JPS63222425A - Manufacture of amorphous silicon alloy film - Google Patents

Abstract

PURPOSE:To prevent the yield of a dangling bond, by changing the temperature of a substrate when a film is formed, in correspondence with the optical band gap in an amorphous silicon film to be formed. CONSTITUTION:Raw material gases from gas cylinders 9a-9c are introduced into a reaction container 1, whose pressure is reduced through an exhaust system 2. An amorphous silicon alloy film is formed on a substrate 5, which is mounted on an electrode 4 between upper and lower electrodes 3 and 4. At this time, when the temperature of the substrate 5 is increased with a heater 6, active species contributing to the film formation are set at stable places on the surface of the substrate 5 with the temperature increase. Since high density network is formed in this way, migration is improved. Meanwhile, when the temperature of the substrate 5 is increased too much, hydrogen is eliminated from the active species or the surface reaction is increased. Therefore, the migration is decreased. Then, the optimum temperature Ts of the substrate 5 is made to be Ts=300 (1.75- deg.ptical band gap)+200.

Description

Detailed Description of the Invention B1 Industrial Application Field The present invention is directed to the production of an amorphous silicon alloy film in which an element that adjusts the optical gap to an arbitrary value is added to amorphous silicon and alloyed with the amorphous silicon. Regarding the method.

(4. Conventional technology) As the use of amorphous solar cells progressed from power sources for small consumer electronic devices such as calculators and wristwatches to photovoltaic power generation, semiconductor junctions also changed from single-layer type to JP-A-58-116779. Development goals are expanding to include laminated (tandem) structures.

Conventionally, the photoactive layer that mainly contributes to power generation in amorphous solar cells is made of amorphous silicon (a-8i) in which dangling bonds that form defects are terminated with hydrogen and/or herogen. ) has been used, and high photoelectric conversion characteristics have been obtained by hydrogenated amorphous silicon (a-E31:H) in which hydrogen is used as a dangling bond terminator.

On the other hand, in a stacked amorphous solar cell, the optical bandgap ICg of the photoactive layer as disclosed in the above-mentioned publication is
So-called multi-bandgap cells with different opts have attracted attention, and the a-8i's g gopt (1,756'V)
Based on the standard, we use high-quality wide bandgap materials such as non-quality silicon carbide and amorphous silicon nitride, which have a wide bandgap, and narrow bandgap materials, such as amorphous silicon germanium and amorphous silicon tin, which have a narrow bandgap. There is an urgent need to develop amorphous silicon alloys. It has not yet been industrialized, except as an amorphous silicon alloy.

This is thought to be due to the addition of an element for optical band gap adjustment to amorphous silicon, which lowers the density of the film network and generates a large number of dangling bonds in the added element. .

(c) Problems to be Solved by the Invention As mentioned above, the present invention is characterized by the fact that the amorphous silicon alloy film has a lower network density than the amorphous silicon film and a large number of dangling bonds are generated in the added elements. This is an attempt to solve the problem of deterioration in film properties.

B) Means for Solving the Problems In order to solve the above problems, the manufacturing method of the present invention decomposes a source gas containing at least a silicon element and an element that contributes to adjusting the optical band gap.

The optical bandgap on the substrate surface is ggopt(ey)
A method of manufacturing an amorphous silicon alloy film, comprising: depositing an amorphous silicon alloy film of The optical bandgap Egopt of
eV].

TB-300x (1,75-ggopt)+200±1
It is characterized by being set to 0.

e) Production As mentioned above, the substrate temperature T8 ("C) during film formation.

Corresponding to the optical bandgap ggopt [eV] of the amorphous silicon alloy film to be formed.

Tll-300X(t7Tl1-300X(+75-E
By setting it to ±10, the mobility of the optical band gap axis node element can be improved, and the element stays in an unstable region and moves to a stable site without forming a dangling bond. Combine these sites to form a network.

(f) Example Figure 1 is a plasma OV for explaining the manufacturing method of the present invention.
This figure shows a film forming apparatus using the D method, and the apparatus itself is well known to those skilled in the art. That is, (1) is a reaction vessel whose pressure is reduced to 10 Torrjd via an exhaust system (2), and (31+4) is a pair of upper and lower parts disposed opposite each other across a reaction space in the reaction vessel (1). electrode.

(5) is a substrate placed on one of the lower electrodes (4) to support the formed film; (6) is the substrate (5);
) is heated and maintained at a predetermined temperature by a heater built into the lower electric bridge (4), and (7) is a pair of upper and lower electrodes (3) of the queen.
High frequency 1 that gives high frequency power to the bar 4)! lX, (8!
L) (8t)) (8C) is a gas cylinder for storing the raw material gas introduced into the reaction vessel (1), (96) (91))
(90) is a mass 70-controller that controls the flow rate of raw material gas flowing out from each gas cylinder (8&) (8b) (80).

Therefore, in such a device, as a raw material gas.

When an a-81:H film was formed using 81H4, S
iH4 flow rate 201:! O/min 1 minute store reaction pressure 0. ITO
Under the film forming conditions of rr frequency power of 30 W and substrate temperature of 200°C,
The +11 dark conductivity (cra) used in amorphous solar cells is 10 to 10 [Ωam-'
), photoconductivity *((r-1)h) is 10-' to 10-5 [
A -817H film having an optical band cap (Rgopt) of 1.75 [eV] and high photoconductivity was obtained.

