JPH0578193B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an improvement in a method for manufacturing a semiconductor device.

(b) Technical background MOS type ICs including MOS transistors, MOS type
Semiconductor devices such as LSI have a relatively simple structure and a relatively short manufacturing process, so they are used as large-capacity memories and large-scale logic circuits.

(c) Prior Art and Problems A conventional method for manufacturing a semiconductor device will be explained step by step with reference to FIGS. 1 to 3 and FIG. 5.

First, a predetermined pattern of silicon dioxide film for element isolation (hereinafter referred to as SiO ₂ film for element isolation) is deposited on a P-type silicon substrate (hereinafter referred to as Si substrate) 1.
form 2.

As shown in FIG. 5, this method involves depositing a thin silicon dioxide film (hereinafter abbreviated as SiO ₂ film) 12 on a Si substrate 11 by thermal oxidation, and then depositing a silicon nitride film (hereinafter abbreviated as Si ₃ N ₄ film) on a Si substrate 11. ) 13 are sequentially stacked by the CVD method, and then the thin SiO ₂ film 12 and the Si ₃ N ₄ film 13 in the area where the SiO ₂ film 14 for isolation between elements is to be formed are etched using photolithography technology. Remove this thin SiO ₂ film 12 and Si ₃ N ₄ film 1
By thermally oxidizing the silicon substrate 11 using the laminated two-layer structure with 3 as a mask, SiO ₂ for element isolation is removed.
A film 14 is formed.

After that, a two-layer structure SiO ₂ film 12 and Si ₃ N ₄ film 13
After removing it by etching, a SiO ₂ film 3 for a gate is formed on the substrate by thermal oxidation of the substrate as shown in FIG. Furthermore, after forming a polysilicon film on the SiO ₂ film 3, a gate electrode in a predetermined pattern is formed using photolithography and plasma etching. 4 in FIG. 1 is the gate electrode formed in this manner.

Thereafter, as shown in FIG. 2, after oxidizing the surface of the gate electrode 4, ions such as AS atoms are implanted in the direction shown by the arrow using the gate electrode as a mask to form the source region 5.
and a drain region 6 is formed.

Further, as shown in FIG. 3, a phosphosilicate glass (PSG) film 7 is formed on the substrate, and then windows are opened in a predetermined pattern using photolithography and plasma etching.

In the figure, 8 and 9 are connection holes between the source region 5 and the drain region 6 formed in this manner. Thereafter, a wiring film 10 made of aluminum (Al) for connecting to the source region and the drain region is formed by vapor deposition to form a semiconductor device.

However, in this method, when the SiO ₂ film 2 for element isolation is formed on the Si substrate using a two-layer structure of thin SiO ₂ and Si ₃ N ₄ film as a mask, the fourth
As shown in the figure, the SiO ₂ film 2 tends to spread in the lateral direction of the substrate from the end A of the SiO ₂ film 2 by a dimension approximately equal to the thickness formed under the substrate. This phenomenon is generally referred to as a bird's beak, and when this bird's beak is formed, the dimensions of the element formation area defined by the SiO ₂ film 2 become narrower, and the number of elements formed in this area is also limited. This has the disadvantage that the degree of integration of semiconductor devices decreases.

Therefore, in order to prevent such defects, Si substrate
By directly forming a Si ₃ N ₄ film without using a SiO ₂ film, this
A method has been adopted in which a substrate is thermally oxidized using a Si ₃ N ₄ film as a mask to form an SiO ₂ film for isolation between elements.
The Si ₃ N ₄ film formed in this way is the result of a reaction between the Si substrate and nitrogen atoms, and the Si substrate and nitrogen atoms are bonded by chemical bonds, so the adhesion is strong.
Therefore, the SiO ₂ film for element isolation is less likely to spread in the lateral direction.

However, when removing the Si ₃ N ₄ film bonded in this way, for example with hot phosphoric acid (H ₃ PO ₄ ), the Si substrate surface becomes rough, and impurities in H ₃ PO ₄ remain on the substrate. There are drawbacks to doing so. Furthermore, even if carbon tetrafluoride is used as a reactive gas and etching is performed by reactive ion sputter etching, there is a drawback that unevenness occurs on the etched substrate.
As a result, the Si ₃ N ₄ film on the Si substrate has the advantages and disadvantages described above.

