JPH02172226A - Method and apparatus for forming silicon oxide film - Google Patents

Abstract

PURPOSE:To facilitate formation of a high quality silicon oxide film which can be made to grow under a low temperature and has a flat boundary surface by a method wherein a substrate is placed in a vacuum chamber in which a molecular beam can be formed and a silicon molecular beam and an oxygen molecular beam are simultaneously applied to the substrate surface to form the silicon oxide film. CONSTITUTION:Oxygen is supplied as oxygen ions or mixture of oxygen ions and an oxygen molecular beam by using an ECR plasma ion source while an Si molecular beam is applied by using an electron gun type evaporator 5 and a voltage is applied to a substrate to implant the oxygen ions into the substrate 3 and a silicon oxide film is formed. With this constitution, a high quality oxide film electrically equivalent to a thermal oxide film can be formed under a growth temperature as a low as 300-400 deg.C. Moreover, by forming the oxide film on an epitaxial buffer layer, the boundary surface between the oxide film and silicon which has a flatness of an atomic order can be obtained.

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.

(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 5i02 particles that accumulate on the substrate, so that many vacancies (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, because the silicon surface was not cleaned, there was a problem that there was a high density of interface states, making it impossible to use it in places where high-quality oxide films were required, such as MOSFET gate oxide films. .

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate such conventional drawbacks,
An object of the present invention is to provide a method for forming a high-quality silicon oxide film that can be grown at low temperatures and has a flat interface.

(Means for Solving the Problems) The present invention provides a method of forming a substrate by placing a substrate in a vacuum container in which molecular beams can be formed, and simultaneously irradiating silicon molecular beams and oxygen molecular beams onto the surface of the substrate. The present invention provides a method for forming a silicon oxide film characterized in that it is formed by simultaneously irradiating oxygen ions or an oxygen molecular beam containing oxygen ions as an oxygen source. Furthermore, by the method of growing a silicon epitaxial buffer layer before forming a silicon oxide film using the method described above to form a silicon oxide film, a good interface between the oxide film and Si can be obtained. It is characterized by being equipped with an electron gun type evaporation device for generating silicon molecular beams and a nozzle for generating oxygen molecular beams. Another silicon oxide film forming apparatus includes means for applying a potential to the substrate, and is equipped with an electron gun type evaporation apparatus for generating silicon molecular beams and a plasma ion source for generating oxygen ions. This is what we provide.

(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 5i02 and the substrate Si crystal, so a lot of energy is required to diffuse oxygen in 5i02 and break the back bond of the substrate crystalline Si, which causes oxidation. It determines the temperature and time. Therefore, the inventors added molecular Si and 02 from the surface side.
When supplied at the same time, oxidation always occurred at the surface;
Moreover, it was discovered that the oxide film could be formed at low temperatures because there was no need to cut the back bond of the Si substrate on which the crystal was assembled.

In addition, unlike the deposition of oxide films by vapor phase growth, this method is performed in the molecular beam region.
It was found that this method is an oxidation of i, and that a more honeyed film can be formed compared to vapor phase growth. Furthermore, by growing a Si buffer epitaxial layer using SiMBE before forming SiO2, the 5i02/Si 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 transition layer. The resulting interface state density could be reduced.

In the oxide film forming method as described above, since an electron gun type evaporation device is used as a Si molecule generation source, it is difficult to raise the partial pressure of oxygen to be irradiated simultaneously with Si molecules to more than 1X10-6 Torr. In this way, when growing in a very dilute oxygen atmosphere, the oxygen concentration taken into the film largely depends on the growth temperature, and becomes higher as the growth temperature is lower. Furthermore, even if grown at room temperature, the oxygen concentration in the film is lower than the stoichiometry of 5i02 because the amount of oxygen is insufficient.

Such an oxide film has a low breakdown voltage and a large leakage current.

Therefore, as shown in Figure 1, if a nozzle is used to generate an oxygen molecular beam, the oxygen partial pressure near the sample substrate can be reduced by 5.
It was possible to increase the oxygen concentration to X 10' Torr, and in room temperature growth, the oxygen concentration could be brought close to the stoichiometry of 5i02. Using this method, the oxide film grown at room temperature showed electrical properties comparable to those of oxide films formed by vapor phase growth. However, since it is formed at room temperature, there are many voids in the film, and its electrical characteristics are worse than that of a thermally oxidized film.

