JPH03123353A - Photomask and its manufacture - Google Patents

Abstract

PURPOSE:To improve the washing resistance, comparing with a photomask provided with a phase shift layer specially by providing a recessed part in a prescribed area in a light transmission area of the photomask. CONSTITUTION:On a substrate 20 consisting of quartz, etc., line-like light shielding areas 21a - 21e and line-like light transmission areas 23a - 23d are provided alternately, and in the parts corresponding to every other area 23a, 23c in the areas 23a - 23d, a recessed part 25 of depth d is formed. Also, it is desirable to set the depth d to a value of the expression. In this regard, lambda; n; k; and l denote wavelength of an exposure light, a refractive index of a mask by the wavelength lambda, 1/4 - 3/4, and '0' or a positive integer, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photomask used in photolithography technology using projection exposure, particularly a photomask for a phase shift method, and a method for manufacturing the same.

(Prior art) In the field of photolithography technology using projection exposure, research is being actively conducted with the aim of establishing a technology that can form fine resist patterns in response to the increasing integration of semiconductor devices. 6 For example, a technique called the phase shift method disclosed in Japanese Patent Publication No. 62-59296 is one of the results of such research.

In this phase shift method, a phase shift layer is provided on a portion of the photomask, and the phase of a portion of the light transmitted through the photomask is shifted by this phase shift layer in order to improve the resolution of the projection exposure method. It is something to do. This principle will be briefly explained below. FIGS. 4(A) to 4(D) and FIGS. 5(A) to 5(D) are diagrams for explaining the same. In particular, FIGS. 4(A) to 4(D) show the light transmitting portion 11a! FIGS. 5(A) to 5(D) are diagrams showing well-known projection exposure using a conventional photomask 11, in which a phase shifter 180 is placed on a predetermined light-transmitting part of the light-transmitting part of the photomask 11. FIG. 3 is a diagram showing a state of projection exposure by a phase shift method using a photomask 11 having a phase shift layer 11b 8 shifted by degrees.

Note that in both figures, llc is a light shielding portion made of a chromium film or the like.

When using a photomask as shown in FIG. 4(A) without a phase shift layer, the direction of the electric field is the same for light transmitted through any light-transmitting part of the photomask (FIG. 4(B)). Therefore, When trying to form a resist pattern that is close to the resolution limit and receives the shadow 1F of light diffraction, the electric fields of each light that has passed through adjacent light transmitting areas overlap on the wafer surface (see Figure 4 (C). )), the contrast in light intensity at each portion of the wafer surface corresponding to the light-shielding portion and the light-transmitting portion becomes small (FIG. 4(D)).

On the other hand, when a photomask as shown in FIG. 5(A) having a phase shift layer ++b is used, the direction of the electric field of the light transmitted through the light transmitting part provided with the phase shift layer is different from that in the case without the phase shift layer. The ratio can be changed by 180 degrees (Figure 5 (B)),
Therefore, if a phase shift layer is provided on one side of the adjacent light transmitting parts, even if these light transmitting parts are adjacent to each other close to the resolution limit, the electric fields of the light that has passed through each of these light transmitting parts will overlap. The electric field near the middle M between the light transmitting parts becomes O (
As a result, the above-mentioned contrast can be increased (FIG. 5(D)), and this phase shift method can improve the resolution in the projection exposure method.

According to the above publication, the phase shift method is said to be effective in forming periodic patterns such as line and space (L/S) patterns.

In addition, in the phase shift photomask disclosed in this publication,
A phase shift layer was separately formed on the photomask.

Additionally, this publication states that materials suitable for forming the phase shift layer are selected from inorganic materials such as magnesium fluoride, titanium dioxide, and silicon dioxide, and organic materials such as polymer materials. Something was said.

(Problem to be solved by the invention) However, the photomask for the conventional phase shift method is
There has been a problem in that the phase shift layer, which is separately provided on the photomask, has insufficient resistance during cleaning of the photomask.

To explain with a specific example, if the phase shift layer is composed of the above-mentioned organic matter, this organic matter will be removed by a mixture of sulfuric acid and hydrogen peroxide solution, which is commonly used for cleaning photomasks. .

