JP2638285B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for forming a mask in an ion implantation step.

[Conventional technology]

Conventionally, a photoresist film is generally used as a mask for the ion implantation process.However, especially in a MOS LSI manufacturing method, a metal film should be used as a mask to prevent gate destruction due to charge-up. There are many. The ion implantation step in the conventional method of manufacturing a MOS LSI using an aluminum film as a mask after gate formation will be described with reference to the drawings.

As shown in FIG. 2A, a gate electrode 2 made of a polysilicon film is formed on a silicon oxide film 3-1 on a silicon semiconductor substrate 1, and the gate electrode 2 is further heat-treated to a thickness of 20 to 50 nm. Cover with silicon oxide film 3-2. The thickness of the gate electrode 2 is about 0.5 to 1.0 μm. As shown in FIG. 2 (b), an aluminum film 4 having a thickness of about 0.5 to 1.5 μm is deposited on the thus prepared substrate having a convex step portion by a sputtering method, and a gate portion is formed. A photoresist film 4 is selectively applied transversely. As shown in FIG. 2C, the aluminum film 4 is wet-etched using the photoresist film 5 as a mask, the photoresist film is peeled off to form an aluminum mask, and ion implantation is performed to select a silicon semiconductor substrate. Introducing impurities,
Form source / drain regions.

[Problems to be solved by the invention]

However, in the above-described conventional method of manufacturing a semiconductor device, when the shape of the gate electrode is poor and the gate electrode is inversely tapered, voids 6 are formed in the shadow portion at the time of aluminum sputtering at the edge portion of the gate, and the gate shape is formed. The coverage of the aluminum film is also poor. Therefore, in the wet etching of the aluminum film in the later step, the void in which the aluminum is eroded from the edge of the photoresist film expands, and a so-called mouse hole 7 is formed. If the ion implantation process is performed in this state, the aluminum film thickness in the mouth hole portion is thin and the maskability is insufficient, so that the lower portion of this portion is also doped with impurities.

That is, in the conventional method, the impurity is doped in a region other than the predetermined region by the mouse hole, and this portion is short-circuited with another diffusion layer region, so that the yield of the semiconductor device is reduced and the semiconductor device cannot be manufactured stably.

[Means for solving the problem]

The method for manufacturing a semiconductor device of the present invention includes a step of growing a silicon nitride film on a substrate having a convex step, a step of applying a metal film and patterning the metal film by photolithography and wet etching, A step of heat-treating the metal film at least at its melting point in an inert gas atmosphere; and a step of ion-implanting the metal film using the mask as a mask.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

1 (a) to 1 (d) are sectional views in the order of steps for explaining an embodiment of the present invention.

First, as shown in FIG. 1A, a silicon oxide film 3-1 having a thickness of about 25 nm and a gate electrode 1 (polysilicon having a thickness of about 1.0 μm) are formed on a silicon semiconductor substrate 1 in the same manner as in the conventional example. Film), and a silicon oxide film 3-2 having a thickness of about 25 nm is formed.

Next, as shown in FIG. 1 (b), after growing a silicon nitride film 8 to a thickness of about 10 to 50 nm by a low pressure CVD method, an aluminum film 4 is sputtered to a thickness of about 1.0 μm in the same manner as in the conventional method. And a photoresist film 5 is selectively formed across the gate portion.

Next, as shown in FIG. 1 (c), the aluminum film 4 is wet-etched using the photoresist film as a mask and the photoresist film is peeled off, as in the conventional method. In this state, when the gate shape is bad as in the conventional method, the mouse hole 7 is formed.

Next, in a heat diffusion furnace, a temperature of 661 to 800 ° C., an inert gas N
₂ Heat treatment in (or Ar). Then, as shown in FIG. 1 (d), the aluminum is in a melt state, the aluminum is buried in the mouth hole portion 7, and the aluminum film surface is also flattened.

If ion implantation is performed after this step, impurities can be doped only in the predetermined region, and the disadvantage that the ion implantation is performed in the lower portion of the mouse hole, that is, in the region other than the predetermined region as in the conventional method, is completely eliminated. In the heat treatment step, a silicon nitride film 8 is provided between the aluminum film 4 and the silicon oxide films 3-1 and 3-2 to prevent a thermal reaction between the aluminum film and the silicon oxide film. At this time, the silicon nitride film slightly reacts with the aluminum, which can be easily selectively etched with hot phosphoric acid or the like after removing the aluminum film for the mask for ion implantation.

Note that a lamp annealing may be used in the heat treatment step instead of the heat diffusion furnace. At this time, the temperature is preferably 661 to 900 ° C., and N ₂ or Ar is preferable as the atmosphere gas. When a diffusion furnace is used, the surface of the aluminum film is transformed into alumina due to the air and it is difficult to etch the aluminum film for the mask, but when a lamp annealer is used, the surface of the aluminum film is not deteriorated and the aluminum film for the mask is not deteriorated. There is an advantage that etching of the film is easy.

According to the above embodiment, the short-circuit failure of the diffusion layer is reduced,
It was found that the yield was improved by about 30% compared to the conventional example.

〔The invention's effect〕

As described above, in the present invention, even when a mouse hole is formed by wet etching at the time of forming a metal mask for ion implantation due to poor gate shape, the metal film is melted by heat treatment to reduce the mouse hole. Since ions are implanted, only predetermined regions can be doped with impurities, which has the effect of stably manufacturing a semiconductor device with high yield and high reliability.

[Brief description of the drawings]

1 (a) to 1 (d) are cross-sectional views in the order of steps for explaining an embodiment of the present invention, and FIGS. 2 (a) to 2 (c) are cross-sectional views in the order of steps for explaining a conventional example. is there. 1 .... silicon semiconductor substrate, 2 .... gate electrode, 3-1,
3-2: silicon oxide film, 4: aluminum film for mask, 5: photoresist film, 6: void, 7 ...
Mouse hole, 8: silicon nitride film.

Claims (1)

(57) [Claims] A step of growing a silicon nitride film on a substrate having a convex step; a step of depositing a metal film and patterning the metal film by photolithography and wet etching; A step of heat-treating the metal film at least at its melting point, and a step of implanting ions using the metal film as a mask.