JPS6242524A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an SiO2 film having no defect on the surface of a metallic silicide by elevating the temperature of the silicide in an inert-gas atmosphere, changing over the inert-gas atmosphere into an oxidizing atmosphere and oxidizing the silicide when the temperature of the silicide reaches a fixed temperature, changing over the oxidizing atmosphere into the inert-gas atmosphere again and lowering the temperature of the silicide. CONSTITUTION:A wafer in which a poly Si layer 17 and a metallic silicide layer 18 are laminated on a substrate 11 is preheated, and the wafer is heated for a fixed time in an inert-gas atmosphere at a temperature lower than an oxidizing temperature and the temperature of the wafer is elevated. When the temperature of the wafer reaches the oxidizing temperature, the inert-gas atmospheres is changed over to an oxygen atmosphere, and the wafer is oxidized for a predetermined time. The oxygen atmosphere is changed over to the inert- gas atmosphere again, and the wafer is cooled slowly. Accordingly, oxidation is started after a point of time when Si in sufficient quantity diffuses in the inert-gas atmosphere, thus coating the wafer with an SiO2 film 20 having no defect.

Description

[Detailed Description of the Invention] [Summary] A metal silicide (hereinafter simply referred to as silicide) is heated in a gradient manner in an inert gas (hereinafter referred to as ramping) to prevent deformation of the silicide. do.

[Industrial application field]

The present invention relates to a method for manufacturing a semiconductor device, and more specifically, to an improvement in a method for oxidizing silicide used in a semiconductor device.

[Conventional technology]

Techniques for using silicide in semiconductor devices have come into practical use, and recently silicide has been used, for example, in gate electrodes of MOS l-transistors.

The process of making it will be explained with reference to the cross-sectional view of FIG.
It is made by a bilayer structure of a silicide layer 18 such as Mo-5i2). In FIG. 2, 12 is a field oxide film, 13 is a source, 14 is a drain, and 15 is a gate a-oxide film. The reason why the silicide layer 18 is used for the gate electrode 16 is that the resistance of the gate electrode can be kept low thereby.

In the manufacturing process of a MOS transistor, the gate electrode 1
Oxidation of the surface of 6 is performed. The reason is that to form the gate electrode 16, polysilicon is sequentially deposited on the semiconductor substrate 11 by, for example, chemical vapor deposition (CVD), MoSi2 is grown thereon by sputtering or CVD, and then The MoSi2 layer and the polysilicon layer are etched to create the electrode shown in FIG. Assuming that the electrode is etched in this step as shown by the dotted line in Figure 2, when the insulating film is made of, for example, phosphorus silicate glass (PSG) in a later step, the two sides of the electrode shown by the solid line and the dotted line PSG is not completely filled in the space between the two, leading to poor insulation.

Alternatively, the source 13 and drain 14 are formed by ion implantation of impurities, but for that purpose, the 5iOz film 15 is
The portion other than the gate electrode is etched once to expose the substrate surface, and a SiO2 film is formed again. The above-mentioned etching is performed using a hydrofluoric acid solution, and at this time, the portion of the gate oxide film designated by reference numeral 19 is also etched.

Therefore, as shown in FIG. 3, the surface of the gate electrode 16 is oxidized to form a silicide oxide film 20 to correct the above defects. For this purpose, the wafer on which the device shown in FIG. 2 has been fabricated is placed in the furnace shown in FIG. 4, and is ramped and thermally oxidized in the order shown in the diagram of FIG. In FIG. 4, 31 is a furnace core tube, 32 is a quartz boat, 33 is a wafer, and 34 is a heater.

Referring to FIG. 5, the wafer is placed in a furnace purged with oxygen, and is slowly preheated to about 800°C over a predetermined period of time to prevent cranking, and then heated to 900°C. heated at 900°C for a predetermined time,
The temperature was then increased to 950°C at a rate of 10°C/min.
After being heated at 950° C. for a predetermined period of time, the atmosphere is changed to an inert gas such as N2 gas and slowly cooled at a rate of 4° C./min. At this time, on the surface of the silicide, MoSi2+ 02-= MOO3+ 5iOz
(1) or MoSi2+ 02- Mo + 5iOz (
It is understood that 21 reactions occur.

[Problem that the invention seeks to solve]

In the silicide thermal oxidation method described above, when the silicide layer was inspected after oxidation, it was observed that powder (interpreted as MOO3 powder) appeared on the surface of the silicide layer, and in some cases, the surface collapsed. Therefore, electrodes with such silicide layers cannot be used.

The present invention was created in view of these points, and it is an object of the present invention to provide a method for carrying out the oxidation of silicide without causing the above-mentioned defects.

