JPS5931032A - Plasma oxide film forming device - Google Patents

Abstract

PURPOSE:To slow the speed of oxidation, and to form the thin oxide film being minute and having little defect by a method wherein the surfaces of semiconductor substrates are oxidized directly in the condition neutralized electrically in a plasma atmosphere. CONSTITUTION:The silicon substrates are heated by an outside heater 2 at 600 deg.C, for example, a high-frequency electric power source 4 is made to act to generate plasma between electrodes 5, the surfaces of the silicon substrates are oxidized according to plasma thereof, and oxidation is continued up to obtain the necessary thickness to form the oxide film. As the heating means of the silicon substrates 8 and plasma thereof, there exists a device furnished with a high-frequency coil 2a for heating to be used both as the coil for generation of plasma, or furnished with the outside heater 2 and electrodes 3 for generation of plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma oxide film forming apparatus used for forming a semiconductor oxide film or nitride film in a plasma atmosphere.

In the manufacture of silicon semiconductor devices, silicon thermal oxide films are widely used for everything from thick field insulating films to thin gate oxide films. In this case, the thickness of the oxide film is 1 to 2
A silicon oxide film with less contamination is required from about μm to about 1000 to 500 A. Furthermore, in order to generate these silicon oxide films, it is necessary to heat the silicon substrate to 900° C. or higher in an oxidizing atmosphere. Heating at such high temperatures is not preferable for miniaturization of elements formed on a silicon substrate. That is, the depth of the junction formed in the silicon substrate is determined by the temperature and time of the heat treatment; the higher the heating temperature, the larger the spread of the diffusion layer, and the more difficult it is to obtain a shallow junction. Furthermore, with the miniaturization of devices, the gate oxide film needs to become thinner to 500A or less. This thin oxide film can be obtained by lowering the oxidation temperature. Furthermore, the density of the unformed oxide film increases at low oxidation temperatures. For these purposes, new oxide film formation methods have been proposed to achieve low-temperature oxidation. For example, one method is to place a silicon substrate in a plasma atmosphere generated by high-frequency oscillation, and to apply a current as an anode side electrode to form an oxide film in oxygen plasma.

However, although it is easy to form a thick oxide film on a silicon substrate with the above conventional method, the characteristics of the oxide film are not sufficient as a gate oxide film, and it is necessary to form an oxide film of even better quality.

FIG. 1 shows the oxidation rates in the case of plasma anodic oxidation (curve ■) and the case of direct plasma oxidation (curve I). In the case of plasma anodization, the oxidation temperature is 6011
Although the temperature is low, the oxidation rate is as high as 02 μm/min, and the surface state density (Surface
5tate density) is also lO1'', which is an order of magnitude larger than the value of a normal oxide film. The method of forming the film by direct plasma oxidation is effective because it forms a film that is stable and has a dense structure, and it can be formed at low temperatures and the oxidation rate can be suppressed.Even in the same oxidation in plasma, the silicon substrate is not used as the anode. If the plasma direct oxidation method is used, the oxidation rate will be less than 1/10th, and the desired oxide film can be formed.Furthermore, as the oxide film thickness decreases, the absolute value of the dielectric breakdown strength of the silicon oxide film decreases. Therefore, it is effective to oxidize a silicon substrate at a low temperature in a plasma atmosphere in order to form a thin oxide film with high density and fewer defects such as pinholes that cause dielectric breakdown.

In this invention, unlike the conventional plasma anodization method,
The semiconductor substrate is made electrically neutral in a plasma atmosphere (
It is characterized by directly oxidizing the surface in a floating state. By using the above method, the oxidation rate can be slowed down, and a thin oxide film with a dense structure and few defects can be realized.

High frequency waves, microwaves, etc. are used to form a plasma atmosphere. Opposing electrodes are provided inside the quartz container (hereinafter referred to as quartz reaction tube), or electrodes are provided outside the quartz reaction tube along the tube wall. Alternatively, a high frequency coil is installed outside the quartz reaction tube to generate plasma. The reaction gas is supplied from outside the quartz reaction tube, and the entire system is IF'
~1 (a device that creates a vacuum of about 1"" torr is also installed.Semiconductor substrate C and below, silicon substrates are taken as an example) can be heated by the same resistance heating as conventional methods, but
Heating can also be performed using a high frequency coil for plasma generation. The silicon substrate is placed in a quartz reaction tube and heated. The present invention provides an apparatus for forming an oxide film on a silicon substrate by supplying a gas such as 02 or N20 at the same time as plasma generation after the inside of a quartz reaction tube is brought to a vacuum level of 1 to 1 to 1 torr. The purpose of This invention will be explained below.

FIG. 2 shows an embodiment of the present invention.

In this figure, 1 is a quartz reaction tube, 2 is an external heater, and 3 is a quartz reaction tube.
Reference numeral 4 indicates an electrode made of metal or SIC, and 4 is a high frequency power source installed externally. Plasma can be generated by the high frequency power supplied from the high frequency power source 4 between the electrodes 3. 5 is a vacuum pump system for obtaining the degree of vacuum necessary to generate plasma. 6 is a gas supply port, and 7 is a filter and purification device.

Is the gas supplied to the filter and purifier 7? : The gas is supplied from the gas supply port 6 through the gas supply port 6. The type of gas is 0, ,
In addition to NO□, CO□, etc., a small amount of diluting gas can be added.

Next, to explain the operation, the silicon substrate is heated to, for example, 600° C. by the external heater 2, the high frequency power source 4 is activated, and plasma is generated between the electrodes 3. The surface of the silicon substrate is oxidized by this plasma, and the silicon substrate is heated to a desired thickness. Oxidation is performed until it becomes oxidized to form an oxide film.

FIGS. 3(a) and 3(b) show the heating means for the silicon substrate 8 and the plasma generating means, respectively.

In FIG. 3(a), the high-frequency coil 2a for heating also serves as a coil for generating plasma;
Figure (b) shows a type equipped with an external heater 2 for heating and an electrode 3 for plasma generation.

A silicon substrate 8 is placed between the electrodes 3.

Note that either the plasma generating means shown in FIG. 3(a) or FIG. 3(b) may be used.

As explained above, the present invention generates plasma by a plasma generating means using high frequency f or microwaves in a quartz container containing a semiconductor substrate into which a required gas is introduced, and oxidizes the semiconductor substrate. Since a film is formed, there is an advantage that a highly stable oxide film can be obtained and burnt at a low temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing oxidation rates in the case of plasma anodic oxidation and the case of direct plasma oxidation, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3(a). (b) is a configuration diagram showing a heating means for a silicon substrate and a means for generating plasma, respectively. In the figure, 1 is a quartz reaction tube, 2 is an external heater, 2a is a high-frequency coil, 3 is a lightning pole, 4 is a high-frequency power supply, 5 is a vacuum pump system, 6 is a gas supply port, 7 is a filter and purification equipment fit, 8
is a silicon substrate. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Makoto Kuzuno - (1 other person) Figure 1 Oxidation time (minutes) Figure 3 (a) Ri3 (b)

Claims (1)

[Claims] A quartz container in which a semiconductor substrate is housed, the internal pressure is kept lower than atmospheric pressure, and a predetermined gas is introduced; and plasma is generated in the quartz container using high frequency or microwave to remove the semiconductor substrate. A plasma oxide film forming apparatus comprising a plasma generating means for direct oxidation.