JPS59207621A - Formation of thin film - Google Patents

Abstract

PURPOSE:To eliminate voids and pin-holes on a substrate by a method wherein reactive gas, which contains the gas which is hard to be decomposed such as N2 and CH4, is preliminarily activated before being subjected to optical CVD. CONSTITUTION:A substrate 3 is placed on a supporting table 4 in a reaction tube 2 and the reaction tube 2 is sealed air-tightly. A valve 11a is opened and the reaction tube 2 is evacuated by an exhaust pump 11b. The substrate and the flow path of the reactive gas are heated to the prescribed temperature by a heater 6 and an induction heater 7 respectively. A valve 10a is opened to the prescribed rate and mercury vapor is introduced with N2 as carrier gas. A low voltage mercury lamp 5 is lit and the substrate 3 is irradiated. MFCs (mass flow controller) of a group 9 of bombs are operated in order to introduce the reactive gas of the prescribed composition of each kind of gas into the reaction tube 2 through an inlet pipe 8. The preliminarily activated reactive gas reaches the neighborhood of the substrate 3 and subjected to optical CVD treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a thin film, and more particularly to a method for forming a thin film by photochemical vapor deposition (photoCVD).

Conventional technology Conventionally, methods for forming thin films using chemical vapor deposition (CVD) include thermal CVD, which is performed while heating a substrate to a high temperature of 600°C or higher, plasma CVD, which uses plasma energy such as glow discharge, and There is a photo-CVD method that uses light energy such as ultraviolet light. Among these methods, the thermal CVD method has the disadvantage that the substrate temperature becomes too high, causing great damage to the substrate. In addition, the plasma CVD method is
There are many factors involved, and it is difficult to control them, resulting in poor reproducibility of the produced film, and pinholes are often generated due to abnormal discharge.For example, in order to obtain high-quality thin films such as amorphous silicon films in solar cells, etc. The substrate temperature is set to 250℃.
It is necessary to maintain the high temperature state above, and the film formation is sensitive to the electron temperature distribution, electron density distribution, gas concentration distribution, etc. in the plasma, and therefore the uniformity of the large area film is not sufficient. It has the following disadvantages.

On the other hand, although the photo-CVD method has the advantage of being able to form a thin film at a relatively low temperature, it also has the following drawbacks.

That is, for example, in the case of l-1 sensitized photoCVD method, about 4.8
The energy of 6 eV acts as a trigger and its use becomes selective, and a large amount of decomposition energy for decomposing the reaction gas cannot be secured. Therefore, N2.02, NHa, C
There is a tendency that gases such as H4 and 82, which have large binding and dissociation energies, cannot be decomposed or are difficult to decompose. Another disadvantage is that the thin film formation rate is slow.

Purpose The present invention has been made in view of the above points, and provides a method for forming a thin film that can form a high-quality thin film without voids or pinholes on a substrate at high speed using a gas made of arbitrary components. The purpose is to provide a method.

Configuration First, the principle of the method of the present invention will be explained. For example, H.O.
In the case of sensitized photolysis reaction, SiH4'' gas supplied near the surface of the substrate and mercury (
When H(+> vapor is irradiated with ultraviolet light of frequency ν, <H(] vapor is photoexcited as shown in equation (1) below, which causes the subsequent reactions shown in equations (2) and (3), for example. is caused.

Ho+hν−−−→)l(]” (1
)H(+”+N2-1→H(] +N2 staff 2
(2) HCl”+SiH+→Si H2+H2+H(1
(3) Here, HQ"Ho** represents photoexcited mercury atoms with different energy units, and the respective energy amounts are 112.7 Kcal/mole (4,86 eV),
107.0Kcal/n+ole(4,64eV
) and the relaxation time is 1.14 xl 0-7sec, 10
-' sec. Therefore, 112.7Kcat/
greater than mo18 or at least 100Kcal
Molecules with bonding/dissociation energy greater than /mole are not decomposed by the photoexcited mercury atoms Hg'', or even if they are decomposed, the efficiency is low.

