JPS61194838A - Thin film forming method by cvd and equipment therefor - Google Patents

Abstract

PURPOSE:To alleviate the production and adherence of a foreign material due to the discharge of reaction gas by reacting O2 gas with reactive gas absorbed to the inner wall of a reaction furnace before conveying a wafer after feeding N2 gas. CONSTITUTION:Semiconductor wafers 5 are aligned on a wafer table 4 in a reaction furnace 1. A heater 10 is energized to heat the wafers 5. Purging N2 gas is fed from a purging gas feeding tube 9 into the furnace, and reaction gas is fed from a reaction gas feed tube 8 into the furnace. Then, N2 gas is fed from the tube 9 into the furnace, and when the reaction gas is purged, the gas absorbed to the inner wall of the furnace remains. When O2 gas is fed from the tube 9, the reaction gas absorbed to the inner wall of the furnace is reacted with the O2 gas to form a foreign material. When N2 gas is fed from the tube 9, fine materials not adhered to the furnace wall of the foreign materials are purged together with the O2 gas. Thus, the projection and adher ence of the foreign material due to the discharge of the reaction gas can be alleviated.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to chemical film formation (hereinafter referred to as CVV) on the surface of a semiconductor wafer.
It is abbreviated as D. chemical vapor deposition, C
chemical
(abbreviation for on)) relates to technology for forming thin films.

In particular, the present invention relates to a CVD film-forming method and a CVD film-forming apparatus that are improved so that solid fine particles do not adhere to the wafer surface.

[Background of the invention]

In CVD, for example, a wafer heated to about 500°C is heated with a reactive gas (SiH, gas, or PH, gas + O2 gas and Si
This is done by supplying H4+PH3+○,).

The above reaction gas is blown onto a wafer in a reactor using N2 gas as a carrier, and a thin film of Sio or phosphorus-1-glass (PSG) is deposited on the surface of the wafer.
Form a thin film. In addition, two-phase film formation of Sx○ and PSG may be performed.6 FIG. 2 is a vertical cross-sectional view showing an outline of the CVD apparatus, and FIG. 3 is a plan layout diagram thereof as well.

A reactor (bell jar) 1 includes a conical buffer 2 covered with a conical cover 3, and a ring-shaped wafer table 4 installed around the buffer 2 so as to be rotatable.
The wafer table 4 is provided with a loader 6 that sequentially supplies semiconductor wafers 5 as workpieces, and an unloader 6 that sequentially unloads the wafers 5.

A reaction gas feed pipe 8 and a purge gas feed pipe 9 are connected to the vicinity of the apex of the conical cover 3.

8a and 9a are a reaction gas feed nozzle and a purge gas feed nozzle, respectively.

The wafer table 4 is provided with a heater 10 to heat the wafer 5 to a predetermined temperature (for example, 500° C.). The reaction gas (S iH
4 or PH, +O, and SiH4+PH, +0
A thin film of SG) is deposited on the surface of the wafer 5.

Conventional CVD operations generally involve heating a semiconductor wafer loaded into a reactor, and adding (i) Nt to the reactor.
Gas is introduced to purge the air in the furnace, (ii) reaction gas is introduced to perform a film forming reaction, (iii) N gas is introduced to purge the reaction gas, (tv) The steps are performed in order, such as unloading the wafer from the furnace.

However, when the film is formed by the CVD operation according to the above-mentioned prior art, there is a problem that Si◯ and fine particles (hereinafter referred to as foreign matter) adhere to the surface of the wafer.

The mechanism by which the above foreign matter is generated and attached is as follows.

FIG. 4 schematically shows an enlarged view of the inner surface of the furnace wall in a state where the reaction gas was purged with N2 gas in step (iii). That is, reactive gas molecules 12 are adsorbed on the inner surface of the furnace wall 11. 13 is a foreign substance attached to the wall surface.

The adsorbed molecules of the reaction gas are gradually released, but the release rate is significantly slower than when purging the furnace gas. FIG. 5 is an explanatory chart in which time is plotted on the horizontal axis and reactant gas concentration in the furnace is plotted on a logarithmic scale on the vertical axis.

