident focus error detection light 12 is reflected toward the objective lens 11 side. The focus error detection light 12 is incident substantially parallel to the optical axis a of the objective lens 11 and is condensed here.
A focus error detection light spot is formed in the vicinity of the exposure light spot formed by irradiation.

There are two reasons why the two light spots (the light spot for exposure and the light spot for focus error detection) are not irradiated to the same place. The first reason is that even if there is a slight angle error between the two light beams (the ultraviolet laser beam 2 and the focus error detection light 12), they are not condensed at the same place.

The second reason is that even if the above-described axial chromatic aberration is corrected for the visible light (the focus error detection light 12) by the correction lens 21, the difference between the wavelengths of the two light beams is actually increased. As a result, chromatic aberration of spherical aberration is also generated in visible light, and the focus error detection light 12 incident on a point away from the center (optical axis a) of the objective lens 11 The reason for this is that the light is condensed in a different place from 2.

The focal plane of the focus error detection light 12 formed on the surface of the glass master 14 does not always coincide with the focal plane of the ultraviolet laser beam 2. The reason is that the function of the focus error detection light 12 is not for recording (exposure), but for detecting a focus error signal.
It is not necessary to focus on a small spot to the limit (wavelength limit). In the first place, the focus error detection light 12 forms a light spot having a spread even on its best image plane because of the chromatic aberration of the spherical aberration described above. For this reason, in a strict sense, it is difficult to define the size of the light spot of the focus error detection light 12 or the diameter of the laser beam on the glass master 14. Sufficient performance can be obtained if more than half of the beam of the focus error detection light 12 falls within a radius of about μm (5 μm to 15 μm).

A glass master 14 on which an exposure light spot and a focus error detection light spot are simultaneously irradiated and formed.
Is mounted on a turntable 15 and chucked on an air spindle (not shown) that rotates with high rotational accuracy by the rotation of a spindle motor 16. With the rotation of the air spindle, the ultraviolet laser beam 2
The focus error detection light 12 and the focus error detection light 12 are both condensed and irradiated onto the glass master 14 via the objective lens 11.

Here, the feed feed motor 18 is rotated to feed the feed feed mechanism 17 to which the spindle motor 16 is fixed in the radial direction of the turntable 15 or the objective lens 11 is moved to the radius of the turntable 15. By moving in the direction, a spiral recording pit row or groove is recorded (exposed) on the surface of the glass master disk 14 placed on the turntable 15. FIG.
In the figure, there is shown a configuration in which the spindle motor 16 is fed in the radial direction.

The laser cutting apparatus A having the above-described configuration
A shows a case where the ultraviolet laser beam 2 serving as a recording laser is irradiated onto the glass master disk 14.
The focus control is performed so that the focal point of the image is always located on the glass master 14. This focus control is performed by moving the objective lens 11 in parallel with the direction along the optical axis a in accordance with the amount of focus shift detected by the optical system (FIG. 2) of the focus error detection light.

As shown in FIG. 2, the optical system of the focus error detection light includes a laser light source 20, a correction lens 21, a mirror 22, and a split photodetector 23. Laser light source 2
0 emits the focus error detection light 12 described above. The focus error detection light 12 may be a helium neon laser having a wavelength of 632.8 nm or a wavelength of 630 nm to 69 nm.
A 0 nm semiconductor laser (visible laser) is used.

Next, a recording laser (ultraviolet laser beam)
The reason why a visible light laser having a wavelength different from 2 is used for the focus error detection light 12 will be described. The photoresist applied to the surface of the glass master recording 14 is exposed by the action of an electric field of light, which is an electromagnetic wave. Therefore, in the case of recording (exposure) on an optical disk using a commercially available organic material, phase change medium or magneto-optical medium, the recording laser
(Ultraviolet laser beam) Since the recording is performed by the effect of temperature rise due to the light irradiation of 2, the recording light amount is different from that which is not recorded when a low-power recording laser is irradiated.
This is a photoresist that has no threshold value for (exposure light amount) and is exposed even at a very low exposure amount.

For this reason, when the same laser is used for both recording and focus error detection, recording (exposure) is performed at an arbitrary radial position of the glass master 14 and the laser is applied to that portion. When irradiated, this irradiation immediately exposes the photoresist in that part,
There is a disadvantage that normal exposure cannot be performed.

