JPS62126641A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To bury the irregularities of a silicon nitride film with silicon, which is yielded by the decomposition of silane gas so as to flatten the surface and to improve protecting ability with acid resistance and waterproof property of silicon itself, by growing the silicon nitride film, stopping the flow of ammonia gas, and flowing only the silane gas for a short time. CONSTITUTION:The pressure of the inside of a reacting tube is reduced by a vacuum pump 8. Then, silane gas and ammonia gas are made to flow on a heated silicon wafer, and a silicon nitride film is grown by a conventional method. When the film having an intended thickness is obtained, a valve for the ammonia gas is closed. Only the silane gas is continuously made to flow on the silicon wafer for several minutes. The time is set so that the appearance of the wafer is hardly changed from that of a silicon nitride film, which has been obtained up to now, when the wafer is taken out. When the silicon nitride film is immersed in acid and wafer, it is found that liquid is strongly repelled and acid resistance and waterproof property are shown.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to low pressure CVD (
Chemical Vapor oepos;tto
n) It relates to a method for manufacturing the device.

[Prior Art] Conventionally, when manufacturing a MOS transistor, a silicon nitride film 4 is used on the surface of a gate oxide film 3 for the purpose of protecting it, as shown in FIG. In the figure, 1.2 is a source and drain of a MOS l-transistor made on a semiconductor, 3 is a gate oxide film (silicon oxide film), 4 is a silicon nitride film, and 5 is aluminum which is a wiring material.

The silicon nitride film 4 has the effect of preventing pinholes in the gate oxide film 3 and contamination from the outside, especially intrusion of alkali metals.

Conventional low pressure CVD is used to generate this silicon nitride film 4.
devices have been used. Its structure is shown in FIG.

In the figure, 6 is a reaction tube, 7 is a heater for an expansion furnace, 8 is a vacuum pump, 9 is a valve for opening and closing gas, and 10 is a silicon wafer.

The inside of the reaction tube is depressurized by a vacuum pump 8, and when a mixture of ammonia and silane gas is passed through a silicon wafer 10 heated to 850"C, a reaction of SiHa+NH3→Si3Na+H2 occurs, and silicon is deposited on the wafer. Nitride film (Si3N
4) is generated.

[Problems to be Solved by the Invention] However, minute irregularities are observed on the surface of the nitride film obtained by the above reaction, and when subjected to chemical treatment, moisture and acid components are absorbed by adsorption. It becomes a film containing
This caused corrosion of aluminum after wiring.

The unevenness of this nitride film largely depends on the purity of the gas, especially ammonia gas, which is highly hygroscopic, but it also has the drawbacks of requiring a large amount of money to purify and requiring careful attention to its management. there were.

Furthermore, acid components once adsorbed into the nitride film are difficult to remove even by washing with water or heat treatment.

[Means for Solving the Problem 1] The present invention has been made based on the above facts, and its purpose is to fill the unevenness of the silicon nitride film with silicon generated by the decomposition of silane gas, flatten it, and further flatten the silicon itself. The process is to produce a silicon nitride film that has enhanced protection capabilities due to its acid and water resistance.

[Embodiments of the invention] The present invention will be explained in detail below.

In Fig. 2, the inside of the reaction tube is 1.0
After reducing the pressure to Torr, silane gas and ammonia gas are flowed through the silicon wafer heated to 850° C., and a silicon nitride film is produced in a conventional manner. When a film of the target thickness is obtained, the ammonia gas valve is closed and only silane gas is allowed to continue flowing over the silicon wafer for several minutes. This time is kept to such an extent that when the wafer is taken out, there is almost no difference in appearance from the silicon nitride film obtained so far.

It can be seen that when the silicon nitride film thus formed is immersed in acid or water, it strongly repels the liquid and exhibits acid and water resistance.

However, its characteristics are almost the same as those of conventional silicon nitride films, and no process changes are required in manufacturing ICs.

Although the gate film of a MOS transistor has been described above as an example, the present invention is effective in all cases where a silicon nitride film is used.

[Effects of the Invention] When reliability tests were conducted on the IC manufactured according to the present invention, it was confirmed that the lifespan was more than twice that of conventional ICs.

In addition, the variation in characteristics was much smaller than that of conventional products, indicating that the material was highly resistant to external contamination.

[Brief explanation of drawings]

Figure 1 shows the structure of a general MOS t-transistor,
FIG. 2 shows the structure of a low pressure CVD apparatus according to the present invention and a conventional manufacturing method. 6...Reaction tube 8...Vacuum pump 9...Gas valve

Claims (1)

[Claims] In a method for manufacturing semiconductor devices using low pressure CVD, in which a silicon nitride film is produced on a semiconductor by a reaction between ammonia gas and silane gas, after growing a silicon nitride film with a predetermined thickness, the ammonia gas is removed, and the silane gas is A method for manufacturing a semiconductor device, characterized in that a semiconductor device is made to flow only for a short period of time.