JPS61124140A - Method of forming oxide film - Google Patents

Abstract

PURPOSE:To obtain a method of forming an oxide film having excellent boundary characteristics and electric characteristics without heating the substrate temperature by emitting a light absorbed efficiently to the grown film simultaneously with oxygen plasma. CONSTITUTION:When a microwave (mu-wave) discharge is used, the microwaves generated by magnetrons 1, 1 are led to quartz cylindrical discharge tubes 1, 8, which generate plasmas 1, 9. Electrons slightly presented in gas in a magnetic field move in a cyclotron motion. When the frequency coincides with that of the microwave to be emitted, an electron cyclotron resonance phenomenon occurs, the electrons absorb the energy of the microwave to efficiently discharge. The light to be efficiently absorbed to the oxide film uses infrared ray generated from a carbon dioxide gas laser. Thus, an SiO2 film is grown on Si at 500 deg.C of 1/2 of the conventional one, and when the light near the absorbing peak of the SiO2 is emitted, the growing of the oxide film becomes remarkable, the infrared ray emitted to the substrate is efficiently absorbed as the thickness increases, and applied as a method of forming the oxide film on an element not performed at high temperature.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for forming an oxide film, and in particular, a method suitable for forming a film with good interface characteristics between a semiconductor substrate and an oxide film at a relatively low temperature. The present invention relates to a method for forming an oxide film.

[Background of the invention]

In insulated gate field effect transistors (hereinafter abbreviated as MO8FETs), which are frequently used in LSIs, insulating films play important roles not only in the gate insulating film, which is the most important, but also in various places. These insulating films, particularly 5in2 silicon films, are formed by heating Si to a high temperature of 900° C. or higher in an oxygen atmosphere. This high-temperature heat treatment allows the SiO2 film to grow without oxygen diffusing into the Si, so that the interface between SiO2 and Si is always kept clean, resulting in optimal interface characteristics for device operation.

Incidentally, the dimensions of semiconductor devices are becoming smaller year by year in order to improve performance, reliability, yield, etc., but the above-mentioned high-temperature heat treatment does not necessarily have a positive effect on the characteristics of micro devices. This is because defects are induced in the substrate and impurities are redistributed due to high-temperature heat treatment.

Therefore, in recent years, attempts have been made to lower the film formation temperature by utilizing the effects of plasma and light.

A typical example of this is optical CVD (Chemical Vap
In our deposition, light that is selectively absorbed by the raw material gas (Si84, etc.) of the insulating film is irradiated to promote decomposition of the gas to form the film at a low temperature of about room temperature. However, in this method, impurities present on the substrate have a direct adverse effect on the interface characteristics, so it is difficult to apply this insulating film to the active region. Furthermore, since the film is formed at a low temperature, the film quality is not necessarily good.

Similarly, as a method of forming a film at a low temperature, for example, JP-A No. 5
5-118639. Showa 57-51972゜Sho 57-51
As shown in Japanese Patent No. 973, there is a method of forming an oxide film on the surface of Si using oxygen plasma. This method, unlike the above-mentioned CVD method, grows a film in a substrate, and therefore has relatively good interfacial properties. However, in order to recover from irradiation damage caused by charged particles in plasma, IEEE Trans, Ele
ctron device.

ED28,1060. (1981).

and “An I mprov” by Sugano.
element of theInterface Pr
operations of Plasma Anod
izedSiO2/ Si System
for the Fabrication of M
A heat treatment at 1000° C. is required, as discussed in the document entitled “OS FET'S”.

In addition, since the electrical breakdown voltage of the formed insulating film is low, J
, Electrochem, Soc,, 128
.

11.2424. “Plasma Oxide” by Ray and Reisman in (1981)
As discussed in the document titled "FET Devices", the film must be densified by heat treatment at 1000° C. These processes raise the entire substrate to a high temperature, so there is no point in forming the film at a low temperature.

In addition to these, Japanese Patent Application Publication No. 56-37633, A
ppl, Phys, Let7, 41.
Boyd and W. 162° (1982)
“○xidation of” by i 1 son
5ilicon 5surfaces by C○2L
As discussed in the literature entitled "Asers," a high-energy, high-output laser beam is irradiated onto the substrate surface in an oxidizing atmosphere or oxygen plasma to instantaneously heat a part of the substrate to near its melting point. , there are also attempts to accelerate the reaction.The feature of this method is that only a small part of the substrate is heated to a high temperature, so the entire substrate does not become hot, but the part that is hit by the laser is rapidly heated and cooled. As a result, point defects are likely to occur within the substrate.Also, when the surface is melted with a high-power laser, there is a major drawback that the unevenness generated on the surface becomes an obstacle to device formation. .

[Purpose of the invention]

An object of the present invention is to provide a method of forming an oxide film having excellent electrical properties such as interfacial properties without raising the substrate temperature in consideration of the above-mentioned problems.