4- Therefore, in the method of the present invention, for example, N2°CH4,
The idea is to preliminarily activate a reactive gas containing gases that are difficult to decompose, such as NH3 and H2, before processing it with the photo-CVD method, thereby increasing the decomposition efficiency and increasing the thin film production rate. In this way, the efficiency of the reaction involving a gas with large bonding/dissociation energy, such as shown by the following formula (4), is increased, and a thin film made of Si 3 N4 is formed at a high speed.

3Si Ha NJ ) + 4NHa <Q
)→5isNa (S) + 128
2 (CI>(4)) Hereinafter, the structure of the present invention will be explained based on specific examples. FIG. 1 is a schematic diagram showing one example of an apparatus for carrying out the method of the present invention. A substrate 3 is installed on the outlet end side inside a cylindrical quartz reaction tube 2.The substrate 3 is provided with its longitudinal direction extending along the longitudinal axis of the reaction tube 2. A low-pressure mercury lamp 5 as a light source is disposed facing the substrate 3 through the tube wall of the reaction tube 2.The low-pressure mercury lamp 5 is, for example, Ultraviolet light with a dominant wavelength of 253.7 nm is emitted and irradiated toward the substrate 3 inside the reaction tube 2. Also, on the outside of the reaction tube 2 and on the almost opposite side of the mercury lamp 5, there is a lamp for heating the substrate 3. A heater 6 made of, for example, a halogen lamp is provided.

An induction heater 7 is fitted on the inlet end side of the reaction tube 2. This induction heater 7 has a high frequency power source (
(not shown) is connected, and its induction heating effect efficiently heats the gas flowing inside the reaction tube 2.

An inflow pipe 8 extends from the end face 2a of the reaction tube 2 on the side where the induction heater 7 is inserted. MFC on 9b, 9c, 9d...
(mass flow controller). Each cylinder 9 is filled with various gases that are components of the reaction gas to be supplied.

On the other hand, the end surface 2b of the reaction tube 2 on the side where the substrate 3 is installed
Two lines of piping 10 and 11 are connected to the . One of the pipes 10 is provided with a valve 10a and a container 10b in which mercury is stored. Then, nitrogen gas N2 as a carrier gas is flowed through this pipe, and mercury vapor is supplied into the reaction tube 2. The other pipe 11 is a vacuum evacuation pipe, and is provided with a valve 11a and an evacuation pump 11b to bring the inside of the reaction tube 2 into a vacuum state suitable for a photochemical reaction.

A thin film forming method performed by the apparatus configured as described above will be described.

First, the substrate 3 is placed on the support stand 4 inside the reaction tube 2, and the reaction tube 2 is sealed. Next, the valve 11a is opened and the exhaust pump 11b is driven to pump the inside of the reaction tube 2, for example, 1Q-3.
A vacuum state of about torr is created. And the heater 6
In addition to heating the substrate to a predetermined temperature that is lower than that of the conventional technology, a high-frequency current is also applied to the induction heater 7 used in the preliminary treatment 7 to heat the substrate to a predetermined temperature that is lower than that of the conventional technology. The gas flow path is heated to a predetermined temperature.

Under the above conditions, the valve 10a is opened by the required amount so as not to substantially change the degree of vacuum inside the reaction tube 2.
Mercury vapor is introduced together with nitrogen gas as a carrier gas. Then, the low-pressure mercury lamp 5 is turned on to irradiate the substrate 3 with ultraviolet light having a wavelength of, for example, 253.7 nn+, and the MFC of each cylinder in the cylinder group 9 is appropriately operated to convert various gases into reactive gases with predetermined compositions. The components are mixed together and flowed into the reaction tube 2 through the inflow pipe 8.