Further, even if the phase shift layer is made of an inorganic material, the phase shift layer may be peeled off during high-pressure pure water cleaning during photomask cleaning due to problems such as adhesion between the phase shift layer and the photomask.

Therefore, the durability of conventional photomasks for the phase shift method has not been satisfactory.

The present invention has been made in view of these points, and therefore, an object of the present invention is to provide a photomask for phase shifting that is more durable than conventional photomasks, and a method for manufacturing the same.

(Means for Solving the Problem) In order to achieve this objective, the inventor of this application has conducted various studies. As a result, instead of separately providing a phase shift layer on the photomask, we focused on processing and forming a phase-shiftable region on the photomask itself.

Therefore, according to the first invention of this application, a photomask used in a photolithography technique using projection exposure is characterized in that a recess with a depth d is provided in a predetermined region of a light transmission region of the photomask. Note that the term "photomask" as used herein also includes a reticle.

Further, according to the second invention of this application, when producing a photomask used in photolithography technology using projection exposure, the above-mentioned light-transmitting area is placed on the photomask in which the light-shielding area and the light-transmitting area have been formed in a predetermined arrangement. forming an etching-resistant mask pattern having an opening that exposes a predetermined region of the regions; and removing a portion of the photomask itself exposed from the opening to a depth d to form a recess. It is characterized by

In carrying out the first and second inventions, it is preferable that the depth djM of the recess described above be a value expressed by the following formula (
However, the characters in the formula are the wavelength of the exposure light, n is the refractive index of the photomask at wavelength λ, k is 1/4 to 3/4, and f is 0 or a positive integer. ).

d=(u+k)λ/(n-1) Here, k is determined depending on how much the phase is to be shifted, and is set from among the above values according to the design. Preferably, k=1/2, and
l is also set according to the design, but as this number increases, the intensity of the light passing through the light transmission area where the recess is,
Since there is a difference in the intensity of light that passes through a light transmission area without a recess, this point and the amount of exposure light are taken into consideration when determining the intensity. Preferably, f=o.

(Function) According to the photomask of the present invention, the phase of the light transmitted through the portion of the light transmission region where the four portions of depth d are present and the phase of the light transmitted through the portion of the light transmission region where there are no concave portions are different from each other at the depth. It shifts by an amount corresponding to d. As a result, exposure can be performed using the phase shift method. However, in the photomask of the present invention, the same effect as the conventional phase shift layer can be obtained by removing a part of the photomask itself rather than adding a phase shift layer separately.

Further, according to the method for producing a photomask of the present invention, a photomask for use in a phase shift method and having excellent durability can be produced in a single manner.

(Example) Examples of the photomask and the method of manufacturing the photomask according to this application will be described below.

Kayaguchi of Hatoma Announcement FIG. 1 is a diagram for explaining an embodiment in which the present invention is applied to a photomask having a line-and-space pattern. 2 is a schematic partial cross-sectional view; FIG.

In FIG. 1, reference numeral 20 indicates a substrate for a photomask. The substrate 20 in this embodiment has a thickness of 0.09 inches (approximately 2.5 inches).
3 mm) and 5 inch square (approx. 127 x 127 m)
m) quartz substrate is used.

On this substrate 20, linear light-shielding regions 21a, 21b, and 21c are provided to form a line and space.

21d or 21e, and line-shaped light transmitting regions 23a, 2
3b.

23c, 23d, or 23d are provided alternately. In this case, these light-shielding areas and light-transmitting areas are formed by leaving a chromium thin film on the substrate 20 every other line.

Roughly speaking, in the photomask of the first embodiment, one of the light transmitting regions 23a, 23b, 23c, and 23d of the substrate 20
A recess 25 having a depth d is provided in a portion corresponding to the alternating light transmitting regions 23a and 23c. Here, the depth d of the recessed portion 25 is a value expressed by the following formula (1). However, in the formula, the wavelength of the exposure light, n is the refractive index of the photomask at the wavelength λ, in this case, the refractive index of the substrate 20 at the wavelength λ, k is 1/4 to 3/4, f
is 0 or a positive integer. Note that preferably k=1/
2, f=o.