[Summary of the invention]

In order to grow an insulating film without heating the substrate to high temperatures, it is necessary to supply energy to promote the reaction instead of heat. Therefore, as mentioned above, the best method is to use chemically active particles in plasma or excitation by light. In particular, when plasma is used, an interface is formed inside the substrate, similar to thermal oxidation, so relatively good interface characteristics can be obtained.

In order to further promote this reaction at low temperatures and improve film quality, the local heating using the laser mentioned above is an effective method. However, at this time, instead of irradiating the substrate with high-power laser light and locally heating the substrate to a high temperature for a short time,
If irradiation with light that is efficiently absorbed by the oxide film on the substrate, such as CO2 laser light, can promote the diffusion of reactive gases in the film, even irradiation with low-energy light can promote film growth and improve film quality. Improvement is possible.

Based on this idea, while oxidizing St in oxygen plasma, the 5in2 film efficiently absorbs 9 to 10μ.
We devised a method for forming an oxide film by irradiating m-band infrared rays.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings below.

FIG. 1 shows a schematic diagram of an apparatus used to specifically carry out the oxide film forming method based on the above-mentioned idea. This device consists of three parts: a discharge section that generates plasma of a reactive gas, a reaction chamber that holds the substrate to be processed and reacts the plasma with the substrate, and a light source that irradiates the substrate with light. has been done.

First, the discharge section that generates reactive gas plasma will be explained. Conventionally, there have been various methods for generating plasma, but the most frequently used method is one that uses high-voltage direct current or a high-frequency electric field typified by 13.56 MHz. In these methods, the device configuration is very simple and plasma can be easily formed, but on the other hand, the electrodes that apply the electric field and the container wall come into direct contact with the plasma, which can become a source of plasma contamination. There is a problem. For this reason, it can be said that it is a plasma generation source that is not very preferable for the growth of oxide films, which requires a very clean atmosphere.

Hojo Therefore, in this method, we use microwave (hereinafter abbreviated as μ-wave) discharge, which is a type of non-polar counterelectrode that does not use electrodes, and utilize the plasma confinement effect of a magnetic field to prevent the reaction between the plasma and the vessel wall. I'm trying to come up with something. Magnetron (1,
The 2.45 GHz μ waves generated in 1) are transmitted through the waveguide (1,
7) to a cylindrical discharge tube (1, 8) made of quartz. The inside of the discharge tube contains a reactive gas (oxygen or nitrogen gas) of about 2×40 −' Torr, and plasma (1, 9) is generated here. At this time, the discharge tube is surrounded by three air-core electromagnets (1, 4), and a mirror magnetic field is formed in the axial direction of the discharge tube. In this magnetic field, a small amount of electrons in the gas undergo cyclotron motion, but when the frequency of the electrons matches the frequency of the injected μ-waves, an electron cyclotron resonance (ECR) phenomenon occurs, and the electrons move into μ-waves. discharge occurs efficiently by absorbing the energy of Therefore, it is possible to create plasma with higher density than other discharge methods.

In addition, a magnet is placed on the back of the substrate to be processed to narrow down the plasma generated in the discharge section, so as shown in the reference diagram, there is no contact between the plasma and the vessel wall, and extremely clean plasma is generated. Is possible.

The pressure of the discharge gas is 5×10-'Torr ~ 5×10-''
Torr range, but the generation from plasma becomes strongest within this gas pressure, and the plasma density also reaches a maximum of 10”/
Co? It will be about.

In this method, carbon dioxide (CO2) is used as light that is efficiently absorbed by the oxide film growing on the Si substrate.
) Infrared rays in the 9-10 μm band generated from a laser were used. Sio2 has absorption based on the vibrations of St and O at 9.3 μm, but it is known that even if it deviates from 9.3 μm, it will absorb enough light as long as the substrate is heated to about 300°C. ing.

The output of the carbon dioxide laser was 3 J, and during the formation of SiO2, irradiation was performed in pulse mode at intervals of 10 Hz. At this output, the surface of Sio2 never melts, and no change is observed on the surface of Sio2 even after long-term irradiation. Furthermore, inside the vacuum reaction vessel, Zn
Infrared light was input through the 13e window.

The holder that holds the substrate to be processed is made of quartz.
It is possible to heat the substrate to about 800° C. using a halogen lamp placed very close to the substrate.

Using the apparatus configured as described above, SiO2 is deposited on Si at a temperature of 500°C, which is half the temperature of conventional high-temperature thermal oxidation.
Two films were grown.

FIG. 2 shows the growth of an oxide film when oxidation was performed using only plasma and when laser irradiation was additionally performed.

