JP2861601B2 - Method and apparatus for selective growth of silicon epitaxial film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for selectively growing a silicon epitaxial film using a molecular beam.

[0002]

_2. Description of the Related Art Gas source silicon molecular beam growth technology (MBE) using disilane (Si ₂ H ₆ ) gas molecular beam
It is attracting attention as a technology that allows selective growth of silicon at low temperatures. However, in the epitaxial growth using a gas source using only Si ₂ H ₆ gas, unlike the case using dichlorosilane, there is no condition that the selective growth does not collapse even if a thick film is grown under a certain growth condition.
It has been found that when irradiated with Si ₂ H ₆ molecules equal to or more than the total number of critical molecules determined by the growth temperature, nucleation of Si occurs on SiO ₂ and the selective growth is destroyed. For example, FIG. 7 shows the relationship between the flow rate of the Si ₂ H ₆ gas when the growth temperature is changed and the time until the selective growth condition is broken. From this figure, the time at which the selective growth condition collapses is S
It can be seen that the flow rate is inversely proportional to the flow rate of i ₂ H ₆ , and that the time required for the collapse to become shorter as the growth temperature increases. Si ₂ this is condition is the selective growth collapses is irradiated on SiO ₂
Determined by the total number of H ₆ molecules, this critical number indicates that it is dependent on the growth temperature. FIG. 8 is an Arrhenius plot of the relationship between the critical total number and growth temperature until the selective growth collapses. It was found that the critical total number was almost converged at one point if the growth temperature was the same even when the growth rate was changed, and that the critical total number was on the Arrhenius plot when the temperature was changed. This indicates that some reaction occurs on the oxide film surface even during the time during which the selective growth is maintained, and that the reaction rate depends on the substrate temperature. Growth temperature 70
At 0 ° C., the supply is rate-determined up to the Si ₂ H ₆ flow rate of 75 SCCM, and the growth rate is proportional to the Si ₂ H ₆ flow rate. Therefore, up to the Si ₂ H ₆ flow rate of 75 SCCM, the thickness of the grown film when the selective growth condition is broken is the same regardless of the Si ₂ H ₆ flow rate. The film thickness that can be selectively grown at a growth temperature of 700 ° C. is about 1000 A. As described above in detail, even if the flow rate of Si ₂ H ₆ and the growth rate are changed, the critical film thickness that can be selectively grown does not change. However, there is a problem that a film having a large thickness cannot be selectively grown. Si ₃ N ₄
A similar phenomenon is observed in the case of the film, and the selectivity is lower than that of the SiO ₂ film.
A.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such conventional disadvantages and to improve selectivity even when a thick film is grown by gas source epitaxial growth using a silane or germane gas. It is to provide a method that does not break down.

[0004]

According to the present invention, in selective epitaxial growth of silicon by molecular beam, a substrate partially covered by an insulating film is arranged in a molecular beam growth apparatus capable of heating the substrate, and a gas phase reaction occurs. Selective growth of a silicon epitaxial film characterized in that the substrate surface is grown by simultaneously irradiating the substrate surface with a silane-based gas molecular beam, a germane-based gas molecular beam, or both, and a chlorosilane molecular beam or a chlorosilane radical. Is the way.

In the present invention, in the selective epitaxial growth of silicon by molecular beam, a substrate partially covered with a silicon oxide film or a silicon nitride film is arranged in a molecular beam growth apparatus capable of heating the substrate, and a gas phase reaction occurs. Irradiating the surface of the substrate with a silane-based gas molecular beam or a germane-based gas molecular beam or both to selectively grow the silicon opening in a region where no silicon is present.
A method for selectively growing a silicon epitaxial film, characterized by alternately performing a step of irradiating a chlorosilane molecular beam or a chlorosilane radical to etch i or Ge or both.

Further, the present invention relates to a molecular beam growing apparatus,
A selective growth apparatus for a silicon epitaxial film, comprising a nozzle for generating a silane-based gas molecular beam, a germane-based gas molecular beam, or a mixed molecular beam thereof, and a plasma ion source for generating chlorosilane radicals.

