JPS62273776A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device, in which the fluctuation of the threshold voltage of an MOS transistor is extremelly fine, in the device having an insulating film, which is formed on a substrate by a sputtering method, by providing a silicon nitride film, which is formed before the formation of the insulating film, between the substrate and the insulating film. CONSTITUTION:A silicon nitride film 8 is formed on the directly upper surface side of a gate electrode 3 and a gate insulating film 2. The silicon nitride film 8 is formed by a pressure reduced CVD method. The thickness of the film is about O.1 mum. By forming the silicon nitride film 8, the fluctuation of the threshold voltage value of an MOS transistor caused by the formation of an insulating film can be suppressed to the small value, even if the insulating film 7 is formed by sputtering thereafter.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Industrial Field of Application] This invention relates to semiconductor devices, and in particular to MOS, which occurs when an insulating film is formed by sputtering in large-scale integrated circuits. Related to preventing damage to transistors.

[Conventional Technique v/I] Figure 4 is a cross-sectional view showing an intermediate step in the manufacturing process of a conventional MOS transistor. film,
3 is a gate electrode made of polycrystalline silicon or the like; 4a and 4b are a source and drain, respectively, which are n-type impurity diffusion layers formed in the silicon substrate 1; 5 is an insulating film made of a phosphorus glass film; 6a; 6b is an aluminum wiring made of an aluminum alloy, and 7 is an mrrA insulating film formed by a bias sputtering method.

Actually, after this, a hole is opened in a desired part of the interlayer insulating film 7, a second aluminum wiring is formed, a final protective film such as a silicon nitride film is formed, and a desired part of the final protective film is formed. Although there are steps such as opening holes, they are not particularly related to the prior art of the present invention, and therefore their explanation will be omitted here.

[Problems to be solved by the invention] In the bias sputtering method, a substrate bias is applied to the normal sputtering method, and etching progresses at the same time as the formation of thin II (silicon oxide film).As a result, the surface of the thin film It is possible to make it very flat. Depending on the conditions of the substrate bias, as shown in FIG. 4, it is possible to obtain an interlayer insulating film 7 with a substantially flat surface, which facilitates microfabrication of the upper layer wiring (second aluminum wiring), not shown. Further, it is possible to prevent disconnection of upper layer wiring and decrease in reliability. However, a problem with sputtering methods, including bias sputtering methods, is that they can damage the MOS transistor and may change its threshold voltage. The reason for this is thought to be that electrons are irradiated onto the substrate during sputtering, and as a result, traps are formed in the gate oxide film 3.

The present invention has been made to solve the above-mentioned problems, and when a semiconductor device with less damage is included, especially when the semiconductor device includes a MOS t-transistor, the MOS t-transistor is
- The object is to obtain a semiconductor device in which the threshold voltage of a transistor varies extremely finely.

[Means for Solving the Problems] A semiconductor device according to the present invention has an insulating film formed on a substrate by a sputtering method. A silicon nitride film is formed.

[Operation] In the present invention, since the silicon nitride film layer is formed before forming the insulating film by the sputtering method, damage to the semiconductor device that occurs during sputtering can be suppressed. In particular, when the semiconductor device includes a MOS transistor, fluctuations in the threshold voltage of the transistor can be suppressed.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

1 FIG. 1 is a sectional view showing an intermediate step in the manufacturing process of a MOS transistor according to a first embodiment of the present invention. In FIG. 1, 1 is a p-type silicon substrate, 2
3 is a gate oxide film, 3 is a gate electrode made of polycrystalline silicon or the like, 4a is a source, 4b is a drain, 5 is an insulating film made of a phosphorus glass film, and 6a.

6b is an aluminum wiring, 7 is an interlayer insulating film, and 8 is a silicon nitride film. The feature of this embodiment is that a silicon nitride film indicated by reference numeral 8 is formed immediately above the gate electrode 3 and gate insulator 11112 as shown.

In this embodiment, the silicon nitride film 8 is formed by a low pressure CVD method, and has a thickness of about 0.1 μm.

By forming the silicon nitride film 8 as shown in the figure,
Even if the insulating film 7 is subsequently formed by sputtering, fluctuations in the threshold voltage of the MOS transistor due to the formation of the insulating film 7 can be suppressed to a small level.

The following table shows the variation Δv of the threshold voltage of the MOS l-transistor used in the first embodiment of the invention shown in FIG.
This shows an example of measurement of th.

As can be seen from the above table, by forming the silicon nitride film 8 to cover the gate electrode 3 and the gate insulator 112, the fluctuation ΔVth of the threshold voltage can be reduced by forming the silicon nitride film 8 to cover the gate electrode 3 and the gate insulator 112. We were able to reduce it to less than half of what it used to be.