Time t0 is the time when the CVD reaction starts, and time t4 is the time when the CVD reaction ends. At the above time point t, the above (river) process (
Since the reaction gas is purged with nitrogen gas, this t
The reaction gas concentration rapidly decreases from □ and reaches almost O at time t.

In the prior art, the step (iv) (wafer unloading) was performed at this point.

However, from time point 1, the adsorbed reaction gas begins to be released (indicated by diagonal lines), and the released reaction gas comes into contact with air (because the furnace is opened for wafer removal). Therefore, the released reaction gas reacts with O9 in the air to generate foreign matter, which adheres to the wafer.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and provides a method that can significantly reduce the generation and adhesion of foreign substances caused by the release of adsorbed reaction gases, and an apparatus suitable for carrying out the above-mentioned method. This is what I am trying to do.

[Summary of the invention]

The basic principle of the method of the present invention created to achieve the above object is as follows. The reactant gas adsorbed on the furnace wall did not have enough time to be released during wafer unloading, and reacted rapidly with the gas, resulting in foreign matter adhering to the wall or in close proximity to the wall. After the 02 gas is generated, the 02 gas is again purged with N and gas, and the forcibly generated foreign matter is discharged together with the 02 gas.

In order to achieve the above object based on the above principle, the CVD thin film forming method of the present invention heats a semiconductor wafer inserted into a reactor, and (i) introduces Nz gas into the above reactor. (ii) supplying a reaction gas to perform a film forming reaction; (iii) supplying nitrogen gas to purge the reaction gas; (iv) removing the wafer from the furnace. In the chemical deposition (CVD) method for unloading, after the step <m> (introducing N 2 gas) and before starting the step (iv) (wafer unloading), zero, The reactor is characterized by feeding gas to cause the reaction gas adsorbed on the inner wall surface of the reactor to react with the 02 gas, and then feeding N and gas again to purge the gas in the furnace.

In addition, the apparatus of the present invention, which was created so that the above-mentioned method of the invention can be easily carried out and fully exhibit its effects, is equipped with a means for heating the wafer inserted into the reactor. In a chemical deposition (CVD) apparatus configured to sequentially supply a reaction gas and a purge gas to (a)
N gas for purging the air inside the furnace, (b) Reaction gas for performing the film forming reaction, (c) N gas for purging the above reaction gas, (d) Adsorbed on the furnace inner wall surface. O, gas, and (e
) The apparatus is characterized in that the N2 gas for purging the 02 gas mentioned above together with the reaction product mentioned above is sequentially introduced in the order of (a) to (e) above.

[Embodiments of the invention]

FIG. 1 shows an embodiment in which the thin film forming apparatus of the present invention is applied and improved to the conventional apparatus described above (FIG. 2) in order to carry out the method of the present invention.

The following two points are different from the conventional device (FIG. 2).

One of the improvements is that the purge gas feed pipe 9 is configured to be able to supply not only N gas but also N gas or 02 gas in a switched manner.

Another improvement is the provision of a supply gas switching device V, which allows (a) operation of supplying N gas from purge gas supply pipe 9, (b) operation of supplying reaction gas from reaction gas supply pipe 8, (C) Operation of supplying N gas from purge gas supply pipe 9, (d) Operation of supplying gas from purge gas supply pipe 9, (e) Operation of supplying N gas from purge gas supply pipe 9. , (f) Stopping the gas feed of both gas feed pipes 8 and 9. The above operations (a) to (f) are configured to be repeated in the above order. In this embodiment (FIG. 1), the supply gas switching device V is provided with an electromagnetically actuated directional control valve with 5 points and 6 positions. The positions (a) to (f) added to the figure correspond to the operations (a) to (f) above, respectively.

