JPS5990853A - Photomask blank - Google Patents

Abstract

PURPOSE:To enable removal of remaining Cr without requiring overetching at the time of development by laminating an N-contg. Cr layer and a C-contg. Cr layer on a transparent substrate in this order. CONSTITUTION:A photomask is obtained by laminating an N-contg. Cr layer 22 comparatively high in nitride degree and a C-contg. Cr layer 23 on a transparent substrate 10 made of soda lime glass finely polished on the surface. Further, an N-contg. Cr oxide layer 32 may be laminated on said Cr layer 23.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a aluminum mask blank used in the manufacture of semiconductors such as semiconductor devices, ICs, and LSIs.

This type of photomask blank is basically
As shown in Figure (a), a chromium layer 2 is laminated on a transparent substrate 1 by a vacuum evaporation method, a sputtering method, an ion plating method, etc., and the surface reflectance is relatively high. As shown in (1)), a chromium oxide layer 3 is further laminated on the chromium layer 2 to prevent reflection.
i (Low reflection) A mask blank) and
As shown in Figure (C), a transparent conductive film 1' made of indium oxide, tin oxide, etc. for antistatic purposes is laminated on a transparent substrate 1, and a conductive transparent substrate 1'' is used. There is a photomask blank with a transparent atomizing film in which the above-mentioned chromium layer 2 is laminated on the substrate 1'', and a chromium oxide layer 3 is laminated on the chromium layer 2.Therefore, in this invention,
When simply referring to a transparent substrate, it includes not only a single transparent substrate such as soda lime glass, which will be described later, but also one with a transparent conductive material.

When such a mask blank is used for a semiconductor device, the chromium layer 2 shown in FIG. 1(a) or the oxide layer 2 shown in FIG. 3. After applying a resist (in this example, a positive resist (~)) on each layer and exposing the desired pattern to an appropriate exposure device,
The pattern formed by exposing the resist is exposed! After the resist of the ζ portion and the chromium layer 2 and oxidized 06 layer 3 below it are removed, the resist that has not been dissolved by the development is peeled off to obtain a photomask for semiconductor manufacturing. .

During the process up to this point, after applying the above-mentioned regimen 1~, the resist film and photomask blank (see 16 for details)
A heat treatment step called brebake is required to improve adhesion with layer 2 or chromium oxide layer 3) and to vapor deposit the solvents in regimes 1 to 1. If a foreign object 5 is placed on the resist 4 during or after this heat treatment step, as shown in FIG. Therefore, since the resist 40 after development remains as shown in FIG.
As shown in C), sea urchin c+lx remaining 20,30 is generated. In this way, the remaining ROM 20.30 has a diameter of approximately 1 (μm)
), which is a fatal defect for a photomask that requires a high precision pattern of 1μIIIA-goo. As a means of removing this chromium residue 20.30 °C,
A-bar etching may be considered, but in that case the pattern dimensions would become extremely thin, making it difficult to control the fine dimensions. Below, this A-bar etching [
These defects will be specifically explained using a conventional photomask blank.

On a transparent glass plate whose surface has been closely polished, apply 1x pressure.
10 (Torr) of Ar and Cl-14 at a molar ratio of 88%:12%, respectively. corresponds to

) are stacked. Next, in the same vacuum, a chromium oxide layer containing nitrogen (as shown in Figure 1) was formed on the chromium layer by similar sputtering in a mixed scum containing Ar and No in a molar ratio of 80% = 20%. It is equivalent to 3. ) were laminated to produce a low fouling blank as shown in Figure 1(b). This low-reflection blank was produced by adding pure water to 165 g of ceric ammonium nitrate and 42 mffl of perchloric acid (70%) after each process of resist coating, fogging phenomenon, and resist 4 top^11 as described above.
When a predetermined pattern is formed by wet etching with an etching solution (19-20℃),
Undercut 1-m with etching time of 50 (scC)
was approximately 0.36 (μm). Here, the undercut amount is the width dimension χ below the resist 41 when one A-bar is cut as shown in FIG.
Chromium layer 21 containing nitrogen and chromium oxide layer 3 containing nitrogen
This is the difference from the maximum width dimension χ2 of 1.

Then, the etching time continued to pass! (-The results of measuring the undercut 1~ and the remaining chromium density are shown in characteristic curves a and b in Figure 3, respectively.According to characteristic curve a, the amount of undercut can be increased by A-bar etching ( Undercut tray 1-tallφa
=0.07μlll/10sec), and according to the characteristic curve, the residual chromium density is reduced.

Next (etching time) / (just etching time)
The relationship between the residual chromium density and the chromium density is shown in characteristic curve C in Figure 4. Here, the just etching time is the time required until the etching rate in the longitudinal direction and the thickness direction is saturated. According to song IIC in the same figure, the remaining chromium density is 0.
In order to reduce the number of particles to 1 (pieces/cm2) or less, the etching time is required to be at least twice the just etching time.

Therefore, conventional photomask blanks have no choice but to undergo A-bar etching as a means of removing chromium residue.
This over-etching has made it difficult to control fine-sized patterns required in semiconductor manufacturing.