However, when considering the insulating film for the gate of MOSFETs in particular, as shown in Figure 1, in the conventional method, the SiO ₂ film 3 for the gate is formed by thermal oxidation of the Si substrate, and it is formed by a direct reaction between the Si substrate and oxygen. Since the film is obtained as a composite material, it is a stable thin film with few defects at the interface and no electrically active traps or ion contamination. However, in subsequent steps, when the gate electrode is formed into a predetermined pattern or through processes such as plasma etching and reactive ion etching, problems arise in that the SiO ₂ film deteriorates and its insulation properties decrease.

On the other hand, in order to improve the performance and degree of integration of large-scale integrated circuits, efforts are being made to miniaturize and miniaturize pattern shapes.In particular, MOSLSI has a relatively simple structure and a relatively short manufacturing process, so large-capacity memory MOSFETs, which are the basic elements used in these circuits, need to have shorter channel lengths and widths, shallow source and drain junction depths, and thin gate insulating films. . Therefore, instead of SiO ₂ film for gates, we used chemically stable and physically dense structure for gates.
If Si ₃ N ₄ is used, improved characteristics can be expected. In order to produce a high-quality Si ₃ N ₄ thin film, for example, a Si substrate may be heated in purified NH ₃ .
In addition, a Si substrate was introduced into the reaction tube, purified ammonia (NH ₃ ) gas was introduced into the reaction tube, and a high-frequency voltage was applied to a high-frequency induction coil outside the reaction tube.
It may also be formed by turning NH ₃ gas into plasma.

Such a method is effective in lowering the reaction temperature and reducing mixed impurities. However, the Si ₃ N ₄ film produced by such a direct nitriding reaction has a thickness of only 100 Å.
It is difficult to form a film thicker than a certain thickness, and it is difficult to increase the film thickness especially in the area around the gate electrode where the electric field is concentrated, resulting in inconveniences such as limiting the magnitude of the applied voltage. was.

(d) Purpose of the Invention The present invention provides a gate insulating film that does not deteriorate like SiO ₂ even after undergoing processes such as plasma etching or reactive ion etching, maintains sufficient insulation properties, is chemically stable, and has a dense structure. thin
A Si ₃ N ₄ film is used, and the film thickness around the gate electrode is increased to withstand large voltages, and the Si substrate surface can be kept smooth even during etching to open the electrode window. The purpose is to

(e) Structure of the invention This object is achieved by the present invention, in which silicon substrate 1
Step 1: Forming a silicon dioxide film 14 for element isolation in a predetermined pattern, and then forming a silicon nitride film 15 by direct nitriding reaction on the silicon substrate 11 defined by the silicon dioxide film 14 for element isolation; After forming a polysilicon film on the surface of the silicon nitride film 15 on the silicon substrate 11, the polysilicon film is patterned to form a gate electrode 16 on the surface of the silicon nitride film 15.
The source 1 is exposed to oxygen plasma to oxidize the silicon nitride film 15 other than the gate electrode, and the gate electrode 16 is used as a mask to introduce impurities into the silicon substrate 11 through the film converted into an oxide film.
9 and a step of forming a drain 20 region.

Further, according to the present invention, after forming the gate electrode 16 in the above, impurities are introduced into the silicon substrate through the silicon nitride film using the gate electrode as a mask to form the source 19 and drain 20 regions, and then the silicon substrate The silicon nitride film on the source and drain regions may be oxidized by exposing it to oxygen plasma.

(f) Embodiments of the Invention The present invention provides a method for forming Si ₃ N ₄ in an oxygen plasma atmosphere.
This is based on the knowledge that it is oxidized at a rate similar to that of the substrate.

An embodiment of the present invention will be described in detail below with reference to the drawings.

Up to Figure 5, it is the same as before, and from Figure 6,
0 to 1 are cross-sectional views showing the steps of the method of manufacturing a semiconductor device of the present invention, and FIG. 11 is a schematic diagram of an apparatus used in the method of manufacturing a semiconductor device of the present invention.