To perform CVD film formation using the above CVD film formation apparatus,
Semiconductor wafers 5 as workpieces are arranged on the wafer table 4 in the reactor 1, the furnace is sealed, the heater 10 is energized to heat the wafers 5 to 500°C, and N gas for purging is supplied from the purge gas inlet pipe 9. , gas is fed into the furnace to purge the air in the furnace, and the reaction gas is fed into the furnace from the reaction gas feed pipe 8.

In the present invention, the reactive gas refers to a gas containing SiH as a main component, or a gas containing PH3 as a main component, and a gas containing SiH as a main component.
It refers to a gas whose main component is a mixture of a gas whose main components are H4 and PH, and a mixture of Of.

By feeding the reaction gas, a film is formed on the surface of the wafer 5, and along with this, the reaction gas is adsorbed on the inner wall surface of the reactor 1.

Next, N gas is fed into the furnace from the purge gas feed pipe 9 to purge the reaction gas, and the film formation is stopped, leaving the reaction gas adsorbed on the inner wall of the furnace.

Therefore, when 02 gas is fed from the purge gas feed pipe 9,
The reactant gas adsorbed on the inner wall of the furnace is O.

Reacts with gas to form foreign matter.

Next, when N gas is fed from the purge gas feed pipe 9,
○ Among the foreign particles forcibly generated by feeding the gas, particles that are not firmly attached to the furnace wall are purged together with the 02 gas and do not attach to the wafer 5. Furthermore, foreign matter firmly attached to the furnace wall does not have any harmful effects.According to experiments conducted by the present invention, by inserting the 02 gas supply process between the N and gas supply processes, The amount of foreign matter adhering to the wafer could be reduced to about 1/10.

〔Effect of the invention〕

As described in detail above, according to the CVD film forming method of the present invention, it is possible to significantly reduce the adverse effect of foreign matter adhering to the wafer due to the release of the reaction gas adsorbed on the inner wall of the furnace.

Further, according to the CVD film forming apparatus of the present invention, the above-described method of the invention can be easily carried out without the risk of mistakes, and its effects can be fully exhibited.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the CVD film forming apparatus of the present invention. FIG. 2 is a vertical sectional view of an example of a CVD film forming apparatus according to the prior art, and FIG. 3 is a plan layout view of the same. FIG. 4 is an explanatory view schematically depicting an enlarged cross section of the inner wall surface of the reactor. FIG. 5 is a chart for explaining the release of reaction gas adsorbed on the inner wall of the furnace. 1... Reactor, 2... Buffer, 3... Cover,
4... Wafer table, 5... Semiconductor wafer, 8.
...Reaction gas feed pipe, 9...Purge gas feed pipe, 1o
... Heater, 11 ... Furnace wall of the reactor, 12 ... Adsorbed reaction gas.

Claims (1)

[Claims] 1. A semiconductor wafer charged into a reaction furnace is heated, (i) N_2 gas is introduced into the reaction furnace to purge the air in the furnace, and (ii) the reaction gas is (iii) N_2 gas is introduced to purge the reaction gas, and (iv) the wafer is removed from the furnace.
), after the step (iii) (injecting N_2 gas) and before starting the step (iv) (wafer unloading), O_2 gas is introduced into the reactor to cool the reactor. The reaction gas adsorbed on the inner wall is reacted with O_2 gas,
A thin film forming method by chemical deposition (CVD) characterized by purging the gas in the furnace by introducing N_2 gas again. 2. In a chemical deposition (CVD) apparatus configured to provide a means for heating a wafer loaded into a reactor and to sequentially feed a reaction gas and a purge gas into the above-mentioned reactor, (a) ) N_2 gas for purging the air inside the furnace, (b) Reaction gas for performing the film forming reaction, (c) N_2 gas for purging the above reaction gas, (d) Adsorbed on the wall surface inside the furnace. O_2 gas for reacting with the remaining reaction gas, and (e) N_2 gas for purging the O_2 gas from the previous section together with the reaction product from the previous section, were added to the above (a).
1. A thin film forming apparatus by chemical deposition (CVD), characterized in that the thin film forming apparatus is configured to sequentially feed the materials in the order of ) to (e).