JP2002008254A - Information recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recorder where a focal position with respect to an objective lens of a main recording beam can be controlled correctly even if the offset quantity added to a focus control system is small. SOLUTION: The difference of a focal depth generated by the difference of a wavelength of a main recording beam C is suppressed by setting a wavelength of a focus error detecting laser 21 to be 400 nm to 450 nm. Thus, the offset quantity added to the focus control system is reduced and thereby, the focal position with respect to the objective lens of the main recording beam is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording apparatus used for producing a master of a high-density optical disk.

[0002]

2. Description of the Related Art A mastering process of an optical disk is generally called a mastering process, and it is a matter of course that a large contribution to the density increase of an optical disk is made by irradiating a glass plate coated with a photoresist with a laser beam to expose the glass plate to a pit group. Alternatively, it is cutting for forming a groove.

In order to increase the density of an optical disk,
In order to form fine pit groups and grooves in the cutting, it is necessary to narrow down the spot size of the laser beam applied to the photoresist-coated glass plate to as small a size as possible. May be shortened.

For example, in the case of a CD (compact disk) having a capacity of 650 MB, a wavelength of 44
A 0 nm He-Cd (Helicad) laser is used, and a 4.7 GB DVD uses a 351 nm wavelength UV laser at the time of DVD cutting. It shows the degree of dependence on wavelength.

[0005] By the way, in the cutting of the optical disk, the focus control of the objective lens for narrowing down the main recording laser beam separately from the main recording laser beam due to the problem of system control of the apparatus (hereinafter referred to as a laser beam recorder LBR). The sub-laser beam is used for error detection. The wavelength of the light source of the sub laser beam is selected to be significantly different from the wavelength of the main recording laser beam so as not to expose the photoresist. For example, He-N with a wavelength of 632 nm
e (helium neon) laser, or 780 nm wavelength
Semiconductor laser is often used.

Therefore, in the LBR focus control, the error detection has a different wavelength even though the object to be controlled is an objective lens for focusing the main recording laser beam on the glass plate coated with the photoresist. It is extremely anomalous because of another laser beam.

Therefore, due to the wavelength dependence of the focal depth of the main recording laser beam and the sub-laser beam, the optimum control position of the objective lens in the focus control system using the sub-laser beam is not necessarily the optimum control position for the main recording laser beam. Will not always be a problem.

[0008] A general approach to avoid this problem is:
By adding a predetermined offset amount to the focus control system established by using the sub-laser beam, the optimum control position for the sub-laser beam is forcibly deviated. This is to shift to the optimal control position of the lens.

[0009]

By the way, recently, the capacity 1
Various types of high-density optical disks of 5 GB or more have been proposed, and the necessity of using a DeepUV laser having a wavelength of 300 nm or less as a light source of a main recording laser beam for cutting these high-density optical disks has been studied.
Actually, recording experiments with lasers in the above-mentioned wavelength band have been started.

Therefore, the difference between the wavelength of the sub-laser beam for controlling the focus of the objective lens for narrowing down the main recording laser beam (632 nm or more as described above) and the main recording laser beam is even greater. This fact further increases the problem that the optimal control position of the objective lens in the focus control system using the sub-laser beam due to the difference in the depth of focus is not always the optimal control position for the main recording laser beam. Will be.

For example, when cutting the above-mentioned DVD, a laser having a wavelength of 351 nm is used as a light source of a main recording laser beam, and a laser having a wavelength of 632 nm is used as a light source of a sub-laser beam.

[0012]

(Equation 1)

The depth of focus given by
Assuming that A is 0.9, the former is 217 nm, the latter is 390 nm, and the difference is 173 nm. On the other hand, when a Deep UV laser having a wavelength of 248 nm is used as the light source of the main recording laser beam, Similar calculations show that the former is 154 nm and the latter is 3 nm.
At 90 nm, the difference reaches 236 nm, which is about 1.4 times as large as that in DVD cutting using a laser having a wavelength of 351 nm as a light source of the main recording laser beam.

In other words, this fact is necessary for the focus control system to shift from the optimal control position of the objective lens by the auxiliary laser beam to the optimal control position of the objective lens for the main recording laser beam as described in the prior art. This means that the predetermined offset amount to be added must be increased by a factor of 1.4.

It is a well-known fact that adding an offset is generally undesirable for a focus control system, and it goes without saying that adding an excessively large offset significantly affects the stability of the control operation.

Accordingly, as described above, the use of a deep UV laser having a wavelength of 300 nm or less as the light source of the main recording laser beam in accordance with the increase in the density increases the addition of an offset which is undesirable for the focus control system. In other words, the focus control system is established in a state where the stability is extremely poor, and there is a possibility that pits or grooves suitable for a desired recording density cannot be formed.

In view of the above problems, an object of the present invention is to provide an LBR, ie, an information recording apparatus, that realizes master disc cutting of a high-density optical disc under stable focus control.

