JPS6292329A - Forming method for insulating film - Google Patents

Abstract

PURPOSE:To form an insulating film having high withstanding voltage and excellent interfacial characteristics by oxidizing a semiconductor substrate at 300-400 deg.C in an oxidizing plasma atmosphere, shaping an oxide thin-film on the surface of the semiconductor substrate and laminating an insulating film on the oxide film. CONSTITUTION:An silicon substrate 1 is oxidized in an oxygen plasma atmosphere. An insulating film 2 is formed through plasma oxidation for 1hr. 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 hydrogen plasma treatment at 350 deg.C are each conducted for 1hr in order to improve the characteristic of the insulating film 3. Accordingly, the insulating film 3 having high withstanding voltage and excellent interfacial characteristics is acquired.

Description

[Detailed description of the invention] Industrial application field The present invention provides a gate insulating film with good characteristics.
The present invention relates to a method for forming a laminated insulating film.

Conventional technology and its problems Conventionally, oxide films used for gate insulating films have been generally obtained by thermal oxidation, which has a low interface state density and provides a high-quality insulating film. 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 thermal oxidation at a high temperature of 41 hours. Therefore, although oxide films obtained by these methods are used as interlayer insulating films and protective films of semiconductor devices, they are not used as gate insulating films of LSIs and the like.

Therefore, there is a need for a method for 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.

Purpose of the Invention The present invention has 1. high pressure resistance in low temperature processes;
Another object of the present invention is to provide a method for forming an insulating film with good interfacial properties.

Structure of the Invention The present invention provides a method of subjecting a semiconductor substrate to an oxidizing plasma atmosphere for 300 minutes.
The present invention relates to a method for forming an insulating film on a semiconductor substrate, the method comprising forming an oxide thin film on the surface of the semiconductor substrate by oxidizing at ~400°C, and then laminating an insulating film on the oxide thin film.

ECR plasma glow discharge or the like is used as the plasma atmosphere.

Although the temperature for plasma oxidation was in the range of 300 to 400°C, it is desirable that it be as high as possible within the allowable range of the process.

The plasma atmosphere is exemplified by oxygen or a mixed gas of oxygen and nitrogen, and it is particularly preferable to use only oxygen.

The degree of reduced pressure during plasma oxidation is 05 to 1.5 T orr.
range is desirable. This is because if the pressure is too high, plasma generation is suppressed, and if the pressure is too low, sputtering occurs.

The thickness of the oxide thin film by plasma oxidation is 10 to 80
A range of people is preferred. If it is too thin, a uniform film cannot be obtained;
Furthermore, if the thickness is increased, the throughput will be significantly reduced. Particularly preferred is a thin oxide film with a thickness of 30 to 60 people.

As a method for laminating an insulating film on the oxide thin film obtained in the above process, atmospheric pressure CVD, plasma CVD, photo-CVD, etc., which are low-temperature oxide film formation methods, can be used. A good insulating film can be obtained.

According to the present invention, when forming an insulating film on a semiconductor substrate,
By oxidizing the semiconductor substrate in advance in an oxidizing plasma atmosphere, an oxide thin film having a transition region with a chemical composition close to that of a thermal oxide film at high temperatures is formed, and an insulating film is further laminated on top of the oxide thin film. The interface structure is similar to that of a thermal oxide film, and in low-temperature processes, the interface state density is low.
An insulating film with a good interface structure can be obtained.

Hereinafter, in order to clarify the effects of the present invention, examples will be specifically described with reference to FIGS. 1 to 5.

FIGS. 1 to 3 show MO using an oxide film according to the present invention.
This figure shows the process of forming an S capacitor. First, a silicon substrate (1) was oxidized in an oxygen plasma atmosphere (FIG. 1). At 400°C in an ITorr atmosphere,
Plasma oxidation is performed for one hour to form an oxide film (2) of several dozen or more sizes. If plasma treatment is performed for a long period of time and at high power, care must be taken because surface damage may become severe and the interfacial properties may deteriorate. Next, an oxide film (3) was laminated by normal pressure CVD at a substrate temperature of 400° C. to a desired thickness of 1000 μm (FIG. 2). The quality of the oxide film is denser and has better characteristics as the film formation temperature is higher, so it is desirable that the two oxide film formation 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, especially 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, an AI electrode (4) is formed on the oxide film (3), and an AJJ electrode (5) is deposited on the back surface of the silicon substrate (1) so that ohmic contact can be made.
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 one not subjected to plasma oxidation (Fig. 5),
A reduction in interface state density of about one order of magnitude was observed.

Effects of the Invention According to the present invention, it is possible to form an insulating film with good interfacial properties in a low-temperature process, making it possible to manufacture thin film transistors on, for example, a glass substrate (strain point: 550 to 600°C). becomes. This technology can be used in active 7-trix 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. 5 is a diagram showing the plasma oxide film (2). FIG. 3 is a diagram showing the interface state density when there is no interface state. The symbols in the figure are as follows. l...Silicon substrate 2...Plasma oxide film 3...Normal pressure CVD oxide film 4.5...Moreover, M and G in FIGS. 4 and 5 indicate the center of the forbidden band. where C and B indicate the lower end of the conduction band, and V and B indicate one end of the valence band. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 y, B, M, G,
C,B. Procedural amendment (voluntary) 22 Name of the invention Insulating film forming method 3 Relationship with the person making the amendment Patent applicant address 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Name
(504) Sharp Corporation Representative Sa
Haku Asahi 4 agent ME 5 diagram

Claims (1)

[Claims] 1. The semiconductor substrate is heated in an oxidizing plasma atmosphere to
A method for forming an insulating film on a semiconductor substrate, the method comprising forming an oxide thin film on the surface of the semiconductor substrate by oxidizing at 0° C., and then laminating an insulating film on the oxide thin film. 2. The method according to item 1, wherein the semiconductor substrate is a silicon substrate. 3. The method according to item 1, wherein the plasma atmosphere is oxygen plasma formed by glow discharge. 4. The oxide thin film formed by plasma is 10 to 80 Å.
2. The method of claim 1, wherein the method has a thickness of . 5. The method according to item 1, wherein the insulating film is formed by atmospheric pressure CVD, plasma CVD, or photo-CVD.