JPH0122730B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] This invention relates to a method in which a positive electrode and a negative electrode are mounted on a substrate placed on a negative electrode located opposite to the positive electrode in a low-pressure oxygen gas atmosphere. The present invention relates to a plasma oxidation device that applies a DC voltage between electrodes to generate a glow discharge, and forms an oxide film through a reaction between oxygen and the surface of a substrate.

[Prior art and its problems]

In such plasma oxidation methods, when the electrical resistivity of the substrate is high or when the thickness of the substrate is large, variations in the thickness of the oxide film to be formed are likely to occur, especially when the substrate is a semiconductor substrate. In this case, it had the disadvantage of significantly deteriorating the electrical characteristics. For example, if the semiconductor substrate has a high specific resistance, the electric field distribution during glow discharge will be non-uniform in each portion of the substrate, and the rate of reaction with oxygen will be non-uniform in each portion of the substrate. As a result, the thickness of the oxide film to be formed on the surface of the substrate becomes non-uniform at each portion of the substrate.

Figure 1 shows the disturbance of the electric field distribution during glow discharge. A high resistivity substrate such as a semiconductor plate 3 is placed on a positive electrode 1 and a negative electrode 2 placed in a vacuum chamber (not shown), and oxygen is introduced. When a DC voltage is applied between the positive electrode 1 and the negative electrode 2 by the power source 4, the electric field is distributed as shown by the arrow 5. That is, the electric field density decreases at the center of the high resistivity substrate 1, and conversely increases at the periphery. This is because glow discharge is likely to occur near angular areas or protrusions, and the discharge current does not flow inside the base having a high resistivity, but instead flows along the surface of the base. The oxide film formed on the surface of the semiconductor board 3 by such glow discharge is formed as an oxide film 6 that is thicker around the substrate and thinner in the center, as shown in cross section in FIG. Ru. This is a drawback that cannot be avoided as long as a conventional means for performing glow discharge is used. Further, when the thickness of the substrate itself is large, the potential difference between the disposed electrodes and the surface of the substrate is large, which causes the formation of a non-uniform oxide film on the surface of the substrate as shown in FIG.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma oxidation apparatus capable of eliminating the above-mentioned drawbacks and forming a uniform oxide film even on the surface of a high resistivity substrate.

[Key points of the invention]

In this invention, a substrate on which an oxide film is to be formed is placed near a negative electrode of a counter discharge electrode that generates a glow discharge, and a screen electrode having the same potential as the negative electrode is placed between the two electrodes to cover the entire surface of the substrate. The aim is to form a uniform electric field density, thereby producing a uniform reaction rate over the entire surface of the substrate, and as a result, to form a uniform oxide film over the entire surface of the substrate.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the invention, and parts common to those in FIG. 1 are given the same reference numerals. The reaction tank 7 containing the positive electrode 1 and the negative electrode 2 is connected to an oxygen cylinder 10 through a vacuum gauge 8, a gas flow meter 9 such as a mass flow meter, and an exhaust system 12 through an exhaust volume adjustment valve 11, respectively. There is. On the substrate 3, which is supported on the cathode 2, there is according to the invention a screen electrode 13 which is placed on the cathode 2 and is at the same potential as the cathode 2.

Using the apparatus having such a configuration, a glow discharge was generated in the reaction tank 1, and an oxide film was formed on the surface of the substrate 3. The formation conditions are as described below.

Substrate: Silicon single crystal, P type, resistance 10 to 30 kΩ
cm, diameter 40mm, mirror surface Reaction temperature: 300℃ Gas used: Oxygen Pressure inside the tank during glow discharge: 0.3Torr Discharge power: DC600V Distance between electrodes: 50mm Discharge time: 120 minutes Screen electrode: From 0.2mm diameter stainless steel wire The material of the negative electrode 2 is the same as that of the screen electrode.
Made of stainless steel. For comparison, an oxide film was formed under similar formation conditions using a conventional apparatus without a screen electrode. 4 and 5 show cross sections of the oxide films formed, with FIG. 4 showing the oxide film formed by the conventional device and FIG. 5 showing the oxide film formed by the device according to the embodiment of the present invention.

As shown in FIG. 4, according to the conventional device, the oxide film 6 is the thinnest at the center, and the thickness A is 400 Å as measured by an ellipmeter. In the middle part, the thickness is
700 Å, and the oxide film 6 is the highest at the outermost periphery.
becomes thicker, and the thickness shown in C is 1000 Å according to similar measurements. In this way, in the conventional method, the surface of the semiconductor substrate becomes non-uniform as shown in FIG. On the other hand, FIG. 5 shows the state of formation of an oxide film on the surface of a semiconductor substrate when an oxide film is formed using the screen electrode 13 of the present invention. As shown in this figure, by using the present invention, an extremely uniform oxide film 6 is formed.
An ellipsometer was also used to measure the film thickness.
The film thickness C is 1000 Å, and if the glow discharge time is the same, the electric field density increases by using the present invention, so if the conditions are the same, the oxide film will be formed about 200 Å thicker than the average thickness in the former case. It also became clear.

Since an extremely uniform oxide film can be easily formed according to the present invention, it is an extremely useful technique when an oxide film is previously formed on a semiconductor substrate, for example, in an ion implantation method. In addition, MIS (Metal-Insulator-
It is thought that it also plays a major role in improving the electrical characteristics of the semiconductor structure.

〔Effect of the invention〕

According to the present invention, it is possible to form an extremely uniform oxide film on the surface of a substrate simply by placing a simple screen electrode on the cathode for generating glow discharge. Therefore, unlike the thermal oxidation method, the plasma oxidation method can be performed without raising the temperature of the substrate, and the thickness of the oxide film is made uniform by the plasma oxidation method. It can be used extremely effectively to form an oxide film on a substrate, and the effects obtained are significant.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of a conventional plasma oxidation apparatus, FIG. 2 is a cross-sectional view of a substrate having an oxide film obtained by the apparatus, FIG. 3 is a cross-sectional view of an embodiment of the present invention, and FIG. , and FIG. 5 are cross-sectional views of substrates having oxide films obtained by the conventional apparatus and the apparatus shown in FIG. 3, respectively. DESCRIPTION OF SYMBOLS 1... Positive electrode, 2... Negative electrode, 3... Substrate (silicon plate), 4... DC power supply, 7... Reaction tank, 10... Oxygen cylinder, 12... Exhaust system, 13... Screen electrode.

Claims (1)

[Claims] 1 Glow discharge is generated by applying a DC voltage to the anode and cathode in a low-pressure oxygen atmosphere on the substrate supported on the cathode located opposite to the anode in a reaction tank that can be directly vented. 1. A plasma oxidation device for forming an oxide film by generating a plasma oxidation device, characterized in that a screen electrode having the same potential as a cathode is disposed between both electrodes.