[0018]

In order to solve the above-mentioned problems, the present invention minimizes the amount of offset to be added to the focus control system, that is, the use of a sub-laser beam as an error detection means for focus control. An information recording apparatus characterized in that the wavelength of the sub-laser beam is changed from 400 nm to 450 nm in order to reduce the difference between the wavelength and the wavelength of the main recording laser beam.

[0019]

Embodiments of an information recording apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an information recording apparatus, that is, an LBR according to an embodiment of the present invention. Figure 1
In the figure, reference numeral 1 denotes a main recording laser that oscillates a main recording beam, and has a wavelength of 248 nm in the Deep UV region. Reference numeral 2 denotes a laser power stabilizer using an optical modulator. The output light (light A) of the main recording laser 1 is used as input light, and the output light (light B) of the laser power stabilizer 2 is ) Is provided for the purpose of stabilizing the power of the power supply to a predetermined value.

Reference numeral 4 denotes an optical modulator, and a signal generator 5
Is provided for performing light intensity modulation on the output light (light beam B) of the laser power stabilizer 2 based on the output signal of The output light (light beam C) of the optical modulator 4 travels straight to the right side of the paper of FIG. 1 through the first beam splitter 6, and its traveling direction is changed to the lower side of the paper by the dichroic mirror 7, so that the objective lens 8 is moved. Irradiation is performed on the glass master 9 on which the photoresist is applied. As described above, since the intensity of the light is modulated based on the output signal of the signal generator 5 by the action of the optical modulator 4 as described above, the sensitivity of the photoresist on the glass master 9 changes. Thus, the output signal of the signal generator 5 is recorded as information.

The aperture ratio (NA) of the objective lens 8 is assumed to be 0.9, and the glass master 9 is rotated at a predetermined rotation speed by a rotation driving means (not shown).

On the other hand, the light beam D is a light beam which is the reflected light of the light beam C applied to the glass master 9 and which is input to the light receiving portion of the video camera 22 by the action of the dichroic mirror 7 and the first beam splitter 6. Further, the output signal of the video camera 22 is input to the oscilloscope 23.

Therefore, the video camera 22 and the oscilloscope 23 constitute an observation optical system for the light beam D, that is, the reflected light of the light beam C applied to the glass master 9. It is provided to monitor whether or not the objective lens 8 is controlled so as to focus on the glass master 9. FIG. 2 is a view showing an example of the reflected light profile of the light beam C, and shows how the waveform observed by the oscilloscope 23 changes depending on the control state of the objective lens 8.

According to FIG. 2, a waveform 100 shows a waveform when the light beam C is correctly focused on the glass master 9, that is, a waveform at the time of the just focus, and the light beam C correctly focuses on the glass master 9. When it is not connected, that is, at the time of defocus, a waveform as shown in waveform 101 is observed.

Next, returning to FIG. 1, the focus control system in the embodiment will be described. Reference numeral 21 denotes a focusing laser which is a light source of a sub-laser beam for detecting a focusing error.
nm semiconductor laser was used.

When a semiconductor laser is used, a collimate lens for converting the output light into parallel light,
Although it is necessary to pass the output light of the semiconductor laser through an optical system composed of a beam shaping prism for equalizing the aspect ratio, it is omitted in FIG. 1 because it has no direct relation to the object of the present invention. did.

A light beam E, which is a sub-laser beam emitted from the focusing laser 21, is transmitted to the second beam splitter 1.
2. The light travels straight through the glass master 9 coated with the photoresist through the dichroic mirror 7 and the objective lens 8, and the reflected light is redirected to the right side of the drawing by the action of the second beam splitter 12 again. The light enters the system 13 (portion surrounded by a dotted line). In the present embodiment, a well-known astigmatism detection optical system including a detection lens 14, a cylindrical lens 15, and a four-segment photodetector 16 is used as the focus error detection optical system.

Accordingly, the photoelectric conversion signals a, b, c, d from the respective photoelements of the four-division photodetector 16 are input to the focus control drive circuit 17, and are calculated as (a + c)-
After the calculation of (b + d), a predetermined loop gain is secured, a predetermined phase compensation is performed, power is amplified, and an actuator 10 for driving the objective lens 8 is excited to achieve focus control.

However, the establishment of the focus control described here is merely the establishment of the focus control of the sub-laser beam (that is, the light beam E) by the focusing laser 21 on the objective lens 8 as described in the background art. ,
This is different from the establishment of the focus control of the main recording beam (that is, the light beam C) on the objective lens 8. Therefore,
As described in the related art, in order for the main recording beam (that is, the light beam C) to correctly focus on the glass master 9 coated with the photoresist, a predetermined offset is applied to the focus control system by the offset adding means 18. You need to add an amount.

The means for determining an appropriate offset amount is based on observing the waveform of the oscilloscope 23 shown in FIG. 2 as described above, and as shown by 100 in FIG. The offset amount to be added by the offset adding means 18 is adjusted so that the peak becomes maximum.

