JP3251665B2 - Method for repairing photomask having phase shift layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of repairing a photomask used for manufacturing a high-density integrated circuit such as an LSI or a super LSI, and more particularly to a phase shift layer for forming a fine pattern with high precision. And a method for repairing a photomask having the following.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs apply a resist on a substrate to be processed such as a Si wafer, expose a desired pattern by a stepper or the like, and then perform development and etching. It is manufactured by repeating a lithography process.

[0003] A photomask called a reticle used in such a lithography process tends to be required to have higher and higher precision as the performance and integration of a semiconductor integrated circuit become higher and higher. The line width of the device pattern formed using these reticles is 1 Mbit DR.
1.2μm for AM and 0.8μ for 4Mbit DRAM
In the case of m and 16 Mbit DRAMs, further miniaturization of 0.5 μm is required, and various exposure methods have been studied to meet such requirements.

However, for example, in the case of a 64 MDRAM class device, a pattern having a line width of 0.35 μm is required, and the stepper exposure method using a reticle hits the resolution limit of a resist pattern. For example, JP-A-58-173
No. 744, Japanese Patent Publication No. 62-59296, and the like have proposed a reticle based on a new concept called a phase shift mask. Phase shift lithography using a phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

[0005] Phase shift lithography will be briefly described with reference to the drawings. FIG. 2 is a diagram showing the principle of the phase shift method,
FIG. 3 is a diagram showing a conventional method, and FIG. 2 (a) and FIG.
(A) is a cross-sectional view of the reticle, FIG. 2 (b) and FIG. 3 (b)
2 (c) and 3 (c) show the light amplitude on the wafer, FIGS. 2 (d) and 3 (d) show the light intensity on the wafer, respectively, and 1 denotes the light intensity on the wafer. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 3A, only a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of glass or the like, and a light transmitting portion of a predetermined pattern is formed. However, in phase shift lithography,
As shown in FIG. 2A, a phase shifter 3 made of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Therefore, in the conventional method, the amplitude of light on the reticle is in phase as shown in FIG. 3 (b), and the amplitude of light on the wafer is also in phase as shown in FIG. 3 (c). While the pattern on the wafer cannot be separated as shown in FIG. 3D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 2B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 2D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated, and the resolution can be improved.

Next, one of the manufacturing steps of the phase shift reticle
An example will be described with reference to FIG. FIG. 4 is a cross-sectional view showing a manufacturing process of the phase shift reticle. As shown in FIG. 4A, a completed chrome reticle having a chromium pattern 6 provided on a substrate 5 is prepared. As shown in FIG. 2B, a transparent film 7 made of SiO ₂ or the like is formed on the chromium pattern 6. Next, as shown in FIG.
An ionizing radiation resist layer 8 of chloromethylated polystyrene or the like is formed on the transparent film 7, and the resist layer 8 is aligned in a conventional manner as shown in FIG. Then, a predetermined pattern is drawn, developed, and rinsed to form a resist pattern 10 as shown in FIG.

Next, after performing a heat treatment and a descum treatment as necessary, as shown in FIG. 1F, the transparent film 7 exposed from the opening of the resist pattern 10 is dried by the etching gas plasma 11. Etching is performed to form the phase shifter pattern 12. The phase shifter pattern 12 is formed by etching gas plasma 1
1 may be performed by wet etching instead of dry etching.

Next, the remaining resist is ashed and removed by oxygen plasma 13 as shown in FIG. Through the above steps, a phase shift mask having the phase shifter 12 as shown in FIG.

Incidentally, in the phase shift lithography as shown in FIG. 2, the thickness d of the phase shifter having the refractive index n
And the wavelength λ of the light source used, d = λ / 2 (n
The relationship of -1) holds. In order to invert the phase of light by 180 degrees and accurately transfer the pattern on the reticle onto the wafer, the phase error must be within ± 10 degrees,
It is known that if the phase is shifted by 10 degrees or more, the pattern dimensions cannot be faithfully reproduced.

Therefore, for example, 365n is used as the exposure light source.
When using m (i-line) light and using SiO ₂ having a refractive index of 1.4 as a phase shifter, the film thickness needs to be 4562 °, and the film thickness error must be controlled within ± 253 °. That is, when a projection-like defect exists on a phase shifter or a transparent glass substrate, the height of the defect is set to 2
It is necessary to keep it within 53 °.

However, in the above-described conventional method for manufacturing a phase shift reticle, a transparent projection-like defect thicker than a normal portion tends to occur on a transparent phase shifter or a transparent glass substrate. However, there is a problem that it cannot be corrected even if is confirmed. Since the phase shifter and the glass substrate are formed of transparent SiO ₂ or the like, most of the projection defects on the phase reticle are also transparent. Generally, a laser defect repairing apparatus used for repairing a protruding defect portion of a chrome reticle irradiates the defect portion with a laser beam having a rectangular cross section corresponding to the size of the defect portion on the reticle to remove the defect portion. The defect that can be corrected is limited to a portion made of a metal or the like that absorbs laser light. Since the transparent projection-like defect of the phase shift reticle hardly absorbs the laser beam, the transparent defect cannot be corrected by such a conventional method.

