JPH04288542A - Phase shift mask and its correcting method - Google Patents

Abstract

PURPOSE:To suppress the reduction of the quantity of light transmitted at the time of transfer. CONSTITUTION:A black defective region 4 enclosed by the pattern 2 of a mask is irradiated with ion beams 5 while feeding a reactive gas to the region 4 and the region 4 is removed by etching. Ions penetrate hardly into the substrate of the mask at the time of irradiation with the ion beams 5 and the reduction of the quantity of light transmitted at the time of transfer is suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask used in an optical lithography process in the manufacture of semiconductor devices and a method for modifying the mask.

0002

[Prior Art] The resolution limit R (μm) of lithography technology using a reduction optical stepper is as follows: R=k1 λ/NA, k1
=0.5. Here, λ is the wavelength (μm), N
A is the numerical aperture of the lens. In optical lithography, the resolution limit is reduced by shortening the exposure wavelength, increasing the NA, and reducing the constant k1 that depends on the resist process, in accordance with the above equation. Currently, i-line (λ=0
．． 365 μm), a stepper with NA=0.5 was realized,
Since k1 =0.5 is also possible, resolution of about 0.4 μm has become possible. In order to obtain a higher resolution limit, it would be possible to shorten the exposure wavelength and increase the NA, but it is technically difficult to obtain an appropriate light source and lens, and furthermore, the depth of focus δ There is a problem that =/2NA2 becomes small.

[0003] As a solution to this problem, Japanese Patent Application Laid-open No. 1987-
Phase shift exposure methods such as those described in Japanese Patent Laid-Open No. 62052 and Japanese Patent Application Laid-Open No. 173744/1982 have been proposed.

The principles of the conventional photomask method and the phase shift exposure method will be explained below. 7 to 9 are diagrams for explaining the principle of the conventional photomask method, and FIG. 10
1 to 12 are diagrams for explaining the principle of the phase shift exposure method. 7 and 10 are cross-sectional side views of the mask in each method, FIGS. 8 and 11 show the electric field intensity on the mask in each method, and FIGS. 9 and 12 show the light intensity on the wafer in each method. . When considering pattern transfer that is lower than the resolution of optical lithography, in the photomask method, the electric field of light transmitted through the mask pattern (main pattern) 2 formed on the mask substrate (SiO2 etc.) 1 is shown in Figure 8. As shown, the waveforms are spatially separated. However, the wafer (not shown) of the light transmitted through the optical system
The upper light intensities overlap each other as shown in FIG. 9, and the pattern cannot be resolved.

On the other hand, in the phase shift exposure method, as shown in FIG.
SiO2 that inverts the phase of light by 180 degrees every other time in a
This is a method of transferring using a mask provided with a phase shift pattern (shifter) 3 such as. The electric field of the light transmitted through the mask of the phase shift exposure method has its phase alternately reversed as shown in FIG. Therefore, when this is projected using the same optical system as the conventional photomask method, the light acts to cancel each other out in the areas where adjacent pattern images overlap. As a result, the light intensities on the wafer become separated as shown in FIG. For this reason, the phase shift exposure method has higher resolution than the photomask method. Experiments have shown that the former has a minimum resolution pattern width approximately half that of the latter.

Next, a method for correcting defects in a phase shift mask in the phase shift exposure method will be explained. 13 to 15 are cross-sectional process diagrams for explaining a method for correcting black defects in a phase shift mask, and FIGS. 16 to 18 are cross-sectional process diagrams for explaining a method for correcting white defects in a phase shift pattern. In these figures, there is Cr on the mask substrate 1.
A mask pattern 2 made of or MoSi is formed. A phase shift pattern 3 made of SiOX or fluororesin is formed at a predetermined position between the mask patterns 2.

