JP2941366B2 - Light beam intensity adjusting method of exposure apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a beam intensity adjusting method of an exposure apparatus used for cutting a master in a master manufacturing process of an optical disc such as an optical video disc and a digital audio disc.

2. Description of the Related Art In a cutting operation performed when an optical disk master is manufactured, a photoresist (photosensitizer) applied on a film on a glass disk serving as a base of the master receives a modulation corresponding to an information signal. After the light beam is emitted and exposed, the exposed portion of the photoresist film is dissolved and removed with a developing solution to form a spiral track composed of a series of concave pits.

Conventionally, constant rotational speed (CAV: constant angular velocity)
When manufacturing a master disc for making a disc, the glass disc is rotated at a constant rotation speed, and the light beam of the exposure device is irradiated on the glass disc at the same speed in the radial direction of the glass disc as in the case of playing the disc. It has been done to move. In order to form all the pits with high precision, it is necessary to make the exposure amount uniform over the entire surface from the innermost position to the outermost position of the portion of the photoresist film to be exposed. , As shown by the straight line A in FIG.
In order to keep the exposure energy per unit track length constant in accordance with the linear velocity linearly increasing from the innermost position to the outermost position, the intensity of the light beam is linearly proportional to the amount of movement. It is changed to do.

The intensity of the light beam is adjusted by adjusting a drive voltage supplied to a light emitting element that emits the light beam, for example, an argon ion laser (hereinafter, referred to as an Ar laser) by a drive voltage generation circuit shown in FIG. Done. That is, in FIG. 7, a constant a representing the slope of the straight line A shown in FIG. 6 is set by the constant setting circuit 1, and the light beam movement amount r as a variable detected by a feed monitoring device (not shown) and this constant The multiplication circuit 2 obtains the product ar of a and the constant a representing the offset amount of the straight line A in the constant setting circuit 1, and the sum of the above ar and this b is obtained in the addition circuit 3. If the driving voltage supplied to the Ar laser is changed as a function of the applied r, the exposure amount p and the moving amount r of the light beam become a linear proportional function.

By the way, the above-described conventional light beam intensity adjustment method includes:
It is assumed that the thickness of the photoresist film provided on the surface of the glass disk prior to the cutting operation is uniform over the entire surface. However, since the photoresist film is formed by adhering a liquid photoresist to the surface of the glass disk, it is not always easy to make the thickness uniform. For example, the thickness is smaller than the innermost and outermost portions. As a result, the thickness of the intermediate portion tends to be large. Therefore, by simply setting the intensity of the light beam and the moving amount thereof in a linear proportional relationship as described above, the optimum exposure amount for forming pits with ideal accuracy can be obtained over the entire surface of the photoresist film. As shown by point ○ in FIG. 6, the optimum value is obtained at the innermost and outermost positions, but the required amount of exposure is not sufficient at the intermediate position. there were.

SUMMARY OF THE INVENTION [Object of the Invention] The present invention has been made in view of the above points,
An object of the present invention is to provide a light beam intensity adjusting method capable of giving an optimum exposure amount over the entire recording portion of a photoresist film.

[Constitution of the Invention] In the light beam intensity adjusting method of the exposure apparatus according to the present invention, while determining the optimum light beam intensity at the innermost and outermost positions of the disk, at least one of the innermost and outermost positions is determined.
The optimum light beam intensity at the intermediate position is determined, and a function showing a curve connecting the optimum light beam intensity at the innermost position, the intermediate position and the outermost position is set, and the light beam intensity at each radial position is set according to this function. It is characterized by adjusting.

[Operation of the Invention] In such a light beam intensity adjusting method, the innermost and outermost portions of the portion of the photoresist film to be exposed and the intermediate portions thereof are exposed to the light beam applied to the photoresist film. Exposure energy corresponding to each film thickness is applied.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an exposure apparatus that implements a light beam intensity adjusting method according to a first embodiment of the present invention. The exposure apparatus emits a light beam to a photoresist film 11a provided on a glass disk 11 which is a base of a master used for press molding of an optical disk to expose the photoresist film 11a.

