JPH04139825A - Method and apparatus for forming silicon oxide film - Google Patents

Abstract

PURPOSE:To produce, at low temperature, a silicon oxide film equivalent to a thermal oxide film by heating a substrate in a vacuum chamber to remove spontaneous oxide from its surface, and irradiating the substrate with disilane molecules and oxygen molecules under the conditions preventing vapor phase reactions. CONSTITUTION:A substrate 21 is heated in a vacuum chamber 26 to remove spontaneous oxide from its surface. Under the conditions preventing vapor phase reactions, the substrate 21 is irradiated with disilane molecules and oxygen molecules to form silicon oxide film. Specifically, the substrate, kept at a voltage, is irradiated with an Si2H6 beam through a nozzle 27, and simultaneously irradiated with an oxygen beam that contains oxygen ions or a mixture of oxygen ions and oxygen from an ECR oxygen plasma ion source 23. According to this method, it is possible, even at a low temperature of 400 deg.C, to form a silicon oxide that shows the same dielectric strength, leakage current and surface level density as a thermal silicon oxide film does.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for forming a silicon oxide film using molecular beams.

[Conventional technology]

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. On the other hand, silicon oxide films can be formed at low temperatures by vapor phase growth.

[Problems to be Solved by the Invention] Among the above-mentioned seven methods for forming silicon oxide films, the method using thermal oxidation requires a high temperature of 800'C or more for thermal oxidation, and the excessive temperature of thermal oxidation causes the formation of impurities. There is a drawback that the impurity brochure formed in the substrate is destroyed by diffusion. On the other hand, in the vapor phase growth method, a reaction between silicon and oxygen occurs in the vapor phase, resulting in S]02 particles that accumulate on the substrate, resulting in a large number of voids in the oxide film. Because of this, the silicon oxide film formed by the vapor phase growth method has a lower breakdown voltage and more leakage current than a thermal oxide film.Furthermore, the silicon surface is not cleaned.
The problem is that it cannot be used in places where a high quality oxide film is required, such as an oxide film with a high interface state density and MO≦.

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 a high-quality silicon oxide film having a flat interface at a low temperature.

[Means to solve the problem]

In the first method of forming a silicon oxide film of the present invention, a substrate is placed in a vacuum container, a natural oxide film on the surface is removed by heating, and then disilane is added to the surface of the substrate under conditions that do not cause a gas phase reaction. A silicon oxide film is formed by simultaneously irradiating a molecular beam and an oxygen molecular beam.

In the second method of forming a silicon oxide film of the present invention, a substrate is placed in a vacuum container, a natural oxide film on the surface is removed by heating, and then disilane is applied to the surface of the substrate under conditions that do not cause a gas phase reaction. A silicon oxide film is formed by simultaneously irradiating oxygen ions or an oxygen molecular beam containing oxygen ions while irradiating a molecular beam.

In the third method of forming a silicon oxide film of the invention, a substrate is placed in a vacuum container, the surface of the substrate is irradiated with a disilane molecular beam to grow a silicon epitaxial buffer layer, and then transported within the same apparatus or in a vacuum. A silicon oxide film is formed by simultaneously irradiating an oxygen molecular beam, oxygen ions, or an oxygen molecular beam containing oxygen ions while irradiating a disilane molecular beam in a separate device.

The silicon oxide film forming apparatus of the present invention includes an electrode for holding a substrate and applying a potential, a nozzle for generating a disilane molecular beam, and a plasma ion source for generating oxygen ions.

[Effect]

The principle of the present invention will be explained. 02 molecules are easily separated and adsorbed onto clean surfaces even at low temperatures near room temperature. However, in the conventional substrate thermal oxidation method, oxidation occurs at the SiC2 and substrate Si crystal interface, so a lot of energy is required to diffuse oxygen in Si02 and break the back bond of the substrate crystal Si. , which determines the oxidation temperature and time. Therefore, the inventor started from the front side of the board by 10
- Molecular Si2H6 and 0 in the vacuum region below Torr
When 2 and 2 were supplied at the same time, the mean free path was larger than the chamber size (approximately 40 cm) and no gas phase reaction occurred, so oxidation always occurred between SiH6 adsorbed on the surface and 02. It was also discovered that an oxide film can be formed at low temperatures because there is no need to cut the hack bonds of the substrate Sj in which crystals are assembled. Unlike the deposition of an oxide film by vapor phase growth, in this method, the oxide film is formed within the molecular beam region irradiated onto the substrate surface, so 5j2I-16 and 02 It has been found that this reaction allows for the formation of thinner films than in vapor phase growth.