As is clear from this figure, there is no big difference between the two in the thin region of the film, but as the film becomes thicker, the film growth rate increases with laser irradiation. Furthermore, interestingly, it was found that irradiation with light close to the absorption peak of SiO2 resulted in more significant growth of the oxide film. These results show that the infrared rays irradiated onto the substrate are effectively absorbed by the SiO2 film as the film thickness increases.

This infrared irradiation not only increases the film growth rate but also
It also shows good effects on electrical properties such as Si/Si○2 interface properties.

FIG. 3 shows the difference in the distribution of interface state density within the substrate to be processed. Even when comparing the sample before heat treatment, the one irradiated with infrared rays has a lower density of interface states;
It can be seen that this difference becomes more noticeable when heat treatment is applied in hydrogen at temperatures of about °C. The results show that a good interface structure can be created without heating the entire substrate due to the local heating effect of infrared irradiation. Furthermore, it has been found that this infrared ray irradiation is also effective in improving the electrical breakdown voltage of the SiO2 film.

〔Effect of the invention〕

According to the present invention, an insulating film having excellent electrical properties such as interfacial properties and breakdown voltage can be formed on a semiconductor substrate at a temperature of about 500° C., which is about half the temperature of conventional methods. Therefore, it can be applied as a method of forming an oxide film to elements where the entire substrate cannot be heated to a high temperature, such as stacked devices such as tertiary element devices and thin film transistors on low melting point substrates.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the apparatus used to carry out the present oxide film formation method, Figure 2 is a diagram showing changes in the oxide film over time, and Figure 3 is a diagram showing the distribution of interface state density in the substrate. It is. 1.1... Magnetron, 1.2... Isolator. 1.3...Baku-monitor, 1.4...Air core electromagnet. 1.5... Plasma, 1.6... Substrate to be processed. 1.7... Waveguide, 1.8... Quartz discharge tube. 1.9...Au plating mirror, 2.0...carbon dioxide laser+, 2.1-Zn-3e window, 2.2...microwave. 2.3... Waveguide, 2.4... Quartz discharge tube. 2.5...Plasma flow, 2.6...Air core electromagnet @/
So-called 2θ lθ /2θ /〃 Saihai 2 Iotsaki PH1 (minutes) Procedure Amendment (Method) Description of the case 1982 Patent Application No. 244431, Title of invention Oxidation film formation Person who makes the amendment Relationship to the incident Patent applicant name (510)
Hitachi Co., Ltd. Manufacturing Co., Ltd. Address: 5-1 Marunouchi-chome, Chiyoda-ku, Tokyo 100 Hitachi Co., Ltd. Manufacturing Co., Ltd. Internal model: Tokyo 212-1111 (main representative) Date of amendment order: 1985 Contents of the March 26 amendment ■, rIEEE Trans, Electron dev described in page 3, line 19 to page 4, line 4 of the specification
“An Improv” by HO and Sugano in Ice, ED28°1060, (1981)
element of theInterface Pro
pertj,es of Plasma Anodiz
edSiO2/ Si System fo
r the Fabrication of MO8
"Improvement of plasma anodization 5i02/St interface characteristics for the production of MOSFET" by Ho and Sugano in IE Transactions Electron Devices Vol. 28, p. 1060 (1981). (IEE Trans. Electron device, ED28, 1060
r (1981) Ho, and, Sugan.
o ”An I improved seven of
theInterfacePropertySof
Plasma anodized SiO2/S
i System for the Fab
ration of MOS FET'S"
) Correct it as J. 2. r J described in page 4, lines 7 to 10 of the specification,
Electrochem, Soc, 1.28
, 1 1. Ray and Reis in 2424, (1981)
“Plasma Oxide FE” by man
TDevjces” J to “Journal of Electrochemistry Society 1
28, No. 11, p. 2424 (1981) by Ray and Reisman et al. 0xi
3. rAppl, Phys, Lett, described on page 4, lines 16 to 19 of the specification.
1, 1 6 2. (1982) by Boyd and Wilson, “Xidation of 5ilicon 5
``oxidation of silicon surfaces by CO□ lasers'' by Boyd and Wilson et al. in Applied Physics Letters, Vol. 41, No. 162 (1982).
Earth. 1 62, (1982), Boyd and
Wilson″○xidation of 5il
j, con 5 surfaces by CO2L
asers”) Correct it as J.

Claims (1)

[Claims] 1. Formation of an oxide film characterized by reacting oxygen plasma with a metal or semiconductor surface to grow an oxide film on the metal or semiconductor surface, the oxide film being grown. An oxide film forming method characterized by irradiating light that is efficiently absorbed by the oxygen plasma at the same time as the oxygen plasma. 2. In the above oxide film forming method, oxygen plasma is formed by applying a high frequency electric field from the outside in a container sealed with dilute oxygen, and the plasma is narrowed by a magnetic field provided in the container. The method for forming an oxide film according to claim 1, characterized in that contact between the vessel wall and the plasma is reduced.