JPS6276612A - Manufacture of semiconductor thin film - Google Patents

Abstract

PURPOSE:To form a semiconductor thin film with superior orientation on a single crystalline or amorphous single crystalline substrate by photo- discomposing a mixture gas consisting of fluorosilane, silane or, desirably, hydrogen. CONSTITUTION:A single crystallineor amorphous single crystalline substrate whose surface is cleaned with washing or etching is placed in a thin film forming device 7 which has at least a light permiating window 1, a substrate holding means 3, a substrate heating means 4, a gas introduction means 5 and a vaccum discharge means 6, and the substrate is heated to 100-400 deg.C under vaccum discharge. The material gas is supplied to the said device, with the flowing ratio of silane to fluorosilane being 0.5-50 and the flowing ratio of hydrogen to the fluorosilane being more than twice he former. As the fluorosilane, SiH4-nFn(integer of n=1-3) or Si2F6 is usable. As the silane, monosilane, disilane, trisilane expressed with SimH2m+2 (integer of m=1-3) are usable. As the III group compounds to be added to the mixture gas, dibolane (B2H6) is usable. As V group compounds, phosphine (PH3) or arsine (AsH3) is usable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing a semiconductor thin film, and particularly to a method for manufacturing a semiconductor thin film with excellent orientation.

[Background technology]

Semiconductor devices utilize crystalline or amorphous semiconductor thin films. Among crystalline semiconductor thin films, many polycrystalline and microcrystalline (eg, microcrystalline silicon) thin films have been studied. These are usually formed on a substrate, but if the substrate is not a single crystal, the formed thin film is likely to be non-oriented.

However, if orientation can be freely imparted to these thin films, it would be possible to impart anisotropy in electrical and optical properties, which would lead to the development of new functions. become. In particular, there has been a demand for a technique for forming an oriented semiconductor thin film on a non-single crystal substrate such as glass or polymer film.

The present inventors previously proposed (Patent Application No. 1983) the production of a low-resistance amorphous (microcrystalline silicon containing hydrogen and/or fluorine) thin film by photodecomposition (photoCVD method) of fluorosilane.
-49231, Japanese Patent Application No. 60-49232).
Furthermore, as a result of further investigation, it was surprisingly discovered that a semiconductor thin film with excellent orientation can be formed on a glass substrate by coexisting silane in the above technique, and the present invention was completed.

[Disclosure of the invention]

In the present invention, a semiconductor thin film with excellent orientation is formed on a single crystal or non-single crystal substrate by photodecomposing (photoCVD) a mixed gas consisting of fluorosilane, silane, and preferably hydrogen.

The fluorosilane used in the present invention is SiH
4-nFn (n=an integer from 1 to 3) or Si2F6 are useful. As the silane, SiH (m=l~3m 2m
Monosilane, disilane, and trisilane represented by +2 (an integer of +2) are effectively used. Furthermore, diporane (B2Ha) is a group II compound, and phosphine (B2Ha) is a group V compound.
PHs) and arsine (AsH3) are useful.

In the present invention, any material, single crystal or non-single crystal, can be used as the substrate. Among the thin film forming conditions of the present invention, the substrate temperature is as low as about 200° C., so a large number of various materials that can withstand this temperature condition can be effectively used. When a single-crystal material, particularly a silicon substrate whose surface has been cleaned, is used, a semiconductor thin film is epitaxially grown from the cleaned surface.

On the other hand, when a non-single crystal material is used, a semiconductor thin film oriented in the (110) direction can be obtained with the raw material gas composition of the present invention.

In the present invention, photolysis is preferably carried out by ultraviolet rays,
It is also possible to utilize the increase/decrease reaction of photolysis.

That is, the present invention photolyzes a mixed gas consisting of fluorosilane, silane, and preferably hydrogen, preferably by irradiation with ultraviolet rays, to form a highly oriented semiconductor thin film on a single crystal or non-single crystal substrate heated to a low temperature. This is the way to do it.

