JPH0813718B2 - Silicon molecular beam growth method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a silicon molecular beam, and more particularly to selective phosphorus doping of silicon using a gas source.

(Prior Art) In the silicon molecular beam epitaxial growth method, a method of heating solid silicon with an electron beam has been conventionally used as a method of generating a silicon molecular beam. In such solid source silicon molecular beam epitaxial growth, doping into the epitaxial film is performed by simultaneously supplying an extremely small amount of dopant from the Knudsen cell containing the dopant during growth. However, in this case, it is necessary that the vapor pressure of the dopant can be appropriately controlled by the heating temperature of the Knudsen cell. Arsenic, phosphorus and antimony are often used as n-type dopants in silicon crystals. However, since the vapor pressure of arsenic and phosphorus was too high, doping with a conventional Knudsen cell was impossible. Therefore, in the conventional silicon molecular beam epitaxial growth method, only antimony can be used as the n-type dopant. Compared with antimony arsenic and phosphorus, it has a lower solid solubility limit and is more likely to diffuse. Therefore, for example, an emitter layer of an npn bipolar transistor that requires steep and n-type high-concentration doping is formed using the silicon molecular beam epitaxial growth method. It was impossible. In addition, since selective growth is impossible with the silicon molecular beam epitaxial growth method using a solid source, it is not possible to form a selective phosphorus-doped silicon epitaxial film only on the exposed silicon portion of a silicon substrate partially covered with an oxide film. It was impossible.

For this reason, in the conventional technique, when a heavily doped layer of phosphorus is formed, a method of implanting phosphorus into an epitaxial layer formed in advance by a method of ion plantation and activating it by heat treatment has been used.

(Problems to be Solved by the Present Invention) Since the conventional silicon molecular beam epitaxial growth method cannot perform phosphorus doping and selective growth is impossible, the emitter layer of the npn type bipolar transistor cannot be formed. In addition, in the alternative ion implantation method, it is impossible to selectively dope only the exposed silicon portion corresponding to the emitter region in the silicon substrate partially covered with the oxide film, and the high temperature for activation after ion plantation is required. Since the heat treatment is required, there is a problem that the doping profile formed in the substrate is blurred by thermal diffusion.

(Means for Solving Problems) In the present invention, in the gas source silicon molecular beam growth method, phosphine is supplied simultaneously with the source gas to perform phosphorus doping of the silicon layer, and in the gas source silicon molecular beam growth method, selective growth is performed. It is possible to provide a method for forming a silicon film selectively phosphorus-doped only on the exposed silicon portion of a silicon substrate partially covered with an oxide film by utilizing the possibility.

(Operation) If a silicon source molecular beam epitaxy method of a gas source method is used as a silicon growth method, a substance in a gas state which cannot be used in the conventional solid source silicon molecular beam epitaxy method can be used as a dopant. If the dopant can be supplied in a gas state, the doping concentration can be controlled by controlling the flow rate, and it becomes possible to use phosphorus as a dopant, which was not available in the conventional solid source molecular beam growth method due to the vapor pressure. Phosphorus becomes a gas at room temperature when it forms a phosphine molecule made of three hydrogen atoms bonded to one phosphorus atom.
Therefore, this phosphine can be used as a source of phosphorus. 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. The probability of collision between gas molecules is also very low. Therefore, this is different from the growth process in the normal chemical vapor reaction growth method in which gas molecules are dissociated in the gas phase and reach the substrate. In gas source silicon molecular beam epitaxial growth, all gas molecules reach the substrate without being decomposed in the gas phase. The gas molecules contribute to the growth by receiving thermal energy and dissociatively adsorbed on the substrate. Dissociative adsorption on the substrate surface occurs due to the reaction between chemically active dangling bonds on the silicon surface and gas molecules. The same applies to the phosphine molecule of the dopant gas. Active dangling bonds necessary for this dissociative adsorption process exist on the clean silicon surface but do not exist on the oxide film. Therefore, in the gas source silicon molecular beam epitaxial growth method, phosphine can be supplied simultaneously with the source gas to form a silicon epitaxial film selectively phosphorus-doped only on the exposed silicon portion of a silicon substrate partially covered with an oxide film. It will be possible. Furthermore, since the gas-source silicon molecular beam growth method allows epitaxial growth even at a low temperature of 600 ° C., the process temperature for obtaining a selective phosphorus-doped layer can be kept low compared to ion plantation.