Thomas Method Next, an example of the photomask manufacturing method of the second invention will be explained using an example of manufacturing the photomask of the above-mentioned example, and FIGS. 2(A) to 2(F) are process diagrams for the explanation. This is a cross-sectional view showing the state of the photomask in the main steps.

First, the light-shielding thin film 20x8 of the substrate 20 (FIG. 2(A)) on which the light-shielding thin film (for example, a chromium film) 23x is formed.
, by patterning using a well-known photomask manufacturing method to form light-shielding regions (21G, 2!d, 2
Only 1e is shown. ), and a light transmitting region (23c, 23d) consisting of an exposed portion of the substrate 20.

), which has not been commonly used in the past (FIG. 2 CB)).

Briefly stated, the well-known photomask manufacturing method includes the following steps (1) and (2).

■--A resist for electron beam drawing is applied onto the surface of the light-shielding thin film 23x of the substrate 20 on which the light-shielding thin film 23x is formed, and this resist is
A resist pattern is obtained by drawing with an electron beam according to the pattern data created by the method (Design), and then performing development.

(2) Using this resist pattern as a mask, the light-shielding thin film 1120x is etched to obtain a light-shielding thin film pattern.

In this example, the length of the continuous light region in the pattern of the light-shielding thin film was 12,000 um. Rani, 1
/10 When using a projection exposure system with a reduction of 0.0.
From line and space (L/S) button of 3 to 1. O
The L/S pattern of um is 0. In order to be able to transfer in 5 um increments, on the substrate 2o, there are 10 sheets each with a width W of 3 um in the light-shielding area and a light-transmitting area (see Figure 2 (B)'J), and 10 sheets with a width of 3.5 um. 10 pieces each,・
----A light-shielding thin film baton having 10 strips each having a thickness of 10 um was formed. Additionally, alignment marks (
) was also formed at the same time.

Subsequently, a phase shift is applied to a predetermined region of the light transmitting region (in this case, every other light transmitting region tii23c of the light transmitting regions) of the structure (i.e., a conventional photomask) shown in FIG. The recessed portion 25 for this purpose is created by the procedure described below.

First, a negative resist for electron beam writing 0E8R-100 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin-coded on the surface of the substrate 20 with the light-shielding area at a speed of 3000 rpm (7 minutes of rotation) to form a resist film with a thickness of 600 nm. A layer 271Fr was obtained (FIG. 2(C)).

Next, electronic M! Exposure device f MEBESI [I
(manufactured by Perkin Elma), ie, the drawing was carried out so that the portions of the resist layer located on every other light transmitting region among the light transmitting regions could be removed by inadvertent development. At this time, drawing was performed with an overlay accuracy of 0.1 um or less by using alignment marks created at the same time as the light-shielding thin film pattern was formed. Note that the electron beam exposure was performed under the conditions that the acceleration voltage was 20 KV and the dose was 50 uc/am2.

Next, the exposed resist layer was developed using a special developer of 0EBR-100 under conditions where the development darkness was set to 3 minutes. As a result, an etching-resistant mask pattern 27b having an opening 27a exposing a predetermined region 23c of the light-transmitting region is formed.
was obtained (Figure 2 (D)).

Next, the structure shown in FIG. 2 (CD) was etched using a DEM451 parallel plate type dry etching apparatus in this example. (manufactured by Sunday ANELVA), set the etching gas to CF m, set the gas flow rate to 850 sec, and set the pressure! 5mTorr
r and RF power! Etching was performed under conditions of 0.12 W/cm2. When the etching time was set to 5 minutes, a recess 25 with a depth d = 400 nm was formed in the portion exposed from the opening 27a of the substrate 20 (Fig. 2 (E)
)”).

Next, an etching-resistant mask pattern 27b made of 0EBR-100 resist! , a mixed solution of sulfuric acid and hydrogen peroxide solution (a mixture of sulfuric acid and hydrogen peroxide solution) was peeled off to obtain a photomask of Example (Second
Figure (F)).