It is an object of this invention to provide a photomask blank with reduced chromium residual density without excessive A-bar blanking. As a means to achieve this purpose, instead of the mixed gas of △1゛ and C1-14 mentioned above, by using ∆I゛ and N2 northern gas, the molar ratio of N2 gas is increased and each layer is It is conceivable to increase the etching speed of
It cannot be a fundamental solution.

Therefore, the inventor of the present invention particularly discovered that while chromium layers containing nitrogen deposited on transparent substrates were conventionally constructed with approximately the same degree of carbonization or nitridation, the chromium layers containing carbon or nitrogen By laminating a chromium layer containing nitrogen as the first layer close to the transparent glass substrate and a chromium layer containing carbon as the second layer, the etching rate is relatively high in the layer near the substrate, and the etching rate is relatively high in the layer far away from the transparent glass substrate. It has been found that by slowing down, chromium residue can be removed without excessive A-bar etching. Hereinafter, examples of the photomask blank according to the present invention will be described in detail.

Figures 5(a) and (b) show the conventional product in Figure 1(a).
) and (1)), respectively, are cross-sectional views according to embodiments of the present invention. FIG. 5(a) shows an example of a mask blank with a relatively high surface reflectance, and a relatively large nitrided pox is placed on a transparent substrate 10 made of soda lime glass whose surface is polished with precision RIII. A chromium layer 22 containing nitrogen (150A in film thickness) is the first layer, and a chromium layer 2 containing carbon with a relatively low degree of nitridation is formed on the chromium layer 22.
3 (500 Δ in film thickness), respectively, and FIG. This is a low-reflection photomask blank made by laminating 250 layers.

Therefore, low-reflection photomask blanks were prepared in which the degree of nitridation of the chromium layer 22 and the degree of carbonization of the chromium layer 23 were relatively changed as shown in the table. Regarding the optical density, the sputtering speed was adjusted so that the desired ratio of 3.0 was reduced by 1q, and the other layers were laminated by the same sputtering method as the conventional method.

According to these Examples 1.2 and 33, the characteristic curves of undercut m versus pre-etching time are the curves +1 and +! of FIG. 3, respectively. and [, both of which show the difference between undercut and undercut 1-rate (ta+1ψd=ta11ψe=ta) compared to the conventional song @a.
++ψf = 0.08 μlll /10 sec) is slightly increased. However, this increase can be ignored since excessive A-bar 1L cutting is not required as in the conventional J. That is, in terms of the characteristics of the remaining chromium density with respect to (etching time)/(just one etching time), Examples 1.2 and 3 are respectively shown by the characteristic curves g, h, and i in FIG. However, if the remaining chromium density is to be 0.1 (pieces/Cll12) or less, the etching time should be set at least 1.3 times the just etching time. Here, the etching rate is determined by the degree of nitridation of the mixed gas l+ of Ar and Nz in the laminated layer of the chromium layer 22, and the degree of carbonization in the mixed gas of Ar and CH in the laminated layer of L1 mm m23. As shown by curves j and k in the fflG diagram, the etching rate tends to increase as the degree of nitridation increases and decreases as the degree of carbonization increases. Therefore, in the present invention, J30 is used as a means to reduce the ratio of one etching time to the just etching time when the remaining comb density is less than the desired density, and the first layer is used to increase the etching speed. Chromium layer 2 containing nitrogen
2 is laminated, and a chromium layer 23 containing carbon, which has a slow etching rate, is laminated as the second layer.
゛, as the degree of nitridation of the chromium layer 22 and the degree of carbonization of the chromium layer 23 are respectively increased (curve Q→11- in Fig. 4)
→i) Avoid reducing the residual chromium density and reduce (etching time)/(just etching time),
It is possible to approach 1.0.

Therefore, according to the present invention, the residual chromium density can be reduced without performing excessive A-bar etching unlike conventional products.

In addition, as a modification of the above embodiment, in addition to the sputtering method, as a lamination method, a pure air vaporization method, an ion plating method, etc. may also be used, and as a transparent substrate, glass, quartz, etc. may be used on boron silicate 1 in addition to soda lime glass. In addition to glass, zaphire, etc., transparent conductive materials can also be used on transparent substrates.
The same effect can be obtained with the low reflection type photomask blank shown in FIG. 5(a), which has a high surface reflectance. Furthermore, although the present invention has been described with the nitrogen-containing chromium layer 22 and the carbon-containing chromium layer 23 separated,
The degree of nitridation may be continuously decreased and the degree of carbonization may be increased as the distance from the vicinity of the interface of the transparent curtain plate 10 increases.

[Brief explanation of drawings]

Figures 1 (a), (b) and <c> are cross-sectional views of conventional photomask blanks, and Figures 2 (a), (1)) and (
C) is a cross-sectional view of each culm of resist 1 - application, exposure phenomenon, and regime 1 - peeling using the blank, Figure 2 (d)
1 shows the amount of undercut, FIG. 3 shows the relationship between the amount of undercut and the remaining chromium density with respect to etching time. FIG. Figure 5 is a cross-sectional view of a photomask blank by Mitsuaki Togi, and Figure 6 is a graph showing the etching speed versus degree of nitridation and degree of carbonization. Characteristic diagram of +*'cS.

Claims (1)

[Claims] 1> A chromium layer containing nitrogen as a first layer on a transparent substrate,
A photomask blank characterized in that a chromium layer containing carbon is laminated as a second layer.