JPS59119353A - Photomask blank - Google Patents

Abstract

PURPOSE:To prevent overetching and to obtain a photomask blank capable of being patterned with high precision suitable for fabricating semiconductors, etc. by forming a chromium oxide layer higher in oxidation degree on the side near a transparent substrate and lower on the other side on said substrate. CONSTITUTION:Chromium is vapor-deposited on the precisely polished surface of a transparent glass substrate 10 first in an atm. of 85:15-70:30 gaseous Ar/ gaseous O2 ratio rich in O2 by the sputtering method or the like to form a layer 22 rich in oxidation degree. Then, a layer 23 lower in oxidation degree is formed by reducing a gaseous O2 content to 95:5-100:0 Ar/O2 ratio. This method makes the etching speed of the film 22 higher than that of the film 23, and a photoresist pattern is formed on the film 23 and subjected to etching, and for example the films 22, 23 are left by the presence of foreign matters, and further they are etched. At that time, overetching is prevented and deterioration of dimensional precision is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask blank used for manufacturing 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 vacuum evaporation, sputtering, ion blating, etc., and has a relatively high surface reflectance, and as shown in Figure (b). The chromium layer 2 as shown in
A chromium oxide layer 3 is further laminated on top to form a low-reflection photomask blank with an anti-reflection layer), and a transparent substrate 1 is coated with antistatic materials such as indium oxide and tin oxide as shown in <C) of the same figure. A transparent conductive film 1' was laminated to form a conductive transparent substrate 1'', and the above-mentioned chromium layer 2 was laminated on this transparent substrate 1'', and a chromium oxide layer 3 was laminated on this chromium layer 2. There is a photomask blank with a transparent conductive film. Therefore, in the present invention, the mere term "transparent substrate" includes not only a single transparent substrate such as soda lime glass, which will be described later, but also a transparent substrate with a transparent conductive film.

When such a photomask blank is used for semiconductor manufacturing, a resist (in this example) is applied on the chromium layer 2 shown in FIG. 1(a) or the chromium oxide layer 3 shown in FIG. Then, a positive resist l-) is applied, a desired pattern is exposed using an appropriate exposure device, and then the pattern formed by developing the resist is exposed. ζ
After that, the resist in that area and the chromium layer 2 and chromium oxide layer 3 underneath are removed (1), and the resist that has not been dissolved due to the above phenomenon is peeled off to obtain a photomask for semiconductor manufacturing.

During the steps up to this point, after applying the resist, the resist film and photomask blank (more specifically, the chromium layer 2
Alternatively, a heat treatment process called pre-beta is required to improve adhesion to the chromium oxide layer 3) and evaporate the solvent in the resist. If a foreign object 5 is placed on the resist 4 during or after this heat treatment process as shown in FIG. Resist 4 after development
Since 0 remains as shown in FIG. 5B, after the next etching solution and resist stripping process, 20.30 chromium remains as shown in FIG.

The remaining ROM 20.30 has a diameter of about 1 (μm), which is a fatal defect for a photomask that requires a highly accurate pattern on the order of 1 μm. Over-etching may be considered as a means for removing this chromium residue 20.30, but in that case, the pattern dimensions will become extremely thin, which will cause problems in controlling the fine dimensions. Defects caused by over-etching will be specifically explained below using a conventional photomask blank.

A pressure of 1x10 was applied on a transparent glass substrate whose surface had been precisely polished.
A chromium layer (650 layers) (corresponding to 2 in FIG. 1(b)) is deposited by planar magnetron direct current sputtering in an Ar gas of -3 (TOrr). next,
In the same vacuum, the molar ratio of Ar and No is 80% = 2
A chromium oxide layer containing nitrogen (Fig. 1 (b)
) corresponds to 3. ) were laminated to produce a low-reflection blank as shown in FIG. 1(b). As mentioned above, after each process of resist application, exposure phenomenon, and resist peeling, this low-reflection blank was etched by adding pure to 165 g of ceric ammonium nitrate and 42 m of perchloric acid (70%) to make 1000 n+. Liquid (19-20℃)
When a predetermined pattern was formed by wet etching, the etching time was 30 (sec).

Next (etching time) / (just etching time)
Characteristic curve a in FIG. 3 shows the relationship between the residual chromium density and the residual chromium density. Here, the just etching time is the time required until the etching rate in the vertical direction (thickness direction) is saturated. According to curve a in the figure, the remaining chromium density is o, 1
In order to reduce the etching time to less than (cn+"), the etching time is required to be more than twice the just etching time.

Therefore, conventional photomask blanks do not require overetching as a means of removing chromium residue.
This over-etching makes it difficult to control fine-sized patterns required in semiconductor manufacturing.