As shown in FIG. 1, the exposure apparatus rotates a glass disk 11 at a constant rotation speed by an air spindle motor 12 and emits a light beam emitted from an Ar laser 13 so as to correspond to an information signal to be recorded. The light is irradiated onto the photoresist film 11a through an objective lens (not shown) included in the moving optical system 15 while being modulated by the modulator 14. The reflecting mirror 17 reflects the light beam emitted from the Ar laser 13 toward the optical modulator 14.
And a reflecting mirror 18 for guiding the modulated light beam obtained through the light modulator 14 to the moving optical system 15. A fixed optical system 20 is composed of the Ar laser 13, the optical modulator 14, the two reflecting mirrors 17 and 18, and other necessary optical elements (not shown). The movable optical system 15 is movable as described later, while the fixed optical system 20 is in a stationary state.

The optical modulator 14 included in the fixed optical system 20 is ON / OFF controlled by an optical modulator control circuit 23 based on a limiter signal emitted from a signal source 22, and the photoresist film 11a
The light beam from the Ar laser 13 is modulated in order to form the original shape of the pit. Although not described in detail because it is well known, in the signal source 22, both the video and audio signals are FM-modulated by the FM modulator, and then these are combined into one signal by a combining circuit (adder). The signals are synthesized, and the amplitude of the synthesized signal is limited by a limiter to form a square wave, which is transmitted as a limiter signal.

On the other hand, the moving optical system 15 is composed of required optical elements such as an objective lens (not shown) for focusing the modulated light beam obtained through the light modulator 14 on the photoresist film 11a as spot light, and the like. It is mounted on the feed table 25. The feed table 25 is reciprocally movable in a direction parallel to the main surface of the glass plate 11 mounted on the air spindle motor 12, and is moved at a constant speed by applying a driving force by the feed mechanism. As described above, since the glass disk 11 is rotated at a constant rotation speed by the air spindle motor 12, the feed table carrying the moving optical system 15 is provided.
With the constant speed movement of 25, the original shape of the spiral track is exposed and formed on the photoresist film 11a by the modulated light beam.

The air spindle motor 12 is a spindle servo circuit.
It is controlled by 28 to keep its rotation speed constant,
The operation of the feed mechanism 26 is controlled by a feed servo circuit 29 so that the feed table 25 moves at a constant speed. And
As for the moving optical system 15, since it is necessary to make the objective lens follow the surface deflection of the rotating glass disk 11, a focus servo mechanism (FIG. 1) that movably supports the objective lens in the optical axis direction and drives it. (Not shown). This focus servo mechanism is a focus servo circuit
By controlling the operation by 30, the modulated light beam is focused on the photoresist film 11a.

On the other hand, a linear scale 32 for detecting the moving amount of the feed table 25, that is, the moving amount of the moving optical system 15 in the glass plate radial direction is provided, and the moving amount detected by the linear scale is a feed monitoring device. The signal is signaled by 33 and sent to the feed servo circuit 29, where the feed servo circuit
29 controls the operation of the feed mechanism 26 based on this signal.

By the way, a drive voltage for causing the Ar laser 13 to emit light is supplied through a drive voltage generation circuit 35. The drive voltage generation circuit 35 receives the detection data of the movement amount r of the light beam from the feed monitoring device 33 every time, and controls the drive voltage as described below based on the data.

