JPH0616492B2 - Method of manufacturing silicon thin film - Google Patents

Description

The present invention relates to a vapor phase growth method of silicon.
In particular, the present invention relates to a method for obtaining a silicon film by bringing a reactive species into a SiH ₂ ( ¹ A ₁ ) state and causing a surface reaction at a bridge site.

(Prior Art) In vapor deposition of silicon, a method of decomposing a source gas by plasma, light or heat to deposit silicon is adopted (Yamazaki et al. T. Yamazaki, T. It.
oh, and H. Ishikawa) IEEE Symposium on VLSI Technol. Dig. Tech pap
erspp 56-57 (1984)).

(Problems to be Solved by the Invention) Conventionally, there was no interest in reactive species generated during decomposition, and many reactive species generated by the above-described excitation method were used as they were. This is because it was not known that only a specific reactive species interacts with the solid surface to cause a surface reaction during film formation. Some of the reactive species supplied to the substrate surface do not participate in the deposition and consequently interfere with the deposition. Therefore, a fairly high temperature is required to form a good quality film, and the deposition rate is high. It is limited.

(Means for Solving the Problems) The present invention is to form a film by utilizing one of the generated reactive species in the SiH ₂ ( ¹ A ₁ ) state. SiH ₂ ( ¹ A ₁ ) generated from the silicon source gas is an electronic state with a high charge distribution on the molecular surface, and it is 3p perpendicular to the molecular surface from two dangling bonds at the bridge site on the substrate surface. When charges are supplied to the orbits, the state changes to the SiH _2- ( ² B ₁ ) state, and the bond between Si and H easily breaks. By utilizing this reaction process, the film formation of silicon can be effectively performed at a low temperature.

(Function) The surface reaction site is determined by the non-bonded electrons of the reaction species and the spatial expansion of dangling bonds on the crystal surface. In SiH ₂ ( ¹ A ₁ ), two unbonded electrons have antiparallel spins in one sp ² hybrid orbital.

The silicon (001) surface has two dangling bonds <11.
It consists of surface atoms in the 0> direction. The reactive species is SiH ₂ (
The surface reaction in the case of ¹ A ₁ ) occurs at the bridge site in the <110> direction on the plane containing the dangling bond, as shown in FIG. Two electrons of sp ² hybrid orbital of SiH _{2 ⁽¹} A ¹⁾ creates a covalent bond with the dangling bonds of the two surface atoms, crystals from sp ² -like charge distribution of SiH _{2 ⁽¹} A ¹⁾ It has a sp ³ -like charge distribution of surface atoms. In addition, the direction in which two H atoms are aligned is the <10> direction and is adsorbed to this surface reaction site. The charge distribution of non-bonded electrons of SiH ₂ ( ¹ A ₁ ) has a high charge density on the molecular surface, and the dangling bond on the crystal surface tends to approach the 3p _π orbit.

By being adsorbed on the surface reaction site, SiH ₂ ( ¹ A ₁ ) changes, and the surface reaction (SiH ₂ ···> Si + H ₂ ) proceeds. In Fig. ₁ , the adsorption of SiH ₂ ( ¹ A ₁ ) causes the electrons of the dangling bond to enter the 3p _π orbit, and the reaction proceeds in the electronic state of SiH _2- ( ² B ₁ ). The mechanism is explained by the stable structure of the reactive species and the total energy and charge distribution. Table 1 shows the stable structures and total energies of SiH ₂ ( ¹ A ₁ ) and SiH _2- ( ² B ₁ ). The total energy of SiH _2- ( ² B ₁ ) is S
Lower than iH ₂ ( ¹ A ₁ ), the progress of the reaction is toward energy stabilization. In addition, as shown in Table 1, R of SiH _2- ( ² B ₁ )
The bond length of _SI-H is about 10% longer than that of SiH ₂ ( ¹ A ₁ ), which makes the dissociation reaction of H ₂ easier. Furthermore, the newly added electrons enter the 3p _π orbit, and the charge distribution is almost spherically symmetric around the Si atom as a whole. Therefore, when adsorbed, it is flat in the <110> direction sp ² -lik
The surface reaction proceeds in the process of changing from SiH ₂ ( ¹ A ₁ ) of e to a spherically symmetric SiH _2- ( ² B ₁ ) charge distribution, and then to a sp ³ -like charge distribution in the crystal. This type of reaction path is different from the usual decomposition reaction by thermal excitation and is caused by the unique charge distribution of SiH ₂ ( ¹ A ₁ ) .Therefore, there is an automatic dissociation path with no energy barrier on the reaction potential curved surface. It does not require thermal excitation to go through. Therefore, the film can be formed at a low temperature. Further, since the surface reaction site is limited to the bridge site, the homogeneous reaction that causes the generation of defects does not occur. Therefore, there are few defects.

