JPS62254434A - Formation of sio2/sin/sio2 film - Google Patents

Abstract

PURPOSE:To thin off a triple-layer film by a method wherein, after an SiN film has been formed, the SiN film is modified by annealing in the N2 atmosphere containing NH3, and the oxygen permeability of the SiN film when an SiO2 film is formed on the SiN film is decreased. CONSTITUTION:A silicon substrate is thermally oxidized in dry oxygen or in the dry oxygen containing HCI, and after a thermally oxidized film 2 of 35 Kt has been formed, an SiN film 3 of about 30 Kt is formed thereon. Then, an annealing process is performed thereon at 1000 deg.C or above in the atmosphere containing 5% or more of NH3 for N2. The SiN film is modified in the N2 atmosphere containing NH3 by performing the above-mentioned method. As a result, an SiN film which transmits no oxygen when the thermally oxidized film is formed on the SiN film, can be obtained and the thinning off of an SiO2/ SiN/SiO2 film can also be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for forming a SiO3/SiN/SiO2 film used as a memory capacitor insulating film of a MOS memory.

<Technical background of the invention and its problems> As LSI devices become more highly integrated, the size of DRAM (random access memory), which is a typical example of MOS memory, is reduced, and the thin film of the memory capacitor insulating film is reduced. is required. However, the conventionally used 5
As the 102 film becomes thinner, it not only becomes difficult to control the film thickness, but also deterioration of dielectric breakdown voltage characteristics, radiation damage resistance,
Problems such as reaction with the gate metal on the same film and deterioration of masking properties for impurity diffusion have occurred. Therefore, in recent years, instead of the 5i02 film, a three-layer film with a 5i02/SiN/SiO□ structure has been introduced (Dielectric Breakdown).
It is superior to S io 2 single layer film and can be used not only as an insulating film for memory capacitors but also as an EEPROM
It is also applied to

However, when the SiN film is made thinner, the SiO
□If you try to form a film by thermal oxidation, the thickness of the SiN film will be less than a certain value (it is reported that it is about 45A: E, 5U)
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VOL, ED-: (0, No, 2 F, 122 (+98
()), gold oxygen permeates through the SiN film, oxidation progresses at the Si interface, and a very thick oxide film grows. By contrast,
When forming a thin SiO2/SiN/SiO2 film, there is a limit to the thickness of the SIN film.

<Objective of the Invention> The object of the present invention is to form a relatively thin S layer on a Si substrate by thermal oxidation.
After forming a SiN film on the iO3 film, the SiN film is
By annealing in an N2 atmosphere containing 3, even if the SiN film is very thin (~45A or less), oxygen will not pass through it during the subsequent thermal oxidation to form the SiO□ film.
The object of the present invention is to provide a method for forming a film, thereby realizing a thinning of the entire three-layer film.

<Example> S formed by heat treating a silicon substrate in an oxidizing atmosphere
A SiN film is formed on the iO2 film, and N2 containing NH3 is
A method of modifying the SiN film by annealing in an atmosphere and forming an SiN film through which oxygen does not pass during thermal oxidation for forming the upper SiO2 film will be described with reference to the following examples.

FIG. 1 is a process diagram.

