JPH06195760A - Exposing apparatus for original plate - Google Patents

Abstract

PURPOSE:To elongate the life of a semiconductor laser by feeding a higher reference voltage so as to set the output amount of light suitable for focus servo only for an exposure period from a predetermined time before the start of exposure to the completion of exposure. CONSTITUTION:The output amount of light from a semiconductor laser 2 is changed corresponding to a value of a reference voltage VREF. The voltage VREF is controlled by a system controller 14. The laser 2 is turned ON from a predetermined time before the actual start of exposure to the completion of exposure, that is, the laser is powerfully turned ON with a high reference voltage suitable for focus servo. The laser is kept in the non-exposure mode for the time period other than the above, and a bias voltage as a tow reference voltage is impressed to the laser. In this manner, a voltage fed to a semiconductor laser driving circuit 1 is variably controlled to set the output amount of light of the laser 2 through the control of the controller 14. Accordingly, while the time of the exposure mode is shortened, it is not obstructed that the start-up is stabely attained in the reduced time and the life of the laser 2 is elongated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a master exposure apparatus for manufacturing an optical disk.

[0002]

2. Description of the Related Art Generally, a He-Ne laser light source or the like is used as a focus light source in this type of master exposure apparatus. However, in recent years, a semiconductor laser is also used for downsizing. Has appeared.

FIG. 2 shows a schematic structure of a master exposure apparatus for manufacturing an optical disc using such a semiconductor laser as a light source. First, the laser light driven by the semiconductor laser drive circuit 1 and emitted from the semiconductor laser 2 passes through the collimator lens 3, is then reflected by the mirror 4, and further passes through the polarization beam splitter 5 and the λ / 4 plate 6 and then the objective lens 7. Then, the light is focused into an extremely small spot and is focused and irradiated on the glass master 8. At this time, the reflected light from the glass master 8 passes through the objective lens 7 and the λ / 4 plate 6 again, and then is reflected by the polarization beam splitter 5 to enter the focus error signal detection optical system (including the detection circuit) 9. Focus error signal FE
Is converted into an electric signal. This focus error signal FE is feedback-applied to the coil of the focus actuator 12 for the objective lens 7 via the compensating circuit 10 and the power amplifier 11 and follows the fluctuation of the rotational surface of the glass master 8 and the fluctuation of the surface height difference in the radial direction. Focus control is performed so that the positional relationship between the glass master 8 and the objective lens 7 is always within a certain specification value.

[0004]

Here, the semiconductor laser 2 is not stable immediately after the power is turned on, it takes a considerable time to obtain a stable light amount, and the output of the semiconductor laser 2 is stabilized. It is an essential element for performing the focus control as described above. Therefore, conventionally, the semiconductor laser 2
In order to ensure the stability of, the light is always turned on when the power is turned on.

However, when considering the life of the semiconductor laser 2, it strongly depends on the lighting time and the laser output light quantity, and if it is constantly lit at a high output, the life becomes short.

The optical disc to be manufactured is WOR.
M (write-once optical disc), MO (magneto-optical disc), C
There are various types such as D (compact disc). The master exposure apparatus is provided with a gain adjusting circuit so as to cope with the difference in reflectance due to the difference in resist film thickness set on the glass master according to each kind of product. As a result, the structure of the focus servo control system becomes complicated, and when an AGC circuit (auto gain controller) is mounted, the size becomes large and the merit of downsizing using a semiconductor laser is halved. .

[0007]

According to a first aspect of the present invention, laser light from a semiconductor laser whose output light quantity is changed by a semiconductor laser drive circuit is focused on a glass master by an objective lens, and the glass master is used. In the master exposure apparatus in which the reflected light is input to the focus servo control system and the focus actuator is feedback-controlled to displace the objective lens to the in-focus position, an exposure period from a predetermined time before the start of exposure to the end of the exposure Control means for giving a higher reference voltage to the semiconductor laser drive circuit for setting an output light quantity suitable for focus servo only, and for giving a lower reference voltage for bias to the semiconductor laser drive circuit during periods other than the exposure period. Was set up.