Next, under the above film forming conditions, BiT (
4 gas and H2-based 2% G e H4 gas at 5Q per minute
cc In addition, hydrogenated amorphous silicon germanium (a narrow bandgap material) is used as an amorphous silicon alloy film.
a-8iGe:H) [g was formed.

Item 1 of Table 1 below shows various characteristic values of the a-31Ge:H film.

, 1-E, Below is Table 1 in the margin.In addition, in the above various characteristic values, the optical band gap I
Cgopt is the optical absorption spectrum (? 〇PLOT
), and the measurement of dark conductivity ya and photoconductivity ph is A.
I! A gap cell structure was used in which Bah was used as an electrode, and the characteristic energy Bah was determined by extrapolating the results of the charge flow measurement in such a structure to the results of the previous measurement of the light absorption spectrum.

In this way, in the a-81G@:H film formed at a substrate temperature (Te) of 200 ("C), I:gOpt
is t5 (eV) and 1.75 (θV) of a-81:H film.
In other words, although it has a high light absorption property, its one-dimensional conductivity (7-ph) is small, and its characteristic energy Bah is also large, resulting in very poor film properties.

Therefore, the substrate temperature (Ts) was increased to 240°C, 275°C, and 300°C as shown in Table 1, Items 2, 5, and 4, and the a-8iGe:H film was When the film was formed, various characteristic values were obtained as shown in Table 1. FIG. 2 depicts the characteristic energy gch in correspondence with the symbols in Table 1. The characteristic energy Eoh is an important value that particularly indicates the state of the tail level, which is one of the defect levels of the a-8iGe:H film, and a small Bah means that the film properties are good. Therefore, a-81G with an optical bandgap (ECgOpt) of 15 (ev):
For the H film, the substrate temperature (Tg) is approximately 275 ('C).
), the film properties can be optimized.

In this way, the film properties of the a-f31Ge:H film are determined by the substrate temperature (
The reason for the TlB) dependence is that the substrate temperature is 200°C.
, 240°C, and 275°C, active species (particularly Ge) contributing to film formation settle on stable sites on the substrate surface, improving migration (mobility) to form a high-density network. Therefore, 200℃, 2
It is thought that the characteristics at 275℃ are better than those at 40℃, and
If the temperature is increased from 75°C to 300°C, the substrate temperature is raised too high, and the migration of Ge decreases due to the detachment of hydrogen from the weak Ge-H bond or the resulting increase in surface reactivity. Characteristics at 500℃ are 27
It is considered to be inferior to 5℃.

Therefore, as mentioned above, when increasing the density of the a-8iGe network, optimization of the film properties is desired.

It is necessary to consider the critical substrate temperature effect, and the substrate temperature 're('c) is as shown in this example (Tel-20 at ggopt-1, 75ev).
Te-275 at 0℃, EigOPt-” 1.5eV
Since ℃ is optimal, a-1 with other Egopt values
91Ge:) (even in the film, as shown in Figure 3).

Optimization of film characteristics can be achieved by setting the temperature range to allow a fluctuation range of ±10° C. around the substrate temperature determined by Te-300 (1,75-Egopt) 4-200.

Figure 4 shows that the optical bandgap (EgOl)t) is 16
2 (IIV) shows the measurement results of the characteristic energy goh of the a-EliGe:H film, substituting the value of EgOp't; -162 (e'i') for the substrate temperature (T-) in the above formula. The film was formed by setting the temperature to 240°C, which was calculated by
As the 5L-31()8:H film of (ev), a film having a characteristic energy Eah of 29 CmeV''J, which is unprecedented, and good film properties was obtained.

(G1. Effects of the invention The manufacturing method of the present invention is clear from the above description.

The substrate temperature 'rs ('c) during film formation is determined by the optical band gap Eg of the amorphous silicon alloy film to be formed.
By setting corresponding to opt(θV), BH
The mobility of gopt regulating elements can be improved, and these elements do not stay at unstable sites and form dangling bonds, but move and combine with stable knights, forming a network at the sites. A high-quality film with high photoelectric properties and few tail levels can be obtained by using the optical band gap adjusting element that causes the low-density network.

[Brief explanation of the drawing]

The first factor is a conceptual diagram of the film forming apparatus used in the manufacturing method of the present invention, Figure 2 is a characteristic diagram showing the dependence of characteristic energy on substrate temperature in the amorphous silicon germanium section, and Figure 6 is the optical band gap. Figure 4 shows the characteristic diagram showing the substrate temperature dependence of 1.62 (e V ).
FIG. 2 is a characteristic diagram showing the characteristic energy of an amorphous silicon germanium film of FIG. (1)...Reaction container, (31(4)...Upper and lower electrodes, (5)...Substrate.

Claims (1)

[Claims] (1) An amorphous material that decomposes a source gas containing at least a silicon element and an element that contributes to adjusting the optical band gap, and deposits an amorphous silicon alloy film with an optical band gap of Egopt [eV] on the substrate surface. In the method for manufacturing a silicon alloy film, the substrate temperature Ts [°C] during film formation of the amorphous silicon alloy film is determined by adjusting the optical band gap Egopt [eV] of the amorphous silicon alloy film.
], Ts=300×(1.75−Egopt)+200±1
1. A method for producing an amorphous silicon alloy film, characterized in that the film has an amorphous silicon alloy film of 0.