In this first embodiment, the insulating film 7 formed by sputtering is formed on the entire insulating film 5 formed of the phosphor glass film, but the insulating film 7 formed by sputtering is formed on at least a part of the phosphor glass 115. Even when the film 7 is formed, by providing the silicon nitride 118, the adverse effect on the transistor caused by forming the insulating film 7 by sputtering can be suppressed to a small extent.

FIG. 2 is a diagram for explaining a second embodiment of the present invention, and shows a cross-sectional view midway through the manufacturing process of a MOS transistor according to the second embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are given the same numbers, so repeated explanations here will be omitted. The feature of FIG. 2 is that a silicon nitride film 8 is formed on an insulating film 5 made of phosphorus glass. In this way, insulation formed by sputtering method! Even if silicon nitride 118 is formed as a layer immediately below 1lI7, the silicon nitride film 8 can alleviate the adverse effect on gate electrode 3 that occurs during sputtering. Therefore, in the structure of the second embodiment, as in the first embodiment, the MO
Fluctuations in the threshold voltage of the S transistor can be suppressed considerably lower than in conventional ones.

FIG. 3 is a sectional view showing an intermediate step in the manufacturing process of a MOS transistor according to a third embodiment of the present invention. In the third embodiment shown in FIG. 3, after forming the gate electrode 3, forming the phosphor glass insulating film 5 and the aluminum wirings 6a and 6b,
A silicon nitride film 8 is formed. In this case as well, as in the embodiment shown in FIG. 2, fluctuations in the threshold voltage of the MOS transistor can be suppressed considerably lower than in the conventional case.

In the third embodiment shown in FIG. 3, the silicon nitride film 8 must be formed on the upper surfaces of the aluminum wirings 6a and 6b, but the silicon nitride film 8 is formed by plasma CVD at a low temperature of about 450°C or less. It may be formed by @ etc.

In the first to third embodiments described above, a semiconductor device including an n-channel MOS transistor was explained as an example, but the present invention is applicable to a p-channel MOS transistor.
The present invention is similarly applicable to semiconductor devices including transistors.

Further, in each of the above embodiments, the silicon nitride film 8 is described as covering almost the upper surface of the semiconductor device on the substrate side, but the silicon nitride film 8 may be any film as long as it covers at least the upper surface side of the gate electrode 3. This is because by covering at least the gate electrode 3 with the silicon nitride film 8, it is possible to prevent an adverse effect on the gate electrode 3 due to the formation of an insulating film that is subsequently formed by sputtering.

Furthermore, in each of the above embodiments, the case where the insulation II 7 is a silicon oxide film has been described, but the type of insulation film is not limited to a silicon oxide film (it may also be an insulation film such as a phosphorus glass film). .

[Effects of the Invention] As explained above, in the present invention, a thin silicon nitride film is formed before forming an insulating film by the sputtering method, so that damage to the semiconductor device caused by the sputtering method can be sufficiently prevented. There is an effect that can be suppressed. Therefore, a highly reliable semiconductor device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an intermediate step in the manufacturing process of a semiconductor device including a MOS transistor according to a first embodiment of the present invention. FIG. 2 is a sectional view showing an intermediate step in the manufacturing process of a semiconductor device including a MOS transistor according to a second embodiment of the present invention. FIG. 3 is a sectional view showing an intermediate step in the manufacturing process of a semiconductor device including a MOS transistor according to a third embodiment of the present invention. Figure 4 shows the conventional MOS
FIG. 3 is a cross-sectional view showing an intermediate step in the manufacturing process of a semiconductor device including a transistor. In the figure, 1 is a silicon substrate, 2 is a gate oxide film, and 3 is a silicon substrate.
4a is a gate electrode, 4a is a source, 4b is a drain, 5 is an insulating film, 68.6b is an aluminum wiring, 7 is an interlayer insulating film, and 8 is a silicon nitride film. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (4)

[Claims] (1) In a semiconductor device having an insulating film formed by sputtering on a substrate on which a predetermined region is formed, silicon nitride is formed between the substrate and the insulating film before forming the insulating film. A semiconductor device characterized by comprising a film. (2) The semiconductor device according to claim 1, wherein the silicon nitride film has a thickness of 0.5 μm or less. (3) The semiconductor device according to claim 1 or 2, wherein the semiconductor device includes a MOS transistor, and the silicon nitride film covers at least a gate electrode of the MOS transistor. . (4) The semiconductor device includes a MOS transistor, and the silicon nitride film is formed as part of a gate insulating film of the MOS transistor. The semiconductor device described.