JPS6161669B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for correcting white spot defects on photomasks.

A lift-off method has conventionally been used to repair white spot defects on photomasks. This lift-off method consists of (1) a process of applying photoresist to the entire surface of a photomask with white spot defects, (2) a process of exposing only the white spot defects using a partial exposure method, and (3) a process of removing the white spots through a development process. (4) forming a metal film on and around the white spot defect or on the entire photomask using vacuum evaporation technology; (5) removing the resist and at the same time forming a window on the resist. The process also involves removing the metal film, which has the drawback of requiring a large number of steps and time.

In addition, conventional methods using partial vapor deposition using a laser have been proposed, but there are many practical problems such as accuracy, film strength, and film uniformity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for correcting white spot defects on a photomask, which eliminates the drawbacks of the prior art and allows correction with high precision in fewer steps and time.

The feature of the method of the present invention is that a metal complex solution is applied to the entire surface of a photomask having white spot defects or only to the white spot defect area and its surrounding area, and a visible or ultraviolet laser is used as a light source to irradiate selected areas of the white spot defect area. At this time, when the amount of laser light transmitted through the hook mask is measured, by appropriately selecting the laser output, a metal film, metal oxide film, or a mixture thereof is deposited from the metal complex, and after the deposition is completed, the laser light The amount of transmitted light becomes constant. Under these conditions, after the completion of the deposition, by continuing the laser irradiation for a certain period of time and then stopping the laser beam irradiation, it is possible to obtain a film that has strong adhesive strength to the photomask, and has good positional accuracy and light shielding properties. , white spot defects can be corrected.

The device of the present invention is characterized by: a means for generating laser light; a rectangular opening slit for shaping the light generated by the means into a rectangular shape of arbitrary size;
an objective lens for condensing and imaging a laser beam shaped into a rectangle by the rectangular aperture slit as a reduced image of the rectangular aperture slit; an X-Y table on which a photomask having a white spot defect is placed; and a photomask. A function to control the position of the X-Y table so that the projected image of the rectangular aperture slit matches the white spot defect position based on the information on the defect position. and a control device having a function of determining completion of white spot defect correction based on a signal from the detector and a function of controlling ON/OFF of a laser beam, and with this configuration, the correction method can be performed. We were able to implement this without fail.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 shows an example of a photomask white spot defect correction apparatus for implementing the method of the present invention.

The white spot defect correction apparatus of the embodiment shown in FIG. a rectangular opening slit 4 disposed on the optical path of the laser beam directed toward the position, and its driving device 27;
Half mirror 5, objective lens 6, photomask 7
An illumination light source 9, a half mirror 10, and an observation optical system 11 for observing and aligning the mask pattern of
and a laser cut filter 12, a slit illumination light source 13, an interference filter 14, a half mirror 15 for observing and displaying the pattern of the photomask 7 and the projected image of the rectangular aperture slit 4, and the laser cut filter 1.
6, an imaging device 17, a monitor TV 18, an X-Y table 20 on which the photomask 7 is placed, its driving devices 21, 21', and a white spot defective portion 8 of the photomask 7.
A condenser lens 23, a detector 24, an interference filter 25, an X-Y table 20, and a shutter 22 for detecting the amount of transmitted laser light transmitted through the metal complex film 19 deposited around the metal complex film 19 and the glass substrate. and a control device 26 that controls the metal complex film 19 and determines the state of metal precipitation from the metal complex film 19.

The laser beam 2 generated from the Ar laser oscillator 1 has its optical path bent by a dichroic mirror 3, reaches a rectangular opening slit 4 whose width in both the X and Y directions can be set independently, and is shaped into an arbitrary rectangle. Ru.

The laser beam 2 formed into an arbitrary rectangular shape by the rectangular opening slit 4 passes through the half mirror 5, is focused by the objective lens, and is irradiated onto the photomask 7 having a white spot defect. Here, in the photomask 7 and the rectangular aperture slit 4, the image of the rectangular aperture slit 4 is transmitted by the objective lens 6 to the reciprocal of the magnification of the objective lens 6, that is, when the magnification of the objective lens 6 is M times, the image of the rectangular aperture slit 4 is 1/M. It is reduced and placed in the projected position.

Observation and alignment of the pattern on the photomask 7 can be carried out using the observation optical system 11 by combining the light from the illumination light source 9 with the half mirrors 5 and 10.
This can be done by In addition, the observation optical system 11
A laser beam cut filter 12 is arranged for the safety of workers.