Next, as shown in Figure 2, the inventor used an ECR plasma ion source to irradiate oxygen with Si molecular beams using an electron gun type evaporation device, or to mix oxygen ions and oxygen molecular beams. It has been found that when oxygen ions are implanted into the substrate by applying a voltage to the substrate, the oxygen concentration in the formed oxide film increases dramatically, especially when grown at high temperatures. In the film grown in this way, even at a growth temperature of 400°C, the oxygen concentration in the film is 5i02
It was possible to create an oxide film with breakdown voltage, leakage current, and interface state density comparable to that of an oxide film formed by thermal oxidation.

In this method, the Si substrate is not oxidized, and since Si is also supplied from the surface side, the substrate does not need to be Si, and a similar oxide film can be obtained even on a compound semiconductor.

(Example) Examples of the present invention will be specifically described. 40 experiments
The experiment was carried out using the apparatus shown in FIG. 1, which is a modified MBE apparatus equipped with a CC electron gun type Si vapor deposition apparatus. The sample wafer has a 4-inch n-type 5i (100), (111) 0.01 to 0.0
A 2Ωcm substrate was used. After RCA cleaning, the sample substrate 3 was transferred to the vacuum container 1, and after depositing 10 A-8Is, it was heated at 800°.
Clean for 1 minute, expose the clean surface, and increase the growth temperature to 50
Aooo the epitaxial layer which is a buffer layer at 0°C
A.I grew up. After lowering the substrate temperature to room temperature, oxygen with a purity of 99.9999% is leaked into the vacuum chamber from the nozzle 4, and from the electron gun Si evaporation device 5, the rate of 5i02 formation is 0.
．． An oxide film was formed on the clean surface by irradiating with a Si molecular beam at a rate of 55 people/s. The oxygen partial pressure was kept constant at 5×10 −5 Torr, and the formation temperature was varied from room temperature to 750°C. The thickness of the formed film was about 1000. Note that the substrate was heated by a heater (not shown) built into the substrate holder 2.

FIG. 3 shows the relationship between formation temperature and refractive index. When the formation temperature was 700°C or higher, nothing was attached to the substrate. Clear interference colors were observed when the formation temperature was below 600°C. The lower the formation temperature, the closer the refractive index is to the refractive index of 5i02, and when formed at room temperature, it matched the refractive index of 5i02. This result is considered to be due to the fact that when the formation temperature is low, the oxygen concentration in the film increases and the refractive index approaches 5i02 because it approaches the stoichiometry of SiO2. Therefore, at low temperatures near room temperature, oxygen molecules really dissociate and 5i0
In order to check whether 2 is formed, the formation temperature was set to 6.
XPS shows the composition of the film when changing from 00°C to room temperature.
I looked it up. The film thickness was kept constant for 100 people. 5i2 in Figure 4
FIG. 5 shows the peak change in the O1s core level. As can be seen from the figure, as the formation temperature decreases, the 5i2p peak shifts to the higher energy side and becomes the peak position corresponding to 5i02 at room temperature. Further, the oxygen 1s peak becomes higher as the formation temperature decreases, and the peak position shifts to the higher energy side and becomes the 5i02 position at room temperature. From the above, it can be seen that the lower the formation temperature, the higher the oxygen concentration in the film, which approaches the stoichiometry of 5i02. However, in the 5i2p spectrum formed at room temperature, a shoulder can be seen on the low energy side of the 5i02 peak, indicating that this film does not completely match the stoichiometry of 5i02 and that 5i-8i bonds also exist. . Next, we investigated the electrical properties of the oxide film formed by this method. FIG. 6 shows the relationship between the dielectric constant determined from the capacitance and the formation temperature.

Similar to the refractive index, the lower the formation temperature, the higher the relative permittivity of SiO□
approached. FIG. 7 shows the relationship between breakdown voltage and formation temperature. The lower the forming temperature, the higher the withstand pressure, and the final breakdown is up to 7M when the forming temperature is 230°C.
V/am, which was comparable to that of an oxide film grown by vapor phase growth. However, when the formation temperature was lowered to room temperature, the withstand voltage decreased and leakage current increased. When the formation temperature is lowered to room temperature,
Leakage current and breakdown voltage deteriorate when grown at room temperature at 5i.
This is thought to be because there are many holes in 02.