First, a method for correcting black defects will be explained. The black defect refers to a phase shift pattern formed in a region between mask patterns 2 formed on the mask substrate 1 where the phase shift pattern 3 should not be formed. In FIG. 13, 4 is a black defect area. This black defect is corrected as follows. That is, as shown in FIG. 14, a focused ion beam (FIB (force
A used beam )) 5 is irradiated and scanned onto the black defect area 4, and the black defect material is etched (milled) and scraped off. For example, a black defect of 1μm2 is 30K.
If an ion beam of eV Ga+ (beam current 300 pA) is used, this black defect can be removed in a few minutes. In this case, a mask substrate such as SiOx (usually made of quartz (SiO2)) 1 is used as the phase shift pattern 3.
If a similar material is used, it will be difficult to detect the etching end point, so it is better to use a dissimilar material, such as a fluororesin. The reason for this is that ions sputtered by etching (secondary ions) are used to detect the end point of etching.
If a material similar to the mask substrate (usually made of quartz (SiO2)) 1, such as SiO This is because the boundary of pattern 3 becomes unclear. After the black defect area 4 is removed, there is a black defect remaining portion 4a on the upper part of the mask pattern 2 as shown in FIG. 15, but there is no problem because the mask pattern 2 does not transmit light.

Next, a method for correcting white defects will be explained. A white defect refers to a region where a phase shift pattern 3 is to be formed between mask patterns 2 formed on a mask substrate 1 but in which no phase shift pattern is formed. In FIG. 16, 6 is a white defect area. This defect is corrected by a film deposition method using the so-called ion beam assist method described below. Figure 17
As shown in FIG. 2, an ion beam (the same beam as used for repairing a black defect) 5 is scanned multiple times over a white defect region 6 to be repaired in a reactive gas atmosphere (SiH4 +O2, etc.). During this time, the reaction gas 9 is ejected from the nozzle 8 onto the white defect area 6. At this time, the nozzle 8 is brought close to the mask substrate 1 until the distance from the mask substrate 1 is approximately several hundred μm, so that the reactive gas 9 hits the white defect area 6. The reaction gas 9 is decomposed by irradiating the reaction gas 9 with the ion beam 5,
A reaction is caused to occur, and a shift material (SiO2 or SiOX) 7 is deposited on the white defect area 6 as shown in FIG. As shown in FIG. 18, the thickness of the shift material (SiO2 or SiOX) 7 when completely deposited is about 100 nm (same as the thickness of the phase shift pattern 3). The thickness of the shift material 7 to be deposited depends on the composition and structure of the shift material 7. The composition and structure of the shift material 7 vary depending on the irradiation conditions of the ion beam 5, the atmosphere of the reaction gas 9, and the like. Therefore, it is necessary to adjust the thickness of the shift material 7 to be deposited by adjusting the irradiation conditions of the ion beam 5, the atmosphere of the reaction gas 9, etc.

[0009]

The conventional method for repairing a mask used in phase shift exposure involves the steps described above, and has the following problems.

In the repair of black defects, the ion beam 5
Since the black defect area 4 is etched by irradiating with There is a problem in that the amount of light transmitted during transfer is reduced.

[0011] Furthermore, in the repair of white defects, SiH4
Because toxic and flammable gases such as .

[0012]Furthermore, as shown below, the film deposition method using the ion assist method has lower accuracy than when etching is used. There was also the problem that it was bad. That is,
When the shift material 7 is deposited as shown in FIG. 18, since the side surfaces are surrounded by the mask pattern 2, the shift material 7
However, for example, if the mask pattern 2 is not provided in the depth direction, so-called skirting occurs when the shift material 7 is deposited, and the shift material does not adhere to the desired dimensions. 7 cannot be formed. Further, even when surrounded by the mask pattern 2 on all sides, it is difficult to form the shift material 7 in complete contact with the inner wall of the mask pattern 2. but,
This problem does not arise when the black defect area 4 is removed using etching.

The present invention has been made to solve the above-mentioned problems, and it is possible to simplify the mask repair device without reducing the amount of light transmitted during transfer, and to remove white defects safely and accurately. The present invention aims to obtain a phase shift mask that can be modified and a method for modifying the same.