Therefore, by using a laser having a wavelength (long wavelength) that is not sensitive to the photoresist applied to the glass master 14 as the focus error detection light 12, the laser beam can be positioned at any radial position on the glass master 14. To record (exposure) the focus error detection light 12
Irradiates the objective lens 11 while performing the servo operation.
Even if the position of the glass master 14 in the radial direction is adjusted, the photoresist at that portion is not exposed by this irradiation, so that recording can be easily started from an arbitrary radius.

Returning to FIG. 2, the focus error detection light 12 emitted from the laser light source 20 passes through the correction lens 21 and is then transmitted to the recording laser (ultraviolet laser beam 2) by the dichroic mirror 9. The light is guided onto the same optical path and is incident on the objective lens 11 together with the recording laser. The correction lens 21 adjusts a combined focal length of a lens system including the objective lens 11 and the correction lens 21 to complementarily correct chromatic aberration of the objective lens 11.
It has an optical property (for forming a focus error detection light spot that is focused on the same position as the position of the exposure light spot formed on the glass master 14 as described later).

The focal length of the correction lens 21 is, when combined with the objective lens 11, the point at which the focus error detection light 12 emitted from the objective lens 11 is condensed (a focus error detection light spot in a focused state). Is set near the light spot for exposure of the recording laser.

Here, the focus error detection light 12 is set in advance so as to be incident on a portion of the objective lens 11 which is substantially parallel to the objective lens 11 and displaced from the optical axis a by an appropriate amount. The diameter of the focus error detection light 12 is sufficiently smaller than the diameter of the pupil of the objective lens 11 on which the focus error detection light 12 is incident, and the focus error detection light 13 which is the reflected light (return light) from the surface of the glass master 14 is used to detect the focus error. At this time, the setting is made so that the focus error is not hindered due to a change in the amount of light due to the inside of the objective lens 11 or the pupil.

The position of the surface of the glass master 14 on which the focus error detection light spot formed by the focus error detection light 12 is formed depends on the focal length of the objective lens 11 due to the wavelength. Does not match the position. The difference between the positions is at most about 200 μm. However, the correction lens 21
Therefore, the beam of the focus error detecting light 12 on the surface of the glass master 14 can be reduced. The flatness of the surface of the glass master 14 is considerably high for the purpose of manufacturing a high-precision, high-density optical disk.

However, if the correction lens 21 is not used, the positions where the light spot for exposure and the light spot for focus error detection are irradiated and formed are different from each other. The detection light spot does not become in focus, the focus error detection light spot becomes considerably large, and information over a wide range is averaged. It will be.

The focus error detecting light 12 condensed by the objective lens 11 is reflected by the surface of the glass master 14 as shown in FIG. When the reflected focus error detection light 13 exits after being incident on the objective lens 11 again, it is emitted at a slightly large angle with respect to the optical axis a of the objective lens 11. Thereafter, the focus error detection light 13 does not pass through the correction lens 21 again, follows the optical path of the focus error detection light 12, is reflected by the mirror 22, and is guided to the light receiving surface of the two-divided photodetector 23. . The separation between the optical path (outward path) of the focus error detection light 12 and the optical path (return path) of the focus error detection light 13 is not the method described here, but what is called polarization separation optics combining a polarizing prism and a と wavelength plate. It is also possible to use a system.

The two-division detector 23 detects a change in the light receiving position of the focus error detection light 13 that occurs when there is a focus error by a differential method. In the return optical system, since the light does not pass through the correction lens 21, the focus error detection light (return beam) 13 is diffused light having a gentle spread. Therefore, a convex lens may be arranged in front of the two-segment detector 23 to reduce the diameter of the return beam so that the detector can easily detect it.

Next, a focus error detecting method according to the method of the present invention will be described with reference to FIG. FIG. 3 shows FIG.
FIG. 2 is a diagram depicting only the vicinity of the objective lens 11. The optical path incident on the surface of the glass master 14, the optical path of the focus error detection light 13 which is the reflected light of the focus error detection light 12, and the surface 14a of the glass master 14 are drawn by solid lines.
Position 14b where surface 14a of glass master 14 is drawn by a broken line
Up to the objective lens 11, the focus error detection light 13 becomes an optical path 13b shown by a broken line. When the focus error detection light 13 re-enters the objective lens 11 and is emitted, the position and direction of the focus error detection light 13 are shifted with respect to the optical path 13a shown by the solid line. Change. This change is received by the two-segment photodetector 23 to obtain a focus error signal.