(Example) An example in which SiH ₂ ( ¹ A ₁ ) is formed by photodissociation and low temperature epitaxial growth is performed will be described. As source gas,
SiH ₄ was used. The molecular orbitals of SiH ₄ are (1a ₁ ) ² , (2a ₁ ) ² , (1t ₂ ) ⁶ , (3a ₁ ) ² , (2t ₂ ) ⁶ , (a ₁ ^* ),
(t ₂ ^* ), Ry. Of these, (2t ₂ ) ⁶ is mainly responsible for Si-H bonds and is called valence electrons. The binding also has some contribution from (3a ₁ ) ² , which is sub va
It is called lence electrons. (1a ₁ ) ² to (1t ₂ ) ⁶ are core electrons and do not contribute to the bond. (a ₁ ^* ) (t ₂ ^* )
Is a dissociated state, which is an antibonding orbital. Ry is in the lidberg state. SiH ₂ ( ¹ A ₁ ) has 2t ₂ orbital a ₁ ^* or t ₂ ^*
It is obtained by exciting to. In this way, SiH ₄ dissociates and SiH ₂ ( ¹ A ₁ ) is generated despite the excitation of electrons not involved in the binding. The reason is that it drops and the bond between Si and H is broken. Which reactive species is generated depends on the orbit of the excited electron. In the case of this embodiment, 100 to 120 eV
Is equivalent to the light. A diagram of the equipment used is shown in FIG. 1 is 2
This is a molecular beam generator that uses the differential pumping of a stage, and has a substrate 2 and an extreme ultraviolet light introduction port 3 in the chamber of the third stage.
The SiH ₄ molecular beam is sent from the nozzle 4 through the slits 5 and 6. 7,8,9 are turbo molecular pumps. SiH ₄ molecules emitted from the nozzle 4 are synchrotron radiation (SR)
Excited by linearly polarized light of 100-120 ev irradiated through port 3 introducing the extreme ultraviolet light obtained by Si,
It becomes H ₂ ( ¹ A ₁ ) and collides with the substrate 2. SiH ₂ ( ¹ A ₁ ) easily grows epitaxially by charge transfer at the bridge site, as described above. The relationship between the epitaxial growth rate and the growth temperature is shown in FIG. For reference, the relationship between the epitaxial growth rate and the growth temperature in the case of a solid source is also shown in the figure. Further, since the single crystal film formed by this method is a coherent growth process, it has few defects. Figure 4 shows the defect densities compared to the case of normal molecular beam epitaxy.

(Effects of the Invention) As described above, the present invention is characterized by optimizing the reaction species and the reaction process in the method of manufacturing a silicon film.
This enables high-quality films to be realized at low temperatures, while increasing the epitaxial growth rate, and has high industrial application value for ULSI, which requires highly accurate material control.

[Brief description of drawings]

Figure 1 shows that it was adsorbed on the silicon (001) plane bridge site.
Schematic diagram showing SiH ₂ ( ¹ A ₁ ). FIG. 2 is a schematic view of the apparatus used in the examples. 1 is a molecular beam generator, 2 is a substrate, 3
Is an extreme ultraviolet light introduction port, 4 is a nozzle, 5, 6 are slits, 7,
8 and 9 are turbo molecular pumps. Third, a diagram showing the relationship between the epitaxial growth rate and the growth temperature in the example. FIG. 4 is a diagram showing defect densities in Examples.

Claims (1)

[Claims] ^1. A method of manufacturing a silicon thin film using silicon hydride as a source gas, wherein SiH ₂ ( ¹ A ₁ ) is generated from silicon hydride, and SiH ₂ ( ¹ A ₁ ) is generated by interaction with a substrate.
^₂ - ₍₂ B ₁₎ to varying manufacturing method of a silicon thin film characterized by depositing silicon.