That is, as shown in FIG.
The drive voltage is controlled so that the relationship between the exposure amount P per unit track length, that is, the light beam intensity, draws a quadratic curve B that is convex upward, for example. In this case, as shown in FIG. 3, the thickness of the photoresist film 11a is not uniform over the entire surface of the portion to be exposed, and the thickness of the intermediate portion between the innermost portion and the outermost portion is small. It is assumed that the film thickness is large. In the case where the thickness of the photoresist film 11a is non-uniform in such an embodiment, the exposure amount P
Is a quadratic function of the light beam movement amount r.
By controlling the drive voltage to, for the light beam emitted from the Ar laser, corresponding to the linear velocity increasing from the innermost position to the outermost position and the innermost position,
The strength corresponding to each film thickness at the outermost peripheral position and the intermediate position is provided. Therefore, an optimal exposure amount can be obtained over the entire surface of the photoresist film 11a to be exposed, and all pits can be formed with high accuracy.

Here, the configuration of the drive voltage generation circuit 35 for supplying a drive voltage to the Ar laser 13 will be described in detail with reference to FIG.

As shown in FIG. 4, when the light beam is at any radial position on the glass plate 11, the drive voltage generation circuit 35
The driving voltage is controlled so as to satisfy P = ar ² + br + c, which is the equation of the quadratic curve B shown in FIG.
That is, the circuit configuration includes a constant setting circuit 41 for setting each of the constants a, b, and c included in the equation, data of the light beam movement amount r sent from the feed monitoring device 33, and required values for these constants. Multiplication circuits 42 and 43 for performing operations and addition circuits
44 and 45. In this configuration, first, a constant a is set by a constant setting circuit 41, and a multiplication circuit 42 obtains a product ar of the light beam movement amount r received from the feed monitoring device 33 and the constant a. The sum ar + b of the second constant b set by the constant setting circuit 41 and this ar is added to the addition circuit 44.
To send out. Next, the ar obtained by the addition circuit 44
+ B is again shifted by the multiplying circuit 43 by the light beam moving amount r.
To obtain ar ² + br. At the same time, a third constant c representing the offset amount of the quadratic curve B is set by the constant setting circuit 41, and the sum ar ² + br + c of the above ar ² + br and c is obtained by the adding circuit 45. That is, the drive voltage supplied to the Ar laser 13 is changed as a quadratic function of the light beam movement amount r.

 The above-described quadratic curve B is set as follows.

First, a glass disk to be exposed by the above-mentioned exposure device
11 is prepared for curve setting. Then, as shown by points 46 and 47 in FIG. 2, the innermost position and the outermost position of the portion to be exposed of the photoresist film 11a provided on the glass disk are experimentally exposed. optimum light beam intensity at the both positions on the basis of the result i.e. determining the exposure amount P ₁ and P _2. Similarly, as shown by point 48, an intermediate position between the outermost inner peripheral position and the outermost position at least one determined determine the optimum exposure amount P ₃ in the intermediate position. Thus, since three or more points 46 to 48 have been determined, a quadratic curve connecting these points is drawn, and a function P =
Find each constant a, b and c of ar ² + br + c. The drive voltage to the Ar laser 13 is controlled by the drive voltage generation circuit 35 based on the function thus obtained as described above, and the light beam intensity at each radial position of the glass disk 11 is adjusted.

FIG. 5 shows an exposure apparatus in which a light beam intensity adjusting method according to a second embodiment of the present invention is performed. The exposure apparatus shown in FIG. 5 has the same configuration as that of the exposure apparatus shown in FIG. 1 except for the parts described below. Therefore, the other parts will not be described in detail. In the following description, the same parts as those of the exposure apparatus shown in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 5, in the exposure apparatus, the drive voltage of the Ar laser 13 itself is kept constant without being varied. Instead, the light beam emitted from the Ar laser 13 and before being modulated by the ON / OFF operation of the light modulator 14 into a modulated light beam that blinks in response to the recording signal is output by another light modulator 48. , The strength is adjusted. The operation of the optical modulator 48 is controlled by an optical modulator control circuit 49. The optical modulator control circuit 49 is a feed monitoring device.
Data of the light beam movement amount r is received from 33, and as shown in FIG. 2, the relationship between the exposure amount P per unit track length, that is, the light beam intensity and this light beam movement amount r draws a quadratic curve B. To control the optical modulator 48. Note that the circuit configuration of the optical modulator control circuit 49 is the same as that of the drive voltage generation circuit 35 shown in FIG. Also, the light modulation 48 by the light modulator control circuit 49
The method of setting the quadratic curve B in FIG. 2 as a reference for the operation control of FIG. 2 is the same as the setting method in the exposure apparatus shown in FIG.

