JPH03102819A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a transistor having a low threshold voltage and high reliability by forming a recess in a silicon substrate at a source electrode forming part, coating the substrate with solution in which fatty acid metal is dissolved in an organic solvent, decomposing, sintering it and forming a metal film in the recess. CONSTITUTION:A BPSG film 10 and a silicon oxide film 9 in a source electrode forming region between gate electrodes 1 are etched, an opening 11 is formed in the region, and a substrate is etched to form an opening 13. Thereafter, tungsten octylate liquid of one type of fatty acid metal is diluted with xylene, a silicon substrate is coated with it, and sintered. Thus, the tungsten octylate is decomposed to form mixed solid solution thin film 12 of tungsten and carbon, thereby burying the opening 13 and preventing introduction of the tungsten to a boundary between the substrate and a silicon oxide film. Thus, a Schottky barrier type MOS transistor having high reliability can extremely easily be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device, and particularly to the formation of a source electrode of a Schottky source type MOS transistor.

(Prior Art) As a conventionally used Schottky source type MOS transistor, there is one shown in FIG. 2, for example. In this type of transistor, there is no diffusion layer that forms the source and drain as in a normal MOS transistor, and the gate electrode 1 is surrounded by a silicon oxide film 2 formed to surround the source electrode 3 and the silicon substrate.
They are only separated from each other. The source electrode 3 and the silicon substrate 5 form a Schottky barrier, and when an electrode is applied to the gate electrode 1, an inversion layer is formed on the surface of the silicon substrate via the silicon oxide s2.

However, the side walls of the gate electrode 1 are covered with a silicon oxide film 2 for isolation from the source electrode 3. For this reason,
Current cannot flow from the source electrode 3 to the drain electrode 4 unless the inversion layer is formed across the gap b corresponding to the thickness of the silicon oxide film on the sidewall.

In other words, in this transistor, the threshold voltage increases by the gap b.

As a means to prevent this, as shown in FIG. 3, the surface of the silicon substrate in the source electrode formation area adjacent to the gate electrode 1 is dug down to the bottom of the edge of the gate electrode 1.
A recess is formed, and selective CVD or CVD is applied to this recess.
A method has been proposed in which a tungsten film 7 is buried by a method, and wiring is formed using an aluminum-silicon alloy or the like on the tungsten film 7 to form the source electrode 3.

However, in the force method of selectively embedding the tungsten film 7 on silicon using such a CVD method, the WF
It is known that when 6 and H2 are used, the growth rate of tungsten is very slow, about several tens of amperes per minute, and a phenomenon occurs where tungsten bites into the interface between the silicon oxide film 2 and the silicon substrate 5 during tungsten growth. There is.

On the other hand, WF8 and SiH, which can suppress the above phenomenon,
When No. 4 was used, there was a problem that the selectivity deteriorated and there were some parts on the silicon where tungsten was not formed, making it impossible to obtain sufficient characteristics.

(Problem to be Solved by the Invention) As described above, the former structure shown in FIG. 2 causes fluctuations in the threshold voltage, and the latter improved structure shown in FIG. 3 leaves a cavity under the gate electrode 1. In addition to increasing the threshold voltage, there is a problem that the wiring itself becomes defective.

Furthermore, since there is no tungsten in this cavity, it is aluminum rather than tungsten that forms the bond with the silicon substrate, resulting in a Schottky contact made of aluminum.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a Schottky barrier type MOS transistor having a low threshold voltage and high reliability.

[Structure of the invention]

(Means for Solving the Problem) Therefore, in the present invention, the surface of the silicon substrate in the source electrode formation area is dug down to the bottom of the edge of the gate electrode, and after forming four parts, a fatty acid metal, which is a compound of a fatty acid and a metal ion, is A liquid dissolved in a solvent is applied to the surface of the silicon substrate to adhere the fatty acid metal to the surface of the silicon substrate, and then this is decomposed and sintered to form a metal film within the recess.

(Operation) In other words, this method is different from the conventional selective CVD method or CVD method.
Instead of filling the recess by forming a tungsten film using method D, this method forms a metal film in the recess by applying and sintering a solution containing a fatty acid metal, which is a compound of a fatty acid and a metal ion. .

According to the above method, by applying a solution containing a fatty acid metal, all four parts are filled with the solution. Since it is sintered in this state, it is possible to completely fill the recess without creating a cavity, and it also prevents tungsten from entering the interface between the silicon substrate and silicon oxide film, improving reliability. be able to.

(Example) Hereinafter, a first example of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1(a), a silicon oxide film is formed as a gate oxide film 8 on the surface of a silicon substrate 5, and then a polysilicon film with a thickness of 40,000 Å is deposited while doping with phosphorus. Then, the gate electrode is patterned by an etching process, and a silicon oxide film 9 having a thickness of 1000 Å is formed in an oxygen atmosphere.