Next, referring to FIG. 4, when the surface of the glass master 14 fluctuates, or when the glass master 14 moves from the inner circumference to the outer circumference, the correction is made by a change in the height of the disk surface. A description will be given of how the optical path of the focus error detection light 13 which is the reflected light of the focus error detection light 12 is deflected when the distance between the lens 21 and the objective lens 11 changes.

The state shown in FIG. 4A is set as a reference state. In this state, it is assumed that the objective lens 11 is set on the glass master 14 without a focus error. The focus error detection light 12 is incident perpendicularly (parallel to the optical axis a) on a portion separated from the center 11a of the objective lens 11 by a distance l.

FIG. 4B shows that the height of the surface of the glass master 14 changes from the state of FIG. 4A (from the surface 14a to the surface 1).
Since the surface position has changed by the distance (change amount d) at 4b), the objective lens 11 has also moved by the same distance. At this time, the incident position of the focus error detection light 12 on the objective lens 11 does not change. As a result, the focus error detection light 12 is reflected by the surface 14b of the glass master 14 and again the emission direction of the focus error detection light 13 emitted from the objective lens 11 does not change, but the emission position changes. The light beam (optical path) 31b of the light 13 is
It will be shifted laterally with respect to the optical path 31a.

A broken line 31a in FIG. 4B is an optical path 31a of the reflected light of the focus error detection light 12 in the state of FIG.
, And shows a state of lateral displacement. This drawing is exaggerated for the sake of explanation.
The amount of change d in the height of No. 4 is about 10 μm. In this case, the lateral shift amount is very small, and the influence on the focus error detection is small.

Further, referring to FIG. 5, the height of the disk surface generated when the glass master 14 is wobbled, or when the glass master 14 is moved from the inner circumference to the outer circumference, as in the prior art. A description will be given of how the optical path of the focus error detection light 13 which is the reflected light of the focus error detection light 12 is deflected when the distance between the correction lens 21 and the objective lens 11 changes due to the change.

The state shown in FIG. 5A is set as a reference state. In this state, it is assumed that the objective lens 11 is set on the glass master 14 without a focus error. The focus error detection light 12 is obliquely incident on a portion separated by a distance 1 from the center 11a of the objective lens 11 at an angle θ (at an angle θ with respect to the optical axis a).

FIG. 5B shows that the height of the surface of the glass master 14 changes from the state of FIG. 5A (from the surface 14a to the surface 1).
Since the surface position has changed by the distance (change amount d) at 4b), the objective lens 11 has also moved by the same distance. At this time, since the focus error detection light 12 is incident obliquely with respect to the optical axis of the objective lens 11, the incident position of the focus error detection light 12 on the objective lens 11 changes.

As a result, the focus error detection light 12 is reflected by the surface 14b of the glass master 14, and the focus error detection light 13 changes again both in the direction of the optical path 31b and the output position after passing through the objective lens 11. I do. A broken line 31a in FIG. 5B indicates the optical path of the focus error detection light 13 in the state of FIG. 5A, and shows a state in which the direction changes simultaneously with the lateral displacement.

Therefore, in the prior art, in addition to the lateral displacement, a large focus error detection occurs due to a change in the optical axis (optical path) due to a change in the angle of incidence. This angle change is relatively large according to the analysis described later, and the influence on the focus error detection cannot be ignored. In particular, the objective lens 11
When the distance between the photodetector and the two-segment photodetector 23 increases, there is a problem that the adverse effect increases.

Next, the focus error detection light 12
When the position of the objective lens 11 fluctuates due to the change of the incident position, the emission direction of the focus error detection light 13
The result of analyzing the change of (optical path direction) by the ray tracing method is described below.

[Analysis conditions]-Focal length of objective lens 11: 2 mm for ultraviolet ray (ultraviolet laser beam 2), 2.3 mm for wavelength of 650 nm (focus error detection light 12)-Numerical aperture of ultraviolet ray of objective lens 11: 0 .9 ・ Focal length of correction lens 21: 120 mm ・ Distance between objective lens 11 and correction lens 21 s: about 100 mm ・ Diameter of focus detection light 12: 0.8 mm ・ Position of 2-split detector 23: from correction lens 21 500
mm point ・ Injection condition of focus detection light 12 to objective lens 11: Example of FIG. 4: perpendicular incidence to point of l = 0.8 mm Example of FIG. 5: to point of l = 0.8 mm, θ = 0. Incident at an incident angle of 5 degrees

As a result of analysis by this ray tracing method,
Table 1 shows the results of defocusing when the focus detection sensitivity and the distance between the lenses (the distance between the objective lens 11 and the correction lens 21ss) change as described above.

