JPS625335B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aperture projection type laser processing method and apparatus for processing defects in a photomask.

When processing defects on a photomask using a conventional aperture projection type laser processing device, the dimensions of the aperture pattern projected onto the photomask and the dimensions actually processed will match depending on the processing size and laser beam power. The drawback was that it didn't. In particular, when the processing dimensions are 1 to 10 μm, which is around several times the wavelength used, the difference between the processing dimensions and the set dimensions becomes large due to the effects of diffraction, etc., and processing that requires high precision at submicron scales. It was difficult to do so. In other words, in the past, depending on the laser beam power, aperture size, etc., the actual processing dimensions could be larger or smaller than the set dimensions, resulting in high-density patterns (circuit patterns, etc.) with a width of 3 to 2 μm. Processed pattern (defects, etc.)
It was difficult to remove it.

SUMMARY OF THE INVENTION An object of the present invention is to provide an aperture projection type laser processing method and an apparatus therefor, which eliminate the drawbacks of the prior art described above and allow processing and correction of a desired size with high precision.

In order to achieve the above object, the present invention has the processing dimension L = w/k (mlog P+n) + (elog P+f) (where k is the magnification, w is the size (dimension) of the aperture, and P
is the power of the laser beam, and m, n, e, and f are each constant), and by surrounding the image of the pattern on the workpiece formed through the objective lens with an electron line, etc. A measuring means for measuring the size of the image of the pattern to be processed is provided, and the value L of the size of the pattern to be processed on the workpiece measured by the measuring device and the power of the laser beam output from the laser oscillator. A calculation means is provided for calculating the value w from the above relational expression using the value P of It is characterized by being able to be processed easily and with high precision.

The present invention will be explained below based on embodiments shown in the drawings. First, we performed projection processing using a 100x objective lens by varying the projection size of the aperture from 0.5 to 10 μm. Similarly, it was confirmed that the following relationship (1) exists.

L=aW+b...(1) where L is the processed size (μm) and W is the projected aperture size (μm). Further, a and b are each coefficients.

By the way, when the output of the laser oscillator, that is, the laser beam power P (KW), is varied from 1 to 10 KW, the value of the coefficient a becomes a straight line when the output P of the oscillator is taken as a logarithm, as shown in Fig. 2. It was confirmed that the following relationship (2) exists.

a=0.074 log P+0.95...(2) Similarly, the above coefficient b is also the following (3) as shown in Figure 2.
It was confirmed that there is a relationship as shown in the formula.

b=0.48 log P+0.071...(3) From these facts, the dimension L to be machined is determined by the relationship between the projected aperture dimension W and the laser oscillator output (laser beam power) P as shown in equation (4) below. It was found that there is a relationship.

L = (0.074logP + 0.95) W + (0.48logP + 0.071) ... (4) Therefore, if the dimension L to be processed is required, the following (5) can be obtained by setting an appropriate laser beam power P. The projected size (width) W of the aperture is determined as shown in the formula.

W=L-(0.48logP+0.071)/0.
074logP+0.95 (5) When an objective lens with a magnification k of 100 times is used, the size (width) w at the aperture plane is expressed by the following equation (6).

w=100W =100{L-(0.48logP+0.071)
}/0.074logP+0.95...(6) Expressing this equation (6) as a general equation, it becomes the following equation (7).

w=KW=k{L-(elogP+f)}/mlogP+
n...(7) Then, if we accurately measure the dimension L to be processed,
The size (width) of the aperture can be set to a corrected size (width) w that is adapted to the machining conditions using equations (6) or (7), and highly accurate machining results can be obtained.

The above results are obtained when green light from a nitrogen laser-excited dye laser is used. In this case, the half-width of the pulse is approximately 6 ns. When using other lasers, the values of a and b will change depending on the wavelength and pulse width, but the slit projection method is still essential for high-precision processing. Next, a laser processing apparatus for repairing defects in a photomask, for example, based on the above principle will be described with reference to FIG. A laser beam 2 emitted from a laser oscillator 1 is passed through a slit drive unit 3 whose position and width are independently variable.
A diaphragm 4 forming a rectangular opening consisting of a set of slits.
The laser beam passes through the aperture 4, enters the objective lens 5 with a magnification of 100 times, and is irradiated onto the defect pattern 7, which is the pattern to be processed on the photomask 6, which is the workpiece placed on the XY table 16. . The aperture 4 and photomask 6 are related to the objective lens 5.
It is placed at a conjugate image position, and the image of the aperture projected onto the photomask 6 is reduced to 1/100.
Since a high magnification objective lens is used, the positioning accuracy of the projected image can be within 0.5 μm, but to ensure this, it is necessary to always focus within ±0.3 μm, and individual operator differences may occur. In order to prevent this from occurring, an air micrometer type automatic focusing mechanism 17 is used. This air micrometer type automatic focusing mechanism 17
An air micrometer 17a is attached to the lower end of the lens barrel 5a that supports the objective lens 5, and the position of the upper surface of the chrome film formed on the photomask 6 is measured. 5a
It is configured to focus by slightly moving the lens in the direction of the arrow.

The objective lens 5 also serves as the objective lens of the observation optical system, and in combination with the relay lens 8 enlarges and projects the mask defect image onto the imaging surface of the imager 9, which is an imaging means. The imager 9 is connected to a display device 11 through a control unit 10, and a defect image magnified approximately 4000 times can be observed. Further, the defect image can also be directly observed from the eyepiece optical system 12.

