JPS637020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a thin film, and mainly relates to an amorphous semiconductor.

For example, when amorphous silicon (hereinafter referred to as a-si) is grown by decomposing monosilane (SiH ₄ ) using the glow discharge method, or when a-si is grown in a hydrogen (H) atmosphere by sputtering. , usually contains about 10% H. In this case, it is believed that the dangling bonds in a-si are compensated by H and become inactive. However, if the bonding form of H and Si is inappropriate, or if a large amount of H is mixed into a-si, a-si
The electrical characteristics of will deteriorate significantly.

The purpose of the present invention is to utilize the natural frequency of the bond between H and si to determine how H is incorporated, which is important for the electrical characteristics of a-si, and to irradiate light with the same frequency as that frequency. si that is considered to have a negative impact on
suppresses and controls the occurrence of specific bonds between and H,
-Improving the characteristics of si.

Conventionally, for example, A-SI has been manufactured by several methods such as sputtering and glow discharge method. a-si
In order to control the amount of hydrogen incorporated into the material and the bonding form between H and Si, we have varied the substrate temperature, the pressure during growth, the power to decompose siH ₄ , etc.

JCKnights et al. Philosophical Mag. 1978 no.
As stated in Volume 37, page 467, a
−si, the film is (si)x
It is said that it can be expressed in the form (Si ₂ H ₄ ) _1-x . In other words, in this case, MHBrodsky et al. Appl. Phys.
As stated in Lett. 1977, Vol. 30, p. 563, excessive H is incorporated into a-si.
In addition, JCKnights et al. mentioned above have only one H bonded to si at a substrate temperature of 250°C or higher, i.e.
It is stated that what appears in the form si-H is the main element in the combined form of si and H. However, if the substrate temperature is only increased to 250℃ or higher, (si) x (si ₂ H ₄ ) _1-x
The shape of will not disappear.

DE if the substrate temperature is over 400℃
As stated by Carlson et al. in J. Electrochem. Soc. 1979, Vol. 126, No. 4, p. 690, H incorporated into a-si escapes, and what remains becomes a dangling bond and becomes a recombination center. Significantly deteriorates the characteristics of a-si. For these reasons, in the conventional method, the substrate temperature for creating a-si is 250
A temperature of ~400°C is appropriate, and good quality a-si cannot be obtained at any other substrate temperature.
Furthermore, as the temperature decreases below 250°C, the si-H ₂ bond form increases more than the si-H bond form, and it can be said that an excess of H exists in a-si near room temperature.

As an example of the deterioration of the a-si electrical characteristics when the substrate temperature is lowered, FIG. 1 shows the photoconductive characteristics when the substrate temperature is changed. The deposition conditions are as follows.

After evacuating with a rotary pump, SiH ₄ diluted with He was introduced into a Belgear until the vacuum level reached 0.2 Torr, and a transparent conductive film made of ITO film (InSnO film) was deposited on quartz glass. 1μm
a-si was grown. Thereafter, an electrode on the a-si surface was formed using an Au vapor deposition film. Substrate temperature is 170~350℃
changed to. In Fig. 1, Γ indicates the current-voltage characteristics during 2.651x irradiation, and the ● mark indicates the current-voltage characteristics in the dark. As shown in Figure 1, when the substrate temperature falls below 200°C, not only the photoconductive properties deteriorate, but also the specific resistance in the dark tends to decrease. The amount of hydrogen contained in a-si is 170 to 350
In the temperature range up to ℃, it was approximately constant at about 12 to 13%, but looking at the infrared absorption characteristics, the peak at 2000 cm ^-1 , which is the absorption of si-H, tends to decrease as the substrate temperature is lowered, and si- It was found that the peak at 2100 cm ^-1, which is the absorption of H ₂ , tends to increase.

During growth as a growth parameter other than substrate temperature.
Optimum conditions are determined by considering the siH ₄ decomposition power, degree of vacuum during growth, etc., but even if the amount of hydrogen incorporated into a-si and the ratio of the bonding form of H changes slightly, si may have an adverse effect. It has not been possible to almost completely eliminate the specific bond form of and H. This is because the bond form of si and H can only be changed indirectly.