[0058]

This focus detection sensitivity can be expressed by the amount of movement of the spot of the focus detection beam (focus error detection light 13) received on the two-divided photodetector 23 when there is a 1 μm defocus. Correction lens 2
When the distance between the objective lens 11 and the objective lens 11 changes, the defocus is performed when the distance between the objective lens 11 and the correction lens 21 is 10 μm.
This is the amount of defocus that occurs when m changes. This is because the movement of the spot of the focus detection beam (the focus error detection light 13) received on the two-segment photodetector 23 when the interval changes changes the focus of the objective lens 11 by an amount corresponding to the defocus. This indicates that the position can be canceled by controlling the position in the direction.

When the wavelength of the ultraviolet laser beam 2 is 0.266 μm, the wavefront aberration becomes 0.07λ.
The defocus amount is 0.12 μm. Due to this wavefront aberration, the center intensity of the exposure light spot is reduced by 20%. This value is equivalent to the depth of focus used in a general sense, but in a cutting machine AA, a 20% reduction in intensity significantly deteriorates the shape of a pit or groove formed by exposure. I can't. Actually, a value of 1/5 or less is required. Therefore, 0.
If the defocus cannot be suppressed to 024 μm or less, stable and good master recording cannot be performed.

Here, according to the present invention (FIG. 4), 10 μm
Even if there is a change in the lens interval of m, sufficiently good focus error detection can be realized, but in the conventional example (FIG. 5),
Defocus almost twice as large as the request occurs. At the time of exposure of the glass master 14, a change in the interval of about 10 μm easily occurs due to polishing accuracy of the master, movement of the recording radius to the inner and outer circumferences, and the like. Therefore, the conventional method cannot perform stable and good master recording.

Further, the incident angle θ of 0.5 ° is a conventional example of a relatively shallow angle, and as the angle increases, the amount of focus offset generated as an error increases accordingly, and the situation worsens. I do. For example, when the incident angle is 1 degree, the error is about twice as large as the error of 0.5 degree.

[0063]

As described above in detail, according to the present invention, in particular, the focus error detecting laser through the correction lens is set so as to be incident substantially parallel to the optical axis of the objective lens. In the case where the surface of the medium to be exposed as a master disk has a minute change in the height position due to surface deflection or the like, the objective lens is moved in the focus direction by the focus control operation described above. Even if the distance between the objective lens and the correction lens changes, the focus error detection laser does not change at the incident position where it enters the objective lens.
After the focus error detection laser passes through the correction lens and the objective lens, return light reflected on the surface of the medium to be exposed and transmitted again through the objective lens is output to focus error detection means (focus error detector). The change of the optical axis of the returning light can be suppressed small.
(Because the optical path of the return light is only slightly translated and shifted according to the rate at which the distance between the objective lens and the correction lens changes), this causes a slight change in the height position on the surface thereof. When exposing a medium to be exposed to light using an ultraviolet laser, a laser exposure apparatus capable of always performing stable and accurate focus error detection and thereby exposing high-resolution pits or grooves can be provided. Can be provided.

[Brief description of the drawings]

FIG. 1 shows recording on a master recording machine (cutting machine) for an optical disc which is an embodiment of a laser exposure apparatus according to the present invention.
(Exposure) Diagram for explaining the optical system

FIG. 2 is a diagram for explaining an optical system of focus error detection light.

FIG. 3 is a diagram for explaining a focus error detection method;

FIG. 4 shows a focus detection laser beam passing through a correction lens which is incident substantially parallel to the optical axis of an objective lens and reflects off the disk master surface when a change in height position occurs on the disk master surface in the present invention. For explaining that the optical path of the return light of the focus error detection laser moves in parallel

FIG. 5 shows that in a conventional master recording machine for an optical disk, when a change in the height position occurs on the surface of the master disk, a focus detection laser through a correction lens enters the optical axis of the objective lens slightly obliquely. Diagram for explaining that the optical path of the return light of the laser for focus error detection reflected from the surface of the disk master later moves

FIG. 6 is a view showing a structure of an objective lens having seven elements in seven groups.

