JPS6292328A - Forming method for insulating film - Google Patents

Abstract

PURPOSE:To form an insulating film having high withstanding voltage and excellent interfacial characteristics by thermally oxidizing a semiconductor substrate at a temperature of 550 deg.C or less, shaping an oxide thin-film on the surface of the semiconductor substrate and laminating the insulating film of the oxide thin-film. CONSTITUTION:An silicon substrate 1 is thermally oxidized at 550 deg.C in a dried oxygen atmosphere. An oxide thinf-ilm 2 is shaped through heat treatment for 1 or 2hr. An insulating film 3 is laminated up to film thickness of 1,000Angstrom at a substrate 1 temperature of 400 deg.C through a normal pressure CVD method. Annealing at 550 deg.C in a nitrogen atmosphere and plasma treatment at 350 deg.C are each conducted for 1hr in order to improve the characteristics of the insulating film 3. Accordingly, the insulating film 3 having high withstanding voltage and excellent interfacial characteristics is shaped.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a laminated insulating film that allows a gate insulating film with good characteristics to be obtained.

Conventional technology and what's between - Plants Conventionally, oxide films used for gate insulating films have been generally obtained by thermal oxidation, which has a low density of interface states and can yield high-quality insulating films. Since high-temperature processing is required, when an element is formed on a glass substrate, the glass substrate melts, making formation difficult. Therefore, in such cases, it is required to form a high quality insulating film at low temperatures. Atmospheric pressure CVD is a method for forming an insulating film at low temperatures.
A method such as a method, a plasma CVD method, a photo CVD method, a plasma anodic oxidation method, etc. are commonly used. When forming an oxide film by the CVD method, although it is possible to improve the characteristics such as increasing the withstand voltage by post-processing the oxide film such as hydrogen treatment and annealing, defects are likely to occur at the interface with the semiconductor, and the interface state The disadvantage is that the density is one to two orders of magnitude higher than that of a thermal oxide film. In addition, in the plasma anodization method, since high voltage is applied to the substrate, electrons and ions irradiate the substrate with high energy, causing damage to the surface and creating an interface between the semiconductor substrate and the formed oxide film. There is still a problem in that the potential density is one to two orders of magnitude higher than that of an insulating film formed by high-temperature thermal oxidation. Therefore, the oxide films obtained by these methods are
Although it is used as an interlayer insulating film or a protective film in semiconductor devices, it is not used in gate insulating films such as r and sr.

Therefore, there is a need for a method of forming an insulating film that can be processed at low temperatures and has good performance that can also be used as a gate insulating film.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for forming an insulating film with high breakdown voltage and good interface characteristics in a process at low temperature.

The present invention is characterized in that a semiconductor substrate is thermally oxidized at a temperature of 550° C. or lower to form an oxide thin film on the surface of the semiconductor substrate, and then an insulating film is laminated on the oxide thin film. A method for forming an insulating film on a semiconductor substrate is provided.

The thermal oxidation temperature is 550°C or lower.

When the temperature exceeds 550° C., the temperature approaches the softening point of glass, making it impossible to form elements on the glass substrate. The temperature is preferably as high as possible without causing distortion to the glass substrate.

The thermal oxidation atmosphere is usually an oxygen or water vapor atmosphere.

The thickness of the oxide thin film formed by low-temperature thermal oxidation is usually 10~
A range of 50 people is preferred. This is because if the film is too thin, a uniform film cannot be obtained, and increasing the film thickness requires oxidation for an extremely long time, resulting in a significant reduction in throughput. Particularly preferred is a thin oxide film with a thickness of 30 to 50 people.

The method of laminating an insulating film on the oxide thin film obtained in the above process can be performed using low-temperature oxide film forming methods such as normal pressure CVD, plasma CVD, photo-CVD, etc. Also, an insulating film with good interfacial properties can be obtained.