Next, a conventional example in which characteristics change by irradiation with light will be described. In 1977, JCKnights discovered that the electron spin resonance (ESR) signal changes sensitively by irradiating the a-Si film with light.
Proc.of.Intern.Conf.on Amorphous and Liquid
Revealed on Semicon.Edinburgh page 433. Also, DLStoebler et al. Appl. Phys.
Lett., Vol. 31, p. 292, 1977, states that when a-si is irradiated with light for a long time, the photoconductive properties deteriorate by nearly four orders of magnitude, and the dark resistance decreases by four orders of magnitude. They proposed a model in which the level density in the forbidden band changes. It can be seen that even after a-si is grown on a substrate, the characteristics of a-si can be changed by light irradiation.

For example, the present invention utilizes the absorption of a specific bonded form of si and H, and uses direct means to absorb this into a-si.
The object of the present invention is to provide a manufacturing method that can form a bonded type that does not adversely affect the electrical characteristics of the a-si, and can dramatically improve the characteristics of a-si.

An embodiment of the present invention will be described in detail using the drawings.

For example, the raw material gas from the introduced body 1 in Fig. 2 is
siH ₄ diluted with Ar or He is introduced into the vacuum device 2 . 1 has not only a raw material gas inlet but also an electrode for generating glow discharge. 3 is a substrate on which a-si is grown; 4 is a heater for heating the substrate; and 5 is a rod for supporting the substrate, heater, etc. A high frequency is applied by the electrode 1, and a discharge is caused in the vacuum apparatus to decompose the introduced gas.
8 is an exhaust port. The above is a conventional high frequency glow discharge capacitively coupled ASI growth apparatus. Reference numeral 10 is a light source that generates light having a wavelength within a certain range, which is used in the present invention, and may be, for example, a halogen lamp provided with a suitable filter, or a laser. The light source 10 irradiates the substrate 3 or its surroundings with light. A method of selecting the growth of light generated from the light source 10 will be described.
CCTsai et al. reported that the absorption peak of the bond between si and H in a-si is known as Solar Energy.
Mat.1979. As stated on page 29 of Volume 1, there is absorption in si-H ₂ stretching mode at 2100 cm ^-1 , si-H stretching mode at 2000 cm ^-1 ,
si−H ₂ stretching mode at 900 and 850cm ^-1 , 640cm
There are absorption peaks of si-H Wagging mode at ^-1 .

Therefore, if you want to eliminate the bond form of si−H ₂ , 2100
It is sufficient to use light with a wave number of cm ^-1 , 900 cm ^-1 , or 850 cm ^-1 , and if you want to eliminate the si-H bond type, use 2000 cm ^-1 ,
Light with a wave number of 640 cm ^-1 may be used. It goes without saying that it is not necessary to use light having exactly the above-mentioned wave number, as long as it is within a wave number range that does not affect other coupling types.

Next, the heating temperature will be described. When heating the substrate, there is no need to use a heater if the light energy density is such that high-quality a-si can be obtained by simply irradiating a specific light onto the substrate surface, and if it is too high, it must be cooled. Although the substrate temperature range varies depending on manufacturing conditions, the temperature range shown in the above conventional example is appropriate. Although the configuration example of the glow discharge method has been described above, the light source 10 may be attached to a conventional device in the sputtering method as well.

Next, the position of the light source 10 will be described. In FIG. 2, the light source 10 is located outside the vacuum device 2, but
If light cannot be irradiated due to the material of the bell gear,
If a-si adheres to the inner wall of the bell gear and cannot be effective, it is necessary to put it into the device 2. In this case, a position must be provided in the apparatus 2 where the light source 10 is not affected by the adhesion of a-si, taking into account the flow direction of the raw material gas and the area where plasma is generated.

FIG. 3a shows an example of a configuration in which the light source 10 is placed inside the vacuum device 2, and 20 is a branch provided for the light source 10 of the vacuum device. FIG. 3b shows a light source 10 outside the branch 20.
The end of the branch 20 is made of a material that easily transmits the light generated from the light source 10, such as quartz glass.

Above, we have described a method for dissociating H using absorption due to resonance vibration of the bond between si and H. Next, we will describe a method for irradiating light with the energy necessary to directly remove H from the bond between si and H.