[0007]

[Function] When SiO ₂ is irradiated with Si ₂ H ₆ gas,
As shown in FIG. 3A, the Si ₂ H ₆ gas molecule is SiO ₂
After being trapped in the metastable state on the surface of the film 21, it is released again. At this time, a small number of Si ₂ H ₆ molecules are decomposed at a certain probability determined by the substrate temperature, and become Si atoms 23 and adhere to SiO ₂ . As shown in FIG.
When the number of Si atoms attached on O ₂ exceeds a certain critical number, nucleation occurs, and a polysilicon island 25 is formed on SiO ₂ . As shown in FIG. 3C, once a polysilicon island is formed, Si
Since the growth rate is the same as the growth rate in the Si opening, the polysilicon island grows rapidly. In the case of growth using a silane-based gas, selective growth is broken through the above-described process. The present inventors have found that, during selective growth using a silane-based or germane-based gas molecular beam, simultaneous irradiation with a chlorosilane gas molecular beam increases the film thickness that can be selectively grown. This is because, during selective growth, Si atoms formed on SiO ₂ react with a plurality of chlorosilane gas molecules simultaneously irradiated with a plurality of chlorosilane gas molecules as shown in the following formula to form SiCl having a high vapor pressure.
₂ , SiCl and SiHCl to evaporate. (Example of dichlorosilane: SiCl ₂ H ₂ → Si + 2
HCl, Si + HCl → SiHCl, Si + HCl → S
iCl + 1 / 2H ₂ , Si + 2HCl → SiCl ₂ + H
₂ ) At this time, since etching by SiCl ₂ H ₂ occurs simultaneously with the growth as shown in this reaction formula, an extremely flat surface is obtained. Furthermore, as shown in FIG. 2, 10 ^- to ⁹ Torr ultrahigh vacuum fitted with a chlorosilane plasma ion source 35 by the nozzle 39 and the ECR for the deposition gas to the vacuum chamber 31 which can be evacuated and is formed by a plasma ion source chloro It was found that simultaneous irradiation with silane radicals had the effect of increasing selectivity even at low temperatures. When chlorosilane radicals are used, the reaction with Si on SiO ₂ is promoted, so that SiC
It is considered that l ₂ , SiCl, and SiHCl are formed and Si is removed from SiO ₂ .

In this method, the chlorosilane molecular beam or chlorosilane radical is continuously irradiated during the growth,
Etching also occurs in the i-opening and Si ₂ H
_Since the effect of SiCl ₂ H ₂ enters the decomposition process of ₆ , the growth rate at the opening decreases. In particular, when plasma ionization is used, plasma is not generated if the partial pressure of SiCl ₂ H ₂ is lowered, so that a large amount of SiCl ₂
We must continue to supply the H _2, can not be ignored etching. In such a case, if the growth is stopped before the nucleation of the polysilicon occurs and the step of irradiating only the SiCl ₂ H ₂ or dichlorosilane radical molecular beam is inserted, the selectivity is maintained even when a thick film is grown. Moreover, the growth rate hardly decreases. This is based on the following principle. When the Si ₂ H ₆ gas is irradiated on the SiO ₂ film 11 as shown in FIG. 1A, the density of Si atoms 13 on the SiO ₂ film 11 increases. Si atoms on SiO ₂ as is irradiated with SiCl ₂ H ₂ or dichlorosilane radicals substrate shown in FIG. 1 (b) before the formation of the polysilicon occurs reacted with SiCl ₂ H ₂ or dichlorosilane radical And evaporates in the form of SiCl ₂ , SiCl, and SiHCl having a high vapor pressure. At this time, the Si epitaxial layer on the Si opening is also etched, Si on SiO ₂
The number of atoms is at most about one atomic layer, and even if the time is properly selected, Si atoms on SiO ₂ can be removed without substantially etching the epitaxial layer (FIG. 1).
(C)). Therefore, it is possible to continue selective growth again (FIG. 1D). In the case of the Si ₃ N ₄ film, the conditions for selective growth can be broadened based on exactly the same principle.

