JPS62139874A - Formation of thin boron nitride film for x-ray mask - Google Patents

Abstract

PURPOSE:To enable stress control of a BN film by using a dopant consisting of an org. metallic compd. in the stage of forming the BN film. CONSTITUTION:The BN film is formed on an Si substrate by bringing diborane and ammonia into reaction by a CVD method. The org. metallic compd. is added as the dopant at <=5% to the diborane. Org. silanes having the structure RnSimH2m+2-n and org. aluminums having the structure RpAlHq are used as the org. metallic compd. In the formulas, R is a satd. or unsatd. org. group of <=6 C and m=1, 2, n=1, 2, 3, 4, p=2, 3, q=0, 1. The compressed stress of the formula film is changed to tensile stress and such film is adequately used a film for X-ray mask.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming a boron nitride thin film (hereinafter referred to as BNII2) which becomes an X-ray transparent substrate of a mask for X-ray phosphorography.

(Prior art and problems) The above-mentioned BN film for X-ray masks is transparent to visible light and X-rays, and has excellent chemical resistance and tensile strength as a ceramic material. It is recognized as a suitable material.

The general method for creating a mask for have, V
- In order to obtain BNIIQ with extremely excellent planarity, it is important that the BN film formed on the Si substrate has a tensile stress of about 1xlo tine/cm'.

However, with conventional methods this is extremely difficult and often results in compressively stressed films being deposited on the substrate.

This is due to the difference in thermal expansion coefficient between Si and BN (thermal expansion coefficient S i =2.3 x 10'/°
C, BN=1. OX 10'/"C).

After forming a BN film on a Si substrate at high temperature, if the temperature is returned to room temperature, the Si substrate with a large thermal expansion coefficient will contract more strongly, so the residual stress in the BN film with a small thermal 111 tensile coefficient becomes compressive stress. This causes distortion on the substrate.

Therefore, in order to obtain a BN film that is excellent as an X-ray mask material, it is necessary to convert this compressive stress into tensile stress.

(Means for solving the problem) Various proposals have been made regarding this, but the representative examples can be summarized into the following three methods.

(a) The ratio of diborane and ammonia is NH3/82H6
= 0.13 to 0.25 (Patent application published 1982-500707).

(b) Add SiH4 to diborane in a range of 7 to 12%. (Same as above) (C) Annealing at 360 to 440°C (US Pat. Method (c) generates a large amount of Si3N, which has poor x1a transmittance, due to the large amount of Si H4 added, and method (c) allows stress control. 2
However, it is difficult to say that it is suitable as a film for an X-ray mask because of its drawbacks such as the extremely limited composition range.

(Structure of the Invention) In view of this point, the present inventors conducted various studies to develop a stress control method for a BN film formed on a Si wafer, with the aim of improving the flatness of the BN film. As a result of repeated efforts, the inventors discovered that the above object can be achieved by using a doping agent made of an organometallic compound when forming a BN film, leading to the present invention.

That is, the present invention is a method in which 5z or less of an organometallic compound is added to diborane as a doping agent when forming a BN film on a Si substrate by reacting diborane and ammonia by the CVD method. BNl1
3 stress control becomes possible, and the effect of being able to change from compressive stress to tensile stress is obtained.

The necessity of using tensile stress becomes clear when considering the flatness of the BN film to be created.In other words, for an X-ray mask, the flatness is required to have an accuracy of within ±0.14 m, but this degree of flatness is not possible. However, Si substrates with flatness of about ±1 lumen are not normally available.
Even with the BN film formed on the substrate, when back-etching the Si substrate, if the BN film under tensile stress can be stretched like the skin of a drum, the flatness will be superior to that of the original Si substrate. BNj1! ll! You should be able to create .

The present invention was made from this viewpoint, and one of its effects is that since the amount of doping agent is small relative to diborane, there is little loss of X-ray transmittance. The reason why the stress in the BN film can be controlled with a small amount of organometallic compound is not clear, but it is incorporated into the BN film in units of M-C (M is Si and/or AM) during film formation, making it metastable. Since the film is deposited in that state, it is thought that the stress will be different from that of the original BN film.

