JPS61144848A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To realize an adequately thick interlayer insulating film and to prevent a gate oxide film from degradating in its voltage-withstanding capability by a method wherein a wet oxidation process is started for a gate electrode material at 850 deg.C to be ended at a temperature lower than 850 deg.C. CONSTITUTION:A field oxide film 22 is formed on an Si substrate 21 ans a P-doped polycrystalline Si film 24 is formed with the intermediately of an SiO2 film 23. The SiO2 film 23 is etched through the mask 24, and is subjected to wet oxidation involving H2 and O2. The wet oxidation starts at 850 deg.C, the temperature is caused to fall to 800 deg. at a rate of 5 deg.C/min to stay there for about 70min, whereby an approximately 650Angstrom -thick SiO2 film 25b is formed on a substrate 21 and an approximately 2,400Angstrom -thick SiO2 film 25a on the polycrystalline Si film 24. The SiO2 film 25b is subjected to etching by using NH4F, whereafter an appoximately 1,500Angstrom -thick SiO2 film 25c is retained in the vicinity of the polycrystalline Si film 24. Next, a gate oxide film 26 is provided, and a P-doped polycrystalline Si gate electrode 27 is built. Thereafter, a prescribed procedure is followed for the completion of a semiconductor device. In a device constructed as such, an interlayer insulating film is made to be thick enough with ease and a gate oxide film is protected from degradation in its voltage-withstanding feature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical aspects of the invention] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a technique for forming an insulating film between electrodes.

[Technical background of the invention]

FIG. 3 shows an example of a technique for forming the first poly-Si and second poly-8i glabella insulating films conventionally used in dynamic RAM memory cells. Taking advantage of the difference in oxidation rate due to the difference in impurity concentration between the 8i group (1) and the l-th p017-St (3), that is, the higher the impurity concentration, the faster the oxidation rate, poly-st
The phosphorus concentration κ in (a) is By increasing the impurity concentration difference with the Si substrate, for example, by oxidizing We at 850°C, a thick acid carbon film (44 ). After that, a second poly-Si (5) may be formed.

However, since this method only uses one type of @direct, there are various problems.

First of all, at temperatures above 850°C, the oxidation time is short (so it is difficult to control the film thickness).
Due to the impurity concentration of y=81, the film thickness is /(rack.

■As a result of the experiment, the temperature of phosphorus diffusion is shown in Figure 4 at 950.
5C is a graph of the acid ratio film thickness of a SiO□ film formed on poly-81 by wet oxidation at 850°C after being performed at 900°C and 900°C. As can be seen, at 900° C. where phosphorus flkK is low, there is no longer a linear relationship between oxidation time and oxide film thickness.

In other words, please use 1ml (to reduce the variation,
The phosphorus concentration of ly-81 must be made high by phosphorus diffusion at 950°C. However, when the concentration is high, (2) the gate oxide film is thin, which causes problems such as defects due to phosphorus penetrating through the gate oxide film and poor breakdown voltage.

For the above reasons, if the temperature is set to 800° C. or less, (1) it takes a long time to oxidize to obtain the desired film thickness, resulting in low throughput and not being suitable for mass production.

■H1 and 0! When burning, the ignition temperature will be low and there is a risk of incomplete combustion.

[Purpose of the invention]

The present invention has been made in view of the above points, and it is possible to control the film thickness while making the interlayer insulating film sufficiently thick, and also to eliminate the breakdown voltage failure of the gate oxide film. The object of the present invention is to provide a method for forming an insulating film between 1 and 2, which makes it possible to eliminate the risk of incomplete combustion between 0 and 0.

[Summary of the invention]

In the present invention, a gate electrode material is selectively formed on a semiconductor substrate via an insulating film, and then a welding process using hydrogen and oxygen is performed.
We start at a temperature of 850 η with the t oxidation method and then reduce the temperature for removal to a temperature below 850° C. to end the wet Q ratio.

〔Effect of the invention〕

According to the present invention, the acid deposition time can be shortened and the film thickness can be controlled. , 8
#! Experimental results looking at changes in the thickness of an oxide film formed at 00°C! As shown in FIG. 2, IcMJ can be controlled so that the oxidation time and oxide film thickness have very good linearity. Therefore, it is easy to obtain the desired film thickness by changing the oxidation time.
come. Also, the film thickness ratio on the 8i substrate and on the poly-8L is about 3.5, and the film thickness ratio at a constant temperature of 850°C is 2.5.
Significant improvement compared to 1ζ. Therefore, a thicker film can be left on the poly-8i.