[Means for solving problems]

FIG. 1 is a diagram showing the sequence of the method of the invention.

In the method of the present invention, after the above-mentioned preheating, the wafer provided with electrodes made of silicide and polysilicon layers to be oxidized is first placed in a furnace purged with an inert gas, such as N2 gas, and heated at 900"C. After heating for the specified time 9
The temperature is raised to 50° C., then switched to an oxygen atmosphere, heated in the oxygen atmosphere for a predetermined time to perform oxidation, then switched to an inert gas atmosphere again and slowly cooled.

[Effect]

In the above method, the silicide is kept in an inert gas atmosphere until a sufficient amount of silicon has diffused into the silicide, and oxidation is started when a sufficient amount of silicon has diffused, thereby increasing the surface of the silicide. It is covered with a SiO:+ film.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In the oxidation of a polysilicon/silicide electrode having a silicide layer on a polysilicon layer, the above reaction fl.
), (It is understood that the conditions for the occurrence of 21 are that silicon is sufficiently diffused into the silicide layer, and this silicon is oxidized to form a sufficient amount of SiO2.

In the conventional example, heating was carried out before silicon was sufficiently diffused into the silicide layer, that is, under the condition of oxidation rate > silicon diffusion rate, Mo03 or Mo was liberated before 5i02 was formed, and it spread to the surface. It is understood that the silicide layer has shifted.

Therefore, in the present invention, the following relationship was created: oxidation rate≦silicon diffusion rate.

Referring to FIG. 1, after preheating the same as in the conventional method, the inside of the furnace core tube in which the wafer is placed is made into an N2 gas atmosphere, and
After heating at ℃ for a predetermined time, the temperature is raised to 950 ℃ at a rate of 10 ℃/min (ramping).

During this time period, silicon in the polysilicon layer diffuses into the silicide layer, but oxidation of the silicide has not yet begun.

When the temperature reaches 950° C., the N2 gas atmosphere is switched to the oxygen gas atmosphere, and oxidation is performed while maintaining the temperature at 950° C. for a predetermined time determined by the thickness of the oxide film to be formed. At this stage, a sufficient amount of silicon has diffused into the silicide layer, so that a sufficient amount of SiO2 is produced under the reaction.

After a predetermined period of time has elapsed, the oxygen gas atmosphere is switched to a N2 gas atmosphere, and the wafer is slowly cooled at a rate of 4° C./min. Finally, the wafer is taken out from the furnace.

In the oxidation of the above-mentioned electrodes in which MoSi2 is provided on a polysilicon layer, no defective products were generated in experiments conducted by the present inventor, and satisfactory oxide films were formed on all electrodes. This was confirmed.

〔Effect of the invention〕

As described above, according to the present invention, there is no generation of defective products in the oxidation of a structure in which a silicide layer is provided on a polysilicon layer, and the yield of manufacturing semiconductor devices is significantly improved. Although the above description has been made using MoS L+ as an example, the scope of the present invention is not limited to that case, but also extends to the case of other silicides such as tungsten silicide. is N
2 gases (but includes other gases such as argon (Ar)).

[Brief explanation of drawings]

FIG. 1 is a diagram of the oxidation sequence of the method of the invention, 'MS2
The figure shows a cross-sectional view of a gate electrode made of polysilicon Ji/silicide layer. Figure 3 is a cross-sectional view of the gate of Figure 2 covered with an oxide film. Figure 4 is a cross-sectional view of an oxidation furnace. FIG. 2 is a diagram of an oxidation sequence. In FIGS. 2 to 4, 11 is a semiconductor substrate, 12 is a field oxide film, 13 and 14 are sources and drains, 15 is a 5i02 film, 16 is a gate electrode, 17 is a polysilicon layer, 18 is a silicide layer, 19 31 is an etched portion of the gate oxide film, 31 is a furnace core tube, 32 is a quartz boat, 33 is a wafer, and 34 is a heater. 1P'r-todenfui 虦i
2nd figure of U1 and the gate of U1 20's stomach fart - face view 3rd
Figure 4

Claims (1)

[Claims] In the oxidation of a metal silicide formed on a polycrystalline silicon layer, the metal silicide is heated in an inert gas atmosphere until the oxidation temperature is reached, and after reaching the oxidation temperature, the metal silicide is inactivated. A method for manufacturing a semiconductor device, which comprises oxidizing for a predetermined period of time in an oxidizing atmosphere created by switching an active gas atmosphere to an oxygen gas atmosphere, and then switching to an inert gas atmosphere to lower the temperature.