The reaction gas introduced into the reaction tube 2 is passed through the induction heater 7
thermal energy is applied and preliminary activation is performed. The preliminarily activated reaction gas reaches a region near the substrate 3 and undergoes photo-CVD reaction treatment there. That is, the photochemical reactions represented by the above-mentioned formulas (1) to (4) occur through the mercury atoms activated by the ultraviolet light emitted from the mercury lamp 5. The sufficiently activated atoms or molecules to form a thin film adhere to the substrate 3 heated to a predetermined temperature to form a desired thin film. In this case, NH3, which was difficult to treat by photochemical reaction in the conventional technology,
Gases such as H2 and H2 are also easily activated or decomposed because they are preliminarily heated and activated in two stages. Therefore, for example, the chemical reaction represented by equation (4) can be smoothly promoted by the photo-CVD method, and a thin film made of Sf 3 N4 can be formed on the substrate at a higher speed. Furthermore, the thin film formed by this method is of good quality and has no pinholes or voids, even though the substrate temperature is set lower than that of conventional plasma CVD methods.

Next, other embodiments of the present invention will be described.

11 in this example! The formation method differs from the above embodiments only in that plasma energy from glow discharge is used to preliminarily activate the reaction gas.

FIG. 2 is a schematic diagram showing an apparatus for implementing the thin film forming method of this example. Incidentally, the same components as those in the above embodiment are given the same reference numerals, and the explanation thereof will be omitted. In FIG. 2, on the side of the reaction tube 2 connected to the inflow pipe 8, there is a pair of parallel plate electrodes 12 for glow discharge.
12 are arranged facing each other and separated by a predetermined distance. Each electrode 12 is connected to a power source 13, whereby a voltage of approximately several hundred volts is applied between the two electrodes 12, 12, causing a glow discharge.

When forming a thin film using such an apparatus, the glow discharge power supply 13 is turned on, and the degree of vacuum in the reaction tube 2 and the temperature of each part are maintained under the set conditions as in the above embodiment. A reaction gas mixed to a predetermined composition is introduced between the parallel plate electrodes 12 and 12 through the inflow pipe 8. When the introduced reaction gas passes between the electrodes 12 and 12,
Energy is given to the plasma generated during that time by the glow discharge action, and the plasma is preliminarily activated in the same manner as in the previous embodiment. The preliminarily activated reaction gas reaches the vicinity of the substrate 3 on the other end side, where it undergoes the same photo-CVD reaction treatment as in the previous embodiment and is sufficiently activated. This results in
NH3 and H2 have large bond/dissociation energy and are difficult to decompose.
These gases are easily activated or decomposed, and a high-quality thin film made of desired components and free from pinholes and voids can be efficiently formed by photo-CVD. Note that, in this case, even if the heating temperature of the substrate 3 is set to a relatively low temperature of 100° C. or less, thin film formation will not be hindered.

In the two examples described above, activated mercury vapor (H(1'')) is used as a catalyst in both cases, but in the method of the present invention, the treatment is divided into two stages. Since the target gas is activated, the supply of mercury vapor can be omitted.

Effects As detailed above, according to the present invention, by preliminarily activating or decomposing the gas to be treated before subjecting it to the photo-CVD reaction, the bonding/dissociation energy, which has been difficult with various conventional CVD methods, can be reduced. Gases with large amounts of gas can also be efficiently processed by the photo-CVD method. Therefore, it is possible to form a thin film containing these gases in a high-quality state without pinholes or voids at a relatively high speed and with high efficiency. However, the present invention is limited to the above-mentioned specific embodiments. Of course, various modifications are possible within the technical scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is a schematic diagram showing another embodiment of the present invention. (Explanation of symbols) 2: Reaction tube 3: Substrate 5: Low-pressure mercury lamp 7: Induction heater 12:
parallel plate electrode

Claims (1)

[Claims] 1. Thin film formation in which a substrate is housed in a reaction vessel and a reaction gas containing a predetermined component is introduced into the reaction vessel to form a thin film made of the predetermined component on the substrate. The method includes a pretreatment step of imparting energy to a predetermined component of the reaction gas, and a thin film forming step of causing a photoCVD reaction of the predetermined component of the pretreated reaction gas to deposit it on the substrate. A thin film forming method characterized by: 2. The thin film forming method according to item 1 above, wherein the pretreatment step is a step of applying thermal energy of 300° C. or higher. 3. The thin film forming method according to item 1 above, wherein the pretreatment step is a step of applying plasma energy by glow discharge.