Furthermore, in order to match the stoichiometry of SiO2 without reducing the oxygen concentration in the high growth temperature range where voids are not formed, a magnet 25 and a waveguide 2 as shown in FIG.
7. An ECR plasma ion source composed of an oscillator 26 was attached to the MBE apparatus (vacuum vessel 1), and oxygen was ionized and supplied. The ionization rate at this time was about 40%. The oxygen partial pressure in the ECR plasma chamber is I x 1O-4
Torr, oxygen partial pressure near the substrate 3 is 5X10-5 Torr
It was r. At this time, a voltage of +500 .mu. was applied to the substrate, and oxygen ions were injected into the substrate at a low rate. FIG. 3 shows the relationship between the growth temperature and refractive index of the oxide film grown in this manner, and FIG. 6 shows the relationship between the growth temperature and dielectric constant. Both the refractive index and the breakdown voltage matched the values of 5i02 when the formation temperature was 400°C or less. Furthermore, as shown in Figure 7, the breakdown voltage is
The maximum voltage was 11 MV/am from 00°C to 400°C, and the leakage current was also small. This value is comparable to that of a thermal oxide film.

Finally, in order to evaluate the flatness of the 5i02/Si interface formed by this method, three
After growing an epitaxial buffer layer of 000 layers, 5i0 of 50 layers 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. Since the buffer layer is grown by MBE, the interface is extremely flat.
When a normal 5i (100) wafer was used, the disturbance at the interface was only one atomic layer step observed every several hundred wafers. 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 if the just plane is used accurately, a flat terrace of several thousand layers can be obtained.

In this way, after growing the epitaxial buffer layer by MBE, the interface state density of the 5i02 MOS capacitor was measured by the Cv method, and it was found to be 1010 cm-2.
It was similar to the interface obtained by thermal oxidation.

Note that although silicon wafers were targeted in this example,
The method of the present invention uses 5O8 (5O8) where silicon exists only on the surface.
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, a silicon oxide film is formed using a Si molecular beam and an oxygen molecular beam.
A high-quality oxide film electrically equivalent to a thermal oxide film can be formed at a low growth temperature of 0°C to 400°C. Furthermore, by forming the layer on the epitaxial buffer layer, it is possible to obtain an oxide film-silicon interface that is flat on the atomic order.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the apparatus of the present invention, Figure 2 is a conceptual diagram of the apparatus of the present invention, Figure 3 is a diagram showing the relationship between the formation temperature and the refractive index, and Figure 4 is the growth temperature. Figure 5 is a diagram showing changes in the 5i2p core level spectrum of XPS when changing the growth temperature. Figure 6 is a diagram showing changes in the 01s core level spectrum of XPS when the growth temperature is changed. Figure 7 is a diagram showing the relationship between the dielectric constant and the formation temperature determined from
It is a figure showing the relationship between breakdown voltage and formation temperature. In the figure, 1... Vacuum container, 2... Substrate holder, 3... Substrate, 4... Nozzle, 5... Electron gun type evaporation device, 6...
・02 cylinder, 7...02 line, 8...valve,
25...Magnet, 261.・Oscillator, 27...
Waveguide, 28... antenna.

Claims (5)

[Claims] (1) Place the substrate in a vacuum container that can form molecular beams,
A method for forming a silicon oxide film, which comprises forming a silicon oxide film on a substrate by simultaneously irradiating the substrate with a silicon molecular beam and an oxygen molecular beam. (2) Place the substrate in a vacuum container that can form molecular beams,
A method for forming a silicon oxide film, which comprises forming a silicon oxide film on the substrate by simultaneously irradiating the substrate with a silicon molecular beam and simultaneously irradiating oxygen ions or an oxygen molecular beam containing oxygen ions. (3) Place the substrate in a vacuum container that can form molecular beams,
After growing a silicon epitaxial buffer layer by irradiating silicon molecular beams on this substrate, while irradiating silicon molecular beams in the same vacuum chamber, oxygen molecular beams,
Alternatively, a method for forming a silicon oxide film comprising forming a silicon oxide film on a substrate by simultaneously irradiating oxygen ions or an oxygen molecular beam containing oxygen ions. (4) A vacuum container equipped with a substrate holding part, an electron gun type evaporation device for supplying a silicon molecular beam into the vacuum container, and a nozzle for supplying an oxygen molecular beam. Silicon oxide film forming equipment. (5) A vacuum container equipped with a substrate holder, a means for applying a potential to the substrate, an electron gun type evaporation device for supplying a silicon molecular beam into the vacuum container, and a plasma ion source for supplying oxygen ions. A silicon oxide film forming apparatus comprising: