JPH02204746A - Method for correcting chipping defect of photomask - Google Patents

Abstract

PURPOSE:To facilitate the adjustment of a slit size and to enhance the efficiency of correction as well as to allow the automation of a correction stage by subjecting a chipping defect to a shaping processing to a rectangular defect by laser beam processing, then correcting the shape by a laser CVD method. CONSTITUTION:While the chipping defect 22 of a chromium pattern 21 is observed by an eyepiece optical system, the slit size is adjusted in such a manner that a slit image 23 completely covers the defect 22. A pattern 21 in the image 23 is then evaporated by a laser beam evaporation method, etc., by which the defect is shaped to the same rectangle 23' as the rectangle of the image 23. The slit size is then reduced by as much as a desired length and a deposited film 24 formed by a laser CVD method is formed; thereafter, the slit size is so widened as to overlap on the pattern 21 and the CVD is executed. Further, the slit width is stored by adopting the constitution which can automatically measure the aperture width of the slit, by which two stages of the CVD as mentioned above are executed automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for repairing defects in a photomask using a laser CVD method.

[Conventional technology]

Photomasks used for manufacturing semiconductor integrated circuits, liquid crystal display devices, etc. have two types of defects called residual defects and missing defects. The former is a defect in which a metal film (Cr film, FeO film, etc.) that serves as a light shielding film remains in unnecessary areas.
The latter, on the other hand, is a defect in which a necessary portion of the metal film is missing. If these defects exist in a photomask, they will cause poor performance of the semiconductor and reduce yield.

Although improvements have been made to the photomask manufacturing process to eliminate these defects, it is currently impossible to eliminate defects. Therefore, it is necessary to repair these defects, and at present, repair of the remaining defects is realized by a repair device using a laser beam, which is widely used as a laser mask repair.

On the other hand, until now there has been no simple method for repairing missing defects, and we have relied on the complicated lift-off method.

Recently, a repair method using a laser CVD method has been put into practical use. This method irradiates the defective parts of a photomask placed in a metal gas atmosphere with laser light, photolyzes or thermally decomposes the metal gas, deposits a metal film on the photomask, and repairs the defects. It's a method. As a metal gas, Cr + M.

etc., are mainly used. The laser beam irradiation method is to focus visible laser beam into a spot and scan the defective part.

There is a method in which the entire defective portion is irradiated with ultraviolet laser light at once using an imaging optical method.

FIG. 3 shows an example of the general configuration of an apparatus in the latter case using the above-mentioned imaging optical method. 1 is a laser light source, and as the laser light source 1, the fourth harmonic of Nd:YAG laser,
A second harmonic of an Ar laser or the like is used. The beam diameter of this laser beam is expanded by the beam expander 2,
And after being collimated.

The light enters a rectangular slit 4 whose opening width is variable. The laser beam, which has been shaped into a desired shape by the slit 4, is reflected by the guichroic mirror 6 and enters the objective lens 10.

The objective lens 10 focuses this laser light onto a photomask 14 through a window 11. Note that the slit and the photomask are arranged so as to have an object point and image point relationship with respect to the objective lens, so that the image of the slit is reduced and formed on the photomask. This is called an imaging optical method. Therefore, the photomask is irradiated with a rectangular laser beam limited by the slit. However, since the laser beam is invisible, the shape of this rectangular slit cannot be observed. Therefore, the shape of the slit can be observed by illuminating the slit with another illumination light source 5 of visible light and forming an image on the photomask in the same manner as laser light. In order to observe this slit image and photomask, in this configuration example, a reflected illumination light source 8. It includes a transmitted illumination light source 20 and an eyepiece optical system 9.

The photomask 14 is attached to the XY sludge 15 in the chamber 19.
placed on top. A metal gas supply device 16 and an exhaust device 18 are connected to the main chamber 19, so that metal gas can be supplied to the surface of the photomask. Since commonly used metal gases are toxic, a trap 17 is provided to detoxify them before exhausting them to the outside. As the exhaust device 18, a rotary pump or the like is usually used.

Conventionally, defect correction using this apparatus is performed as follows. First, while observing the defective part of the photomask using the eyepiece optical system, move the photomask and place the defective part in the laser beam irradiation position.

That is, it is aligned to the position of the slit image. Next, the slit size is adjusted so that the slit image completely covers the defective part.