When the surface condition of the recessed portion 25 of the thus obtained photomask of Example was observed, it was found that there was no surface roughness and the surface was sufficiently transparent. In addition, in the actual production process,
The opening 27a shown in D) is the light transmission area t! fi23c, and the light-shielding regions 21c and 21d on both sides were partially exposed from the etching-resistant mask pattern 27b, but since the light-shielding thin film (chromium film) itself exhibits etching resistance, this portion was not used when forming the recess 25. It was found that no damage was caused by etching.

Note that the recess 25 with a depth d of 400 nm has an i-line (wavelength 3
65 nm), the light transmitted through a light transmitting region with a recess (for example, the light transmitting region 23G) and the light transmitting region without a recess (for example, the light transmitting region 23b, 23d).
The ideal depth of 38'8 nm (d= (l+k) input/
(n-1). However, K=1/2. f=
It is O. ) is considered to be sufficiently close to

Panin 1 Next, a patterning experiment was conducted as described below using a photomask prepared according to the procedure described using FIGS. 2(A) to 2(F). Note that the projection exposure apparatus has a numerical aperture (NA) of 0.42 and a reduction rate of 1/lO.
, and the exposure light is i-line (wavelength 365 nm).
) is used.

First, a 3-inch silicon substrate was prepared, and a TSMR-365iB resist (Tokyo Ohka Kogyo Co., Ltd.) was applied on this silicon substrate.
Co., Ltd. resist) was spin-coated to a film thickness of 1.2 μm, and then soft-baked for 1 minute at 90° C. using a hot plate.

Next, this baked silicon substrate and the photomask of the example were each set in a RAIOIVL II projection exposure apparatus, and exposure was performed while changing the exposure amount and focus to various values independently.

Next, the exposed silicone substrate was heated using a hot plate.
Next, the baked silicon substrate was baked at a temperature of 10°C for 1 minute.
Paddle development was carried out for 60 seconds using a vacuum cleaner manufactured by Co., Ltd.).

The dimensions of the obtained resist pattern were measured and observed using a scanning electron microscope II (S-6000, newly manufactured by Hitachi Seisakusho, Ltd.) capable of length measurement.

As a result, when the exposure amount was 150 mJ/am2, 0
．． 35um L/S pattern reduces exposure to 180mJ/
It was found that L/S patterns of 0.30 um were formed as designed when am2. Furthermore, 0.35umL when the exposure amount is 150mJ/cm"
It was found that the /S pattern was similarly obtained over a focus range of 1.6 um. Furthermore, the exposure amount is 150
0.40umL/S Bakun in the case of mJ/am' is
It was found that similar results were obtained over a focus range of 2.4 μm.

In contrast, a photomask of a comparative example (FIG. 2 CB
), we conducted a similar patterning experiment as described above, and found that no matter how much we changed the exposure amount or the focus, we could get a 0.35 um L/S pattern, a 0.30 um L/S pattern, a 0.30 um L/S pattern, None of the patterns could be resolved. Also, in the photomask of the comparative example, 0.4
Although the umL/S pattern could be resolved, its focus range was 0.6 um, which was very narrow, 1/4 of that in the example.

As is clear from the results of this patterning experiment, it is possible to implement the phase shift method by providing a recess with a predetermined depth in a predetermined region of the photomask, thereby improving the resolution of the resist pattern and improving the focus margin. It turns out that this can be achieved.

Next, the cleaning resistance of the photomask of the example and the photomask of the comparative example was examined as described below. The photomask of the comparative example is the photomask 11 having the structure shown in FIG. 5(A), in which the phase shift layer 11b is 0E8R
-100 resist photomask of Comparative Example 1,
A photomask of Comparative Example 2 in which the phase shift layer 11b was composed of a 5if2 film formed by sputtering was prepared.

The photomasks of Example, Comparative Example 1, and Comparative Example 2 were each washed with a mixed solution of sulfuric acid and hydrogen peroxide solution and with high-pressure pure water.

As a result, as a matter of course, no change was observed in the photomask of Example. On the other hand, the photomask of Comparative Example 1 had a phase shift layer 1 formed on the photomask.
1b has completely disappeared, and the photomask of Comparative Example 2 is Si
It was found that part of the O□ film had peeled off.

