JPH0616493B2 - Silicon film formation method - 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 setting a reactive species in a ¹ A ₁ state and causing a surface reaction at a bridge site.

(Prior Art) In silicon vapor phase epitaxy, a method of decomposing a source gas by plasma, light or heat to deposit silicon is adopted. (Ishitani et al. (A. Ishitani e
al.), Applied Physics Letters (Appl.Phy
s.Lett.), 52, (1985) 2956) (Problems to be solved by the invention) Conventionally, there was no interest in the reactive species generated during decomposition, and many The reaction seed was used as it was. This is because it was not known that only a specific reactive species interacts with the solid surface in the film formation to cause a surface reaction. 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 Problems) The present invention is to form a film by utilizing ^{one of} the reactive species generated in the ¹ A ₁ state. SiCl ₂ ( ¹ A ₁ ) generated from a chlorine-based source gas of silicon has two unbonded electrons in an sp ² hybrid orbit, that is,
In the electronic state with a high charge distribution on the molecular surface, when charges are supplied from the two dangling bonds to the orbits perpendicular to the molecular surface at the bridge site on the substrate surface, it changes to the ² B ₁ state, The present inventors have found that the bond between Cl and Cl is easily broken and hydrogen is easily reduced. By utilizing this reaction process, the film formation of silicon can be effectively performed at a low temperature.

(Operation) The principle of the present invention will be described. The surface reaction site is determined by the non-bonded electrons of the reaction species and the spatial extent of the diggling bond on the crystal surface. In SiCl ₂ ( ¹ A ₁ ), two unbonded electrons have antiparallel spins in one sp ² hybrid orbit. Figure 1 shows the charge distribution of SiCl ₂ ( ¹ A ₁ ). In FIG. 1, the central atom is Si and the left and right atoms are Cl. Figure 1 shows the space charge distribution of valence electrons calculated based on the wave function obtained by the SCF method. The charge distribution is a plane (molecular surface) formed by three atoms, and several planes perpendicular to the plane are selected, and the distribution on that plane is expressed by isocharge density lines. A thicker isopycnic line means a higher charge density. The display range of charge density is 0.0955 × 10 ^{-1 −} 3.2000 × 10
^-1 e / au ³ . In Fig. 1, the two non-bonded electrons of Si show high charge density near the molecular plane, and it is expressed that they are in the sp ² hybrid orbital.

The silicon (001) surface has two dangling bonds <11.
It consists of surface atoms in the 0> direction. On-top, hollow, <110> direction bridge, and <110> direction bridge sites can be considered as the surface reaction sites. Among these, as shown in FIG. 2, the surface reaction occurs at the bridge site in the <110> direction on the plane containing the dangling bond. Because the following required for the crystal to grow
This is because the Si atom position is there, and when reacting at other sites, the Si atom after the reaction must move. In addition, the change from the sp ² -like charge distribution of SiCl ₂ ( ¹ A ₁ ) to the sp ³ -like charge distribution of crystal surface atoms after adsorption is SiCl ₂ ( ¹ A ₁ ).
This is because the two electrons in the sp ² hybrid orbital form dangling bonds of the two surface atoms, and covalent bonds there, respectively. In addition, the direction in which two Cl atoms are aligned is the <110> direction and is adsorbed on this surface reaction site. SiCl
_As shown in Fig. 1, the charge distribution of the ₂ ( ¹ A ₁ ) non-bonded electrons has a high charge density on the molecular surface, and the dangling bond on the crystal surface approaches the 3p _π orbit. Cheap.

Adsorption at the surface reaction site causes a change in SiCl ₂ ( ¹ A ₁ ) and a surface reaction (SiCl ₂ + H ₂ ···> Si + 2HCl) proceeds. In Fig. 2, the adsorption of SiCl ₂ ( ¹ A ₁ ) is
The electrons of the dangling bond enter the 3p _π orbit, and SiCl
_The reaction progresses with an electronic state of _2- ( ² B ₁ ). SiCl
_{If 2} ( ¹ A ₁ ) is used, the surface reaction proceeds in this process as explained by the safe structure of SiCl _2- ( ² B ₁ ) and the total energy and charge distribution. Table 1 shows the stable structure and total energy of SiCl _2- ( ² B ₁ ) with one electron added to SiCl ₂ ( ¹ A ₁ ). SiCl ₂ - total energy of ⁽² B ₁₎ is SiCl _{2 ⁽¹} A ¹⁾ less than, the progress of the reaction is the direction of the energy stabilization. In addition, as shown in Table 1, the bond length of R _SI-Cl of SiCl _2- ( ² B ₁ ) is about 10% longer than that of SiCl ₂ ( ¹ A ₁ ), which is different from that of H ₂ . Reaction is likely to occur. Furthermore, as shown in Fig. 3, 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, the sp ² flattened in the <110> direction
The surface reaction proceeds in the process that the charge distribution changes from -like SiCl ₂ ( ¹ A ₁ ) to spherically symmetric SiCl _2- ( ² B ₁ ), and then becomes 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 SiCl ₂ ( ¹ A ₁ ). 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.