An object of this invention is to provide a photomask blank with reduced chromium residual density without excessive overetching. One way to achieve this goal is to increase the etching rate of each layer, but in this case the undercut rate increases, making it difficult to control fine dimensions, and this cannot be a fundamental solution. .

Therefore, among the chromium layers laminated on a transparent substrate, the present inventor divided them into a layer close to the transparent glass substrate and a layer far from the transparent glass substrate.
It has been found that by making the etching rate relatively fast in nearby layers and slow in distant layers, chromium residue can be removed without excessive overetching.

Hereinafter, examples of the photomask blank according to the present invention will be described in detail.

FIGS. 4(a) and 4(b) are sectional views according to an embodiment of the present invention, corresponding to FIGS. 1(a) and 1(b) of the conventional product, respectively. FIG. 4(a) shows an example of a photomask blank with a relatively high surface reflectance.
This is a photomask blank formed by laminating a chromium layer 22 containing oxygen with a relatively high oxidation degree, and a chromium layer 23 containing oxygen with a relatively low oxidation degree on top of the chromium layer 22, as shown in FIG. Further, a chromium oxide layer 32 (thickness 250
This is a low-reflection photomask blank made by laminating layers.

Therefore, for this low-reflection photomask blank, the chromium layer 22 and the chromium layer 23 were prepared with relatively different degrees of oxidation as shown in the table, and the film thickness of the chromium layer 22 and 23 was
A chromium oxide layer 32 similar to the nitrogen-containing chromium oxide layer described above is laminated on the chromium layer 23, and the desired value of optical a degree is 3.0. The sputtering speed is adjusted so as to obtain the desired result, and the other layers are laminated by the same sputtering method as the conventional method.

According to these Examples 1.2.3 and 4, the characteristics of the remaining chromium density with respect to (etching time)/(just etching time) are as shown in the characteristic curves of FIG.
Indicated by ld and e. That is, in any embodiment,
If the remaining chromium density is to be 0.1 (pieces/cm2) or less, the etching time should be increased by at least 1.4 times the just etching time. Here, the relationship between the etching rate and the mixing ratio in the mixed gas of Ar and O2 in the lamination of the chromium layers 22 and 23 is as shown by the curve f in FIG. tends to increase as the value increases. Note that when the mixing ratio of OL is 40% or more, the surface of the target (chromium in this example) is significantly oxidized, making measurement difficult, and is therefore not shown in the figure.

As the degree of oxidation of the chromium layer 22 is made larger than that of the chromium layer 23 (curve b-+c→d→e), the remaining chromium density is made smaller and (etching time)/(just etching time) is made smaller. It can be brought close to 1.0.

Therefore, according to the present invention, the residual chromium density can be reduced without excessive overetching unlike conventional products.

In addition, as a modification of the above embodiment, a vacuum evaporation method, an ion blating method, etc. may be used in addition to the sputtering method as a lamination method, and as a transparent substrate, in addition to soda lime glass, boron silicate glass, quartz glass, sapphire, etc. may be used. , a transparent substrate with a transparent conductive film may be used,
Furthermore, the same effect as the low reflection type can be obtained with the photomask blank having a high surface reflectance shown in FIG. 5(a). Further, the present invention also provides a chromium layer 22 and a chromium layer 23.
Although the oxidation degree has been described separately, the degree of oxidation may be decreased continuously as the distance from the vicinity of the interface of the transparent substrate 10 increases.

[Brief explanation of the drawing]

Figures 1 (a), (b) and (C) are cross-sectional views of conventional photomask blanks, and Figures 2 (a), (b) and (C) are resist coating and exposure diagrams using the blanks. , sectional view of each step of resist stripping, Fig. 2(d) is a sectional view showing the amount of undercut, Fig. 3 is a sectional view showing the amount of undercut)/
FIG. 4 is a cross-sectional view of a photomask blank according to the present invention, and FIG. 5 is a characteristic diagram showing etching rate versus oxidation degree. 10...Transparent substrate, 22...Chromium layer with high oxidation degree, 23...Chromium layer with low oxidation degree, 32...Chromium oxide layer Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office1. Indication of incident 1981 Special i1
! i2, title of the invention Photomask blank 3, supplement i
Person who does T 1! [Relationship] Patent applicant address: 160-13-12 Nishi-Shinjuku, Shinjuku-ku, Tokyo
7' E l 03 (348) 1221 ho ■
Glass name Yasutani Glass Co., Ltd. (R date: March 29, 1981) 5. Subject of amendment (1) Column 6, "Brief explanation of one drawing in the specification", Contents of amendment

Claims (1)

[Claims] 1) Layering a chromium layer containing oxygen on a transparent substrate,
Alternatively, a photomask blank comprising a chromium oxide layer further laminated on the chromium layer, wherein the oxidation degree of the chromium layer is higher in the layer closer to the transparent substrate and lower in the layer farther from the transparent substrate. .