JPS63244884A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To form an electrode onto a shallow impurity diffusion region in low concentration, and to obtain a semiconductor device having LDD structure capable of stably maintaining characteristics by selectively depositing high melting-point metallic films onto the top face and side face of a gate electrode consisting of polysilicon. CONSTITUTION:The surface of a P-type silicon substrate 11 is thermally oxidized to shape a gate oxide film 12, and a polysilicon film 13 is deposited onto the oxide film 12 through a decompression CVD method. Arsenic ions are implanted, using the etched polysilicon film 13 as a mask to form an N<-> region 14. A W film 15 is deposited under decompression by employing the mixed gas of WF6 and H2. The W film 15 is deposited only onto the top face and side face of the film 13 through selective CVD at that time. Arsenic ions are implanted again, using the film 15 as a mask to shape an N<+> region 16. The surface of the W film 15 is exposed to a nitrogen atmosphere to form a tungsten nitride film 18. A thick gate oxide film 19 is shaped onto the N<+> and N<-> regions through oxidation in an oxidizing atmosphere, and the thickness of the oxide film in an edge region in the gate insulating film is also thickened. A wiring is formed, and a protective film is deposited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor device and a method for manufacturing the same, and is particularly used for manufacturing a semiconductor device having an LDD structure.

(Prior Art) With the recent increase in the density of semiconductor devices, in order to improve the reliability of fine transistors against hot electrons, LDDs (LDDs) having shallow and low concentration drains in addition to normal drains have been developed.
Transistors with a drain structure are increasingly being used.

A transistor having such an LDD structure will be explained with reference to FIG. 2, which is a cross-sectional view of the device.

A gate oxide film 2 is formed on the surface of a semiconductor substrate 1, and a polysilicon film 3 doped with phosphorus or arsenic is deposited thereon, and this polysilicon film 3 is etched into a desired gate pattern. Using this patterned polysilicon film 3 as a mask, arsenic ions are shallowly implanted into the semiconductor substrate 1 to form an n- region 4. Further, a substantially fan-shaped spacer 5 is formed on the side wall of the polysilicon film 3. This spacer can be formed by depositing polysilicon over the entire surface and doping it with phosphorus or arsenic, then depositing an oxide film over the entire surface using the CVD method, and etching back the oxide film using the RIE technology. Furthermore, the semiconductor substrate 1 outside the spacer 5 has an n region obtained by deeply ion-implanting arsenic at a high concentration using the spacer as a mask.

However, the conventional LDD structure transistor is n″
Since there is a spacer made of an oxide film on the ``region 4'' and no particular gate electrode is provided, the transistor characteristics tend to change when a long-term reliability test is performed on the transistor.

(Problems to be Solved by the Invention) As described above, in conventional LDD structure semiconductor devices, it is difficult to maintain transistor characteristics over a long period of time because shallow drain 1tlal cannot be achieved. .

The present invention was made to solve such problems, and an object of the present invention is to provide a semiconductor device with an LDD structure that can stably maintain characteristics, and a method for manufacturing the same.

[Structure of the invention]

(Means for Solving the Problems) According to the semiconductor device according to the present invention, a first gate electrode formed on a predetermined region on a semiconductor substrate via an insulating film, and a a first shallow and low concentration impurity diffusion region formed in a lateral semiconductor substrate;
a second gate electrode selectively provided on the top surface and sidewalls of the gate electrode, and a deep and highly concentrated second impurity diffusion region formed in the semiconductor substrate on the side of the second gate electrode. It is characterized by having the following.