First, as shown in FIG. 5, a patterned protective film having a two-layer structure of a SiO ₂ film 12 and a Si ₃ N ₄ film 13 having a predetermined pattern is formed on a P-type Si substrate 11 as in the conventional method.

Next, using the two-layer protective film as a mask, the substrate is thermally oxidized to form a SiO ₂ film 14 with a thickness of 1 μm for isolation between elements.
to form. After that, the two-layer structure SiO ₂ film 12 and
After removing the Si ₃ N ₄ film 13 by etching, the substrate is placed on a carbon stand 10 coated with silicon carbide (SiC) in a quartz reaction tube 101 as shown in FIG.
After evacuating the inside of the reaction tube to a vacuum level of approximately 100 Torr, high-frequency power with a frequency of 200 KHz and an output of 7 KW is applied to the high-frequency induction heating coil 103 around the substrate to heat the substrate to approximately 1100°C. ammonia (NH ₃ ) from the gas introduction pipe 104.
Gas is introduced to form nitrogen gas plasma, which is the decomposition of NH ₃ gas, inside the tube. The reaction between this nitrogen gas plasma and the Si substrate creates isolation regions between elements.
In the region defined by the SiO ₂ film 14, a Si ₃ N ₄ film 15 with a thickness of 100 Å is formed as shown in FIG.
At this time, a part of the SiO ₂ film 14 for element isolation is also Si ₃ N ₄
It becomes covered with a membrane.

Thereafter, a poly-Si film with a thickness of about 4000 Å is formed on the substrate by thermal decomposition of monosilane (SiN ₄ ) gas, and this is formed into a gate electrode in a predetermined pattern by photolithography and plasma etching. Reference numeral 16 in FIG. 6 is the gate electrode formed in this manner.

In this state, the substrate is again
After installing the reaction tube 101 in the figure on a support base 102 made of silicon carbide and evacuating the inside of the reaction tube to a degree of vacuum of 100 Torr, the gas introduction tube 10
4, oxygen gas is introduced into the reaction tube using a high frequency induction heating coil 103, and a frequency is applied to the coil.
Heat by applying high frequency power of 200KHz output 7KW,
An oxygen gas plasma is generated and heated to about 800° C. in the oxygen plasma.

In this step, as shown in FIG. 7, the Si 3 N 4 film 15 in the area defined by the element isolation SiO ₂ film 14 is oxidized, and the Si ₃ N ₄ film 15 on the source and drain regions is oxidized.
When the Si ₃ N ₄ film is completely converted to the SiO ₂ film 17, the oxidation is stopped. Further, a slight SiO ₂ film 18 is also formed on the surface of the gate electrode 16.

Here, the conversion rate of the above Si ₃ N ₄ film to SiO ₂ film is approximately
50 Å/min. When oxygen plasma treatment is performed for 2 minutes, the Si ₃ N ₄ film is oxidized at a rate comparable to that of the Si substrate, so that when converted to an SiO ₂ film, the film thickness becomes approximately twice or more.

Thereafter, a source region 19 and a drain region 20 are formed by ion-implanting arsenic (AS) atoms into the region where the source is to be formed and the region where the drain is to be formed as shown by the arrows using the gate electrode 16 as a mask.

Afterwards, as shown in Figure 8, it was used for surface protection.
After forming the PSG film 21, the PSG film 21 and the bottom
The SiO ₂ film 17, in which the Si ₃ N ₄ film has been oxidized, is selectively etched by plasma etching to form a connection hole 22 with the source region and a connection hole 23 with the drain region as shown in FIG. Open.

In this way, the device formation area on the Si substrate can be
Since the Si ₃ N ₄ film is oxidized, it can be easily plasma etched, so the time required for etching is shortened, and the surface of the etched Si substrate becomes smooth, and the SiO ₂ film removes the phosphorus in the PSG film. It is also prevented from diffusing into the source and drain regions during the process.

In addition, in the device formation region defined by the SiO ₂ film for device isolation, the Si ₃ N ₄ film becomes a thick SiO ₂ film at the edges, including around the gate electrode, so that The device does not deteriorate easily even if the electric field is concentrated.

