JPH07118452B2 - Silicon epitaxial growth method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silicon epitaxial growth method for epitaxially growing silicon on a substrate surface by a photo-excited vapor phase epitaxy method (hereinafter, referred to as photo CVD method).

[Conventional technology]

For example, when epitaxially growing silicon on the surface of a silicon substrate, the conventional thermal CVD method requires about 9
By heating to a high temperature of 00 ° C. or higher, a reaction gas (also referred to as a source gas) is thermally decomposed and epitaxially grown on the substrate surface. However, in such a high temperature process, there are harmful effects such as substrate warpage, generation of crystal defects, and increase in film stress.

Therefore, in order to improve these points, it is required to lower the temperature of epitaxial growth (for example, about 800 to 850 ° C or lower), and as a method for that, use of the molecular beam epitaxy method, plasma CVD method, optical CVD method, etc. is tried. Has been.

Of these, focusing on the photo-CVD method, the method using monosilane (SiH ₄ ) as the reaction gas or disilane (Si
Several methods using ₂ H ₆ ) have been reported (for example, see “Opttronics” (1985) No. 10, p. 61-64).

[Problems to be solved by the invention]

However, the method using monosilane has the advantage that the price of monosilane is much lower than that of disilane (for example, about 1/4 to 1/5 per gram of silicon), but monosilane is directly excited to dissociate. There is a problem that the growth rate of the crystal film is low at the low temperature (similarly to the thermal CVD method) at the above low temperature because there is no light source effective for the purpose.

On the other hand, in the method using disilane, there is a light source effective for directly exciting and dissociating disilane to some extent, and although a film growth rate is obtained to some extent even at the above low temperature, as described above. The problem is that disilane is very expensive.

Therefore, it is an object of the present invention to provide a silicon epitaxial growth method that can solve both of the above problems in the photo-CVD method.

[Means for solving problems]

The silicon epitaxial growth method of the present invention is a method of epitaxially growing silicon on a substrate surface by photoexcited vapor phase epitaxy, in which the temperature of the substrate during processing is set to 80
It is characterized in that the temperature is about 0 ° C. to 850 ° C., light having a wavelength of about 193 nm to 220 nm and capable of exciting dizirane is used, and a mixed gas of disilane and monosilane is used as a reaction gas.

[Action]

It has been found that the method as described above can provide a considerably higher film growth rate than the case where only monosilane is used as the reaction gas, and in some cases, a higher film growth rate than the case where only disilane is used. It is considered that this is because the disilane excited by light as described above interacts with the monosilane to excite the monosilane and dissociate its molecular bond. Moreover,
According to the above method, the use ratio of disilane, which is more expensive than monosilane, is reduced, and thus the reaction gas is more economical than the case of using disilane alone.

〔Example〕

FIG. 1 is a schematic view showing an example of an apparatus used for carrying out the present invention. A substrate (for example, a silicon substrate) 8 held by a susceptor 4 is housed in a growth chamber 2 that is evacuated to a predetermined vacuum degree by a vacuum pump 16, and the substrate 8 is heated to a predetermined temperature by a heater 6. It has become so.

Then, in the growth chamber 2, the gas G is passed through the gas introduction pipe 18.
To supply. The gas G is a mixture of a reaction gas composed of a disilane gas from the gas source 20 and a monosilane gas from the gas source 21, and a hydrogen gas from the gas source 22 as a carrier gas for the reaction gas, which will be described later.

Further, the light 14 from the light source 12 is applied to the surface of the substrate 8 or the vicinity of the surface through the entrance window 10. As the light 14, a light having a wavelength capable of exciting disilane is used here. That is, since disilane has an absorption edge for light absorption accompanying electronic state excitation in the vicinity of about 220 nm, it is preferable to use light 14 having a wavelength of about 220 nm or less. Then, disilane can be directly excited to cause dissociation of its molecular bond.

As the light source 12 for obtaining the light 14 in the above wavelength range, for example, a laser, a mercury lamp, a mercury-xenon lamp or the like can be adopted. Among them, relatively high energy and wavelength
It is preferable to use an ArF excimer laser that can obtain a laser beam of 193 nm.