There is no bridge site on the (111) surface, but on the kink (11
1) The bridge site also appears on the surface. Therefore, SiCl ₂ ( ¹ A ₁ )
When is used, silicon grows only on the kink on the (111) plane. Since the kink bridge sites of the (111) plane appear alternately on the two atomic planes, the step flow of two monolayers grows on the (111) plane.

(Example) An example in which SiCl ₂ ( ¹ A ₁ ) is formed by photodissociation and atomic layer epitaxy (ALE) is performed will be described as an example. Si ₂ Cl ₆ was used as the source gas. The method for producing SiCl ₂ ( ¹ A ₁ ) from Si ₂ Cl ₆ by photodissociation is described in B.P.Radics (BPRuzsicska et al.), Chemical Physics Letters (Chem. Phys. Lett.), 113, (1985). ) 67. The same method was used also in this example. FIG. 4 is a schematic view of the growth apparatus used in this example. Reference numeral 1 is a molecular beam generator that uses a two-stage differential pumping, and has a substrate 2 and an ArF excimer laser light introduction port 3 in the chamber of the third stage. The Si ₂ Cl ₆ molecular beam is sent from the nozzle 4 through the slits 5 and 6. 7,8,9 are turbo molecular pumps. The Si ₂ Cl ₆ molecule emitted from the nozzle 4 is emitted from the ArF excimer laser 10 irradiated through the port 3.
Photolyzed by 193 nm light to become SiCl ₂ ( ¹ A ₁ ) Substrate 2
Is adsorbed on. The electron configuration of SiCl ₂ ( ¹ A ₁ ) is (8a ₁ ) ² (6b ₂ ) ² (9a ₁ ) ² (7b ₂ ) ² (10a ₁ ) ² (3b ₁ ) ² (2a ₂ except the core electrons. ) ² (8b
₂ ) ² (11a ₁ ) ² . (100) 2 dangling bonds on the surface enters the 3p _[pi orbitals of ^{_{SiCl 2 (1 A 1),}} SiCl 2 - making ⁽² B _1). The electron configuration of SiCl _2- ( ² B ₁ ) is (8a ₁ ) except for the core electrons.
² (6b ₂ ) ² (9a ₁ ) ² (7b ₂ ) ² (10a ₁ ) ² (3b ₁ ) ² (2a ₂ ) ² (8b ₂ ) ² (11a ₁ )
² (4b ₁ ) ¹ becomes. Here, SiCl ₂ adsorbed H ₂ molecular beam
- ⁽² B ₁₎ to ^{_{collide, SiCl 2 - (2 B 1}} ) + H 2 → Si + by causing a reaction of 2HCl, was fixed Si in the gas phase to the surface. At this time, the substrate temperature may be room temperature. This is because the adsorption probability is higher at low temperature. However, since it adsorbs to other than the bridge site at an excessively low temperature, heating from room temperature to about 500 ° C. is desirable so as to desorb from other sites whose adsorption potential is smaller than that of the bridge site. However, as in this example, SiCl is present at all reaction sites on the surface.
Room temperature is better for adsorbing ₂ ( ¹ A ₁ ) and forming a new layer of elemental surface. Light was used as energy for hydrogen reduction. Heating desorbs SiCl ₂ ( ¹ A ₁ ), which is not preferable for ALE. The required light is 2.4e
It is light with an energy of V, 2.97 eV. These lights excite SiCl _2- ( ² B ₁ ) into SiCl _2- ( ² B ² ) and SiCl _2- ( ² A ₁ ). Due to the increase of internal energy, these molecular states are almost automatically hydrogen-reduced. The processes such as selection of reactive species, adsorption, photoexcitation, and surface reaction as described above are the only methods capable of accurately growing atomic layers one by one, despite homoepitaxial growth.

In this example, Si ₂ Cl ₆ was used as the chlorinated substance of silicon as the source gas, but other chlorinated substances (SiH ₂ Cl ₂ , SiHCl ₃ , Si
Cl ₄ etc.)

(Effects of the Invention) In the VLSI process technology that requires ever higher precision controllability, the ALE technology according to the present invention is an important technology for VLSI manufacturing. The present invention enables atomic plane level control and meets the need for lower process temperatures.

[Brief description of drawings]

Charge distribution diagram of FIG. 1 SiCl ₂ ⁽¹ A _1), shows a SiCl ₂ ⁽¹ A ₁₎ adsorbed on the second FIG silicon (001) plane bridge site, the 3S
Charge distribution diagram of iCl _2- ( ² B ₁ ), Fig. 4 Schematic diagram of SiCl ₂ ( ¹ A ₁ ) generator.

Claims (1)

[Claims] 1. A method of manufacturing a silicon thin film using a chlorinated product of silicon as a source gas, wherein SiCl ₂ (
¹ A ₁ ), and by interaction with the substrate, SiCl _2-
A method for producing a silicon thin film, which comprises depositing silicon by changing to ( ² B ₁ ).