Accordingly, the present applicant has filed Japanese Patent Application No. Hei.
In No. 45, a colored layer is formed on a transparent protruding defect portion, and then a laser beam having a wavelength absorbed by the colored layer is irradiated on the colored layer on the defective portion to select such a defective portion. A correction method to eliminate the problem is proposed.

In Japanese Patent Application Laid-Open No. 4-125624, after an etching gas is adsorbed on the surface of a phase shift reticle, an energy beam such as ultraviolet light, a focused ion beam, or an electron beam is selected for a transparent projection defect. A correction method has been proposed in which etching is performed by selective irradiation.

[0015]

However, these repairing methods are difficult to accurately correct the transparent projection-like defects by precise etching, and require a pre-process. It was hard to say.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a method capable of accurately correcting a projection-like defective portion of a photomask having a phase shift layer by a simple method. To provide.

[0017]

SUMMARY OF THE INVENTION In view of the above problems, the inventor of the present invention removes and corrects a projection-like defect of a phase shift reticle by physically scratching it, and stably supplies a highly accurate reticle. They have found that they can be manufactured, and have completed the present invention based on such knowledge.

That is, the method for repairing a photomask having a phase shift layer according to the present invention is the same as the method for repairing a phase shift photomask having a transparent projection-like defect portion on a phase shift layer or a glass substrate. The method is characterized in that the transparent protruding defect is scratched and physically removed by a fine probe having a sharp tip.

[0019]

According to the present invention, a transparent protruding defect on a phase shift layer or a glass substrate is physically removed by scratching with a fine probe having a pointed tip of a stylus type shape measuring instrument, so that the surface shape can be measured. In the inspection step, the projection-like defect can be corrected with high accuracy by a simple method at the same time.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for repairing a photomask having a phase shift layer according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing each step of a method of repairing a phase shift photomask according to the present invention, in which 1 is a transparent substrate formed of soda lime glass, low expansion glass, quartz glass, or the like; 2 is a light shielding layer made of chromium, chromium oxide, chromium oxynitride, molybdenum silicide, etc., 3 is SOG (spin on glass), sputter Si
A transparent phase shifter made of O ₂ or the like, 4 denotes a transparent projection-like defect on the transparent substrate 1, 20 denotes a probe, and 21 denotes a remaining portion of the transparent projection-like defect.

First, a phase shift reticle having a transparent projection defect 4 as shown in FIG.
As shown in the figure, the probe 20 having a sharp tip is positioned on the defect portion 4 to be corrected, and is brought close to the lateral position as shown by the arrow. Then, as shown by the arrow in FIG. Is moved along the surface of the substrate 1 as shown in FIG.
As shown in FIG. 2, the transparent projection-like defect portion 4 is scraped off by the moving probe 20, and as shown in FIG.
And the defective portion 4 is removed. Transparent projection defect 4
Is on the phase shifter 3 as well. The thin remaining portion 21 remaining on the substrate 1 or the phase shifter 3 hardly shifts the phase of the incident light, so that it does not affect the transfer.

Actually, the transparent protruding defect portion 4 on the substrate 1 was scraped off with a stylus of a stylus type film pressure gauge DECTAC (manufactured by Sloan) at a stylus pressure of 100 mg.
The black defect of the phase shifter 3 composed of was successfully removed.

[0023]

In the phase shift photomask, since a transparent material is used for the phase shifter, transparent projection-like defects are easily generated, and such defects lower the effect of the phase shift. There is a problem that a phase shift reticle manufactured at a high cost cannot be used. However, according to the correction method of the present invention, a transparent probe-like defect on a transparent phase shifter layer or a glass substrate, which has been difficult to correct with high accuracy in the past, is a fine probe with a pointed tip of a stylus type shape measuring instrument. In the process of measuring and inspecting the surface shape, the projection-like defect can be accurately corrected by a simple method at the same time in the step of measuring and inspecting the surface shape.

According to the present invention, an expensive phase shift reticle including a transparent projection defect which has been conventionally treated as a defective product can be used again in a high quality state.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the steps of one embodiment of a method for repairing a phase shift photomask according to the present invention.

FIG. 2 is a diagram illustrating the principle of the phase shift method.

FIG. 3 is a diagram showing a conventional method.

FIG. 4 is a cross-sectional view showing a step of manufacturing a phase shift photomask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 2 ... Light shielding layer 3 ... Phase shifter 4 ... Transparent protrusion-like defect part 20 ... Probe 21 ... Remaining part of a defect part

Claims (1)

(57) [Claims] 1. A method for repairing a phase shift photomask having a transparent projection-like defect on a phase shift layer or a glass substrate, wherein the transparent projection-like defect is detected by a fine probe having a pointed tip of a stylus type shape measuring instrument. A photomask having a phase shift layer, wherein the photomask is physically removed by scratching.