[0009]

EXAMPLES Examples of the present invention will be specifically described.
Here, a silicon gas source MBE apparatus was used. A turbo molecular pump with a displacement of 1000 l / s was used as the main exhaust pump. Si ₂ H ₆ gas and SiCl ₂ H
_{The two} gases were controlled in flow rate by a mass flow controller, and were supplied from different diagonal SUS nozzles from 100 mm below the substrate. Mixing these gases at high pressure is dangerous because of the danger of explosion. Substrate is 4 inch Si
On a (100) single crystal substrate, a CVD oxide film pattern having a thickness of 4000 A is formed. The growth is performed at a substrate temperature of 700.
C. and a gas flow rate of 5 SCCM. The determination of whether or not the cells were selectively grown was determined by in-situ RHEED measurement. After removing the grown substrate to the atmosphere, SE
The state of selective growth and crystallinity were observed with M and TEM, and the oxide film pattern was removed with hydrofluoric acid, and the thickness of the selectively grown film was measured with a step gauge.

[0010] The substrate temperature was set to 700 ° C. When flow Si ₂ H ₆ molecules line 5 SCCM, Si ₂ H ₆ partial pressure of the growth chamber 6 × 10 ^{- 4} Torr, and the growth in the Si opening begins. At this time, 0.5 SC from another nozzle on the substrate
Irradiation with CM SiCl ₂ H ₂ molecular beam. The pressure in the growth chamber is set to 10 ⁻³ Torr or less so that a gas phase reaction does not occur. With this growth, the selectivity did not collapse even when a thick film of 1 μm or more was grown. The growth rate is SiCl ₂ H
_It was reduced to 1/5 of the case where ₂ was not irradiated. This is Si
SiCl ₂ due to etching on the surface and the presence of Cl
This is probably because the decomposition process of H ₆ changes. When the substrate is irradiated with SiCl ₂ H ₂ , the substrate temperature is set at 6 ° C.
If the temperature is lowered to 50 ° C. or lower, the etching rate for Si is sharply reduced, so that the effect of SiCl ₂ H _{2 on} the selectivity is lost. Therefore, as shown in FIG.
Attach dichlorosilane plasma ion source by R,
Instead of SiCl ₂ H _2, where a higher growth in SiCl ₂ H ₂ reaction efficiency dichlorosilane radicals irradiated, from 600 ° C. or higher, it was found effective against selectivity. In this case, the growth rate was reduced to 1/5 of that without irradiation with dichlorosilane radical.

In order to suppress the decrease in growth rate, Si ₂ H
Next, a method of alternately irradiating _six molecular beams and SiCl ₂ H ₂ or dichlorosilane radical molecular beams will be described. FIG. 4 shows a time chart of the flow rates of Si ₂ H ₆ and SiCl ₂ H ₂ . Growth rate at the growth temperature of 700 ° C. is 500A / min, since the critical thickness selectivity is destroyed is approximately 1000A, for etching Si over SiO ₂ before the selectivity is lost, due to the Si ₂ H ₆ The growth time was 1 minute. Thereafter, the supply of the Si ₂ H ₆ gas was stopped, and etching was performed with SiCl ₂ H ₂ or dichlorosilane radical gas. The etching time is 1 to
It was varied between 60 seconds. After etching, Si ₂ H
_The process of feeding ₆ and growing for 1 minute was repeated. FIG.
Shows the substrate temperature dependence of the relationship between the etching time and the critical film thickness at which the selectivity is lost in the case of SiCl ₂ H ₂ , and the growth rate. When the substrate temperature is 700 ° C., if the etching time exceeds 10 seconds, the critical film thickness sharply increases,
Moreover, it was found that the growth rate hardly changed.
FIG. 6 shows the substrate temperature dependence of the relationship between the etching time and the critical film thickness at which the selectivity is lost and the growth rate in the case of dichlorosilane radical. Substrate temperature is 600
Even at ℃, it was found that when the etching time exceeded 10 seconds, the critical film thickness sharply increased and the growth rate hardly changed, confirming that the present invention was effective.