In the present invention, it is essential to perform photoCVD in a state where fluorosilane and silane coexist, and more preferably, a gas mixed with hydrogen is irradiated with ultraviolet rays. Thin films obtained by forming thin films by adding a Group Ⅰ compound or a Group V compound to the mixed gas are given the characteristics of p-type and n-type semiconductors, respectively. The mixed gas ratio can be expressed as the raw material gas supply flow rate (capacity) ratio to the thin film forming apparatus that forms the semiconductor thin film. The preferred ranges are as follows. Fluorosilane/silane ratio; 0
．． 5 to 50, particularly preferably 1 to 20, and further,
In order to form a highly oriented thin film on a non-single crystal substrate, this ratio ranges from 1 to 15. The ratio of hydrogen/fluorosilane is 2 times or more, particularly preferably 5 times or more. If the amount of hydrogen added is too large, the growth rate of the single crystal will decrease, so the preferred hydrogen/fluorosilane mixing ratio is 2 to 20 times, particularly preferably 5 to 15 times. Group ■ compound or V
The ratio of group compound/silane is appropriately determined depending on the resistivity of the semiconductor thin film. A range of 1X10"" to 5.times.10@-2 is sufficient for this ratio, and this value becomes smaller in the case of epitaxial growth.

The method of forming the mixed gas is not particularly limited.

For example, it is useful to introduce a premixed gas outside the forming apparatus, or to mix hydrogen within the forming apparatus so as to satisfy the above dilution degree. Group (1) compounds and Group V compounds are usually used in a diluted state because they are easily decomposed or extremely toxic. It is convenient for handling to use a compound of Group 1 or Group 2, fluorosilane, silane, etc. diluted with hydrogen.

In the present invention, the light source that generates the ultraviolet light used for photolysis is not subject to any critical conditions and is not particularly limited. Specific examples include a mercury lamp, a rare gas lamp, a mercury-rare gas lamp, and a hydrogen discharge tube. In these light sources, it is practically convenient to use a low-pressure mercury lamp, which is a type of mercury lamp. Photolysis can be carried out directly or indirectly via a sensitizer, if desired. From a practical standpoint, a mercury sensitization method using mercury as a sensitizer is effectively used. When using monosilane with m=1 in the general formula as the silane, only the mercury sensitization method is effective. Disilanes and trisilanes with m=2 and m=3 are useful both directly and indirectly. Trisilane has a high boiling point of 53° C. and exists as a liquid at room temperature, so it must be gasified by some means. Therefore, from the viewpoint of photodecomposition reaction of mixed gas, disilane (m=
2) is a preferred raw material.

Furthermore, one of the excellent features of the present invention is that the semiconductor thin film can be formed at a low temperature of 300° C. or lower.

When a single crystal substrate is used, epitaxial growth can be performed at a substrate temperature of 200°C. The growth temperature can be further reduced, but in this case the growth rate must be reduced accordingly. Growth rate is approximately 0.1A/sec
In the case of the above practical values, the substrate temperature should be approximately 100°C or higher (O) There are no particular limitations on the mixed gas pressure or irradiation light intensity during photolysis. When used as a mercury reservoir, there are no particular limitations on the temperature of the mercury reservoir, the flow rate of the carrier gas for transferring mercury vapor to the thin film forming apparatus, etc. These conditions affect the growth rate of the thin film,
As described above, the semiconductor thin film can be grown effectively by appropriately changing the substrate temperature depending on the growth rate.

[Preferred Modes for Carrying Out the Invention] Next, embodiments of the present invention will be described. light transmission window, substrate introduction means,
A single-crystal or non-single-crystal substrate whose surface has been cleaned by cleaning and/or etching is placed in a thin film forming apparatus having at least a substrate holding means, a substrate heating means, a gas introduction means, and a vacuum evacuation means, and the substrate is heated under vacuum evacuation. board ioo~400
Heat to ℃. When introducing the raw material gas, a part of it is introduced into the apparatus via a mercury reservoir as necessary. The raw material gas has a flow rate ratio of fluorosilane to silane of 0.
5 to 50, and the flow rate ratio of hydrogen to fluorosilane is at least twice that of the fluorosilane. Furthermore, when p-type and n-type doping is performed, group II and group V compounds are added to the silane at IX 10-' to 5
It is sufficient to introduce it into the device in ×1σ2 circulation.

The pressure inside the apparatus is set to 10 Torr or less using a vacuum evacuation means, and a low-pressure mercury lamp is turned on to start film formation.

Formation of a thin film begins when the lamp is turned on, so the lamp is turned off when the required film thickness is reached, taking into consideration the film formation rate. Further, the film forming time can be determined while measuring the film thickness using a film thickness monitor. Synthetic quartz is suitable for the light transmitting window of the device, but by applying high boiling point oil to this window, film formation on the light transmitting window can be suppressed.

〔Effect of the invention〕

The present invention provides a highly oriented semiconductor thin film including a single crystal thin film at a substrate temperature of 300° C. or lower, or even 200° C. or lower. Therefore, for high integration,
The present invention provides an extremely useful technology for the field of manufacturing semiconductor devices, where low-temperature formation technology for semiconductor thin films and semiconductor devices is eagerly awaited.