This is based on the following principle. When Si21-16 molecular beam is irradiated onto the 8j02 layer 1] as shown in Fig.
1” After being dragged to the metastable state of 2, it leaves again.

At this time, when the 02 molecular beam is also irradiated at the same time, Fig. 4(b)
As shown in
Molecules 12 and 02 molecules react to form 5j02. Since the partial pressure during growth is 10-'' to 10-3'rorr, there is a sufficient probability that 5j286 molecules and 02 molecules will collide on the surface.

At this time, the probability that these molecules will react and form 5i02 depends on the substrate temperature.

Furthermore, the surface is cleaned before SiO3 formation, and Si
By growing a Si buffer epitaxial layer using the MBE method, the 5i02/Sj interface can be made flat on the atomic order, reducing the breakdown voltage due to electric field concentration due to the unevenness of the interface and the interface due to the interfacial transition layer. It is not possible to reduce the level density.

Since the method for forming a silicon oxide film as described above uses a molecular flow region, it is difficult to increase the partial pressure of oxygen to be irradiated simultaneously with Si2H6 molecules to more than X10-3 Torr. As described above, growth in a very dilute disilane and oxygen atmosphere has the problem that a sufficient refining rate cannot be obtained when the substrate temperature is lowered.

Therefore, as shown in FIG. 1, the inventor irradiated Si2H6 molecular beam from the disilane gas nozzle 27, and
When oxygen was supplied as oxygen ions or a mixture of oxygen ions and oxygen molecular beams using the CR oxygen oxygen primer ion source 23 and a voltage was applied to the silicon substrate 2], oxygen ions were implanted into the silicon substrate. It has been found that the growth rate of silicon oxide film increases dramatically.

In the film grown in this way, even at a growth temperature of 400°C, the oxygen concentration in the film matches the stoichiometry of 5i02, and the breakdown voltage, leakage current, and interface state density are similar to that of a silicon oxide film formed by thermal oxidation. I was able to create something similar. This is because since oxygen is supplied in dissociated form, the reaction efficiency with Si2H6 molecules on the surface is promoted, especially at low temperatures.

In this method, Si for 5i02 formation is also supplied from the surface side of the substrate, rather than oxidizing the Si substrate, so the substrate does not need to be Si, and a similar silicon oxide film can be obtained even on a compound semiconductor. Ta.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a silicon oxide film forming apparatus for explaining one embodiment of the present invention.

In FIG. 1, a holding electrode 22 for holding and heating a silicon substrate 21 is provided in a vacuum container 26 via an insulating plate. And 28 disilane gas cylinders
There are provided a disilane gas nozzle 27 connected to a disilane gas nozzle 27, and an ECR oxygen plasma ion source 23 to which an oxygen cylinder 24 and a high frequency oscillator 25 are connected. A method for forming a silicon oxide film on a silicon substrate 21 using this apparatus will be described below.

The sample is 4 inch n-type 5i (100) (111) 0
．． A 01 to 0.02 Ωcm substrate was used. Silicon substrate 2
After RCA cleaning, the substrate No. 1 was transported into the formation chamber and held on the holding electrode 22, and cleaned at 860° C. for 10 minutes to expose the clean surface, and an epitaxial layer serving as a buffer layer was grown for 3000 A at a growth temperature of 600° C. After the substrate temperature has reached the growth temperature, oxygen and disilane with a purity of 99.9999% are leaked into the formation chamber from the oxygen cylinder 24 and the disilane gas nozzle 27 to form a silicon oxide film on the clean surface. Oxygen partial pressure is 5
X], 0'Torr was kept constant and the formation temperature was varied from 400'C to 800°C.

FIG. 2 is a diagram showing the relationship between formation temperature and formation rate.

As shown by straight line A in Fig. 2, the forming temperature is 600°C.
It was found that a practical formation rate can be obtained at a temperature of 400°C or higher, but it is extremely slow at a formation temperature of 400°C. Next, we investigated the electrical properties of the silicon oxide film formed by this method.

FIG. 3 is a diagram showing the relationship between the breakdown voltage and formation temperature of a silicon oxide film. As shown by straight line A in FIG. 3, the breakdown voltage increases as the formation temperature increases, and the final breakdown was IIMV/cm when the formation temperature was 600° C. or higher, which was comparable to that of an oxide film formed by thermal oxidation. However, the formation temperature is 40
When the temperature was lowered to 0'C, the withstand voltage decreased and the leakage current increased. The reason why leakage current and breakdown voltage worsen when the formation temperature is lowered to 400°C is thought to be because Si2H6 and 02 cannot react sufficiently at low temperatures, resulting in a state of SiOx (x>2). .