Further, according to the method for manufacturing a semiconductor device according to the present invention,
A process of forming an insulating film on a semiconductor substrate, a process of depositing a polysilicon film on this insulating film, a process of doping this polysilicon film with impurities and etching it into a desired gate pattern, and a process of etching the polysilicon film into a desired gate pattern. A process of shallowly implanting ions at a low concentration into the semiconductor substrate using the pattern as a mask, a process of selectively depositing a high melting point metal film on the top and side surfaces of the polysilicon pattern, and a process of implanting ions into the semiconductor substrate using the high melting point metal film as a mask. The process includes a process of deeply implanting ions at a high concentration into the film, a process of increasing the oxidation resistance of the surface of the high-melting point metal film, and a process of increasing the thickness of the edge region of the gate insulating film by oxidizing. It is characterized by:

(Function) In the semiconductor device according to the present invention formed in this way, since the electrode is formed on the shallow and low concentration impurity diffusion region, current control is also possible in this region, so that it can be used for a long period of time. Can maintain stable characteristics.

Furthermore, according to the method for manufacturing a semiconductor device according to the present invention, a high melting point metal film is selectively deposited on the top and side surfaces of the polysilicon gate electrode, so the semiconductor device described above can be manufactured stably. becomes.

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

FIG. 1 is a cross-sectional view of each element showing the manufacturing process of a semiconductor device according to the present invention.

FIG. 1(c) or FIG. 1(d) shows a semiconductor device according to the present invention, in which a shallow groove is formed in the semiconductor substrate 11 on the side of a gate electrode 13 formed on the upper surface of the semiconductor substrate 11. The semiconductor substrate 11 on the side of the first impurity diffusion region 14 with a low concentration and the second gate ff electrode 15 made of tungsten formed on the upper surface and sidewalls of the gate electrode 13.
A deep and highly concentrated second impurity diffusion region 1 formed within the
6.

Therefore, since the gate electrode exists also on the first impurity diffusion region which is shallow and has a low concentration, current control in this region becomes possible, and a semiconductor device having more stable characteristics can be obtained.

Next, a method for manufacturing a semiconductor device according to the present invention will be explained with reference to FIG.

First, the surface of the p-type silicon substrate 11 is thermally oxidized to a thickness of 1
A gate oxide film 12 of 50A is formed, and a polysilicon film is deposited on the oxide film to a thickness of 150A by low pressure CVD. This polysilicon is doped with arsenic to lower its resistance. Thereafter, the photoresist is patterned according to a predetermined gate pattern, and the polysilicon film is etched using this as a mask. Next, using the etched polysilicon film 13 together with the photoresist pattern as a mask, arsenic ions are implanted into the n- region 14.
form. At this time, the gate oxide film 17 in the n'''' region 14'' has become thinner during the etching and cleaning process (FIG. 1(a)).

Next, using a mixed gas of tungsten fluoride (WF6) and hydrogen (H2) (mixing ratio WF6/H2-1/60), a tungsten film was formed to a thickness of about 2000A at a substrate temperature of 550℃ under a reduced pressure of 0.2Torr. Deposit it at a distance. At this time, deposition occurs only on the polysilicon and does not deposit on the oxide film, resulting in so-called selective CVD, and the polysilicon film 1
Tungsten 15 is deposited only on the top and side surfaces of 3.

By again implanting arsenic ions using this tungsten l1i15 as a mask, an n region 16 is formed. Since the ion implantation at this time is performed at a higher energy and higher dose than when forming the impurity diffusion region 14, the n+ region 16
has a higher concentration and is deeper than the n- region 14 (FIG. 1(b)).

With this, the LDD structure transistor is basically completed, but as mentioned above, the gate oxide film 1
7 is thin, and the electrical withstand voltage deteriorates particularly at the edges, which may lead to breakage. To prevent this, it is effective to add an oxidation step to increase the thickness of the oxide film at the edge. However, since tungsten undergoes abnormal oxidation or peels off when exposed to an oxidizing atmosphere, the surface of the tungsten film 15 is first exposed to a nitrogen atmosphere at 800°C to form a tungsten nitride film 18 (see Fig. 1). (
C)).