The above is an explanation of the embodiments of the photomask of the present invention and its manufacturing method. However, the present invention is not limited to the above-described embodiments, and may be modified to a certain extent as described below.

The above embodiment was an example in which the present invention was applied to a photomask for line and space patterns. However, the present invention can also be applied to photomasks for space patterns and hole patterns.

An example in which the present invention is applied to a hole pattern photomask for negative resist will be explained with reference to FIGS. 3(A) and 3(B). Here, FIG. 3(A) is a plan view of a hole pattern photomask to which the present invention is applied, and FIG. 3(B) is a sectional view thereof taken along the line II.

This photomask is used for forming a hole pattern using W +
The area W2 XW2(Wl
>W2) is provided as a light transmitting region 32b, and the rest is a light shielding region 31. Roughly, the periphery of the light-shielding region 31 is a light-transmitting region 1tt32a, and a photomask is used in which a recess 25 with a depth d is provided in a portion corresponding to the light-transmitting region 32b of the light-transmitting regions 32a and 32b of the substrate 2o. be.

However, the area of the region given by WI XW+ is small, close to or below the resolution limit of the projection exposure method. Roughly speaking, it is assumed that the area of the region given by W and XW is sufficiently small so that the resist is not exposed to light passing through it. According to this hole batten photomask, the phase of the light that passes through the light transmitting region 32a and the phase of the light that passes through the light transmitting region 32b are shifted.
Exposure using the phase shift method becomes possible as in the embodiment.

Furthermore, it is obvious that the devices, chemicals, etc. used in each example are merely illustrative and can be changed to other suitable ones.

(Effects of the Invention) As is clear from the above description, according to the photomask of the first invention, by removing a portion of the photomask corresponding to a predetermined region of the light transmitting region to a predetermined depth d. The same effect as when a phase shift layer is provided is obtained. For this reason, the durability is much better than that of conventional photomasks for phase shift methods in which a phase shift layer is provided separately. In other words, its durability is exactly the same as that of a normal photomask for projection exposure. Further, according to the photomask of the present invention, although it can be handled in the same way as a normal photomask for projection exposure, it is possible to improve resolution and focus margin.

Therefore, according to the photomask of the present invention, patterns for semiconductor devices, which will become increasingly finer in the future, can be formed using the current exposure method.

Further, according to the method for producing a photomask of the present invention, a photomask for use in a phase shift method and having excellent durability can be easily produced.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing a photomask according to an example. FIGS. 2(A) to (F) are process diagrams showing an example of a photomask manufacturing method. FIGS. 3(A) and (B) ) is a diagram for explaining a modification, and FIGS. 4(A) to (D) and FIGS. 5(A) to (D) are diagrams for explaining a conventional technique. 20... Substrate for photomask, 21a to 21e... Light blocking areas 23a to 23d... Light transmitting areas 23a, 23c... Predetermined area 25 among the light transmitting areas
--- Concavity 23x with depth d --- Light-shielding thin film (chromium film) 27 --- Resist layer, 27a --- Opening 27b
--Etching-resistant mask pattern 31--Light blocking area, 32a, 32b = Light transmitting area 32b...
- A predetermined area of the light transmission area.

Claims (3)

[Claims] (1) A photomask used in photolithography technology using projection exposure, characterized in that a predetermined region of the light transmission region of the photomask is provided with a recessed portion having a depth d. (2) The photomask according to claim 1, characterized in that the depth d of the recess is a value expressed by the following formula (where λ is the wavelength of the exposure light, and n is the wavelength λ of the photomask). refractive index, k is 1/4 to 3/4, l is 0 or a positive integer). d=(l+k)λ/(n-1) (3) When producing a photomask used in photolithography technology using projection exposure, an opening is formed on the photomask after forming light-shielding areas and light-transmitting areas in a predetermined arrangement to expose a predetermined area of the light-transmitting area. A method for manufacturing a photomask, comprising the steps of: forming an etching-resistant mask pattern having the structure; and removing a portion of the photomask itself exposed from the opening to a depth d to form a recess.