[Explanation of symbols]

2 Ultraviolet laser beam (ultraviolet laser) 11 Objective lens 12 Focus error detection light (Focus error detection laser) 13 Focus error detection light (Return light) 14 Glass master (exposed medium, disc master) 21 Correction lens 23 Split light Detector (Focus error detecting means) a Optical axis AA Laser cutting device (laser exposure device, disk master making device)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Tsurukubo 3-12-12 Moriyacho, Kanagawa-ku, Yokohama-shi, Kanagawa Japan F-term (reference) 5D119 AA22 AA28 BA01 BB09 DA01 EA03 EB12 EC03 EC14 EC40 EC47 FA03 FA13 5D121 BB01 BB21 BB38

Claims (3)

[Claims] 1. An objective lens for converging an incident ultraviolet laser beam for exposure and emitting it to a medium to be exposed to be exposed, and forming on the medium to be exposed by irradiation of the ultraviolet laser emitted from the objective lens. The focus error detection laser, which is used for detecting the in-focus state and is a visible light laser, is used so that the light spot to be exposed exposes the medium to be exposed as an in-focus exposure light spot. The laser passes through a correction lens having an optical characteristic to correct chromatic aberration between the ultraviolet laser generated by passing through the lens, and focuses the focus error detection laser by passing through the objective lens. Irradiating the object lens with return light reflected from the exposed medium irradiated with the focus error detection laser, Is supplied to focus error detecting means for detecting the in-focus state without passing through the correction lens again after passing through the correction lens. When the detection output of the focus error detecting means is in the in-focus state, the objective lens is focused. If the detection output of the focus error detection unit is not in focus, the position of the objective lens is not adjusted in the focus direction until the detection output of the focus error detection unit is in focus. A focus control means for performing a series of focus controls to be controlled, wherein the laser for focus detection via the correction lens is set to be incident substantially parallel to the optical axis of the objective lens. A laser exposure apparatus characterized by the above-mentioned. 2. A light spot forming step of forming a light spot on the medium to be exposed by condensing an ultraviolet laser for exposure through an objective lens and irradiating the medium with light to be exposed, A focus used as a visible light laser, wherein the focus is a visible light laser so that a light spot formed on the medium to be exposed exposes the medium to be exposed as an exposure light spot in a focused state. After passing the error detection laser through a correction lens having an optical characteristic to correct chromatic aberration between the ultraviolet laser and the ultraviolet laser generated by passing through the objective lens, the laser is substantially parallel to the optical axis of the objective lens. The laser beam is incident, condensed, and irradiated on the medium to be exposed, and the return light reflected from the medium to be exposed irradiated with the laser for focus error detection passes again through the objective lens. After passing the correction lens, the focus lens is supplied to focus error detection means for detecting the in-focus state without passing through the correction lens again, and when the detection output of the focus error detection means is in the focus state, the objective lens is moved in the focus direction. Without position control, if the detection output of the focus error detection means is not in focus, until the detection output of the focus error detection means is in focus,
A focus control step of performing a series of focus controls for controlling the position of the objective lens in a focus direction. 3. An apparatus for producing a master disc for producing a disc substrate which constitutes a disc substrate constituting a disc-shaped recording medium, comprising: condensing an incident ultraviolet laser for exposure; An objective lens that emits toward the master disc side coated with a photosensitive agent, and an exposure light spot in which a light spot formed on the master disc by irradiation of the ultraviolet laser emitted from the objective lens is in a focused state. As an exposure on the disc master, between the ultraviolet laser generated by passing a focus error detection laser which is used to detect the focus state and is a visible light laser through the objective lens. Through a correction lens to correct the chromatic aberration of
The focus error detection laser is condensed by passing through the objective lens and irradiated onto the disk master, and return light reflected from the disk master irradiated with the focus error detection laser is reflected by the objective. After passing through the lens again, the focus error is supplied to focus error detecting means for detecting the in-focus state without passing through the correction lens again, and when the detection output of the focus error detecting means is in the in-focus state, the objective lens is turned off. If the position is not controlled in the focus direction and the detection output of the focus error detection means is not in focus, the objective lens is moved in the focus direction until the detection output of the focus error detection means is in focus. A disc master making apparatus having a focus control means for performing a series of focus controls for position control; There, the disk mastering device being characterized in that set to be incident substantially parallel to the optical axis of the correction lens the focus detection laser is the objective lens through.