Further, the light from the slit illumination light source 13 is transmitted through an interference filter 14 at a specific wavelength, and then through a dichroic mirror 3, and is then transferred to a photomask 7 by an objective lens 6 as a projected image of the rectangular aperture slit 4.
imaged on top. Here, the dichroic mirror 3 has a characteristic of reflecting the wavelength of the laser beam 2 and transmitting a specific wavelength of the slit illumination light. The image of the rectangular opening slit 4 created by this slit illumination light can also be observed by the observation optical system 11.

Furthermore, the pattern of the photomask 7 and the projected image of the rectangular aperture slit 4 can be observed on the monitor TV 18 using the half mirror 15, the laser cut filter 16, and the imaging device 17.

A metal complex solution is applied onto the photomask 7 having white spot defects, and a metal complex film 19 is formed by drying.
is formed. The X-Y table 20 can be adjusted so that the white spot defect 8 matches the projected image of the rectangular opening slit 4. Also, X
- The Y table 20 can be driven manually or by table drive devices 21, 21', and is formed hollow so that the laser beam 2 can pass therethrough.

Adjust the width of the rectangular opening slit 4 while observing with the observation optical system 11 or the monitor TV 18,
The projected image is made to match the size of the white spot defect 8.

After positioning, the shutter 22 is opened and the laser beam 2 is irradiated onto the white spot defect 8. At this time, the laser beam 2 is irradiated onto exactly the same area as the projected image of the rectangular opening slit 4 by the slit illumination light source 13, passes through the metal complex film 19 and the glass substrate of the white spot defect 8, and is emitted by the condenser lens 23. The laser light amount is input to a detector 24 for the amount of laser light.

In order to prevent errors caused by light from the illumination light sources 9 and 13, an interference filter 25 that transmits only the laser beam 2 is placed in front of the detector 24.

Generally, since the focal length of the objective lens 6 is short, the transmitted laser light spreads rapidly, so a condenser lens 23 is used, but this is not always necessary.

In addition, although the shutter 22 is used to turn on and off the laser beam 2, the same operation can also be performed using an electro-optic or acousto-optic modulator, and furthermore, the power source of the Ar laser oscillator 1 can be controlled. This can also be done by doing the following:

The control device 26 has the following functions. That is, the function reads the position information detected by the defect inspection device from a magnetic medium or the like, drives the table drive devices 21 and 21' of the X-Y table 20, and reproduces the white spot defect position, and the detection of the laser light intensity. Vessel 2
It has the function of receiving electrical signals from 4 and determining the deposition state of the metal film, and controlling the shutter 22, modulator, and power supply to emit laser light 2.
It has a function to turn it on and off. Furthermore, if the size of the white spot defect is known in advance, the slit width can be set by driving the drive device 27 for changing the width of the rectangular opening slit 4.

Next, one aspect of a method for correcting the white dot defect portion 8 of the photomask 7 using the white dot defect correction apparatus shown in FIG. 1 will be described.

A metal complex solution such as a silver complex solution is applied to the entire surface of the photomask 7 having the white spot defect 8 or to the white spot defect 8 and its surrounding area, and is dried to form a metal complex film 19.
After forming, place it on the X-Y table 20,
Control device 2 based on position information from the defect inspection device
6 drives the table drive devices 21, 21' to at least the observation optical system 11 or the imaging device 1.
The white spot defect portion 8 is made to be within the field of view 7.

Next, while observing the projected image of the rectangular opening slit 4 by the slit illumination light source 13, precise positioning and setting of the slit width are performed. At this time, adjustment is made so that the projected image of the rectangular opening slit 4 does not protrude from the normal pattern and sufficiently covers the white spot defect 8.

Next, the shutter 22 is opened to irradiate the white spot defect portion 8 with the laser beam 2 oscillated from the Ar laser oscillator 1 . The irradiated laser beam 2 passes through the metal complex film 19 and the white spot defect 8 of the photomask 7, passes through the condenser lens 23 and the interference filter 25, and enters the laser beam amount detector 24.

Therefore, changes in the amount of laser light are converted into electrical signals and sent to the control device 26. The control device 26 memorizes the amount of transmitted light at the start of irradiation with the laser beam 2, and at regular intervals, for example, every 0.1 seconds, compares the amount of transmitted light at that time with the amount of transmitted light just before, that is, 0.1 seconds before, and at the start of laser irradiation. Compare with the amount of transmitted light. Then, the amount of transmitted light becomes less than 10% of that at the start of irradiation.
The time measurement starts when the time becomes equal to or no longer decreases to the time just before that (0.1 seconds before), and after irradiating the laser beam 2 for a certain period of time, a signal is sent to the shutter 22, and the laser beam 2 is irradiated. to stop.