In each of the above embodiments, the photoresist film was used.
The intensity of the light beam applied to the light beam 11a is adjusted upward by following a convex quadratic curve B, as shown in FIG. 3, which is the innermost periphery of the portion of the photoresist film 11a to be exposed. This is because the thickness of the portion located between these portions and the outermost peripheral portion is larger than that of the portion. Therefore, conversely, when the thickness of the intermediate portion is thinner than the innermost portion and the outermost portion, the light beam intensity is changed along a quadratic curve convex downward. Become. In addition, since the intensity adjustment based on the quadratic curve cannot be used depending on the mode of the change of the film thickness in the glass disk radial direction, a curve represented by a cubic function or a higher-order function or another function is set. Then, the light beam intensity is adjusted according to this curve.

Further, in each of the above embodiments, the present invention has shown the read-only optical discs such as the optical video disc and the digital audio disc as the discs for which the master is to be manufactured. Needless to say, the present invention is also applied to the manufacture of a master of a phase change optical disk such as a rewritable optical disk. When manufacturing a master for such a phase-change optical disk, it is effective to reduce the pitch of the pre-groove or to create the pre-groove by changing the pitch to increase the density of information recording.

As described in detail above, in the light beam intensity adjusting method of the exposure apparatus according to the present invention, a function indicating a curve connecting the optimum light beam intensity at the innermost circumference, the outermost circumference, and the intermediate position of the disk is set, and this function is set. The light beam intensity at each radial position is adjusted according to.

Due to such a configuration, the light beam applied to the photoresist film is given an intensity corresponding to the film thickness of the innermost portion, the outermost portion, and the intermediate portion of the portion of the photoresist film to be exposed. An optimum exposure amount can be obtained over the entire surface of the portion to be exposed, and all pits can be formed with high accuracy, contributing to higher density of information recording.

[Brief description of the drawings]

FIG. 1 is a block diagram of an exposure apparatus according to a light beam intensity adjustment method as a first embodiment of the present invention, and FIG. 2 is a quadratic curve showing a light beam intensity adjustment mode in the exposure apparatus shown in FIG. FIG. 3 is a partial sectional view of a glass disk having a photoresist film to be exposed by the exposure apparatus shown in FIG. 1, and FIG. 4 is a drive voltage included in the exposure apparatus shown in FIG. FIG. 5 is a block diagram showing a circuit configuration of a generating circuit, FIG. 5 is a block diagram of an exposure apparatus according to a light beam intensity adjusting method as a second embodiment of the present invention, and FIG. 6 is a light beam in a conventional light beam intensity adjusting method. FIG. 7 is a block diagram of an arithmetic circuit for implementing a conventional light beam intensity adjustment method. Explanation of reference numerals of main parts 11 ... Glass disc 11a ... Photoresist film 13 ... Ar laser 14,48 ... Optical modulator 23,49 ... Optical modulator control circuit 33 ... Feed monitoring device 35 ... Drive Voltage generation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/26

Claims (1)

(57) [Claims] 1. An optical disk device according to claim 1, wherein an optimum light beam intensity at an innermost circumference and an outermost circumference position of the disk is determined, and an optimum light beam intensity at at least one intermediate position between the innermost circumference and the outermost circumference position is determined. Set a function showing a curve connecting the optimal light beam intensity at the intermediate position and the outermost position,
A method of adjusting the light beam intensity at each radial position according to this function.