(Example) The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram of a gas source silicon molecular beam growth apparatus for explaining an embodiment of the present invention. A 4-inch p-type Si (100) wafer 1 was used as the substrate. This substrate is loaded into the gas source silicon molecular beam growth apparatus 2. This silicon substrate is heated at 900 ° C. for 10 minutes by the heater 3 on the back side of the substrate in the ultrahigh vacuum silicon molecular beam growth apparatus. This process results in a clean Si (100) surface. The cleanliness of the surface can be observed by observing the characteristic 2 × 1 surface superstructure on the clean Si (100) surface in the diffraction pattern of the reflection high-energy electron beam diffractometer composed of the high-speed electron gun 4 and the fluorescent screen 5. confirmed. The silicon substrate is maintained at 630 ° C. on this clean surface, and disilane, which is a source gas for silicon growth, is supplied from the gas cell 6. 5% phosphine diluted with silane is used for phosphorus doping. This phosphine gas is supplied from the phosphine gas cylinder 7 to the sub chamber 8. At the same time, disilane is also supplied from the disilane gas cylinder 9 to the sub chamber, and these are mixed in the sub chamber and irradiated from the gas cell toward the substrate. The flow rate of disilane gas supplied to the sub-chamber was 41 sccm, and the flow rate of silane-diluted phosphine was changed in the range of 0 to 0.5 sccm by the needle valve 10. The substrate is partially irradiated with this.
The flow rate of gas emitted from the gas cell toward the substrate is ~ 1s.
It is ccm.

Fig. 2 shows a film thickness of 0.4μ formed on a Si (100) substrate partially covered with an oxide film of 1μm by the above method.
The result of secondary electron scanning microscope observation of the surface and cross section of the epitaxial film of m is shown in a schematic view. As is apparent from the figure, it was found that even when phosphine doping was performed, the epitaxial film selectively grew only in the silicon opening.

FIG. 3 shows a pn diode composed of a substrate and a phosphorus-doped n-type silicon epitaxial film selectively grown on the p-type Si (100) substrate partially covered with an oxide film obtained in FIG. It shows the current-voltage characteristics. As is clear from the figure, the epitaxial film obtained by using this method exhibits good pn diode characteristics. It can be seen that epitaxial films selectively doped with phosphorus in these silicon openings are obtained.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to form a silicon epitaxial film selectively phosphorus-doped only on the exposed silicon portion of a silicon substrate partially covered with a mask material.

[Brief description of drawings]

FIG. 1 is a schematic view of a gas source type silicon molecular beam epitaxial growth apparatus for explaining an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are silicon epitaxial films produced in the embodiment of the present invention. FIG. 3 is a schematic view of a secondary electron scanning micrograph of each surface and cross section of FIG. 3, and FIG. 3 is a view showing current-voltage characteristics of the pn diode manufactured in the example.
In the figure, 1 is a Si substrate, 2 is a gas source silicon molecular beam growth apparatus, 3 is a substrate heater, 4 is a high-speed electron gun for reflection high-energy electron diffraction, 5 is a fluorescent screen, 6 is a gas cell, 7
Is a phosphine gas cylinder, 8 is a sub-chamber, 9 is a disilane gas cylinder, and 10 is a needle valve.

Claims (1)

[Claims] 1. In a silicon molecular beam growth method, a silane-based gas and a phosphine gas diluted with the silane-based gas are supplied onto a silicon substrate partially covered with the mask to cover the silicon substrate with the mask. A silicon molecular beam growth method characterized in that a phosphorus-doped silicon film is selectively formed only on a non-existing portion.