JPH038331A - Method and apparatus for forming silicon oxide - Google Patents

Abstract

PURPOSE:To improve a boundary between SiO2 and Si in case of growing an epitaxial layer on an SiO2 film and to form the SiO2 film of high quality at a low temperature by simultaneously radiating with a Si molecular beam and O2 molecular beam containing Si3 molecular beam or ozone when the SiO2 film is formed on a substrate. CONSTITUTION:When an SiO2 film is formed on a Si substrate, Si is supplied to the surface without oxidizing the substrate, and the SiO2 film of high quality is formed at a low temperature on the Si substrate. Thus, even if the substrate is not the Si but compound semiconductor, desirable SiO2 film is obtained. To this end, a surface to be generated on a top in a vacuum tank 1 is directed downward, the substrate 2 is disposed, Si is radiated from an electron gun depositing unit 4 disposed at a bottom and O3 gas is radiated from a nozzle 3 to the lower surface of the substrate 1. Here, in order to supply O3 to the nozzle 3, O2 is passed from a gas cylinder 6 provided out of the tank 1 into a synthetic quartz reaction chamber 7 to be heated by a Hg-Xe lamp 5 to be supplied to the nozzle 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method and apparatus for forming silicon oxide,
More specifically, the present invention relates to a method and apparatus for forming high quality silicon oxide at low temperatures.

(Prior Art) Conventionally, silicon oxide films have been formed by thermal oxidation of a silicon substrate or vapor phase growth. High quality silicon oxide film can be obtained by thermal oxidation of silicon substrate,
Furthermore, since the interface is formed within the silicon substrate, the density of interface states is also low. However, thermal oxidation requires a high temperature of 800° C. or higher, and there is a drawback that the impurity profile formed in the substrate is destroyed by diffusion of impurities during the thermal oxidation process. On the other hand, vapor phase growth allows formation of an oxide film at low temperatures. However, in this vapor phase growth, a reaction between silicon and oxygen occurs in the vapor phase, forming 5iC)z particles that accumulate on the substrate, so that many voids are present in the oxide film. Therefore, an oxide film formed by vapor phase growth has a lower breakdown voltage and more leakage current than a thermal oxide film. Furthermore, since the silicon surface is not cleaned, there is a large density of interface states, making it unsuitable for use in areas where high-quality oxide films are required, such as gate oxide films in MOS devices. . Furthermore, gate oxide films of MOS devices tend to become thinner as LSIs become more densely packed, and it is expected that a film thickness of 100 mm or less will be required in the near future. Particularly in DRAMs, it is difficult to reduce the capacity to prevent soft errors caused by alpha rays, and therefore it is necessary to compensate for the decrease in capacity due to miniaturization by making the oxide film thinner. Furthermore, as the chip size increases, the area occupied by the gate region becomes larger, and an oxide film with excellent electrical insulation properties without breakdown voltage defects is required over a large area. On the other hand, even if the oxide film becomes thinner, it is practically difficult to lower the operating voltage, and oxide films tend to be used under higher electric field strength than before. However, as the thermal oxide film becomes thinner, many defects such as pinholes and weak spots occur that cause insulation failure. The reason for this is that the influence of the SiO layer existing at the interface between Si and 5i02 becomes negligible as the oxide film becomes thinner, and also that the influence of the SiO layer existing at the interface between Si and 5i02 becomes negligible as the oxide film becomes thinner.
Alternatively, it is thought that the surface may be contaminated due to adhesion of bacteria.

Therefore, the inventor conducted extensive research and found that an oxide film could be formed at a low temperature by simultaneously supplying molecular Si and O2 to the substrate. Furthermore, unlike the deposition of an oxide film by vapor phase growth, this method is performed in a molecular beam region, so oxidation of Si occurs on the surface rather than a vapor phase reaction. For this reason, it was found that a thinner film could be formed compared to vapor phase growth. Furthermore, by growing a Si buffer epitaxial layer using the Si molecular beam growth method before forming 5i02,
It was possible to make the i02/Si interface flat on the atomic order, and it was possible to reduce the breakdown voltage caused by electric field concentration due to the unevenness of the interface and the interface state density caused by the interface transition layer. However, when growing in a very dilute oxygen atmosphere, the oxygen concentration incorporated into the film was highly dependent on the growth temperature, and the lower the growth temperature, the higher it was. Furthermore, even if the film is grown at room temperature, the oxygen concentration in the film is lower than the stoichiometry of SiO because the amount of oxygen is insufficient. Such an oxide film had a low breakdown voltage and a large leakage current.

The purpose of the present invention is to eliminate such conventional drawbacks,
An object of the present invention is to provide a method and apparatus for forming high quality silicon oxide at low temperatures.

