JPS5946108B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and particularly to prevention of overhang during etching.

A conventional method for manufacturing a field effect type (hereinafter abbreviated as MOS type) semiconductor device will be explained with reference to FIGS. 1a to 1g. A field silicon oxide film 2 having a thickness of about 7000λ is uniformly formed on a semiconductor substrate 1 of one conductivity type, for example, a P-type, by thermal oxidation method (Fig.
) The substrate 3 is selectively exposed by ordinary photolithography (b in the same figure), and a gate silicon oxide film 4 of 1,000 to 1,500 layers is formed on the exposed substrate 3 by a thermal oxidation method (c in the figure).
), and then a polycrystalline silicon film 5 of about 4000 Λ is uniformly formed over the entire surface (d in the same figure), and the polycrystalline silicon film 5 is selectively removed by ordinary photolithography to form a gate electrode 6. (Figure e).

Using the polycrystalline silicon film 6 as a mask, the gate silicon oxide film 4 is selectively removed with a buffered hydrofluoric acid solution to expose the substrate. Thereafter, an impurity layer T having a conductivity type opposite to that of the substrate 1 is formed to serve as a source or drain region (f in the same figure). After that, a silicon oxide film 10 is formed by thermal oxidation method and (CVD method).
After forming, contact holes are formed in the substrate 1 and the polycrystalline silicon film 6, and wiring is performed using a conductor layer 11 such as aluminum to obtain a MOS type semiconductor device. (Figure g). In this manufacturing method, as shown in FIG.
Since the field oxide film 2 is also etched at the same time, the polycrystalline silicon film 5 on the field oxide film 2 is in an overhang state 9.
become.

As shown in FIG. 2, the side etching amount of the overhang 9 is almost the same as the side etching amount a of the overhang 8 of the polycrystalline silicon film 6 on the gate oxide film 4, but in the depth direction, the gate oxide film In the part 4, the silicon substrate 1 acts as a stopper against etching and is not etched to a thickness greater than the thickness b of the gate oxide film 4, but in the part of the field oxide film 2, it is etched to a thickness B2 which is thicker than the thickness of the gate oxide film 4. be done. After that, when thermal oxidation is performed as shown in FIG. 8 will disappear.

However, since the growth rate is slow in the field oxide film 2, the growth thickness 1 of the oxide film 2 is small and the overhang 9
' exists, and the step c is larger than the step on the gate oxide film. Next, even if a SlO2 film is coated by the CVD method, this step difference is hardly reduced, so that a so-called step breakage phenomenon often occurs at this step portion when a gold layer is deposited.

Furthermore, as shown in FIG. 3, if a thick metal layer 12 of aluminum or the like is formed by vapor deposition or the like in the area where the overhang 11 corresponding to the overhang 9' in FIG. Even if there is no etching liquid, the etching liquid will penetrate into the overhang 11, and the metal layer will be etched from the overhang 11 side, causing problems such as pattern width details 12' and wire breakage.

There is also a known manufacturing method in which overetching is prevented by forming a silicon nitride film on the entire surface of the gate oxide film 4 and the field oxide film 2 in the step shown in FIG. This is undesirable because it is difficult to control the silicon film thickness and there is an adverse effect on the characteristics of the semiconductor device due to the composite insulating film gate.

For example, when a silicon nitride film is formed on a gate oxide film when manufacturing a MOS transistor, an inversion layer may be difficult to form in the gate region. The present invention focuses on the above-mentioned drawbacks of the conventional example, and provides a method for manufacturing a semiconductor device in which overhang during etching is prevented and electrodes, etc., are formed after etching without breakage or disconnection. This is what we provide.

Embodiments of the present invention will be explained below. Figure 4 a-g
1 is a process diagram showing an embodiment of the present invention, in which a thick portion of the first layer film, for example, a silicon dioxide film, that is, a field silicon oxide film 22 is uniformly formed on a substrate, for example, a P-type semiconductor substrate 21, by a thermal oxidation method. For example, after forming 6,000 patterns (FIG. 1A), a predetermined pattern is formed using a normal etching technique (FIG. 2B).

On the substrate 24 exposed by the etching, a thin portion of the first layer, for example, about 1,000 silicon dioxide films, ie, a gate silicon oxide film 25, is formed (FIG. 3(c)). Next, a second layer film, for example a polycrystalline silicon film 26, is formed uniformly over the entire surface with a thickness of about 4000 λ (FIG. 4(d)). A polycrystalline silicon film 26 is formed using ordinary photolithography technology.
is formed into a predetermined pattern 27 and used as a gate electrode.

