JPH0575263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a defect inspection and film thickness measuring device for resist masters for optical disks.

BACKGROUND ART There is an optical method as a method for recording video, audio information, etc. on a disk-shaped recording medium. In this optical method, a resist master is created by applying photoresist to the surface of a glass disk serving as a substrate to form a resist film, and a laser beam focused on a minute point is applied to the resist film of the resist master. The information is recorded by the length of the pits (dents) obtained by exposing them to light in a so-called bit-by-bit method in which they flicker in response to video or audio information, and then developing the pits and their repetition period.

By the way, in the case of optical discs, signal loss, which is usually referred to as dropout, is a problem, so at the stage of creating the resist master disc, the disc surface is inspected for defects such as dust and scratches that can cause dropout. It is necessary to keep it. It is also very important to keep the thickness of the resist film coated on the surface of the glass master disk constant.
Similarly, it is necessary to measure the thickness of the resist film.

Conventionally, when inspecting defects on the surface of the resist master disk and measuring the thickness of the resist film, a device for defect inspection and a device for measuring the film thickness were prepared separately, and for example, when the defect inspection was completed, The processing procedure used was to manually move the resist master from the defect inspection device to the film thickness measurement device, and then measure the film thickness, thus avoiding the high costs associated with preparing two devices. In addition, there were disadvantages in that inspection and measurement were time consuming.

Summary of the invention The present invention was made to eliminate the drawbacks of the conventional devices as described above, and by integrating both devices, it is possible to reduce costs and shorten the time required for inspection and measurement. The purpose of the present invention is to provide a resist master defect inspection and film thickness measurement device.

The defect inspection and film thickness measurement device for resist masters for optical disks according to the present invention uses an ellipsoidal mirror to share the optical system for defect inspection and film thickness measurement, and also performs defect inspection and film thickness measurement in parallel. It is structured so that you can get it.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing a defect inspection and film thickness measuring apparatus for a resist master for optical disks according to the present invention. In the figure, a resist master disk 1 is supported by a turntable 2 and rotated by a spindle motor 3. As shown in FIG. An optical head 4 is provided above the resist master 1 for optically inspecting defects on the surface of the master and measuring the thickness of the resist film. The optical head 4 is screwed onto a helical shaft 5 extending in the radial direction of the resist master disk 1 via a member not shown, and as the shaft rotates, it moves in a direction corresponding to the direction of rotation. The helical shaft 4 is rotationally driven by a feed motor 6.
A radial position detector 7 for detecting the radial position of the optical head 4 is provided, and the detector supplies information corresponding to the radial position of the optical head 4 to the motor control circuit 8. As this radial position detector 7, well-known means such as a variable resistor whose resistance value changes as the optical head 4 moves may be used.
The motor control circuit 8 controls the movement position of the optical head 4 by controlling the rotational speed and direction of the feed motor 6, and also controls each movement position of the optical head 4 based on the radial position information from the radial position detector 7. The spindle motor 3 is controlled by CLV (Constant
Linear Velocity) control.

The reason why the spindle motor 3 is controlled by CLV is as explained below. That is, as shown in FIG. 2, it is assumed that there is a scratch 9 with a constant width t (mm) in the radial direction from the inner circumference to the outer circumference on the surface of the resist master disk 1, and the rotational speed of the master disk is f
(times/sec) and the inspection radius (radius of the moving position of the optical head 4) is R (mm), then the detection pulse width W obtained by inspection by the optical head 4 is W=t/2πR・f(sec ), and if the rotation speed f of the master is constant, the inspection radius R
Therefore, the detection pulse width W changes. In order to use this detection pulse width W as a reference for the size of a defect by inspection, the detection pulse width W must also be output at a constant value for a constant width t. Therefore, it is necessary to perform the inspection with 2πR·f=V (linear velocity) constant. Inspecting with CLV control means f = K/R (K: a certain constant), which makes W = t/2πK, and the flaw width t and detection pulse width W are proportional regardless of the inspection radius R. I will do it.

Next, the specific configuration of the optical head 4 for optically inspecting defects on the surface of the resist master 1 and measuring the thickness of the resist film will be described based on FIG. 3. -Ne laser 10 is provided. This He-Ne laser 1
The laser beam emitted from 0 is beam splitter 1
1, and is separated into first and second laser beams by this beam splitter 11. The first laser beam enters the objective lens 12, is converged by the objective lens 12, and is irradiated onto the surface of the resist master disk 1 at a predetermined angle as a minute spot. On the other hand, the second laser beam is transmitted to the photodetector 1.
3 and is converted into an electrical signal according to the amount of light.

An ellipsoidal mirror 14 is provided above the resist master disk 1, and the ellipsoidal mirror 14 is arranged in such a positional relationship that one focal position of the ellipsoidal mirror 14 corresponds to a spot position on the surface of the resist master disk 1. Two transparent holes 14a and 14b are provided in the peripheral wall of the ellipsoidal mirror 14, and the irradiated light that has passed through the objective lens 12 is guided into the ellipsoidal mirror 14 through one of the transparent holes 14a. The reflected light from the resist master 1 based on this irradiation light is transmitted to the ellipsoidal mirror 14 via the other transparent light 14b.
The light is guided outside, enters the photodetector 15, and is converted into an electrical signal corresponding to the amount of light. A mask 16 is provided at the bottom of the ellipsoidal mirror 14 to block light reflected from the back surface of the resist film of the resist master 1 .