(Means for Solving the Problems) The present invention provides silicon (Si) molecular beams and ozone (
O3) A silicon oxide formation method characterized by simultaneous irradiation with a molecular beam or an oxygen (O□) molecular beam containing ozone, an electron gun evaporation device in a vacuum chamber for generating silicon molecules, and an ozone molecular beam generation This silicon oxide forming apparatus is characterized by comprising a reaction tube capable of irradiating ultraviolet light and a nozzle connected to the reaction tube for spouting ozone into a vacuum chamber. Furthermore, if a silicon epitaxial layer is grown on the substrate by a molecular beam growth method before silicon oxide is formed by the above method, the interface between silicon oxide and silicon can be made good.

(Operation) The principle of the present invention will be explained. 02 molecules easily dissociate and adsorb onto clean surfaces even at low temperatures near room temperature. However, in conventional substrate thermal oxidation, oxidation occurs at the interface between 5iOz and substrate Si crystals, so a lot of energy is required to diffuse oxygen in 5iO2 and break the back bond of substrate crystalline Si, which causes oxidation. It determines the temperature and time. As shown in Figure 2, when molecular Si and O2 are simultaneously supplied from the surface side, oxidation always occurs at the surface.
Moreover, since there is no need to cut the back bond of the Si substrate on which the crystal is assembled, the oxide film can be formed at low temperatures. but,
In the above oxide film formation method, an electron gun type evaporation device is used as the Si molecule generation source, so it is difficult to increase the partial pressure of oxygen that is irradiated simultaneously with Si molecules to more than 1 x 10-'Torr. When growing in a very dilute oxygen atmosphere, the oxygen concentration incorporated into the film was highly dependent on the growth temperature, and the lower the growth temperature, the higher it was. Furthermore, even when grown in a greenhouse, the oxygen concentration in the film is lower than the stoichiometry of 5102 because the amount of oxygen is insufficient. Such an oxide film had a low breakdown voltage and a large soak current. Therefore, in order to increase the oxidizing power of oxygen, the inventors introduced oxygen into ozone or ozone and oxygen molecular beams by flowing oxygen into a synthetic quartz reaction tube irradiated with ultraviolet light, as shown in Figure 1. It has been found that when the oxide film is supplied as a mixture of the following, the oxygen concentration in the formed oxide film increases dramatically compared to the case where the 02 molecular beam is irradiated. The film grown in this way has a growth temperature of 300°C.
However, the oxygen concentration in the film matched the stoichiometry of 5i02, and the breakdown voltage, leakage current, and interface state density were comparable to those of the oxide film formed by thermal oxidation.

This method does not oxidize the substrate Si, and since Si is also supplied from the surface, the substrate does not need to be Si.
Similar oxide films were also obtained on other materials, such as compound semiconductors.

(Example) Examples of the invention will be specifically described. The experiment is 40c
Molecular beam growth (MBE) equipped with an electron gun type Si evaporator
This was done using a device. The sample wafer has a 4-inch n-type 5
i(100), (111) 0.01 to 0.02 Ωcm substrates were used.

After RCA cleaning, the sample wafer was transported into the formation chamber, and after depositing 10 A-8I layers, it was cleaned for 800°011 minutes, the cleaned surface was exposed, and an epitaxial layer as a buffer layer was formed at a growth temperature of 500°C. We have grown by 3,000 people. After lowering the substrate temperature to the forming temperature, oxygen containing 30 to 40% ozone is leaked into the forming chamber from the nozzle, and an S of 0.55 A/S (converted to a forming rate of 5 in 2) is released from the electron gun type Si evaporator.
An oxide film was formed on the clean surface by irradiation with i-molecule beam. The oxygen partial pressure was kept constant at 5×10 Torr, and the formation temperature was changed from room temperature to 7.
The temperature was varied up to 50°C. The thickness of the film formed was approximately 1,000 people. Ozone was formed by introducing oxygen with a purity of 99.9999% into a synthetic quartz reaction tube and irradiating it with a Hg-Xe lamp with an output of IKW. The oxygen flow rate was 31/min, and the ozone concentration at this time was 30 to 40%.