Therefore, summing up the above, the wavelength of light 14 is
It is preferable to use light having a wavelength of about 193 nm to 220 nm and capable of exciting disilane. In addition, the temperature of the substrate 8 during the treatment is set to 800 ° C. to 850 ° C. in order to reduce the harmful effects such as the warp of the substrate, the generation of crystal defects, and the increase of the film stress while keeping the film growth rate high. It is preferable to keep the temperature at about ° C.

Since monosilane has an absorption edge of light absorption in the vicinity of about 150 nm, direct light absorption hardly occurs with light having a wavelength longer than that, for example, ArF laser light as described above, and therefore excitation-dissociation of monosilane It hardly happens.

The table below shows an example of the experimental results of epitaxially growing a silicon film on a silicon substrate under various conditions using the above apparatus. In this case, first, the growth chamber 2 is evacuated to the order of 10 ⁻⁷ Torr, and then the 1-inch silicon substrate 8 previously placed on the susceptor 4 is replaced with the heater 6
At a predetermined temperature, and the gas pressure as described above is reduced to about
It was continuously flushed at 20 Torr. The thermal CVD (cases I to III) is for comparison, and the light 14 is not irradiated. In that case, the temperature of the substrate 8 was 850 ° C. or 1010 ° C. Optical CVD
In the cases (Cases IV to VI), an ArF excimer laser was used as the light source 12, and the laser light in that case had an energy of 200 mJ / pulse at 100 Hz. The temperature of the substrate 8 was 850 ° C. in all cases.

As can be seen from the above table, when the reaction gas is monosilane alone (cases I and IV), the film growth rate is the same in both thermal CVD and photo CVD, and the effect of laser light in photo CVD is not observed.

Next, when the reaction gas is disilane alone (cases II and V),
In the photo-CVD (Case V), the film growth rate is high even though the substrate temperature is lower than that in the thermal CVD.
This is because disilane was excited by laser light and dissociated.

Furthermore, when a mixture of disilane and 20% (volume%) of disilane was used as the reaction gas (cases III and VI), light C
In VD (case VI), an even higher film growth rate was obtained than in the case of disilane alone (case V). Moreover, there was no difference in film quality. It is considered that this is because the disilane was directly excited by the laser light, and the excited substance then interacted with the monosilane, whereby the monosilane was excited and the molecular bond was dissociated. Moreover, in this case, the use ratio of disilane, which is more expensive than monosilane, is reduced, so that the reaction gas is more economical than when only disilane is used.

The proportion of monosilane mixed with disilane is not necessarily limited to the above 20%, and other proportions have the effect of improving the film growth rate and the economic effect of the reaction gas even if there is a degree difference. can get. In that case, if the proportion of monosilane is too high, the effect of the excitation reaction due to light absorption in disilane decreases and approaches the mere thermal CVD method.Therefore, the lower the proportion of monosilane in the reaction, the more expensive disilane is used. The ratio of monosilane is, for example, 1 because the ratio increases and the economic effect decreases.
It is preferable to keep it within the range of about 45%. Within such a range, the effect of improving the film growth rate at low temperature,
It is possible to make the effect of reducing the cost of the reaction gas compatible with each other.

Finally, although the case of homoepitaxial growth in which silicon is epitaxially grown on a silicon substrate has been illustrated above, the present invention is not limited to this, and is also applicable to, for example, heteroepitaxial growth in which silicon is epitaxially grown on a sapphire substrate. Can be applied.

〔The invention's effect〕

As described above, according to the present invention, epitaxial growth with an excellent film growth rate can be achieved while lowering the growth temperature, and the cost of the reaction gas can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus used for carrying out the present invention. 2 ... Growth chamber, 6 ... Heater, 8 ... Substrate, 12 ... Light source, 14 ... Light, G ... Gas

Claims (1)

[Claims] 1. A method of epitaxially growing silicon on a substrate surface by photoexcited vapor phase epitaxy, wherein the temperature of the substrate during processing is set to about 800 ° C. to 850 ° C., and the wavelength of light is about 193 nm to 220 nm, and disilane A method for epitaxially growing silicon, which uses light that can be excited and uses a mixed gas of disilane and monosilane as a reaction gas.