In addition, in the invention described in claim 2, a detecting means for detecting a voltage signal corresponding to the amount of light reflected from the glass master is provided, and the voltage signal of the detecting means at a time point near the focus after the glass master is mounted. Based on the above, the control means determines the reference voltage value for setting the output light amount suitable for the focus servo.

In this case, according to the third aspect of the invention, the reference voltage value is variably determined so as to make the total gain of the focus servo system constant.

[0010]

According to the first aspect of the invention, the power-on period of the semiconductor laser by the oscillation of an appropriate light amount for focus servo is limited to the minimum necessary exposure period, and the bias is set to a low level during other periods. Since the reference voltage applied to the semiconductor laser drive circuit is changed by the control means so that the semiconductor laser is driven by the reference voltage, it is possible to extend the life of the semiconductor laser as compared with the case where the power is constantly turned on.
In addition, since the driving for bias is performed except during the exposure period, it becomes stable in a short time at the rise of exposure.

Here, in the invention according to claim 2,
Since the reference voltage value is determined based on the voltage signal corresponding to the amount of light reflected from the glass master after focusing on the glass master after the glass master is mounted, a good gain for focus control can always be obtained.

In particular, according to the third aspect of the present invention, the output voltage of the semiconductor laser is controlled by varying the reference voltage value to make the total gain of the focus servo system constant, so that the gain adjustment is initially set. It will be good if the gain adjustment section can be made simple,
It is possible to realize focus servo with a constant gain, even for variations in the resist film thickness of the glass master disk and for glass master disks of different types having different resist film thicknesses.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. The basic configuration is similar to that of FIG. 2, and the same parts as those shown in FIG. 2 are denoted by the same reference numerals. First,
As described above, the reflected light from the glass master 8 is input to the focus error signal detection optical system (focus servo control system) 8 and used to generate the focus error signal FE. At the same time, the focus error signal detection optical system 8 In this case, this is used as a detection means to generate an RF signal (voltage signal) corresponding to the total amount of reflected light. A system controller 14 is provided to which the RF signal is input as a digital signal via the A / D converter 13 at any time. The system controller 14 serves as a control means to variably control the reference voltage V _REF given to the semiconductor laser drive circuit 1 in order to set the output light quantity of the semiconductor laser 2, and the reference voltage V _REF is supplied via the D / A converter 15. V _REF is configured to be fed back to the semiconductor laser driving circuit 1.

The semiconductor laser 2 changes its output light quantity according to the value of the reference voltage V _REF . Here, the control of the reference voltage V _REF by the system controller 14 is performed as shown in FIG. That is, the lighting time of the semiconductor laser 2 (= oscillation operation time of an appropriate light amount for focus servo) is from a predetermined time before the actual start of exposure to the end of exposure, which is a high reference voltage V _REF (H ), The power is turned on (exposure mode), and the bias voltage of the low reference voltage V _REF (L) is applied in the non-exposure mode during the other time. The reason why the exposure mode is set to a predetermined time before the start of the exposure is because the time until the semiconductor laser 2 is actually turned on stably is expected.

In this way, the value of the reference voltage V _REF given to the semiconductor laser drive circuit 1 in order to set the output light quantity of the semiconductor laser 2 under the control of the system controller 14 is variably controlled, so that the exposure mode time in which the power is turned on is changed. Since the minimum bias voltage necessary for speeding up the stabilization of the rise in the exposure mode in the non-exposure mode is applied based on the reference voltage V _REF (L) in the non-exposure mode as much as possible, the rise stability is short. The life of the semiconductor laser 2 can be extended without impairing the time.

Next, the method of determining the reference voltage V _REF will be described. First, as a premise, in the focus control circuit, the gain adjustment unit has previously adjusted the total gain of the focus control loop with respect to the resist film thickness serving as the reference of the glass master 8 so as to be within a certain specified value (design value),
The corresponding reference RF signal (= total reflected light amount at the in-focus position) is also measured and determined.