If you irradiate light with the energy necessary to take one H from si-H ₂ , si-H ₂ will become si-H, and si-
The bond between si and H can be removed by irradiating light with the energy necessary to remove H from the H bond.

For example, when the raw material gas is SiH ₄ , the photochemical decomposition energy of SiH ₄ is about 6.7 eV, and when SiH ₄ is converted to Si
and 4.4eV to decompose into two H ₂ , SiH and H ₂ and H
It takes 5.9eV to decompose into SiH ₂ and H ₂ , 2.1eV to decompose into SiH 2 and H 2 , and 4.1eV to decompose into SiH ₃ and H.

However, the bond energy between si and H is about 3.5 eV, and when this light is irradiated onto the a-si surface grown on the substrate, it is absorbed in the a-si, and depending on the irradiation conditions, the film generates heat and the necessary H is absorbed. dissociate. For this reason, a-
When irradiating light with energy greater than the forbidden band width of si, make sure that the light does not hit the substrate directly, or irradiate pulsed light to ensure that a-si is H.
We devised measures to ensure that the temperature did not reach the point where it would dissociate. Further, it is desirable that the distance between the irradiation section and the substrate be within the mean free path.

Although the above configuration example has been explained focusing on the A-Si manufacturing method, particularly the glow discharge method, the present invention is not limited to A-SI manufacturing, and can also be applied to alloys or semiconductors containing several elements to improve their characteristics. It also applies to manufacturing methods that do not generate specific interatomic bonds.

The light emitted according to the present invention is roughly divided into two types. In other words, there are two types of light: one with an energy larger than the forbidden band width of the thin film, and the other with a smaller energy.
The latter method can be used to directly irradiate the substrate, including heating the substrate, but the former method causes the thin film to generate abnormal heat, so it is necessary to irradiate it by applying pulsed light or preventing light from directly hitting the substrate. is necessary.

As an example, we investigated how H is incorporated into a-si by irradiating the above two types of light using a-si, and it was possible to almost completely eliminate the bond between specific si and H. When irradiated with light that changes the si-H ₂ bond type to the si-H bond type, better characteristics than the conventional a-si electrical characteristics were observed.

As described above, the present invention not only provides a manufacturing method that dramatically improves the properties of amorphous materials, which are considered promising in the future, but also expands the range of applications of amorphous materials and greatly contributes to industry.

[Brief explanation of the drawing]

Fig. 1 is a photoconductive characteristic diagram of the A-SI film when the substrate temperature is changed, Fig. 2 is a diagram showing a schematic configuration example of a device used in H of the present invention, and Fig. 3 a and b are diagrams of the present invention. FIG. 2 is a schematic diagram of another example of the configuration of main parts of a thin film forming apparatus used for. 1... Raw material gas inlet and electrode, 2... Vacuum device, 3... Substrate, 4... Heater, 10... Light source.

Claims (1)

[Claims] 1. In addition to discharge plasma deposition reaction, Si
The bond energy between and H is 2100cm ^-1 , 900
cm ^-1 , light containing a wave number of 850 cm ^-1 or 2000 cm ^-1 ,
A method for producing a thin film, characterized in that light containing a wave number of 640 cm ^-1 is irradiated simultaneously without directly hitting the substrate, or it is irradiated as pulsed light. 2. The method of manufacturing a thin film according to claim 1, wherein the thin film is made of an amorphous silicon film containing hydrogen. 3 In addition to the sputtering reaction, 2100 cm ^-1 , 900 cm ^-1 , and 850 cm ^-1 were found due to the bond energy between Si and H.
A method for producing a thin film, characterized by irradiating the substrate with light having a wavelength of , or light having a wave number of 2000 cm ^-1 or 640 cm ^-1 simultaneously without hitting the substrate directly, or irradiating the substrate with pulsed light. 4. The method for manufacturing a thin film according to claim 3, wherein the thin film is made of an amorphous silicon film containing hydrogen. 5 In addition to the discharge plasma deposition reaction, light containing energy of 6.7 eV, 4.4 eV, 5.9 eV, 2.1 eV, and 4.1 eV, which corresponds to the bond energy of gaseous compounds containing Si and H, is simultaneously applied to the substrate. 1. A method for producing a thin film, the method comprising: irradiating it without directly hitting it, or irradiating it with pulsed light to form amorphous silicon containing hydrogen.