Although the CVD method is not particularly defined in the present invention, the Si substrate and B
Considering the difference in thermal expansion coefficient of the N film, the low temperature plasma method is advantageous in terms of its effect of reducing stress in the BN film.

The diborane and ammonia used in this case are of course hydrogen as the diluent gas and carrier gas.

As the organometallic compound that may be used in combination with helium, nitrogen, argon, etc., organometallic compounds such as A, St, etc. with a small atomic number are suitable because they have good X-ray transmittance,
Examples include organic silanes (I) and organic aluminums (rr) having the following structures.

RnS il, lH2ffi+ 2-n(I) RA exchange H
(II) p q (where R is a saturated and/or unsaturated organic group having 6 or less carbon atoms, m = 1.2; n = 1 ° 2.3, 4. p = 2
．． 3. q=o, 1) These organometallic compounds are e.g.
eSiH3゜ (Me is a methyl group and below) CH=CH-
S iHM e 2 S i H2, (E t is the same below the ethyl group) CHS i H1M e A l,
E t 3A 41, etc. The organic group is preferably a saturated or unsaturated methyl group, ethyl group, propyl group, ethynyl group, vinyl group, phenyl group, etc. having carbon a6 or less, because gasification during the reaction is easy. be.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Plasma CVD with parallel plate electrodes of 300+nφ
Using an apparatus, diborane diluted with 10% hydrogen and 10% nitrogen in the chamber at 13.56 MH2 (73% frequency).
Ammonia diluted with water was introduced and a reaction was carried out. The Si substrate used has an axis <100> thickness (t s
) 33 Q pbm, and the flatness (warpage δ) was within 3 gm.

(Examples 1 to 8) BMW 2 was formed on a Si substrate using the above-mentioned apparatus. As the dopant used (A) M e 3S i
HI (B) CH=CH=S i3H, (C) Me2-SfH
, (D) CHSiH, (E) Me3An, CF) EL3An were used.

The implementation conditions and results were as shown in Table-1.

(Comparative Examples 1 to 8) Using the above apparatus, B was deposited on a Si substrate without adding a dopant.
A N film was created.

The experimental conditions and results are as shown in Table-2.

The test methods in Tables 1 and 2 are as follows.

(a) Wafer warpage (δJLm) The height of warpage (concave or convex) of a 2-inch Si wafer is I
Indicated by Lm.

(b) The film thickness (tf) on the wafer is a value measured by using a stylus-type film thickness meter to measure the difference in level of a masked Si wafer piece separately formed in the same lot.

(c) The stress (σ) applied to BN was calculated using the following formula.

δ=wafer warpage, ts=silicon substrate thickness, ρ=wafer radius, cis-Poisson's ratio, E=Young module.

E/ (I-y) =2.3 x 1012fia/
Crn'(d) Findings Samples prepared in Examples and Comparative Examples were treated with nitric fluoroacetic acid (HNO3:HF: CH3CO0H=4:1:1) from the Si substrate side.
When back-etched with water, Examples 1 to 8 all remained as smooth, colorless and transparent films, whereas the films of Comparative Examples 1 to 8 all sagged and were easily destroyed by washing with water after etching. Ta.

Claims (1)

[Claims] 1. In forming a boron nitride thin film on a Si substrate by reacting diborane and ammonia by a CVD method, it is characterized by adding 5% or less of an organometallic compound to diborane. A method for forming a boron nitride thin film for X-ray masks. 2. A method for forming a boron nitride thin film for an X-ray mask according to claim 1, using an organosilane (I) and/or an organoaluminum (II) having the following structure as the organometallic compound. (I) R_nSi_mH_2_m_+_2_-_n (II) R_pAlH_q (However, R is a saturated and/or unsaturated organic group having 6 or less carbon atoms, m = 1, 2, n = 1, 2, 3, 4; p = 2
, 3; q=0, 1 integer)