[0014]

A phase shift mask according to the present invention is characterized in that a part of the phase shift pattern is a recess formed by digging into a mask substrate.

A first aspect of the phase shift mask repair method according to the present invention is a phase shift mask repair method for repairing defects in a phase shift pattern of a phase shift mask. By irradiating the black defect area with an ion beam while supplying a reactive gas according to the phase shift pattern material to the black defect area where the phase shift pattern is formed in an area where the phase shift pattern should not be formed, the black defect area is The method is characterized in that the formed phase shift pattern is removed by etching.

[0016] The phase shift pattern according to the present invention has a second
In this aspect, in a phase mask repair method for correcting a defect in a phase shift pattern of a phase shift mask, a phase shift pattern is formed in a region where a phase shift pattern is to be formed between mask patterns formed on a mask substrate. The mask substrate under the white defect area is etched away by irradiating the ion beam while supplying a reactive gas according to the material of the mask substrate to the white defect area where the phase shift pattern is not originally formed. The present invention is characterized in that the phase of the light that passes through the region and the phase of the light that passes through the etched white defect region are opposite to each other.

[0017]

[Operation] In the phase shift mask according to the present invention,
Since part of the phase shift pattern is formed by a recess dug into the mask substrate, white defects can be corrected by etching the mask substrate.

A first aspect of the method for correcting a phase shift pattern according to the present invention is that a phase shift pattern is formed in a region where a phase shift pattern should not be formed between mask patterns formed on a mask substrate. By irradiating the black defect area with an ion beam while supplying a reactive gas according to the phase shift pattern material, the phase shift pattern formed in the black defect area is etched away, so fewer ions enter the mask substrate. Become.

The second phase shift pattern according to the present invention
In this embodiment, ions are supplied to the white defect area where the phase shift pattern is not formed between the mask patterns formed on the mask substrate, while supplying a reactive gas according to the material of the mask substrate. By irradiating the beam, the mask substrate under the white defect area is etched away, and the phase of the light that passes through the area where no phase shift pattern is originally formed and the phase of the light that passes through the etched white defect area are changed. I made it to be in reverse phase, so
Deposition eliminates the need to correct white defect areas.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 are cross-sectional process diagrams showing an embodiment of a method for repairing a phase shift mask according to the present invention, and show a method for repairing black defects. Foreign matter mixed in when applying the resist used during etching of mask pattern 2, mask substrate 1 during etching of mask pattern 2
A black defect area 4 is formed as shown in FIG. 1 in the same way as in the prior art, which is caused by foreign matter sitting thereon or resist residue due to resist exposure or development abnormalities. The thickness of the black defect region 4 is the same as the thickness of the phase shift pattern 3.

The black defect region 4 is irradiated with the ion beam 5 while the reactive gas 9 is injected from the nozzle 8 . Then, Figure 2
As shown in FIG. 2, the black defect region 4 is gradually etched physically and chemically. The reaction gas 9 is such that the black defect area 4 is S
If the black defect region 4 is made of fluororesin, use hydrogen fluoride gas such as CHF3 or a mixed gas of hydrogen fluoride gas and a rare gas; if the black defect region 4 is made of fluororesin, use oxygen gas or a mixed gas of oxygen gas and a rare gas. Use.