A photodetector 17 is arranged at the other focal position of the ellipsoidal mirror 14. For example, if there is a defective part such as a scratch on the surface of the resist master disc 1, the irradiation light is applied to that part (one focal position). is scattered, and the scattered light is efficiently focused by the action of the ellipsoidal mirror 14 on the photodetector 17 located at the other focal position. Photo detector 1
7 outputs an electrical signal of a level corresponding to the amount of incident light, and supplies it to the defect detection circuit 18. When a defect such as a scratch exists on the surface of the resist master 1, the output signal of the photodetector 17 partially increases in signal level as shown in FIG.
By setting , a defect detection pulse as shown in FIG. 4b can be obtained. This detection pulse is supplied to a defect counter circuit 19. As mentioned earlier, the pulse width W of the detection pulse is the width t of the defective part.
The defect counter circuit 19 can count the number of defects for each pulse width by setting several types of windows for the pulse width. will be carried out.

In the above embodiment, the number of defects is counted for each size of the defective part, but the radial position of the detected defective part is stored based on the position detection information of the radial position detector 7 in FIG. It is also possible to do so.

On the other hand, each output signal of the photodetectors 13 and 15 is supplied to a film thickness calculation circuit 20. In the film thickness calculation circuit 20, the reflectance P on the surface of the resist master 1 can be determined by dividing the output of the photodetector 15 by the output of the photodetector 13 and calculating the ratio of the amount of light incident on each detector. In this embodiment, since the reflectance P and the thickness h of the resist film have a relationship as shown in FIG. 5, by calculating the reflectance P based on the outputs of the photodetectors 13 and 15,
This means that the film thickness h can be measured within the range of 1000 to 2000 Å. In addition, since the film thickness of the resist film of the resist master disk 1 is within the above range, it is practically sufficient if the film thickness h can be measured within the range of 1000 to 2000 Å. Note that the measurement range can also be changed by changing the light source wavelength.

In the case of this film thickness measurement, as in the case of defect detection, the radial position of the portion where the film thickness changes greatly is stored based on the position detection information of the radial position detector 7 in FIG. is also possible.

In addition, in the above embodiment, the resist master 1
Although the case has been described in which the defect inspection and the film thickness measurement of the resist film are performed in parallel, the apparatus according to the present invention can also be used to inspect defects on the surface of the glass master in the pre-process of creating the resist master 1. In this case, the resist film is also not coated, so naturally only defect inspection is performed.

Effects of the Invention As explained above, in the defect inspection and film thickness measuring device for a resist master for optical disks according to the present invention, a beam from a single laser is applied to the surface of a resist master as a minute spot at a predetermined angle. The defect inspection system and film thickness measurement system share the same means for irradiation, and the film thickness is measured based on the reflected light from the board surface at a predetermined angle, and an ellipsoidal mirror is used to collect the diffusely reflected light from the board surface. Since the structure is such that defect inspection can be performed by at least receiving light,
Defect inspection and film thickness measurement can be performed in parallel, making it possible to reduce the size and cost of the device and shorten the time required for inspection and measurement by integrating both defect inspection and film thickness measurement devices. Become.

Furthermore, since a minute spot is scanned over the surface of the master disc at a constant linear velocity, the type and size of defects on the surface of the master disc can be easily determined from the pulse width of the output level of the light receiving means.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a resist master defect inspection and film thickness measuring device according to the present invention, FIG. 2 is a diagram showing a case where there are scratches on the surface of a resist master, and FIG. 3 is a diagram similar to FIG. FIG. 4 is a waveform diagram of the output signal a of the PIN photodiode 24 and the detection pulse b of the defect detection circuit 25 in FIG. 3, and FIG. 5 is a waveform diagram of the resist master disc. FIG. 3 is a diagram showing the relationship between the reflectance of a board surface and the thickness of a resist film. Explanation of the symbols of the main parts, 1...Resist master,
3...Spindle motor, 4...Optical head, 1
0... He-Ne laser, 11... Beam splitter, 13, 15, 17... Photo detector, 1
4...Elliptical mirror.

Claims (1)

[Claims] 1 An apparatus for inspecting defects on the surface of a resist master for optical disks coated with a resist film and measuring the film thickness of the resist film, which uses a single laser and a first laser beam emitted from the laser. and means for separating the first light into a second light; means for irradiating the first light onto the surface of the resist master disk as a minute spot at a predetermined angle with respect to the disk surface; a rotating means for rotationally driving the resist master disc so as to scan at a constant speed; a rotating means for rotating the resist master disc so as to scan the resist master disc at a constant speed;
a means for measuring the film thickness of the resist film based on a light amount ratio with respect to the light of the resist film; and a means for measuring the film thickness of the resist film based on a light amount ratio with respect to the light of an ellipsoidal mirror,
Defects in a resist master disk for an optical disk, characterized in that it comprises a light receiving means arranged at the other focal position, and a means for inspecting defects on the surface of the resist master disk based on the output level of the light receiving means. Inspection and film thickness measurement equipment.