The measuring means for measuring the position and vertical and horizontal dimensions of the defect image 14, which is an image of the pattern to be processed, is the display device 11.
and an image control section 10. The image control unit 10 includes an electronic line measurement function, and can produce two independently adjustable pairs of electronic lines on the screen of the display device. Each line of the pair can be moved left and right or up and down independently, and when the defect image 14, which is an image of the pattern to be processed, is surrounded by these four electron lines, the image is automatically Measurements are taken of its position and horizontal and vertical dimensions. Based on the position information of the pattern to be machined from the image control unit 10, the arithmetic control unit 18 operates to finely move the X-Y table 16 via the operation control unit 19, which is a control means, to detect defects in the pattern to be machined. The final position is made by aligning the center with the optical axis. Further, based on the information on the dimension measurement result L from the image control section 10 and the preset laser beam power P, the calculation control section 18, which is a calculation means, calculates w=k{L-(elogP+f)}/mlogP+
Size (width) of aperture 4 that should be set based on n
This signal enters the operation control section 19, which is a control means, and is sent to the aperture drive section 3, which adjusts the aperture 4 to the optimum size (width).

Therefore, what the operator needs is the display device 11.
All you have to do is surround the upper defect image 14 with electron line pairs 13 in both vertical and horizontal directions and press the laser irradiation button. After irradiation, confirm that the defect image 14 has disappeared and move to the next defect position using the operation control unit 19. When the move button is pressed, information is retrieved from the cassette tape 15 in which the defect address set in the control section 19 is recorded, and the XY table 16 is operated to bring the next defect within the field of view of the display device 11. Then, the operation of surrounding this with an electron line and pressing the laser irradiation button is repeated. During this time, the automatic focus mechanism 17 automatically adjusts for out-of-focus due to waviness of the mask surface, and the operator does not need to make any adjustments.

By providing a measurement means for measuring the size of the pattern to be processed and an adjustment means for automatically adjusting the size of the aperture, defects that exist in photomasks etc. that have high-density patterns of 3 μm or 2 μm width, for example, can be eliminated. can be accurately removed and fixed.

As explained above, the present invention provides a measuring means for measuring the size L of a pattern to be processed, and a value determined by the size L of the pattern to be processed and the laser beam power P obtained by the measuring means. Since the laser processing method and its device are equipped with an adjusting means for adjusting the size of the aperture, it is possible to perform laser processing accurately according to the size of the pattern to be processed, and it is possible to perform laser processing in the vicinity of the pattern to be processed. It is possible to prevent the existing circuit patterns from being affected. Furthermore, since the present invention is equipped with an automatic focusing means and an automatic defect locating means, there is no need to adjust the focus while processing the pattern to be processed, which not only reduces the working time to 2/3. , correction errors due to out-of-focus due to individual differences in eyes do not occur, and the desired dimensional accuracy can be reliably obtained.

In addition, automatic defect locating automatically brings defects into the field of view, which greatly shortens defect repair work.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the projected aperture dimensions and the actually obtained processing dimensions at a laser power of 4KW, and Figure 2 shows the relationship shown in Figure 1 when the laser beam power P is changed. FIG. 3 is a diagram showing changes in the coefficients a and b of the relational expression expressed by . Explanation of symbols, 1...Laser oscillator, 3...Aperture drive section, 4...Aperture, 5...Objective lens, 6...
Photomask, 7... Defect pattern, 9... Imager, 10... Image control section, 11... Display device, 1
3...Electron line pair, 14...Defect image, 16...
...XY table, 17... Automatic focus mechanism, 18...
...Arithmetic control unit.

Claims (1)

[Claims] 1. The size of the pattern to be processed on the workpiece is measured by a measuring means, and the size of the pattern to be processed on the workpiece is output from a laser oscillator set to the measured size L. Based on the laser beam power P, w=k{L-(elog P+f)}/mlog
P+n (k is the magnification, e, f, m, n are each constant)
Calculate w from the relational expression, adjust the size of the diaphragm formed so that the size can be changed so that it has the corresponding w value, and pass the laser beam oscillated from the laser oscillator through the diaphragm whose size has been adjusted. A laser processing method using an aperture projection method, characterized in that the pattern is formed into a predetermined pattern through a lens, the pattern is projected onto a workpiece by an objective lens, and the pattern is positioned on the workpiece pattern to perform laser processing on the workpiece pattern. 2. A laser oscillator, a diaphragm whose size is variable so as to form a laser beam emitted from the laser oscillator into a predetermined pattern, a driving means for varying the size of the diaphragm, and a laser beam emitted from the laser oscillator through the diaphragm. An objective lens projects the pattern to be obtained onto the workpiece, and an imaging means captures an image of the workpiece pattern on the workpiece formed through the objective lens, and determines the position and location of the image of the workpiece pattern. A measuring means for measuring the size, a value L of the size of the workpiece pattern on the workpiece measured by the measuring means, and a value P of the power of the laser beam output from the set laser oscillator. is input, and based on these values L and P, w=k{L-(elog P+f)}/mlog
P+n (k is the magnification, e, f, m, n are each constant)
Driving the arithmetic means for calculating the value w from the relationship, and the driving means, the size of the aperture is adjusted to the value w determined by the arithmetic means, and
and control means for positioning the laser pattern projected by the objective lens on the pattern of the workpiece on the basis of the position of the pattern of the workpiece measured by the measuring means. Aperture projection type laser processing equipment featuring: