JPS59182521A - Formation of silicon hydrite thin film - Google Patents

Abstract

PURPOSE:To make the form of coupling hydrogen mainly SiH rather than SiH2 by controlling the applied energy and the speed of film formation within a specific region. CONSTITUTION:A substrate, on which a silicon hydrite film is to be formed, is put in a reaction chamber in which a glow discharge can be effected. While the gas containing disilane is supplied into this reaction chamber in such a manner that the formation speed of the thin film is to be 20Angstrom /sec, the silicon hydrite thin film is formed by the glow discharge energy of more than 10KJ per unit mass of disilane under the depressurization of less than 10 Torr. With this constitution, the number of molecules in the coupling form of SiH becomes larger than that of molecules in the coupling form of SiH2 in the thin film and the excellent photoelectric characteristics can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an amorphous N-film having excellent photoelectric properties, and more particularly to a method for forming a hydrogenated silicon thin film.

Because of the excellent photoelectric properties of hydrogenated silicon thin films, studies are underway to apply them to various uses.

On the other hand, although various papers have been shown to have high-speed M film properties, it has been impossible to form such a thin film at high speed while maintaining good photoelectric properties.

Now, when disilane is used as a raw material for forming a silicon hydride thin film, it is expected that it will be possible to form a silicon hydride thin film at high speed because disilane is more easily decomposed than silane. However, in reality, a large amount of hydrogen was incorporated into the thin film, so the photoelectric properties were not as good as expected (8.
tal, J, J, 8, P, 22(2), L115
(1983)).

However, it is known that in order to maintain good photoelectric properties, the hydrogen-silicon bond form in the hydrogenated silicon thin film is preferably SiH rather than SiH2.

In order to balance the contradictory characteristics of high-speed film formation and maintaining high-performance photoelectric properties, the present inventors conducted intensive studies focusing on the bonded hydrogen in the thin film, and as a result, the applied energy and film-forming speed were adjusted to a specific value. The present invention was completed by discovering that the form of bonded hydrogen can be made to be mainly SiH by controlling the amount within a certain range.

That is, the present invention provides: ``In forming a hydrogenated silicon thin film by glow discharge decomposition of a disilane-containing gas, the energy applied to the disilane is 10 KJ or more per unit mass of disilane, and the hydrogenated silicon formed is A method for forming a hydrogenated silicon thin film in which the formation rate of the thin film is controlled to a high speed range of 20 people/sec or more, so that more bonding forms of SiH than bonding forms of S+H2 exist in the thin film.J It provides:

The present invention will be explained in detail below.

In the present invention, the disilane to be subjected to glow discharge is a compound represented by the general formula 5inH2n+z, where n=2. Of course, it is preferable to have high purity, but it also contains trisilane, tetrasilane, etc., which behave in the same way as disilane during glow discharge (n = 3.4 in the above general formula). There is nothing wrong with that. However, disilane can be synthesized by physical methods, such as by separating monosilane (n-1 in the general formula), which changes into disilane by silently discharging it, or by chemical methods such as reducing hexachlorodisilane. manufactured by a method. However, in order to mass-produce hydrogenated silicon thin films, it is practically convenient to use chemically synthesized raw materials that can be obtained in large quantities with stable quality.

In the present invention, the disilane-containing gas refers to disilane alone or disilane in a diluted state G as shown in Examples below. The diluent gas is preferably hydrogen, helium, argon, or the like.

In the hydrogenated silicon thin film of the present invention, the Si in the thin film is
The bonding forms of H are made to exist in a larger number than the bonding forms of SiHλ, and this is specifically shown in the infrared absorption spectrum chart of FIG. In chart reading, the absorption from 1960 to 2000 cm-' is S
In addition to iH, absorption of 2060 to 2100 cm" or Si
Each corresponds to H2. Therefore, a in the figure shows a case where a sufficiently large energy defined by the present invention is applied, and b shows a case in which a smaller energy is applied.

As is clear from this, when the energy specified in the present invention is applied, it corresponds to SiH.
It can be seen that the absorption at 2060 to 2100 cm-', which corresponds to 5 iHz, is greater when the frequency is less than that.

In the present invention, when forming a hydrogenated silicon thin film by glow discharge decomposition of a disilane-containing gas, the energy applied to the disilane is set to IOK per unit mass of disilane.
J or higher.