W, 1 As shown in Figure (a), a silicon substrate (e.g.
P(100), 15-20 Ω·) was thermally oxidized at 800°C in dry oxygen or in dry oxygen containing HCI.
After forming a thermal oxide film (SiO□ film) 2 with a thickness of 5^, a SiN film 3 with a thickness of about 3OA is formed thereon by the LPCVD method. After this, in an atmosphere containing 5% or more of NH3 to N2,
It is desirable that the annealing temperature at which the annealing is performed at 000°C or higher is as high as possible in the integrated circuit manufacturing process;
It has been experimentally found that if annealing is performed at 0°C or higher, the effect of modifying the SiN film can be achieved with approximately 2 hours of annealing. Further, it was found that when the concentration of NH3 relative to N2 is about 2%, there is no effect of modifying the SiN film, but when the concentration is 5% to 8X, good results are shown. However, high concentration of NH3t-
Care must be taken when handling it, especially at high temperatures, as there is a possibility of an explosion of NH3. NH3 requires a purifier to remove water, and in the experiment shown in this example, 9
9.999% or more of NH3t was obtained using a refined purifier. SiN was purified in an N2 atmosphere containing NH8 using the method described above.
The membrane was modified and heated at 950°C (Fig. 1(b) l').
Thermal oxidation was carried out for 20 minutes using steam oxidation of
When a SiO2 film 4 was formed in a similar manner, the SiO□ film grew to about 2OA. In the nine cases in which the experiment is carried out, the film after thermal oxidation on the SiN film is 100 OA (refractive index 'k of the SiO□ film is 1.46 for the SiO□ equivalent film) and is measured by ellipsometry on the Si substrate. The film had grown to a certain extent (measured value). This value was the same as the thickness of the SiO□ film formed on the Si substrate by performing steam oxidation at 950° C. for 20 minutes.

These results are shown in the second reason.

Figure 2 shows the experimental results of SiO□/St using the present invention.
After performing thermal oxidation treatment to form the eighth layer of SiO□ film on the N film, SiO3/SiN/Si on the Si substrate is
O3 film t-3i This figure shows the SiO3 equivalent film thickness measured by ellipsometry as an O□ equivalent film.

According to this figure, the film thickness of the SiN film annealed in an N2 atmosphere containing NH3 does not increase in the subsequent thermal oxidation treatment even if it is about 30^; If you do not do it at all, 60
It can be seen that for an SiN film thinner than about 70 A, the film thickness increases greatly in the subsequent thermal oxidation treatment, and becomes approximately the same thickness as the SiO2 film obtained when the Si substrate is directly oxidized.

From the above results, it is considered that the SiN film annealed in the N2 atmosphere containing NH31 changes to a property that does not allow oxygen to pass through during the subsequent heat treatment in the oxidizing atmosphere. It has also been found that this effect is produced by using an N2 atmosphere containing NH3.<Effect of the Invention> As explained in detail above, the method of the present invention allows
Even if the SiN film formed on the iO□ film is very thin,
SiN that does not allow oxygen to pass through when forming a thermal oxide film on the SiN film
It is possible to make the 5i02/5iN7S 102 film thinner. By reducing the thickness of the conventional SiN film to 45A or less, for example, 5io2/SiN/5i
02 film thickness 120^/30^/20^ and Ruco are formed.
A three-layer film equivalent to 60 SiO□ can be obtained.

This film has extremely low defect density and can be used as an insulating film for high-density memory capacitors.

[Brief explanation of drawings]

FIG. 1 is a process diagram of an embodiment of the present invention, and FIG. 2 is a diagram of an eighth layer of Si formed on a SiO2/SiN film by a friend experiment using the present invention.
After performing thermal oxidation treatment to form an O□ film, Si
FIG. 3 is a diagram showing the SiO2-equivalent film thickness measured by ellipsometry using the SiO/SiN/SiO2 film on the substrate as a SiOz-equivalent film. Explanation of symbols 1: Silicon substrate, 2: SiO2 film, 3: SiN film, 3
': SiN film annealed in N2 atmosphere containing NH'i,
4: 5i02 membrane.

Claims (1)

[Claims] 1. After forming a SiO_2 film on a silicon substrate by thermal oxidation, a SiN film is formed on it, and then a SiO_2 film is formed on it by thermal oxidation to form a SiO_2/S
In the method of forming an iN/SiO_2 film, the above Si
After the N film is formed, the SiN film is modified by annealing in an N_2 atmosphere containing at least NH_3, and the oxygen permeability of the SiN film is reduced during the formation of the SiO_2 film on the SiN film. , SiO_2/SiN/S
Method for forming an iO_2 film.