Thereafter, as shown in FIG. 10, a metal film made of aluminum (Al) is formed by vapor deposition and then etched into a predetermined pattern to form a wiring film of Al to connect the elements. Reference numeral 24 in FIG. 10 indicates the Al wiring formed in this manner.

In the above embodiment, after the Si ₃ N ₄ film 15 is oxidized, the source and drain regions are formed using the gate electrode as a mask, but before the Si ₃ N ₄ film 15 is oxidized, the state shown in FIG. Alternatively, the source and drain regions may be formed using the same method, and then the Si ₃ N ₄ film may be oxidized.

(g) Effects of the Invention As described above, in the method for manufacturing a semiconductor device of the present invention, a chemically stable Si ₃ N ₄ film with a dense structure is formed on a silicon substrate defined by a silicon dioxide film for element isolation. is formed by a direct nitridation reaction, so this Si ₃ N ₄ film does not deteriorate even during the etching process when forming the gate electrode, and these Si ₃ N ₄ films are oxidized after forming the gate electrode and become SiO. ₂ , the film thickness is doubled, so the withstand voltage around the gate electrode is also high, and the Si substrate surface can be kept smooth even when the window is opened when forming the source and drain electrodes.

On the other hand, since the gate insulating film below the gate electrode is a thin Si ₃ N ₄ film with a dense structure, it satisfies the requirements for miniaturization and therefore improves the characteristics of the semiconductor device.
A highly reliable semiconductor device can be obtained.

[Brief explanation of drawings]

Figures 1 to 3 and 5 are cross-sectional views showing the steps of a conventional semiconductor device manufacturing method, Figure 4 is a diagram showing defects in the conventional semiconductor device, and Figures 6 to 10 are cross-sectional views showing the steps of a conventional semiconductor device manufacturing method. FIG. 11, which is a sectional view showing the steps of the method for manufacturing a semiconductor device of the present invention, is a schematic diagram of an apparatus used in the method for manufacturing a semiconductor device of the present invention. In the figure, 1 and 11 are Si substrates, 2 and 14 are SiO ₂ films for isolation between elements, 3 is a gate oxide film, and 4 and 1
6 is a polysilicon gate electrode, 5 and 19 are source regions, 6 and 20 are drain regions, and 7 and 21 are
PSG membrane, 8, 9, 22, 23 are connection holes, 12,
18 is a SiO ₂ film, 13 and 15 are Si nitride films, 17 is an SiO ₂ film obtained by oxidizing the Si nitride film, 10 and 24 are Al wiring films, 101 is a reaction tube, 102 is a substrate installation stand, 1
03 is a high frequency induction coil, 104 is a gas introduction pipe,
A indicates the end.

Claims (1)

[Claims] 1. After forming a silicon dioxide film 14 for element isolation in a predetermined pattern on a silicon substrate 11, a silicon nitride film is formed by a direct nitriding reaction on the silicon substrate 11 defined by the silicon dioxide film 14 for element isolation. 1
5, and after forming a polysilicon film on the surface of the silicon nitride film 15 on the silicon substrate 11, patterning the polysilicon film to form a gate electrode 16 on the surface of the silicon nitride film 15, 11 in oxygen plasma to oxidize the silicon nitride film 15 other than the gate electrode, and using the gate electrode 16 as a mask, impurities are introduced into the silicon substrate 11 through the film converted into an oxide film to form the source 19 and drain 20. 1. A method of manufacturing a semiconductor device, comprising the step of forming a region. 2 After forming the silicon dioxide film 14 for device isolation in a predetermined pattern on the silicon substrate 11, a silicon nitride film 1 is formed by a direct nitriding reaction on the silicon substrate 11 defined by the silicon dioxide film 14 for device isolation.
After forming a polysilicon film on the surface of the silicon nitride film 15 on the silicon substrate 11, the polysilicon film is patterned to form a gate electrode 16 on the surface of the silicon nitride film 15. Using as a mask, impurities are introduced into the silicon substrate 11 through the silicon nitride film to form the source 1.
9 and drain 20 regions, the silicon substrate 11 is exposed to oxygen plasma to oxidize the silicon nitride film 15 on the source/drain regions.