JPH02296797A - Formation of selective boron-doped layer - Google Patents

Abstract

PURPOSE:To allow the selective growth of a boron-doped layer by growing Si by a molecular beam epitaxial method for gaseous source Si on a Si partially coated with a film material and simultaneously doping boron thereto by using HBO2. CONSTITUTION:For example, a 4-inch n type Si (100) substrate 1 is loaded in a molecular beam growth device 2 for gaseous source Si. The substrate 1 is then heated for 10 minutes at 900 deg.C by a heater under the rear side of the substrate in the device 2 in which an ultra-high vacuum is maintained. The substrate 1 is kept at 630 deg.C and gaseous disilane is supplied from a gas cell 6 to the clean surface thereof obtd. in such a manner. An HBO2 Knudsen cell 7 is used for the purpose of boron doping and is heated to 700 deg.C. The flow rate of the gaseous disilane supplied to a sub-chamber 8 is regulated to 41sccm and the flow rate of the gas to be projected from the cell 6 toward the substrate 1 is regulated to nearly 1sccm. The B-doped selective epitaxial film 10 is formed on the substrate 1 partially coated with the oxide film 9 by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to silicon epitaxial growth selectively doped with boron.

(Prior Art) In the silicon molecular beam epitaxial growth method, a method of heating solid silicon with an electron beam has conventionally been used as a method of generating silicon molecular beams. In such solid source silicon molecular beam epitaxial growth, the epitaxial film is doped by simultaneously supplying a very small amount of dopant from a Knudsen cell containing the dopant during growth. Boron is often used as a p-type dopant in silicon crystals. However, selective growth is not possible with the silicon molecular beam epitaxial growth method using a solid source, so it is necessary to form a boron-doped silicon epitaxial film selectively only on the exposed silicon parts of a silicon substrate partially covered with an oxide film. was impossible. For this reason, for example, when creating a high-speed npn bipolar transistor, it is desirable to epitaxially grow a p-type base layer on a self-line using an oxide film pattern, but conventional silicon molecular beam growth technology cannot meet these demands. Ta.

(Problems to be Solved by the Invention) A problem to be solved by the present invention is to realize selective growth of a boron-doped layer, which was impossible with the conventional silicon molecular beam epitaxial growth method.

(Means for Solving the Problems) The present invention supplies boron from HBO2 at the same time as the source gas in the gas source silicon molecular beam epitaxial growth method to dope the epitaxial layer with boron. The present invention provides a method for forming a silicon epitaxial film selectively doped with boron only in the exposed silicon portion of silicon partially covered with a film material by taking advantage of the fact that it can grow.

(Function) In gas source silicon molecular beam epitaxial growth, the degree of vacuum during growth is 10-5 Torr or less, and under such a high vacuum, the gas is not in thermal equilibrium with the substrate temperature. Also, the probability of collision between gas molecules is extremely small. For this reason, the growth process in the usual chemical vapor phase reaction growth method, in which gas molecules dissociate in the gas phase and reach the substrate, cannot be applied. In gas source silicon molecular beam epitaxial growth, all gas molecules reach the substrate without being decomposed in the gas phase. These gas molecules contribute to growth by receiving thermal energy on the substrate and dissociating and adsorbing them. Dissociative adsorption on the substrate surface occurs due to the reaction between chemically active dangling bonds on the silicon surface and gas molecules.

The active dangling bonds necessary for this dissociation and adsorption process exist on the clean silicon surface, but not on the oxide film. Therefore, in the gas source silicon molecular beam epitaxial growth method, it is possible to selectively form a silicon epitaxial film only on exposed silicon parts of a silicon substrate partially covered with an oxide film. If boron is simultaneously supplied to the silicon substrate during selective growth by gas source silicon molecular beam growth, the selective epitaxial growth portion can be doped with boron. Boron doping is performed by evaporating HBO2 using a Knudsen cell. HBO2 is used because the vapor pressure of boron itself is too low to be doped from a Knudsen cell. HBO2 has a vapor pressure about three orders of magnitude higher than boron. When HBO2 is used for boron doping, it flies from the Knudsen cell to the substrate in the form of HBO2, dissociates on the substrate surface, and B is adsorbed to the surface. In this process as well, it is the dangling bonds on the surface that govern the dissociation and adsorption. For this reason, for the same reason that selective growth is possible in the gas source silicon molecular beam growth method mentioned earlier, boron doping using HBO2 is selected only for silicon openings on a silicon substrate with a pattern such as an oxide film. It happens. Therefore, when boron doping is performed using HBO2 in the gas source silicon molecular beam growth method, selective growth of a boron-doped layer becomes possible.