One of the characteristics of the present invention is that it focuses on the factor "glow discharge energy per unit mass of disilane", and the glow discharge energy is expressed by the following formula (I).
This is the value calculated by

"Glow discharge energy" - (applied glow discharge power) * (weight fraction of disilane) / ((raw material gas flow rate) * (average molecular weight /
22.4) ) (+) For example, 500 cc/m of raw material gas consisting of disilane (Si+H6) diluted to 10 vol 1% with helium (He)
The energy when applying a glow discharge power of 150 W to It may be used as is. If the reflected wave is large, it is preferable to use the value obtained by subtracting the reflected wave power from the traveling wave power).

That is, average molecular weight of raw material gas - (62,2184*0.1 +
4.0026*0.9) =9.824 (g
) The average molecular weight of SiH is 62.2184 * 0.1 / 9.824 = 0.
633, so by substituting these into the above formula (I),
The energy per unit mass of disilane is: “The energy J = (150*0.633) /
((0,5/60) * (9,824/22.4>
) = 26.0 * 10 [J/g-3i, H Rakoma 10 If J is written as KJ, the energy is approximately
26 KJ/g-3i2H6.

The present inventors have found that by using the above-mentioned factor "glow discharge energy per unit mass of disilane" as a parameter, the thin film formation rate and the flow rate of disilane can be almost uniquely correlated. ) (In the case of glow discharge by applying discharge energy of loKJ or more per unit mass of disilane, the thin film formation rate is hardly affected by the glow discharge energy,
We discovered a phenomenon in which the rate of change depends only on the flow rate of disilane (in other words, in this region, if the source gas velocity is constant, the thin film formation rate is constant).

) However, here, as shown in Figure 1, the energy is smaller than this value (for example, in the case of b in the figure, 8.6K
J/g-3i, the energy of LH6) is applied, the peak ratio is S i H/ S i
Hλ#0.9, and the object of the present invention cannot be achieved. On the other hand, energy larger than this value such as a (for example, in the case of a, 26 KJ/g-3i2Ht
) is applied, the peak ratio is SiH/S i H2, # 1.2.

Furthermore, as is clear from Figure 2, which shows the relationship between glow discharge energy ■ and photoelectric characteristics (here, photoelectric characteristics are expressed as photosensitivity (-photoconductivity σ-ph/dark conductivity σd)), l0KJ/ For the region of large applied energy ~ on g S iz HG Id, (σph/σd) ≧ 1
A thin film with very poor photoelectric properties such as 0.0 can be obtained.

It should be noted that in conventional glow discharge decomposition,
In order to avoid damage to the membrane due to plasma, it was believed that the lower the power consumption, the better. However, as mentioned above, with disilane, it has become clear that the photoelectric properties of the film cannot be improved unless energy, including power consumption, is increased. In other words, this shows that monosilane in the prior art, which achieves favorable results at low power expressed as discharge power per unit electrode area, and disilane in the present invention cannot be discussed in the same way.

In the present invention, as described above, the amount of applied energy is controlled within a specific range, and the formation rate of the hydrogenated silicon thin film to be formed is controlled within a high speed range of 20 persons/sec or more.

In other words, controlling the formation rate to a high rate of 20 persons/sec or more means that it is necessary to supply a large amount of disilane-containing gas into the glow discharge atmosphere.

Figure 3 shows the relationship between the thin film formation rate R and the applied energy (■) using the raw material gas flow rate as a parameter in the case of disilane diluted with He.
In the figure, the formation rate in the region where the formation rate R is not affected much by the applied energy I is determined, and the supply amount of the disilane-containing gas is determined so that this becomes 20 persons/sec (in addition, Of course, if no diluent gas is used, the amount of raw material gas supplied may be smaller).

In the present invention, the formation of a hydrogenated silicon thin film is typically performed at a temperature range of 100 to 450'C. In addition, in the examples described later, an example was shown in which the thin film formation temperature was 300°C.

However, the present invention is characterized in that even if the forming temperature of the thin film is constant, the bonding form of hydrogen in the thin film can be changed arbitrarily by changing the applied energy. It can be said that this is an advantageous technology that cannot be found anywhere else.

For the glow discharge decomposition operation of the present invention, a glow discharge decomposition method known per se may be applied as is.