By irradiating the metal complex film 19 with laser light 2 and depositing a metal film, the white spot defect 8 of the photomask 7 is corrected.

This completes the correction of one white spot defect 8.
After observing as necessary, when the operator issues a signal indicating completion of correction, the X-Y table 20 is driven to the next defect position.

After depositing a metal film on all white spot defects 8,
The photomask 7 is cleaned to remove the metal complex film 19 other than the part where the metal film has been deposited, and the repair work is completed.

Figure 2 shows an example of the change in the amount of transmitted laser light during correction using the method of the present invention. Changes in the amount of transmitted light are shown assuming that the amount of transmitted light immediately after the start of laser beam irradiation is 1.

In FIG. 2, a solid line, a broken line, and a dashed-dotted line indicate the difference in power density of the irradiated laser beam at the white spot defect, and the power density decreases in order. When the power density is high, as shown by the solid line, a metal film or metal oxide film precipitates in an extremely short period of time, and the amount of transmitted light decreases rapidly.After reaching the minimum value, the laser beam irradiation is stopped. If this continues, the amount of transmitted light will begin to increase rapidly and will eventually become saturated.

When the power density is low, as shown by the dashed line in Figure 2, it takes time for the metal film or metal oxide film to start depositing, but once the deposition begins, the amount of transmitted light decreases rapidly. If the laser beam irradiation is continued after reaching the minimum value, the amount of transmitted light does not change for a certain period of time, but eventually begins to increase.

When the power density is medium, as shown by the broken line in FIG. 2, the characteristics are intermediate between the previous two conditions. The changes shown in Figure 2 are simply data obtained when a rectangular metal film and metal oxide film are deposited on a glass substrate on which a silver complex film is formed, but in actual white spot defect repair, As shown in FIG. 3, white spot defects 31a, 3 present in the pattern 30 formed on the photomask substrate 29
Depending on the size and shape of 1b, 31c, 31d and the set size of laser irradiation areas 32a, 32b, 32c, 32d, the time from the start of laser beam irradiation until the metal film or metal oxide film is deposited is determined. to differ greatly.

That is, when correcting an actual white spot defect, in most cases, a part of the laser beam irradiation area 32 overlaps the normal mask pattern 30.
Due to absorption of laser light by the metal film in the normal pattern, the temperature rises faster than in the part where only the complex film is present, and the precipitation progresses quickly and rapidly spreads from the precipitated part to the entire irradiated area.

Therefore, when actually correcting white spot defects,
The time until the precipitation of the metal film and metal oxide film is completed (the time until the amount of transmitted light reaches its minimum in Figure 2) is from a fraction of the time to several tenths of the time in Figure 2. . However, the behavior of the metal film or metal oxide film after the deposition is completed is controlled only by the irradiation power density and is not affected by the size of the white spot defect or the degree of overlap between the mask pattern and the irradiation area.

Next, the laser beam is irradiated for a certain period of time from the point at which the deposition of the metal film or metal oxide film is completed, that is, the amount of transmitted light becomes the minimum, and the deposited metal film or metal oxide film is separated from the glass substrate. The adhesion strength is increased, but the time varies depending on the irradiation power density. In Figure 2, 0.2 relative time is good for the transmitted light amount condition shown by the broken line, 1 relative time is good for the transmitted light amount condition shown by the dashed line, and the transmitted light amount condition shown by the solid line has too high a power density and is not suitable. If the irradiation time is too long even at the power density, the deposited metal film or metal oxide film may be damaged or the light-shielding property may be reduced. However, the appropriate power density varies depending on the composition and thickness of the complex film.

The metal complexes described in this example are metal complexes in the narrow sense, that is, one or more metals are bonded to a central atom and other atoms or atomic groups, that is, ligands, to form a complex. This concept includes metal salts produced in normal solution reactions in addition to the atomic groups that make up the two atomic groups.

In one embodiment of the present invention, a solution of silver nitrate, carboxylic acid, and additives in an organic solvent is used as the metal complex. At this time, carboxylic acid silver salt is formed in a dissolved state in the solution. Among the silver salts, carboxylic acid silver salts are preferably used because they dissolve well in organic solvents and form good films even when the organic solvents are evaporated. Various types of carboxylic acids can be used, but among dicarboxylic acids having two carboxylic acid groups, citraconic acid has particularly excellent film-forming properties.

In addition, as an organic solvent, in addition to alcohol-based, cellosolve-based, carbitol-based, and glycol-based organic solvents, dimethyl sulfoxide, dimethyl acetamide, dimethyl formamide, etc. can be used, but a mixture of methyl cellosolve and acetonitrile is optimal. .