First, xPS observation was performed to investigate the composition of the formed film. The membrane pressure was kept constant for 100 people. 5i in Figure 2
2p shows changes in core level peak. As can be seen from the figure, as the temperature (formation) decreases by 1 degree, the 5i2p peak shifts to the higher energy side and becomes the peak position corresponding to SiO at room temperature. It can be seen from this that the lower the formation temperature, the closer the film composition becomes to 5i02. In addition, in the 5i2p spectrum formed at room temperature and at 200 °C, 8102
On the low energy side of the peak, there is no shoulder seen in films obtained only by oxygen irradiation, indicating that these films are completely made of Si.
It was found that the O2 stoichiometry was met. Next, we investigated the electrical properties of the oxide film formed by this method. FIG. 3 shows the substrate temperature dependence of the characteristics. When the board temperature is room temperature or 200°C, the leakage current is small and no breakdown occurs even at 70V, but when the board temperature exceeds 400°C, breakdown occurs immediately and the leakage current also increases. I found out that there are many. The reason why the electrical characteristics deteriorate at 400° C. is considered to be because the composition deviates from SiO□ at this temperature, as seen from the xPS data shown in FIG. Furthermore, when comparing those grown at room temperature and those grown at 200°C, the one grown at 200°C has less leakage current. This is considered to be because a higher growth temperature allows a more honeyed film to be formed in a region where the stoichiometry is appropriate.

Next, in order to compare the films formed in the O2 atmosphere and the films formed in the O3 atmosphere, the film thickness dependence of the characteristics of the films formed by each method was investigated. Film thickness is 200 and 500
The number of people was 1,000. Figure 4 shows the results. a) is 5
A film formed in an 02 atmosphere of ×lO°5 Torr, b) is a film formed in an 02 atmosphere containing 03 of 5×10′ Torr. From this, it can be seen that the leakage current of the film formed in the 02 atmosphere containing 03 is lower than that of the film formed in the 02 atmosphere by more than three orders of magnitude, and the breakdown current is also larger.

Finally, in order to evaluate the flatness of the 5i02/Si interface formed by this method, three
After growing an epitaxial buffer layer of 0.000%, the growth temperature is 200°C and 5 x 10'Torr.
250 SiO□ were formed in an atmosphere of

Because the buffer layer was grown by MBE, the interface was extremely flat, and when a normal 5i (100) wafer was used, the only disturbance at the interface was a one-atomic layer step that would be observed every few hundred. This is what is present on the original MBE growth buffer layer. The density of this one-atomic layer step depends on the slope of the wafer surface and is exactly
When using surfaces, it was possible to obtain a flat terrace for several thousand people. In this way, after growing an epitaxial buffer layer by MBE, the interface state density of a MOS capacitor formed with SiO was estimated by the CV method, and it was found to be 10
am' level, and was equivalent to the interface obtained by thermal oxidation.

Note that in this example, silicon wafers were targeted;
The method of the present invention uses 5O8(
Silicon on 5apphire) substrates and more generally 5OI (Silicon on In5ulat) substrates.
or) Of course, it can also be applied to substrates, etc. In addition, since this method does not oxidize the substrate Si but also supplies Si from the surface, the substrate does not essentially need to be Si, and a high-quality oxide film can be obtained on a compound semiconductor as well. It was confirmed.

(Effects of the Invention) As described above in detail, according to the present invention, oxidation is always performed on the surface, so there is no need to cut the substrate Si back bond or diffuse oxygen in the oxide film, so
An oxide film electrically equivalent to a thermal oxide film can be formed even at a low growth temperature of from 300°C. Furthermore, by forming an oxide film on the Si epitaxial buffer layer, it is possible to obtain an atomically flat interface between the oxide film and silicon. If oxygen (O2) is irradiated with ultraviolet rays and then Si is supplied together with a Si molecular beam as an oxygen source molecular beam, an oxide film with good sweetochiometry can be obtained.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the apparatus of the present invention. Figure 2 shows the 5i2p of xPS when the growth temperature is changed.
Figure 3 shows the dependence of ■characteristics on substrate temperature; Figure 4 shows (a) and (b) the dependence of ■characteristics on film thickness of silicon oxide film. FIG. 3 is a diagram showing the film thickness dependence of the ■characteristics for a film formed in a 0□ atmosphere and a film formed in an O3 atmosphere.

Claims (1)

[Claims] 1. Silicon (Si) molecular beams and ozone (O_3
) A silicon oxide forming method characterized by simultaneous irradiation with a molecular beam or an oxygen (O_2) molecular beam containing ozone. 2. Oxidation characterized by comprising the steps of growing a Si epitaxial layer on a substrate by a Si molecular beam growth method, and forming silicon oxide on this Si epitaxial layer by the method according to claim 1. Silicon formation method. 3. A vacuum chamber in which a substrate can be installed is equipped with an electron gun evaporation device for generating silicon molecular beams and a nozzle for generating ozone molecular beams, and the nozzle is connected to a reaction tube having an oxygen inlet, and the reaction tube is connected to the inside of the reaction tube. 1. A silicon oxide forming apparatus comprising: ultraviolet light irradiation means capable of irradiating gas introduced into the silicon oxide forming apparatus.