〔Example〕

The present invention will be explained in more detail below by way of Examples.

Example 1 Ultraviolet light transmitting window 1 and substrate introduction means 2 as shown in FIG.
, substrate holding means 3, substrate heating means 4, gas introduction means 5,
A thin film forming apparatus 7 having a vacuum evacuation means 6 is used. p of the substrate 8 for film attachment using the substrate introduction means 2.
Place the mold silicon ueno\- on the substrate holding means. The cleaned substrate was heated to 200° C. by the substrate heating device while being evacuated by the vacuum pumping device. Note that 6I and 9I are exhaust means for the substrate introduction/takeout chamber 15. Next, disilane/difluorosilane/hydrogen was introduced at a flow rate ratio of 1/10/150, and a control valve 9 installed in the evacuation means was used to introduce 2 To
Hold at a pressure of rr. A part of the difluorosilane introduced through the conduit 10 is placed in a mercury reservoir 11 heated to about 40°C.
Introduce it by passing it over it.

Note that 13, 14, and 16 are introduction pipes for disilane, hydrogen, diborane, phosphine, etc. When the temperature of the substrate and the pressure inside the thin film forming apparatus are constant, the low pressure mercury lamp 1
2 is turned on and turned off when the film thickness reaches approximately 6000A. The average film deposition rate was 0.8 A/S.

After cooling, the substrate was taken out and observed. The surface of the substrate was a mirror surface with no clouding. Observation of the surface using a reflection electron beam diffraction device revealed Laue spots identical to those of the substrate, and single crystals were detected from the substrate surface. It was confirmed that the thin film was grown epitaxially. This single crystal thin film was of extremely weak n-type, and its specific resistance was 50=70Ω·me.

Example 2 Example 1 was carried out, except that a glass plate (Corning 7059) was used as the substrate and 4000 ppm (volume ratio) of PH3 was added to disilane. The film formation rate was 0.95 A/S, and reflection electron diffraction results confirmed that the film was oriented in the (110) direction. The electrical conductivity was 1.33/CrIL, and the resistance was sufficiently low.

Examples 3 to 10, Comparative Example 1.2 The procedure of Example 1 was repeated except that the type and amount of fluorosilane were changed. The conditions and results are shown in Table 1. Table 1 also shows examples for comparison.

Examples 11 to 17 In Examples 3 to 5 and 7 to 10, a glass plate (Corning 7059) was used as the substrate instead of a silicon wafer. As an example for comparison, thin films were formed by changing the flow rate ratio of fluorosilane. The results are shown in Table 2.

When the difluorosilane/silane flow rate ratio was set to 20, the electron beam diffraction image of the obtained thin film was ring-shaped, indicating that it was in a non-oriented state.

Example 18 In Example 1, monosilane (Si
1-14). Film deposition rate is 0.15A/s
However, epitaxial growth was confirmed by electron diffraction. The resistivity was 90 to 120Ω.

Example 19 The procedure of Example 18 was followed except that a glass plate was used as the substrate. The film formation rate was 0.18 A/S, and electron beam diffraction confirmed orientation in the (110) direction.

or above (for example, as shown in the examples, 200
The present invention, which is capable of growing a single crystal or highly oriented thin film at a substrate temperature as low as .degree. C., is an extremely effective invention for lowering the temperature of manufacturing semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a longitudinal section of a thin film forming apparatus useful for carrying out the present invention.

Claims (7)

[Claims] (1) A method for producing a semiconductor thin film, which comprises forming a semiconductor thin film on a substrate by photolyzing a mixed gas consisting of fluorosilane and silane. (2) Fluorosilane is SiH_4_−_nF_n(n
= 1 to 3) or Si_2F_6, the method for manufacturing a semiconductor thin film according to claim (1). (3) Silane is Si_mH_2_m_+_2 (m=1~
3) A method for manufacturing a semiconductor thin film according to claim (1). (4) The method for manufacturing a semiconductor thin film according to claim (1), using a mixed gas to which a Group III compound or a Group V compound is added. (5) The method for manufacturing a semiconductor thin film according to claim (1), wherein the substrate is a single crystal or non-single crystal material. (6) The method for producing a semiconductor thin film according to claim (1), wherein the photodecomposition is performed by irradiation with ultraviolet rays. (7) A mixed gas consisting of fluorosilane, silane, and hydrogen is photodecomposed by irradiation with ultraviolet rays and formed on a single crystal or non-single crystal substrate heated to a low temperature.
1) The method for manufacturing a semiconductor thin film as described in item 1).