Furthermore, in order to improve the reaction efficiency of Si2H6 and 02 at low temperatures and to match the stoichiometry of Si02 without reducing the oxygen concentration, oxygen was added using the ECR oxygen plasma ion source 23 shown in FIG. was ionized and supplied. The ionization rate at this time was about 40%. The oxygen partial pressure in the ECR plasma chamber is], X10-'Torr, and the oxygen partial pressure near the silicon substrate 21 is 5X], 0" Torr
Met. At this time, +5000V is applied to the silicon substrate 21.
, and oxygen ions were implanted into the silicon substrate 21 at a low speed. The relationship between the formation temperature and formation rate of the silicon oxide film grown in this manner is shown by the straight line B in FIG. 2, and the relationship between the formation temperature and breakdown voltage is shown by the straight line B in FIG. growth rate,
A remarkable improvement in both the breakdown voltage and the formation temperature was observed when the formation temperature was 400° C., indicating that sending oxygen plasma was useful.

Next, in order to evaluate the flatness of the 5i02/Si interface formed by this method, a
After growing an epitaxial buffer layer of 00A, a SiO of 50A was grown using oxygen ions at a growth temperature of 300°C.
2 was formed and the cross-sectional lattice image of the interface was observed. The slanted interface on which the buffer layer is grown by MBE is extremely flat;
When using a normal 5i (100) substrate, the disturbance at the interface is
Only one atomic layer step was observed every few tens of OA. 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 substrate surface, and if a precisely sloped surface is used, a flat terrace of several thousand amps cannot be obtained. In this way, after growing the epitaxial buffer layer by MBE, the S
When the interface state density of the MOS capacitor in which iO□ was formed was measured by the CV method, it was on the order of 10 lOcm'', which was equivalent to the interface obtained by thermal oxidation.

Although this example targeted a silicon substrate, the method of the present invention applies to SOS (
Silicon on 5apphire) substrates and more generally SOI (Silicon on In5u) substrates.
Of course, it can also be applied to substrates etc. In addition, this method does not oxidize the substrate Si but also supplies Si from the surface side, so the substrate does not essentially need to be Sj, and a high-quality oxide film can be obtained on a compound semiconductor as well. It was confirmed.

〔Effect of the invention〕

As described above in detail, according to the present invention, a silicon oxide film electrically equivalent to a thermal oxide film can be formed at a low growth temperature of 300°C to 400°C. Also,
By forming it on the epitaxial buffer layer, it is possible to obtain an interface between the silicon oxide film and silicon that is flat on the atomic order.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a silicon oxide film forming apparatus for explaining an embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the formation rate and formation temperature of silicon oxide film, and Fig. 3 is a diagram showing the relationship between silicon oxide film formation rate and formation temperature. FIG. 4 is a diagram showing the relationship between film breakdown voltage and formation temperature, and is a cross-sectional view of a Sin layer for explaining the present invention in detail. DESCRIPTION OF SYMBOLS 11... SiO2 layer, 12... Disilane molecule truffled into a metastable state, 21... Silicon substrate, 22
...Holding electrode, 23...ECR oxygen plasma ion source, 24...Oxygen cylinder, 25...High frequency oscillator,
26... Vacuum container, 27... Disilane gas nozzle, 28... Disilane gas cylinder.

Claims (1)

[Claims] 1. After placing a substrate in a vacuum container and removing the natural oxide film on the surface by heating, disilane molecular beams and oxygen molecular beams are applied to the surface of the substrate under conditions that do not cause gas phase reactions. A method for forming a silicon oxide film, characterized by forming a silicon oxide film by simultaneously irradiating with. 2. After placing the substrate in a vacuum container and removing the natural oxide film on the surface by heating, oxygen ions or oxygen ions are added to the substrate surface while irradiating the substrate surface with a disilane molecular beam under conditions that do not cause gas phase reactions. A method for forming a silicon oxide film, comprising simultaneously irradiating oxygen molecular beams containing oxygen to form a silicon oxide film. 3. Place the substrate in a vacuum container, irradiate the surface of the substrate with a disilane molecular beam to grow a silicon epitaxial buffer layer, and then irradiate the substrate with a disilane molecular beam in the same device or in a separate device that can be transported in vacuum. A method for forming a silicon oxide film, characterized in that a silicon oxide film is formed by simultaneously irradiating oxygen molecular beams, oxygen ions, or oxygen molecular beams containing oxygen ions. 4. A silicon oxide film forming apparatus comprising an electrode for holding a substrate and applying a potential, a nozzle for generating a disilane molecular beam, and a plasma ion source for generating oxygen ions.