Next, as shown in FIG. 1(b), a BPSG film 10 with a thickness of 6000 Å was deposited and heated at 900°C for 20 minutes in a nitrogen atmosphere.
The BPSG film is planarized by annealing for 30 minutes.

Further, the BPSG film 10 and the silicon oxide film 9 in the source electrode formation region between the gate electrodes 1 are etched by photolithography and reactive ion etching processes to form an opening 11 in the source electrode formation region.
The substrate was etched by isotropic etching, and as shown in Figure 1 (
As shown in e), an opening 13 is formed.

Thereafter, as shown in FIG. 1(d), a tungsten octylate solution, which is a type of fatty acid metal, was diluted with xylene, and this was applied to the surface of the silicon substrate, and was heated for 50 minutes under reduced pressure.
Sinter by heating to 0°C. As a result, tungsten octylate is decomposed and a mixed solid solution thin film 12 of tungsten and carbon is formed. At this time, since the tungsten octylate solution is a liquid, in principle it completely spreads to the opening 13 under the gate electrode 1.

The film thickness obtained by one application and sintering of this tungsten octylate solution varies depending on the dilution concentration, so the application and sintering are repeated multiple times as necessary.

After obtaining the tungsten-carbon mixed solid solution thin film 12 with a desired thickness in this manner, an aluminum-silicon alloy film 14 with a thickness of 10,000 Å is formed on the entire surface by a sputtering method as shown in FIG. 1(e).

This is to reduce the resistance of the source as a whole.

Finally, place 15 titanium and 1 nickel on the back side of the silicon substrate.
6 and silver 17 with a film thickness of 2000A. 6000A
, 3000A to form the drain electrode 4 as shown in FIG.
form the PSG protection IIi18.

In this way, the opening 13 can be completely filled without creating a cavity in the opening 13, and tungsten can be prevented from entering the interface between the silicon substrate and the silicon oxide film, making it extremely easy to fill the opening 13. A highly reliable Schottky barrier type MOS transistor can be formed.

Furthermore, this method has simple and stable steps, and does not require an expensive CVD device, so it can also reduce costs.

Furthermore, when applying a xylene diluted solution of tungsten octylate, due to its surface tension, a large amount of tungsten octylate tends to adhere to areas such as the opening 13 under the gate electrode, and is preferentially buried. This is an advantageous method not only for improving the embedding characteristics but also for improving the shape of the step.

Further, the higher fatty acid is not limited to octyl acid, but may be neodecanoic acid or other fatty acids.

Furthermore, in addition to tungsten, the metals that can be combined with this higher fatty acid include aluminum, titanium, cobalt, copper,
It can be appropriately selected from zirconium, molybdenum, etc.

〔Effect of the invention〕

As described above, according to the method for manufacturing a semiconductor device of the present invention, when forming the source electrode of a Schottky barrier type MOS transistor, four portions extending below the gate electrode are formed on the substrate surface, and the four portions are filled in the recessed portion. A solution of fatty acid metal dissolved in an organic solvent is applied to the surface of the silicon substrate to adhere the fatty acid metal to the surface of the silicon substrate, which is then decomposed and sintered to form a metal film. On the other hand, since the source wiring is provided, it is possible to obtain a transistor with a low threshold voltage and high reliability.

[Brief explanation of drawings]

1(a) to 1(') are diagrams showing the manufacturing process of the Schottky barrier type MOS transistor of the first embodiment of the present invention, and FIGS. 2 and 3 are shots of the conventional example, respectively. FIG. 2 is a diagram showing a key barrier type MOS transistor. 1... Gate electrode, 2... Silicon oxide film, 3...
・Source electrode, 4...Drain electrode, 5...Silicon substrate, 6...Gap, 7...Tungsten film, 8
...Gate insulating film, 9...Silicon oxide film, 10.
... BPSG film, 11... Opening of source electrode formation region, 12... Solid solution of tungsten and carbon (source electrode t!!ii), 13... Opening, 14... AI-S
i alloy film, 15... titanium, 16... nickel, 1
7...Silver. 1st figure 4

Claims (1)

[Claims] (1) In a method for manufacturing a Schottky source type MOS transistor configured to form a Schottky junction between a source electrode formed on the surface of a silicon substrate and the silicon substrate, a gate electrode forming step of forming a gate electrode; an insulating film forming step of forming an insulating film on the upper layer of the gate electrode;
A recess formation step in which a recess is formed on the silicon substrate surface of the source electrode forming part to reach the lower part of the edge of the gate electrode, a coating step in which a solution of a fatty acid metal dissolved in an organic solvent is applied to the silicon substrate surface, and the silicon substrate Manufacturing a semiconductor device comprising: a source electrode forming step consisting of a sintering step of thermally decomposing a fatty acid metal coated on the surface and forming a metal film in the recess; and a drain electrode forming step. Method.