The ion beam 5 has a G of 30 KeV, for example.
a+ (Beam current is 300pA, beam diameter is 0.1μ
mφ) is used. In the atmosphere of the reaction gas 9,
By scanning the black defect area 4 multiple times with the ion beam 5, the black defect area 4 is completely etched away as shown in FIG. The thickness of the black defect region 4 is the same as the thickness of the phase shift pattern 3 as described above. The thickness of the phase shift pattern 3 is set to such a thickness that the optical path difference between the light that passes through the area where the phase shift pattern 3 is not provided and the light that passes through the area where the phase shift pattern 3 is provided is an odd number multiple of 1/2 wavelength. There is. Therefore, when the black defect area 4 is completely removed, the light that passes through the etched area 10 from which the black defect area 4 has been completely removed, and the light that passes through the white pattern area 11 where the phase shift pattern 3 is not originally provided. The optical path difference becomes an even number multiple of 1/2 wavelength, and the above two transmitted lights are in phase,
The phase of the light passing through the phase shift pattern 3 is opposite to that of the light, and the black defect has been corrected. In this case, the ion beam 5
Since the irradiation is performed in the atmosphere of the reactive gas 9, ions do not enter the mask substrate 1 in large numbers as in the conventional case. Therefore, there is less reduction in the amount of light transmitted during transfer than in the past. In addition, since the depth of ion penetration is shallow, several hundred angstroms or less, light etching using buffered HF and plasma treatment on the mask substrate 1 (mask pattern 2
When is Cr, fluorine radical ions are used. ), the ions in the mask substrate 1 can be removed.
Color center can be eliminated.

FIGS. 4 to 6 are cross-sectional process diagrams showing another embodiment of the method for correcting a phase shift pattern according to the present invention, and show a method for correcting white defects. White defect areas 6 are formed as shown in FIG. 4, as in the prior art, caused by pinholes formed during resist application, resist residue or peeling due to abnormal resist exposure, and the like.

The white defect region 6 is irradiated with the ion beam 5 while the reactive gas 9 is injected from the nozzle 8 . Then, Figure 5
As shown in FIG. 2, the mask substrate 1 in the white defect area 6 is gradually etched physically and chemically. The mask substrate 1 is
It is usually made of SiO2, and therefore a hydrogen fluoride gas or a mixed gas of a hydrogen fluoride gas and a rare gas is used as the reaction gas. The ion beam 5 used is the same as that used for repairing the black defect shown above. The etching depth d of the mask substrate 1 is set to such a depth that the optical path difference between the light passing through the etching region 20 and the light passing through the white pattern region 11 is an odd multiple of 1/2 wavelength. By such etching, the light passing through the white defect area 6 and the light passing through the adjacent white pattern area 11 interfere and cancel each other out, so that the white defect is corrected.

The depth d can be adjusted by adjusting the irradiation time of the ion beam 5 if the beam current is constant. Since the optical path difference is expressed as (n-1)・d (where n is the refractive index of silica glass), the wavelength of the transmitted light is expressed as λ (nm).
Then, the depth d should be determined so that the following relational expression holds true.

(n-1)・d=(2m-1)λ/2 (however, m=1, 2,...) Here, using the i-line of a mercury lamp as an example of the exposure light source, Then, the i-line is λ=3
65 nm, n=1.476 (refractive index when λ=365 nm), and from the above equation, d is about 383 nm. Also in the correction of white defects, since the mask substrate 1 is etched by irradiating the ion beam 5 in the atmosphere of the reactive gas 9, a reduction in the amount of light transmitted during transfer can be prevented for the same reason as described above. Furthermore, since white defects are repaired by etching, the accuracy is on the same level as that for repairing black defects, and since SiH4 is not used, the mask repair apparatus can be simplified.

In the above embodiment, 30 KeV Ga+ was used as the ion beam 5, but for example, In+
Even if other ions such as ions are used, the same effects as in the above embodiment can be obtained. Also, the energy and current of the ion beam 5 are:
It is sufficient to set the conditions to have the best etching efficiency and high processing accuracy, and the conditions are not limited to the above embodiments. Further, the mask substrate 1 is not limited to quartz glass, but may be made of fluoride such as CaF.

[0028]

As described above, according to the phase shift mask of the present invention, a part of the phase shift pattern is formed by a recess dug into the mask substrate, so white defects can be corrected by etching the mask substrate. This can be done by As a result, the white defect correction accuracy improves.

As described above, according to the first aspect of the method for correcting a phase shift mask according to the present invention, the phase shift pattern is not formed between the mask patterns formed on the mask substrate in the region where the phase shift pattern should not be formed. The phase shift pattern formed in the black defect area is etched away by irradiating the ion beam with a reactive gas depending on the material of the phase shift pattern while supplying the black defect area where the shift pattern is formed. Therefore, fewer ions enter the mask substrate during ion beam irradiation. As a result, there is an effect that the amount of light transmitted during transfer is increased compared to the conventional method.