Next, a second layer film, that is, a polycrystalline silicon film 27 having an end portion on the thick portion of the first layer film, that is, the field silicon oxide film.
and a third layer film serving as an etching mask for the first layer film, spanning both a part or the entire surface of the field silicon oxide film 22 that is in contact with the end of the polycrystalline silicon film 27; For example, a photoresist film 28 is formed. (Figure e
). Thereafter, using both the polycrystalline silicon film 27 and the photoresist film 28 as etching masks, the gate silicon oxide film 25 is etched to expose the semiconductor substrate 29. At this time, the field silicon oxide film 22 is also etched at the same time, but unlike the conventional method, the field silicon oxide film 22 is masked with a photoresist film 28, so the end portion 30 of the polycrystalline silicon film is in an overhang state. No. The step 30 of the polycrystalline silicon film 27 on the field oxide film 22 does not change even after etching the gate oxide film 25, and only a step is formed in the field silicon oxide film 22 at the end portion 31 of the photoresist film. By the way, although the photoresist film 28 may be in an overhang state at the stepped portion 31, since the photoresist film 28 is removed, this does not affect the effects of the present invention in any way (f in the same figure).

Next, the photoresist film is removed and an impurity layer of a conductivity type opposite to that of the substrate is formed in the exposed portion 29 of the substrate. Then, by thermal oxidation or CVD, the exposed semiconductor substrate 29 and the polycrystalline silicon film 27 or the entire surface are coated with dioxide. The silicon film 32 is approximately 3
000λ is formed. Furthermore, holes for electrode contacts are selectively formed and metal wiring 33 made of aluminum or the like is formed. (G in the same figure) According to this embodiment, no undercut occurs at the end of the polycrystalline silicon film 27 on the field oxide film 22, so the thermal oxide film 32 after forming the impurity layer may be thin, and Even if the thickness of the metal wiring 33 is thinner than the thickness of the polycrystalline silicon film 27, disconnection will not occur.

Moreover, an MO using the polycrystalline silicon film 27 as a gate electrode
S-type field effect transistor, so-called silicon gate M
The method of forming the source and drain regions using the polycrystalline silicon film 27 as a mask, which is a feature of the OS, is not impaired in any way, and can be formed in a self-aligned manner as in the conventional method. In the above embodiment, even if a Si3N4 film is used as the third layer film,
Furthermore, it goes without saying that a metal film such as MO may be used as the second layer film.

The present invention is not limited to the above-mentioned embodiments. For example, the substrate is a polycrystalline silicon film, the first layer film is a vapor-grown silicon dioxide film or
Needless to say, an Sl3N4 film or a vapor-grown silicon dioxide film may be used for the N4 film and the second layer film, and a photoresist may be used for the third layer film.

As explained above, the method for manufacturing a semiconductor device of the present invention includes:
When the first layer film is etched, a third layer film is formed so as to cover the edge of the second layer film, spanning the thickened area of the first layer film and the second layer film on the same area. Therefore, over-etching of the first layer film is not performed in this portion, and the etching liquid does not penetrate into the same portion as in the conventional method.

Therefore, during the subsequent formation of electrodes, etc., there will be no disconnection due to step breaks or details caused by the etching solution. In addition, since over-etching is not performed, the difference in level between the first layer film and the second layer film does not become steep, and the thickness of the electrodes etc. formed subsequently does not have to be as thick as in the past. Even if it is thinner than the thickness of the two-layer film, no breakage will occur. Furthermore, since the present invention does not require the use of a silicon nitride film to prevent overetching as in the known technology, the gate insulating film does not become a composite type when manufacturing a MOS transistor, and the characteristics can be improved. It is.

That is, the present invention is applicable to manufacturing various semiconductor devices.
The present invention is intended to enhance the reliability of the semiconductor device and improve the yield during manufacturing without complicating the well-known manufacturing technology.

It has sufficient practical and industrial value.

[Brief explanation of drawings]

Figures 1a-g1 Figures 2 and 3 are cross-sectional views for explaining a conventional method of manufacturing a semiconductor device, and Figures 4a-g are process cross-sectional views for explaining an embodiment of the present invention. It is. 21... Substrate, 22, 25... First layer film (silicon dioxide film), 27... Second layer film (polycrystalline silicon film), 28... ...Third layer film (photoresist film), 32...Silicon dioxide film, 33...
・Metal wiring.

Claims (1)

[Scope of Claims] 1. A step of forming a first layer film having regions having different thicknesses on a semiconductor substrate; a step of selectively forming a second layer film serving as an etching mask for the layer film; forming a third layer film serving as an etching mask for the first layer film over the second layer film formed on the thick region of the film; A method for manufacturing a semiconductor device, comprising the step of etching the first layer film using a third layer film as a mask to remove the thin film region and expose the semiconductor substrate. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the first layer film is an insulating film, and the second layer film is a conductive film. 3. The method of manufacturing a semiconductor device according to claim 1 or 2, wherein the third layer film is a photoresist film.