Figure 4 shows the observed image at this time. In FIG. 4, 21 is a chromium 9 tan, 22 is a defect, and 23 is a slit image. After doing this, when the laser beam is irradiated for a predetermined period of time, a metal film is deposited within the range of the slit image, and the correction is completed. Chromium carbonate/L/bonyl was used as the metal gas, and Nd:YAG laser's fourth harmonic (wavelength 0) was used as the laser beam.
．． 266 μm).

Defects of about 100 μm can be repaired in about 10 seconds. The film thickness in that case is about 1500λ.

The film thickness is about the same as that of normal chromium gas.

FIG. 5 shows the cross-sectional shape of the photomask after the above modification. With this type of equipment, the deposit size that can be deposited at one time is limited by the laser power and the performance of the objective lens, and currently 25
It is about μm2. Therefore, defects larger than this are corrected by repeating the above correction several times.

FIG. 6 shows a case where it is desired to further increase the adhesion strength of the deposited film, and it has been found that it is better to carry out the correction in two steps. This is shown in the plan view in (al) and the cross-sectional view in (a2).
a first step of forming a deposited film 24, (b
The slit size is enlarged to completely cover the defective part 22 as shown in the top view in l) and the cross-sectional view in b2.
Do D.

This consists of a second step of forming the deposited film 24 again.

However, in this case, in order to increase the adhesion strength of the deposited film, the first
The laser power in the second process is about two to three times higher than that in the second process. Note that the film formation area in the first step is as close as possible to the edge portion.

It is better to reduce the gap, and the film does not necessarily need to be thick enough to completely block light.

Experiments have shown that approximately 500λ or more is sufficient. Therefore, the laser beam irradiation time in the first step may be about the same as that in the second step.

[Problem to be solved by the invention]

In the conventional photomask defect repair method using the laser CVD method described above, the adhesion strength can be increased by dividing the CVD process into two. However, the defect shape is not necessarily rectangular and may have a complicated shape, which poses several problems. Toga #4;λ Figure 7 shows an example of this.As shown in (a), the gap between the edges becomes too large to ensure sufficient adhesion strength, or as shown in (b), Another problem is that the first step has to be performed many times with various slit sizes, making the correction step complicated. Furthermore, since adjustment of the slit size is left to the judgment of the operator, there is a risk that the adhesion strength depends on the operator's habits and skill level.

The present invention aims to solve the above-mentioned problems of the conventional methods, and provides a photomask defect repair method that improves repair efficiency and eliminates operator errors.

[Means to solve the problem]

A method for repairing defects in a photomask according to the present invention is as follows.

A laser beam is focused on the defective part of the photomask.

In the method of repairing the defect by depositing a metal film on the defective part by laser CVD, the defect is first shaped into a rectangular defect by laser processing, and then the rectangular defect is removed by laser CVD. It is characterized by correction.

〔Example〕

Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 is a process diagram showing an embodiment of the present invention.

(,) shows the state in which a missing defect was observed and the slit size was adjusted to completely cover the defect. In this state, a predetermined laser beam is irradiated to show the slit.

In (c), the slit size is slightly reduced.

A second step of performing CVD on the glass surface within the defect is shown. Finally, (d) shows the third step of enlarging the slit size and performing CVD so as to completely cover the defect and overlap the chrome pattern. Second. The third step is the first step described in the conventional method. Second
The process is the same as that of The difference from the conventional method is that a step of shaping the defect into a rectangle is added before CVD.

Here, a method for shaping a defect into a rectangle will be described below. This is based on the laser evaporation method used when repairing residual defects on photomasks. In other words.

The pulse width is several ns to several tens of ns, and the energy is several hundred μ.
This is based on a processing method in which when a photomask is irradiated with J's laser beam using the above-mentioned imaging optical method, the chromium pattern within the slit image is instantly melted and evaporated and removed. Generally, photomask defect repair equipment uses laser light.

Ability to correct both residual and missing defects.

It is equipped with two types of laser light sources, the above-mentioned pulse laser light source and a CW laser light source (in some cases, a CW excitation Q-switch/mother-miss laser light source), and is configured so that the optical path can be switched at any time. Therefore, there is no problem in shaping the missing defect into a rectangular shape as described above.