(Example) The present invention will be described below using the drawings. Figure 1 shows
FIG. 1 is a schematic diagram of a gas source silicon molecular beam growth apparatus for explaining the present invention in detail. The board is a 4 inch n-type 5i (
100) Wafer 1 was used. This substrate is loaded into a gas source silicon molecular beam growth apparatus 2. This silicon substrate is heated at 900° C. for 110 minutes using a heater 3 on the back side of the substrate in an ultra-high vacuum silicon molecular beam growth apparatus. This process results in a clean 5i (100) surface. The cleanliness of the surface is 2×, which is characteristic of a clean 5i (100) plane, in the diffraction pattern of a reflection high-speed electron diffractometer consisting of a high-speed electron gun 4 and a fluorescent screen 5.
This was confirmed by the observation of a 1-surface superstructure. Disilane, which is a source gas for silicon growth, is supplied from the gas cell 6 to this clean surface of the silicon substrate while maintaining the temperature at 630°C. HBO2 Knudsen cell 7 is used for boron doping. The temperature of the HBO2 cell was 700°C. The disilane gas flow rate supplied to the subchamber 8 was 41 seconds. A part of this is irradiated onto the substrate. The gas flow rate irradiated from the gas cell toward the substrate is ~lsecm.

Figure 2 shows a film with a thickness of 0 created on a 5L (100) substrate partially covered with an lpm oxide film by the above method.
．． The results of secondary electron scanning microscopy observation of the surface and cross section of a 4 μm epitaxial film are shown. As is clear from the figure, even when boron doping is performed, the epitaxial film grows selectively only in the silicon openings.

Figure 3 shows the partially covered n with oxide film obtained in Figure 2.
Type 5i (100) A p-
This figure shows the current-voltage characteristics of an n-diode. As is clear from the figure, the epitaxial film obtained using this method exhibits good pn diode characteristics. It can be seen from this that an epitaxial film is obtained in which the silicon openings are selectively doped with boron.

Note that the effectiveness of the present invention is determined when the substrate temperature is 600°C to 700°C.
Confirmed in the °C range. Further, the gas source may be not only disilane gas but also silane gas such as SiH4, 5i3HB, or halogen silane gas such as 5iH2CI2. Further, the film material used for the mask is not limited to an oxide film, but may be any film material other than silicon, such as a nitride film.

(Effects of the Invention) As described in detail above, according to the present invention, a boron-doped silicon layer grows due to the reaction between the chemically active dangling board on the silicon surface and the raw material, so that the silicon layer is partially coated with the film material. It becomes possible to form a silicon layer selectively doped with boron only in the exposed silicon portions of the covered silicon.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a gas source type silicon molecular beam epitaxial growth apparatus for explaining the present invention in detail, and FIG. 2 is a cross-sectional view of a selectively boron-doped silicon epitaxial film produced in an example of the present invention. FIG. 3 is a schematic diagram of a secondary electron scanning micrograph, and is a diagram showing the current-voltage characteristics of a pn diode composed of a boron-doped p-type dinocone epitaxial film and a substrate prepared in an example. In the figure, 1 is a 4-inch n-type 5i (100) substrate, 2 is a silicon molecular beam growth device, 3 is a substrate heater, 4 is a high-speed electron gun for reflective high-speed electron beam diffraction, and 5 is a fluorescent light for reflective high-speed electron diffraction pattern observation. Screen, 6 is gas cell, 7 is H
BO2 Knud Sensel, 8 is subchamber, 9 is 5
i02.10 is a B-doped selective epitaxial film.

Claims (1)

[Claims] (1) A method for forming a selective boron-doped layer, which comprises growing silicon on silicon partially covered with a film material by gas source silicon molecular beam epitaxial growth and simultaneously doping boron using HBO_2.