According to the second aspect of the method for repairing a phase shift mask according to the present invention, a phase shift pattern is formed in a region where a phase shift pattern is to be formed between mask patterns formed on a mask substrate. By irradiating the ion beam while supplying a reactive gas according to the material of the mask substrate to the white defect area where there is no white defect, the mask substrate under the white defect area is etched away, and the area where the phase shift pattern is originally not formed is penetrated. The phase of the light passing through the etched white defect area is opposite to the phase of the light passing through the etched white defect area, so it is possible to avoid toxic substances such as SiH4, unlike conventional methods.
There is no need to use self-combustible gas, and there is no need to correct white defects by deposition. the result,
This has the effect that the mask repair device can be simplified and white defects can be repaired safely and accurately.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional process diagram showing a method for repairing a black defect among the methods for repairing a phase shift mask according to the present invention.

FIG. 2 is a cross-sectional process diagram showing a method for repairing black defects among the methods for repairing a phase shift mask according to the present invention.

FIG. 3 is a cross-sectional process diagram showing a method for repairing black defects among the methods for repairing a phase shift mask according to the present invention.

FIG. 4 is a cross-sectional process diagram showing a white defect repair method among the phase shift mask repair methods according to the present invention.

FIG. 5 is a cross-sectional process diagram showing a white defect repair method among the phase shift mask repair methods according to the present invention.

FIG. 6 is a cross-sectional process diagram showing a white defect repair method among the phase shift mask repair methods according to the present invention.

FIG. 7 is a diagram for explaining the principle of a conventional photomask method.

FIG. 8 is a diagram for explaining the principle of a conventional photomask method.

FIG. 9 is a diagram for explaining the principle of a conventional photomask method.

FIG. 10 is a diagram for explaining a phase shift exposure method.

FIG. 11 is a diagram for explaining a phase shift exposure method.

FIG. 12 is a diagram for explaining a phase shift exposure method.

FIG. 13 is a cross-sectional process diagram showing a conventional method for correcting black defects.

FIG. 14 is a cross-sectional process diagram showing a conventional method for correcting black defects.

FIG. 15 is a cross-sectional process diagram showing a conventional method for correcting black defects.

FIG. 16 is a cross-sectional process diagram showing a conventional method for correcting white defects.

FIG. 17 is a cross-sectional process diagram showing a conventional method for correcting white defects.

FIG. 18 is a cross-sectional process diagram showing a conventional method for correcting white defects.

[Explanation of symbols]

1 Mask substrate 2 Mask pattern 3 Phase shift pattern 4 Black defect area 5 Ion beam 6 White defect area 9 Reactant gas

Claims (3)

[Claims] 1. A phase shift mask, wherein a part of the phase shift pattern of the phase shift mask is a recess formed by digging into a mask substrate. 2. A phase shift mask repair method for repairing a defect in a phase shift pattern of a phase shift mask, wherein a phase shift pattern is formed in a region between mask patterns formed on a mask substrate where the phase shift pattern should not be formed. The phase shift pattern formed in the black defect area is etched away by irradiating the black defect area with an ion beam while supplying a reactive gas depending on the phase shift pattern material to the black defect area where the black defect area is formed. How to modify the phase shift mask. 3. A phase shift mask repair method for repairing a defect in a phase shift pattern of a phase shift mask, wherein a phase shift pattern is formed in a region where a phase shift pattern is to be formed between mask patterns formed on a mask substrate. By irradiating the unformed white defect area with an ion beam while supplying a reactive gas according to the material of the mask substrate, the mask substrate under the white defect area is etched away, and the phase shift pattern is originally formed. A method for repairing a phase shift mask, characterized in that the phase of the light that passes through the etched white defect area and the phase of the light that passes through the etched white defect area are opposite to each other.