Next, an advantage of the present invention in that slit adjustment during CVD can be automated will be described. Here, the slit is driven by a motor.

For example, it is assumed that the opening width can be recognized by driving/mistaking, or that the opening width can be automatically measured by other detection methods. If you do this, the first
The slit size is memorized in the second step, and the slit size is automatically reduced by about 1 μm in the second step.
D, and in the third step, the thickness is automatically increased by about 5 and CVD is performed. Of course, the laser beam and irradiation time can also be programmed according to the slit size. In this way, once the slit size is set by the operator in the first step, everything can be automated.

FIG. 2 is a process diagram showing a second embodiment of the present invention. This means that if the defect size is large, the pick defect size is 1.
Maximum CVD area possible in one cycle (approximately 25 μm on the conventional mounting side)
This is an example in the case of exceeding 2). For example, assume that the defect size is approximately 50 layers. In this case, the first step is performed in four steps.

That is, the slit size is set to about 25 μm2.

Perform laser processing in order. Figure (b) shows an intermediate stage of this process. In this manner, after completing four processing steps, the second step of CVD is performed. In this case, the slit size is set to about 23 μm, and the process is divided into four steps and carried out sequentially. (C) shows the end of this second step. Finally, perform the third step.

In this case, the slit size should be about 20 μm2.

CVD is performed on the entire defect in 9 times. Figure (d) shows an intermediate stage of the third process. In this step, adjacent deposited films must be formed so as to overlap little by little so that no gaps are formed.

Next, it will be explained that the process can be automated in this embodiment as well. First, as shown in Figure 2 (,), in order to find out the size of the defect, the center position of laser processing (usually the cross line position of the eyepiece) is aligned with the diagonal positions P1 and p2 of the defect, and its coordinates are Calculate the defect size from the value. Thereafter, the area is equally divided into small regions, and the center coordinates of each small region are calculated. Next, the slit size is automatically adjusted to this small area size, the XY stage is automatically moved to its center position, laser processing is performed, and the first step is completed. In the next second step, the center position of each small region is made the same and the slit size is changed from the first step to 1μm.
CVD is performed one after another by reducing the amount. In the third step, the optimum slit size and the center coordinates of each small region are calculated based on the size and shape of the entire defect, and the steps are sequentially executed in the same way as the second step. For this purpose, it is necessary to store in advance a relational expression between the size of the defect and the optimum small area size in the computer.

As described above, according to the present invention, if the operator first performs the work to find out the size of the defect, the subsequent steps can be completely automated.

〔Effect of the invention〕

As explained above, in the present invention, the defect is shaped into a rectangle by laser processing in advance and then corrected by the laser CVD method. This makes it easy to adjust the slit size when performing CVD, and this also reduces operator variations. I was able to reduce this.

This has the effect of improving the reliability of correction. Furthermore, if the defect is large, the conventional method requires a lot of trouble to correct it.
According to the present invention, since the correction process can be automated, there is an advantage that not only the efficiency of correction is improved, but also mistakes by operators do not occur.

5... Slit illumination light source, 6... Guicroic mirror, 8... Reflective illumination light source, 9... Eyepiece optical system.

10... Objective lens, 14... Photomask, 16
...Metal gas supply device, 19...Chamber, 20.
...Transmitted illumination light source, 21...Chrome pattern, 22.
... Loss defect, 23... Slit image, 24-... Deposited film, 25... Glass substrate.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a first embodiment of the present invention. Fig. 2 is a process diagram showing the second embodiment, Fig. 3 is a general configuration diagram of a conventional device, Fig. 4 is an observed image of a photomask, and Fig. 5 is a process diagram showing the second embodiment.
The figure is a cross-sectional view of a photomask after defect correction, and FIGS. 6 and 7 are correction process diagrams using a conventional method. Explanation of symbols: 1...Laser light source, 2...Beam expander, 3...Gicroic mirror, 4...Suri〇- (b) (C) (d) Figure 4 (α1) Figure 6 (α2) (bl) (b2) Ward 7 (α) (b)

Claims (1)

[Claims] 1. In a method of repairing a defect by focusing a laser beam on a defective part of a photomask and depositing a metal film on the defective part by laser CVD method, the defect is first processed into a rectangular defect by laser processing. Shaped, then laser C
A photomask defect repair method comprising repairing the rectangular defect using a VD method.