In the present embodiment, a main recording laser having a wavelength of 248 nm is used as a light source for a main recording laser beam, and a focusing laser having a wavelength of 400 nm is used as a light source for a sub laser beam. When the respective focal depths are again calculated by (Equation 1), the former is 154 nm, the latter is 247 nm, and the difference is 93 nm. As described in the problem to be solved by the invention, the main recording laser A Deep UV laser having a wavelength of 248 nm is used as a light source of the beam, and a wavelength of 632 n is used as a light source of the sub laser beam.
The depth of focus when using a laser of m
Recall that m and 390 nm, and the difference was 236 nm. In this embodiment, by changing the wavelength of the light source of the sub-laser beam for focus control to a smaller direction, the difference in the depth of focus is obtained. Can be suppressed from 263 nm to 93 nm.

This fact indicates that the optimum control position for the sub-laser beam is forcibly deviated, that is, the offset to the focus control system for defocusing and shifting to the optimum position of the objective lens for the main recording beam. It means that the amount of addition can be extremely small,
This means that the offset addition amount can be reduced to 93/263 (= 35%). Therefore, although the addition of the offset to the focus control system is necessary, the amount does not impair the stability of the focus control system.

The reason is, as described in the background of the invention and the problem to be solved by the invention, in the case of a DVD, a main recording beam having a wavelength of 351 nm is used at the time of cutting, and an error detecting means for focus control is used. The auxiliary laser beam has a wavelength of 632 nm. The difference in the depth of focus at this time is 173 nm, in other words, 1
Although it was necessary to add an offset amount equivalent to 73 nm, the fact that there is no problem with the stability of focus control despite the fact that it is larger than 93 nm in the present embodiment indicates that the spread of DVD discs Because it has proved.

Moreover, according to the present embodiment, it has been clarified by the previous discussion that the offset amount to be added to the focus control may be smaller than that in the above-described DVD cutting. It is possible to promote the stability of the focus control more than before.

A similar discussion was made, as in the present embodiment, by using a main recording laser having a wavelength of 248 nm as a light source of a main recording laser beam and a wavelength of 400 n as a light source of a sub-laser beam.
When applied to the case where a focusing laser is used at a wavelength of 450 nm instead of m, the calculation result of the depth of focus at that time is again 154 nm according to (Equation 1).
In the latter case, the difference is 278 nm, and the difference is 124 nm. Compared with 93 nm when a focusing laser having a wavelength of 400 nm is used as a sub-laser beam light source,
Although there is an increase of 31 nm, as described in the problem to be solved by the invention, when a Deep UV laser having a wavelength of 248 nm is used as a light source of the main recording laser beam and a laser having a wavelength of 632 nm is used as a light source of the sub-laser beam. Compared with the difference of 236 nm, which is the difference in the depth of focus, the value is sufficiently small. In addition, at the time of cutting a DVD, the main recording beam having a wavelength of 351 nm is used, and the sub-laser beam as an error detecting means for focus control is used. 173 of difference in depth of focus when wavelength is 632 nm
nm, forcibly deviating from the optimum control position for the sub-laser beam, that is, adding an offset to the focus control system for defocusing and shifting to the optimum position of the objective lens for the main recording beam. Can be concluded that they do not hinder the stability of the focus control system.

It is to be noted that the wavelength is 400 as in this embodiment.
The sensitivity of a sub-laser beam having a wavelength of 248 nm to a photoresist whose photo-sensitivity has been optimized with respect to a main recording beam having a wavelength of 248 nm is as follows.
Since there is a great difference in the energy of Deep UV light of nm, there is almost no energy. Therefore, there is no influence due to the irradiation of the sub-laser beam, for example, there is no deterioration in the quality of the reproduced signal after disc-forming.

[0038]

As described above, according to the present invention, the wavelength of the auxiliary laser beam for detecting the focus error is set to 400 nm.
In this case, cutting of a high-density optical disc having a main recording beam having a wavelength of 300 nm or less can be realized under stable focus control.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an information recording apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a profile of reflected light of a main recording beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main recording laser 2 Laser power stabilizer 3 Power setting means 4 Optical modulator 5 Signal generator 6, 12 Beam splitter 7 Dichroic mirror 8 Objective lens 9 Glass master 10 Actuator 13 Focus error detection optical system 14 Detection lens 15 Cylindrical lens 16 Four-division photodetector 17 Focus control drive circuit 18 Offset addition means A, B, C, D, E rays a, b, c, d Photoelement photoelectric conversion signal

Continued on the front page F term (reference) 5D090 AA01 BB01 CC01 CC16 DD03 DD05 EE01 FF05 FF11 HH01 KK06 KK13 KK15 LL01 LL08 5D118 AA06 AA13 BA01 BF03 CA11 CD02 CG03 CG07 CG13 CG26 5D119 AA22 BB03

Claims (2)

[Claims] 1. An information recording apparatus comprising a main laser beam for recording a signal and a sub-laser beam for automatic focus control, wherein the sub-laser beam has a wavelength of 4
An information recording device having a wavelength of from 00 nm to 450 nm. 2. The information recording apparatus according to claim 1, wherein the main laser beam for recording the signal has a wavelength of 300 nm or less.