Next, oxidation is performed in an oxidizing atmosphere at 900 DEG C. to form a thick gate oxide film 19 on the n and n- regions, and also increase the thickness of the oxide film in the edge region of the gate insulating film. (Figure 1(d)
)).

After that, the interlayer insulating film is deposited, contact holes are formed,
The semiconductor device is completed by forming wiring, depositing a protective film, etc.

In the semiconductor device obtained in this way, stable characteristics can be maintained for a long time due to the double gate electrode, and since the insulating film on the surface of the semiconductor substrate in the active region is sufficiently thick, the gate electrode Pressure deterioration is less likely to occur at the edges.

In the above embodiments, nitriding was used to improve the oxidation resistance of tungsten, but carbonization can also have the same effect.

Furthermore, it is also possible to reduce the processing temperature and processing time by using nitrogen or carbon plasma during these nitriding or carbonizing treatments.

Furthermore, although tungsten is used as the second gate electrode material formed around the polysilicon gate electrode in the above embodiment, other high melting point metals that can be subjected to selective CVD may be used.

〔Effect of the invention〕

As described above, according to the semiconductor device according to the present invention, since the gate electrode is also present on the shallow and low concentration first impurity diffusion region, current control in this region is possible, and stable characteristics can be maintained. Obtainable. Furthermore, since the gate oxide film on the impurity diffusion region is thickened, the reliability of the transistor can be greatly improved.

Further, according to the method for manufacturing a semiconductor device according to the present invention, a semiconductor device having such excellent characteristics can be manufactured extremely stably.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor device according to the present invention and a method for manufacturing the same, and FIG. 2 is a cross-sectional view of a semiconductor device having a conventional LDD structure. 1.11...Semiconductor substrate, 2.12...Gate oxide film, 3,13...Polysilicon, 4,14...n-
Area, 5... Spacer, 6, 16...n Area, 1
5... Tungsten film, 17... Thinned gate oxide film, 18... Oxidation resistant film, 19... Oxide film. Applicant's agent Yumi Sato 1 Figure

Claims (1)

[Claims] 1. A first gate electrode formed in a predetermined region on a semiconductor substrate via an insulating film, and a shallow gate electrode formed in the semiconductor substrate on the side of the first gate electrode. a first impurity diffusion region with a low concentration; a second gate electrode selectively provided on the top surface and sidewalls of the first gate electrode; and a second gate electrode provided in the semiconductor substrate on the side of the second gate electrode. A semiconductor device comprising: a deep and highly concentrated second impurity diffusion region; 2. The semiconductor device according to claim 1, wherein the surface of the second gate electrode is covered with an oxidation-resistant film. 3. Claim 1 or 2, wherein the first gate electrode is polysilicon doped with impurities, and the second gate electrode is a high melting point metal that can be selectively deposited on the surface of the polysilicon. semiconductor devices. 4. A step of forming a gate insulating film on a semiconductor substrate, a step of depositing a polysilicon film on the insulating film, and a step of doping the polysilicon film with an impurity and etching it into a desired gate pattern. , a step of shallowly implanting ions at a low concentration into the semiconductor substrate using the polysilicon pattern as a mask; a step of selectively depositing a high melting point metal film on the top and side surfaces of the polysilicon pattern; A step of deeply implanting ions at a high concentration into the semiconductor substrate using the film as a mask, a step of increasing the oxidation resistance of the surface of the high melting point metal film, and a step of performing oxidation to increase the thickness of the edge region of the gate insulating film. A method for manufacturing a semiconductor device, comprising a step of increasing . 5. The method of manufacturing a semiconductor device according to claim 4, wherein the step of increasing the oxidation resistance of the surface of the high melting point metal film is nitriding or carbonizing. 6. The method for manufacturing a semiconductor device according to claim 4 or 5, wherein the high melting point metal is tungsten. 7. The process of selectively depositing a high melting point metal film is selective CV.
A method for manufacturing a semiconductor device according to any one of claims 4 to 6, which is method D.