Further, in order to improve the adhesion between the deposited metal film, metal oxide film, or mixture thereof and the substrate, the objective can be achieved by adding titanium alcoholate, but titanium tetrabutyrate is most suitable.

A complex film of 0.1 to 1 micron is formed using the above solution as a coating liquid, and the metal film and titanium oxide film deposited by the method described above have extremely strong adhesion strength to the substrate and have a low transmittance for wavelengths of 3500 Å to 5000 Å. 2 to 10% can be obtained.

Further, in this example, an Ar laser oscillator is used as a laser light source, and one or both of wavelengths of 5145 Å and 4880 Å are used, but the invention is not limited to this. For example, the ultraviolet wavelength of Ar laser, the basic wavelength of YAG laser, etc. waves, and their harmonics,
A dye laser can also adequately achieve this purpose.

Further, after depositing a metal film, a metal oxide film, or a mixture film thereof, the complex film other than the deposited portion can be completely removed by washing with methyl cellosolve, acetonitrile, or a mixture of both.

The present invention has the configuration described in detail above, and according to the method of the present invention, white spot defects can be repaired in fewer steps and in about 1/10 of the time compared to the conventional lift-off method, and moreover, The adhesion strength between the metal film, metal oxide film, or their mixture film deposited on the defective part and the substrate is high, and the light shielding property can be repaired with high precision, thus improving the production yield of semiconductor devices. It has a hugely improving effect.

Furthermore, the apparatus of the present invention has the effect of reliably implementing the method for correcting white spot defects.

[Brief explanation of the drawing]

FIG. 1 is a system section showing an example of a white spot defect correction apparatus for carrying out the method of the present invention, FIG. 2 is a diagram showing changes in the amount of transmitted light when a white spot defect is corrected by the method of the present invention, and FIG. The figure shows an example of a white spot defect and a laser beam irradiation area when a white spot defect is corrected by the method of the present invention. 1...Ar laser oscillator, 2...Laser light, 3
...Dichroic mirror, 4...Rectangular aperture slit, 6...Objective lens, 7...Photomask,
8... White spot defect portion, 11... Observation optical system, 17...
...Imaging device, 18...Monitor TV, 19...Complex film, 20...X-Y table, 21, 21'...
X-Y table drive device, 22...shutter,
24... Laser light amount detector, 26... Control device, 27... Rectangular opening slit driving device, 29
...Photomask substrate, 30...same pattern,
31... White spot defect area, 32... Laser beam irradiation area.

Claims (1)

[Scope of Claims] 1. After applying a metal complex solution to at least the white spot defect area and its surrounding area of a photomask having white spot defects, the white spot defect area is selectively irradiated with a laser beam to form a metal film and a metal complex solution. Deposit an oxide film or a mixture thereof, measure the amount of transmitted light through the photomask that changes during the deposition process, and after the amount of transmitted light rapidly decreases and then becomes constant, continue irradiating the laser beam for a certain period of time. A method for correcting white spot defects on a photomask, characterized by stopping irradiation. 2. The method for correcting white spot defects on a photomask according to claim 1, wherein the metal complex solution is a solution prepared by adding at least silver nitrate, carboxylic acid, and titanium alcoholate to an organic solvent. 3 means for generating laser light; a rectangular aperture slit for shaping the laser light generated by the means into a rectangle of arbitrary size; and a rectangular aperture slit for shaping the laser light into a rectangular shape by the rectangular aperture slit. An objective lens for condensing and forming a reduced image of
- A Y table, a detector that detects the amount of transmitted light transmitted through the white spot defect of the photomask, and an X-Y table that uses information about the defect position to match the projected image of the rectangular opening slit with the white spot defect position. A function to control the position of the laser beam, a function to judge the completion of white spot defect correction based on the signal from the detector, and a function to control the position of the laser beam.
1. A white spot defect correction device for a photomask, comprising a control device having an ON/OFF control function. 4. The control device detects a signal immediately after the start of laser beam irradiation and a certain period of time among the signals sent to the control device from a detector that detects the amount of transmitted light transmitted when the white spot defect is irradiated with the laser beam. storing the signal at each elapsed time, and comparing the signal immediately after the start of the irradiation, the signal at each elapsed time, and the signal immediately before that,
Laser light irradiation is continued for a specific period of time from when the amount of transmitted light has decreased below a certain percentage compared to when the irradiation started, and when it no longer decreases when comparing the amount of transmitted light after a certain period of time and the amount of transmitted light just before that. 4. The photomask white spot defect correcting apparatus according to claim 3, further comprising a function of stopping the irradiation after the irradiation continues.