The breakdown voltage between the 8i substrate and 1polyrVIe or between 1poly and 2poly is improved, and the reliability of the semiconductor device is improved.

In addition, since there is no need to increase the concentration of phosphorus IlK in l poly, it is possible to lower the phosphorus diffusion temperature and shorten the diffusion time, so even if the insulating film under l poly becomes thinner, impurities (phosphorus) can be It is also possible to prevent development that would penetrate through the insulating film and reach the St substrate, causing gate breakdown voltage failure.

In addition, the reaction between H1 and 08, which is initiated by the combustion acid, can be carried out at a relatively high temperature (for example, 850° C. or higher) where the reaction is stable, so the safety of one operation can be maintained.

[Embodiments of the invention]

An embodiment of the present invention will be explained using the first factor.

First, after forming about 6 selected field oxide films (22) on the Si substrate (21),
For example, 900° C., 3
0 minutes.

1st poly-8i (24
) to form.

(1st image) Next, if necessary, 1st poly-8i
The first gate oxide film (23) may be etched using (24) as a mask.

Next, perform a wet acid ratio containing, for example, H5 and 0
By lowering the temperature of the furnace to 800°C and then keeping the temperature constant at 800°C for about 70 minutes, the 8i0 temperature of about 650 people on 81 substrates was
z film (25(b)), on po 1 y-8i I about 240(l st□, form a film (25(R>)).

(Fig. 1b) For example, using Nl(, F, 8tQ□
The film (25(b)) is etched. At that time 1 s
8i of about 250A only for the problem of poly-8i
The zero quadrant (25(c)) is left behind.

(Figure 1C) After that, a 2nd gate oxide film (26
) After forming 1, for example, 2 with phosphorus-diffused poly-8i.
A nd gate electrode (27) is selectively formed. (FIG. 1d) Then, a 4jAM or other conductor device is dynamically manufactured using conventional techniques. [Other embodiments of the invention] In the above embodiment, an 8iQ1 film (25(b)
) was removed, the 2nd gate oxide film (26) was formed, but the 113iQ on the 1st poly-81
, and the second gate oxide film may be formed simultaneously. For example, if the 2nd gate oxide film is set to about 300A, p
About 1200 molecules can be formed on oly-8i, and S
8 IQ on t substrate.

Since there is no etching process for the film (25(b)),
SiQ at the peripheral edge of 1stpoly-8i, film (25(a
) Since the decrease in film thickness of ) does not occur, the 1st p
The withstand voltage (insulation) between oly-8i and the 2nd gate electrode is improved, and high reliability can be achieved.

Also, before and after this wet oxidation, other atmospheric gases such as dry
ol, Ar or N! Heat treatment such as the following may also be performed.

For example, N until the wafer temperature stabilizes in the furnace.
By keeping the film in an atmosphere, oxidation does not proceed, and the film thickness can be controlled better. Further, by performing dr7Q1 etc. at high temperature, the withstand voltage of %StO is improved.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the process of one embodiment of the present invention, and Fig. 2 is a process cross-sectional view of one embodiment of the present invention.
FIG. 3 is a cross-sectional view of a conventional process, and FIG. 4 is a characteristic diagram showing experimental results of oxidation speed in wet oxidation at 850° C. In fig. 1.21・-St substrate, 2, 4, 23, 22° 25.2
6-8i0. Membrane, 3.24...1st poly −
8i, 5.27-2nd gate electrode 11 (2nd po
ly-8i). Representative Patent Attorney Kensuke Chika (and 1 other person) No. 1
Figure 2 Cedar

Claims (3)

[Claims] (1) When oxidizing the semiconductor substrate and gate electrode material after selectively forming the gate electrode material on the semiconductor substrate via an insulating film, in water vapor containing at least water vapor,
and by performing an oxidation heat treatment that starts at a first temperature and lowers it to a second temperature lower than the first temperature, the oxide film on the surface of the gate electrode material becomes thicker than on the surface of the semiconductor substrate. A method for manufacturing a semiconductor device, characterized by: (2) The above-mentioned claim is characterized in that polycrystalline silicon is used as the gate electrode material, the impurity concentration of the polycrystalline silicon surface is higher than that of the semiconductor substrate surface, and the first temperature is 850° C. or lower. 2. A method for manufacturing a semiconductor device according to item 1. (3) The method includes the step of leaving a thermal oxide film only on the surface of the gate electrode material by removing the thermal oxide film on the surface of the semiconductor substrate after heat treatment, or 2. The method for manufacturing a semiconductor device according to item 2.