Further, a substrate temperature of 70 SC is supplied by supplying ₄ SCCM of Si ₂ H ₆ gas and 1 SCCM of germane (GeH ₄ ) gas.
At 0 ℃ was carried out Ge _{0. 2} Si _{0. 8} mixed crystal growth. Further, Ge was grown on Si by supplying ₅ SCCM of GeH ₄ gas. In both cases, the relationships shown in FIGS. 5 and 6 are exactly the same, and it was found that this method is also effective for the growth of Ge _x Si _{1 -x} mixed crystals and Ge. Also, using this method of stopping growth and irradiating with SiCl ₂ H ₂ gas or dichlorosilane radical just before selective growth collapses,
By alternately sending the Si ₂ H ₆ gas and the GeH ₄ gas, it was possible to selectively grow the super lattice structure of the Ge 3 layer and the Si 7 layer over 200 periods.

Although the present embodiment is directed to a silicon wafer, the method of the present invention employs an SOS (Silicon on Sapphir) in which silicon exists only on the surface.
e) Substrate and more generally SOI (Silicon on)
The present invention can be applied to an insulator substrate or the like. Further, in this embodiment, an example using Si ₂ H ₆ gas and GeH ₄ gas has been described, but silane gas (SiH ₄ ),
Trisilane gas (Si ₃ H ₈ ), digerman gas (Ge
₂ H ₆ ) or the like. Although dichlorosilane is used for etching, SiHCl ₃ , SiCl ₄ or the like may be used. Further, in the present embodiment, the selectivity with respect to the SiO ₂ film was described, but the Si ₃ N ₄ film, SiN _x , SiO 2
_x N _y, also the present invention in the case of film such as Ta ₂ O _5, LiNbo ₃ is effective.

[0014]

As described above in detail, according to the present invention, the Si atoms formed on the insulating film during the selective growth using the silane-based gas and the germane-based gas before the nuclei of the polysilicon are formed. By evaporation using chlorosilane etching, the conditions for selective growth can be broadened and a thick film can be grown.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a conceptual diagram of the growth apparatus of the present invention.

FIG. 3 is a conceptual diagram of a conventional example.

FIG. 4 is a time chart of Si ₂ H ₆ flow rate and SiCl ₂ H ₂ flow rate.

FIG. 5 is a diagram showing the substrate temperature dependence of the relationship between the etching time and the critical film thickness at which selectivity is lost and the growth rate in the case of SiCl ₂ H ₂ .

FIG. 6 is a diagram showing the substrate temperature dependence of the relationship between the etching time and the critical film thickness at which selectivity is lost and the growth rate in the case of dichlorosilane radicals.

FIG. 7 is a diagram showing the relationship between the flow rate of Si ₂ H ₆ gas when the growth temperature is changed and the time until the selective growth condition is broken.

FIG. 8 is a diagram showing the relationship between the total number of critical Si ₂ H ₆ molecules and the growth temperature until the selective growth collapses.

[Explanation of symbols]

 11,21 oxide film 12,22 silicon substrate 13,23 silicon atom 24 metastable adsorbed disilane molecule 25 polysilicon island

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/203 C30B 23/08 C30B 29/06 504 H01L 21/205

Claims (3)

(57) [Claims] In a selective epitaxial growth of silicon by a molecular beam, a substrate partially covered by an insulating film is arranged in a molecular beam growth apparatus capable of heating the substrate, and the substrate surface is formed in a region where a gas phase reaction does not occur. A selective growth method for a silicon epitaxial film, wherein the silicon epitaxial film is grown by simultaneously irradiating a silane-based gas molecular beam, a germane-based gas molecular beam, or both, and a chlorosilane molecular beam or a chlorosilane radical. 2. In selective epitaxial growth of silicon by molecular beam, a substrate partially covered by an insulating film is arranged in a molecular beam growth apparatus capable of heating the substrate, and the substrate surface is formed in a region where a gas phase reaction does not occur. Selectively growing silicon openings by irradiating silane-based gas molecular beams or germane-based gas molecular beams or both, and chlorosilane molecular beams or chlorosilane to etch Si and / or Ge on the insulating film. A method for selectively growing a silicon epitaxial film, comprising alternately performing a step of radiating radicals. 3. A molecular beam growth apparatus comprising a nozzle for generating a silane-based gas molecular beam, a germane-based gas molecular beam, or a mixed molecular beam thereof, and a plasma ion source for generating chlorosilane radicals. Selective growth equipment for silicon epitaxial film.