According to the present invention, when an insulating film is formed on a semiconductor substrate, the semiconductor substrate is thermally oxidized at 550°C or lower in advance to form an oxide thin film having a transition region with a chemical composition close to that of a thermally oxidized film at high temperatures. By forming an insulating film and then laminating an insulating film on top of the two layers, the interface structure becomes similar to that of a thermal oxide film, and an insulating film with a good interface structure and low interface state density can be obtained in a low-temperature process. be.

Hereinafter, in order to clarify the effects of the present invention, examples will be specifically described with reference to FIGS. 1 to 5. 1 to 3 show a process for forming a MOS capacitor using an oxide film according to the present invention. First, a silicon substrate (1) was thermally oxidized at 550° C. in a dry oxygen atmosphere (FIG. 1). Even at such a low temperature, an oxide thin film (2) ranging from 10 to several dozen was formed by treatment for 1 to 2 hours. Next, an oxide film (3) was laminated by atmospheric pressure CVD at a substrate temperature of 400°C to the desired film thickness of 1,000 layers (second
figure). Thermal oxidation has a slow oxidation rate at low temperatures, and CVD
Since the quality of the film is denser and has better characteristics as the film forming temperature is higher, it is desirable that the two oxide film forming steps of the present invention be performed at as high a temperature as possible within the range of the manufacturing process.

Next, in order to improve the properties of the oxide film, particularly the upper oxide film (3), annealing at 550°C in a nitrogen atmosphere and hydrogen plasma treatment at 350°C were performed for 1 hour each. Finally, the oxide film (3) J: Nihe! forming an electrode (4), and
A! Make ohmic contact with the back side of the silicon substrate (1)! By depositing the electrode (5), M
An OS capacitor was fabricated (Fig. 3).

The C-■ characteristics of the MOS capacitor manufactured as described above were examined, and the interface state density was evaluated. As shown in Figure 4,
Compared to the material not subjected to low-temperature thermal oxidation (Fig. 5), it was observed that the interface state density was reduced by about one order of magnitude.

Effects of the Invention According to the present invention, an insulating film with good interfacial properties can be formed in a low-temperature process, making it possible, for example, to manufacture thin film transistors on a glass substrate (strain point: 550 to 600°C). Become. This technology can be used in active matrix panels using inexpensive glass substrates, and is expected to be applied to large-area thin displays.

[Brief explanation of drawings]

Figures 1, 2, and 3 show MO using stacked oxide films.
FIG. 4 is a diagram showing the interface state density of the laminated oxide film formed by the method of the present invention, and FIG. FIG. 3 is a diagram showing the interface state density in the case where there is no. The symbols in the figure are as follows. ■...Silicon substrate 2...Low temperature thermal oxide film 3...Normal pressure CVD oxide film 4.5...A! Further, in FIGS. 4 and 5, M and G indicate the center of the forbidden band, C and B indicate the lower end of the conduction band, and V and B indicate the upper end of the valence band. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 V, B, M, G,
C,B. Procedural amendment (voluntary) 2. Name of the invention Insulating film forming method 3. Person making the amendment Relationship to the case Patent applicant address 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Name
(504) Sharp Corporation Representative Sa
Haku Asahi 4, Agent 5, Date of amendment order (voluntary) 3, Subject of amendment Figure 5, 7 of "Drawings", Contents of amendment as attached.

Claims (1)

[Claims] 1. A semiconductor substrate characterized in that a semiconductor substrate is thermally oxidized at a temperature of 550° C. or lower to form an oxide thin film on the surface of the semiconductor substrate, and then an insulating film is laminated on the oxide thin film. A method of forming an insulating film on top. 2. The method according to item 1, wherein the semiconductor substrate is a silicon substrate. 3. The method according to paragraph 1, wherein the thermal oxidation is carried out with dry oxygen or steam. 4. The oxide thin film formed by low-temperature thermal oxidation is 10-5
2. The method of claim 1, having a thickness of 0 Å. 5. The method according to item 1, wherein the insulating film is formed by atmospheric pressure CVD, plasma CVD, or photo-CVD.