However, when the glass master 8 is actually mounted, the system controller 14 moves when the objective lens 7 is lowered by the vertical mechanism (not shown) and is positioned near the in-focus state.
Takes the RF signal at that time and compares it with the reference RF signal when the resist film thickness becomes the reference. When this RF signal is different from the reference RF signal, the system controller 14 gives the changed reference voltage V _REF to the semiconductor laser drive circuit 1 via the D / A converter 15 and the semiconductor laser 2
Change the output light intensity. As a result, the RF signal is controlled to be constant even if the resist film thickness changes, and the gain of the focus control system is made constant.

According to such a method of determining the reference voltage V _REF , not only when the resist film thickness of the glass master 8 varies (difference depending on the exposure product type), but also various kinds of glass master plates having different resist film thicknesses are used. 8, the gain of the focus control system due to the difference in the reflected light amount (RF signal) is also changed by changing the reference voltage V _REF based on the comparison with the reference RF signal at the time of the reference resist film thickness. Can be kept constant. Therefore,
The gain adjustment unit in the focus control circuit is only initialized and does not need to be adjusted later. That is, the total gain can be adjusted without adding an AGC circuit or the like.

As described above, according to the present embodiment, the focus control circuit can be simply constructed, and high-performance multi-product exposure capable of dealing with glass masters having various resist film thicknesses without impairing the exposure control quality. It can be realized with accuracy.

[0020]

According to the first aspect of the invention, the power-on period of the semiconductor laser by the oscillation of an appropriate light amount for focus servo is limited to the minimum necessary exposure period,
During the other period, the reference voltage applied to the semiconductor laser drive circuit is changed by the control means so that the drive is performed based on the lower reference voltage for bias.
The life of the semiconductor laser can be extended compared to the case of constantly turning on the power, and since the drive for bias is performed except during the exposure period, it can be stabilized in a short time at the start of exposure, and focus servo operation It does not hinder the operation.

According to the second aspect of the present invention, the reference voltage value is determined based on the voltage signal corresponding to the amount of light reflected from the glass master at the time of focusing near after the glass master is mounted. A good gain can always be obtained for focus control.

In particular, according to the third aspect of the invention, the output voltage of the semiconductor laser is controlled by varying the reference voltage value to make the total gain of the focus servo system constant. It is only necessary to make the initial settings, and the gain adjustment section can be made simple. Therefore, even for variations in the resist film thickness of the glass master, and for glass masters of different types with different resist film thickness, The focus servo can be realized with a constant gain.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a configuration diagram,
(B) is a timing chart showing a reference voltage application state.

FIG. 2 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 1 Semiconductor Laser Driving Circuit 2 Semiconductor Laser 7 Objective Lens 8 Glass Master 9 Focus Servo Control System / Detecting Means 12 Focus Actuator 14 Control Means

Claims (3)

[Claims] 1. A laser beam from a semiconductor laser whose output light quantity is varied by a semiconductor laser drive circuit is focused on a glass master by an objective lens, and reflected light from this glass master is input to a focus servo control system. In the master exposure apparatus in which the focus actuator is feedback-controlled to displace the objective lens to the in-focus position, in order to set the output light amount suitable for the focus servo only during the exposure period from a certain time before the exposure start to the exposure end. The master exposure apparatus is provided with a control means for applying a higher reference voltage to the semiconductor laser drive circuit and applying a lower reference voltage for bias to the semiconductor laser drive circuit during a period other than the exposure period. 2. An output light quantity suitable for focus servo based on a voltage signal of the detection means at a time point near focusing after mounting the glass master disk, provided with detection means for detecting a voltage signal corresponding to an amount of light reflected from the glass master disk. 2. The master exposure apparatus according to claim 1, further comprising a control unit that determines a reference voltage value to be set for the master exposure apparatus. 3. The master exposure apparatus according to claim 2, wherein the reference voltage value is variably determined so as to make the total gain of the focus servo system constant.