That is, a substrate made of glass, stainless steel, ceramics, etc. on which a hydrogenated silicon thin film is to be formed is placed in a reaction chamber capable of glow discharge. Then, while supplying a disilane-containing gas into the reaction chamber such that the thin film formation rate was 20 people/sec, IOK J per disilane vehicle mass was added.
By applying the above glow discharge energy, a hydrogenated silicon thin film is formed under reduced pressure below IOT orr.

The hydrogenated silicon thin film obtained in the present invention is useful for semiconductor devices, and can be particularly suitably applied as a photoactive layer of an amorphous silicon solar cell. Needless to say, it is also useful for use in photoreceptors.

The present invention will be explained in more detail in the following examples.

Example 1 A silicon wafer with a specific resistance of 3000 Ωcm or more was placed in an RF capacitively coupled glow discharge facility having parallel plate electrodes equipped with substrate heating means, evacuation means, and gas introduction means.
A Konning Co., Ltd. 7059 glass substrate was installed and heated to 300° C. while being evacuated to 10 Torr or less using an oil diffusion pump. Next, 90 to 5003 CCM of 10% disilane diluted with helium was introduced, and 13.56
Pressure 1-5 Tor while applying power with frequency of MHz
A hydrogenated silicon thin film was formed by glow discharge at r.

The results are shown in FIGS. 1, 2 and 3.

In Figure 1, a shows the result with a power of 150 W and b shows the result with a power of 50 W, but since the gas flow rate is 1503 CCM, when the applied energy is calculated using the above formula H), these are 26 KJ/g, respectively.St and H et al., 8 .6 KJ/g
-3iz Hc. In figure a, 1980cm
While the peak at 2060 cm-' is larger than the peak at 2060 cm-', this is reversed in the figure, making it clear that the bonding form of SiH increases as the applied energy increases. . Therefore, the corresponding photoconductivity is 3.0 for a and b, respectively. ．． 4. * 10' (Ω・0
m door, 1.8*IQ-'(Ω·cm)', and a is about 19 times better than b. Also, photosensitivity (σ
ph/σd) is 2.5*10 for a and b, respectively. 1.
1*lO1+, and a is about 23 times better than b. The improvement ratio of photoconductivity and photosensitivity (19 to 23 times) agrees well, probably because the photoelectric properties were improved by increasing the applied energy.

FIG. 2 shows the changes in photosensitivity by varying the applied energy (2) when 10% disilane was used at 500 SCCM and 300 SCCM, respectively.

In the figure, A indicates 500 SCCM, and B indicates 300 SCCM. Approximately 10KJ/g Si.

It is clear that by applying energy of H6 or higher, a thin film with an excellent photosensitivity of over 10 can be obtained.

Figure 3 shows 500 SCCM of 10% disilane,
The relationship between the applied energy ■ and the thin film formation rate R was investigated for 300 SCCM and 92 SCCM. 1, ■ and ■ in the figure are 500 SCCM and 3 respectively.
Compatible with 005CCJI and 92SCCM. It can be seen that if an energy of about 10 KJ/g Si:c 1% or more is applied, the thin film formation rate R is almost determined by the amount of disilane supplied. (In addition,
In 5005CCH, IOK J/g
Even in the energy range of S iL H6 and above, the formation rate R gradually increases, but this is because the thin film forming apparatus used in the experiment has not yet been sufficiently optimized to supply a large amount of raw material. . ) As can be seen from the corresponding FIG. 2, the improvement in photosensitivity shows a nearly saturated phenomenon.

[Brief explanation of the drawing]

FIG. 1 is an infrared absorption spectrum diagram of a hydrogenated silicon thin film. In the figure, a indicates the present invention, and b indicates a comparative example. Figure 2 is a graph showing the relationship between photosensitivity (σph/σd) and applied energy 1, and Figure 3 is a graph showing the thin film formation rate R.
It is a graph showing the relationship between the applied energy and the applied energy. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] (1) When forming a hydrogenated silicon thin film by glow discharge decomposition of a disilane-containing gas, the energy applied to the disilane is 10 KJ or more per unit mass of disilane, and the formation rate of the hydrogenated silicon thin film is A method for forming a silicon hydride thin film in which a greater number of bonding forms of SiH than 5iH1 are present in the thin film by controlling the flow rate within a high speed range of 20 persons/sec or more.