JP3139835B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for obtaining a highly reliable oxide film in forming an oxide film after film formation by a CVD method. .

[0002]

2. Description of the Related Art A capacitor oxide film of a charge storage capacitor of a DRAM (dynamic RAM) and an oxide film on a loading gate of an EPROM (rewritable PROM) are formed of polycrystalline silicon (hereinafter referred to as polycrystalline silicon) formed by a CVD method. In many cases, a crystal Si is abbreviated by thermal oxidation, and then a polycrystalline Si serving as an electrode is formed by a CVD method.

The reliability of the above oxide film depends on the thermal oxidation process and CV
It depends on the cleanliness from the D step and the heat treatment conditions.

[0004] Cleaning of the thermal oxidation step and optimization of the heat treatment conditions are easier than in the CVD step.

In the CVD process, since a highly reactive gas is used, metal contaminants such as Fe, Ni, and Cu used in pipes and furnace materials react with the film-forming gas to form Si. There is a high possibility that the wafer will be contaminated and segregated at, for example, crystal grain boundaries in the film. By lowering the deposition temperature of the CVD film,
Although it is possible to reduce the amount of metal contamination, there is a concern about deterioration of the film quality.

Further, among the metals taken into the CVD film, in particular, Fe tends to segregate in the oxide film, so that the oxide film is sufficiently thinner than the CVD film, such as a gate oxide film. In this case, Fe in the CVD film is concentrated in the oxide film, and the reliability of the oxide film is significantly reduced.

[0007]

As described above, for example, the polycrystalline Si film formed by the CVD method includes Fe, Ni, Cu used for a furnace material at the time of film formation.
And other metal contaminants. Thereafter, when an oxide film is formed on such a polycrystalline Si film, there is a problem that Fe or the like is easily segregated in the oxide film, the dielectric strength of the oxide film is deteriorated, and the reliability is significantly reduced.

On the other hand, supersaturated oxygen is mixed in a Si single crystal substrate usually used as a substrate for LSI elements. These oxygens generate BMD (micro defects such as oxygen precipitates) inside by heat treatment, and gettering is performed there. Therefore, it is desirable that the BMD does not exist in the element formation region but is distributed in large numbers outside this region. Although the BMD distribution and density change due to the heat treatment during the device manufacturing process, maintaining proper BMD distribution and density is an important issue.

A first object of the present invention is to provide a method of manufacturing a semiconductor device in which after forming a CVD film, a metal impurity taken in the film is removed to form a more reliable oxide film. Another object of the present invention is to provide a semiconductor device in which a BMD distribution in a semiconductor substrate on which an oxide film is selectively formed can be easily adjusted to an appropriate distribution without damaging the oxide film. It is to provide a method of manufacturing the device.

[0010]

A means for solving the action] semiconductor of the present invention
The manufacturing method of the body device is such that the hydrogen ion
Into the CVD film, and then reduce the temperature to 800 ° C or higher.
Heat-treating said CVD film in a neutral atmosphere;
Forming an oxide film on the VD film or on the CVD film;
It is characterized by having .

First and second reference examples related to the present invention
The method of manufacturing a semiconductor device according to
Heat-treating said CVD film in an intrinsic atmosphere;
Forming an oxide film on the CVD film or on the CVD film
And characterized in that:

The above reducing atmosphere is preferably a reducing gas containing at least hydrogen. In the present invention, the heat treatment in a reducing atmosphere is performed at 800 ° C. or more.
However, in the reference example, it is particularly desirable to carry out at a temperature of 1100 ° C. or higher. It is desirable to use a thermal oxide film as the oxide film formed on the CVD film.

For example, when the CVD film is polycrystalline Si, C
Metal impurities such as Fe taken into the VD film tend to segregate at crystal grain boundaries. After forming a CVD film as in the present invention
Even if hydrogen ions are not implanted into the CVD film, when heat treatment is performed in a high-temperature reducing atmosphere, these metal impurities are pulled out from the CVD film by the outward diffusion and the reduction reaction of the crystal surface, and the high-purity CVD is performed. A film is obtained, so that a highly reliable oxide film can be formed. The effect is 11
This is particularly important at high temperatures of 00 ° C. or higher, and is particularly important when the special measures of the present invention are not taken. Further C
The polycrystalline Si immediately after VD film formation has fine irregularities on the surface due to the influence of the grain boundaries. However, by performing a heat treatment at a high temperature of 1100 ° C. or more, the irregularities are flattened, and the polycrystalline Si film is thermally oxidized. This is considered to be one of the causes of the improvement of the breakdown voltage of the oxide film formed by the above.

As a result of applying the manufacturing method of the present invention to the formation of a capacitor composed of a Si monoxide film-Si, the heat treatment temperature is set to 800 ° C. by implanting hydrogen ions in advance.
Even in this case, a decrease in leakage current was observed. This is C
In addition to the above effect that metal impurities escape from the VD film,
It is considered that dangling bonds resulting from the mismatch of the Si-oxide film interface are terminated by hydrogen atoms.

Incidentally, a third reference example related to the present invention will be described.
The method of manufacturing a semiconductor device shown in FIG.
After the D film is formed, a step of heat-treating the CVD film in a reducing atmosphere is included.

In the manufacturing method according to the third embodiment , oxygen is diffused at high speed in the CVD film and the substrate surface layer without reducing the oxide film on the substrate, thereby purifying the CVD film and reducing the substrate. The BMD distribution in the interior is optimized.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hydrogen after forming a CVD film as in the present invention
Without implanting ions into the CVD film, a high-temperature reducing atmosphere
A first reference example in which a manufacturing method in which heat treatment is performed in an atmosphere is applied to a capacitor manufacturing process of a DRAM having a stacked capacitor cell structure will be described.

FIG. 1 is a sectional view showing a main part of the structure of the DRAM. Although not shown, a gate electrode (word line) is formed on the P-type silicon substrate 1 from which the element is separated.
2. A MOSFET comprising a gate oxide film 3, an N ⁺ drain region 4 and an N ⁺ source region 5 is formed by a known method. Next, the upper surface thereof is covered with an interlayer insulating film (SiO ₂ ) 6, a contact hole is formed in the interlayer insulating film 6, and a polycrystalline S which is connected to the source region 5 and becomes the lower capacitor electrode 7 by the CVD method.
i Film is formed on the entire surface. Next, in an atmosphere of 100% H ₂ ,
Heat treatment at 00 ° C for 70 seconds. Next, the substrate was heated in a dry oxygen atmosphere to form an oxide film 8 on the surface of the polycrystalline Si film including the lower capacitor electrode 7, and further deposited and patterned polycrystalline Si as shown in FIG. A storage capacitor including the electrode 9, the capacitor oxide film 8, and the lower capacitor electrode 7 is formed. Finally, the entire surface is an oxide film 1
0, a contact hole reaching the drain region 4 is formed, and an Al bit line 11 is formed to complete the process.

DRA to which the method of the first embodiment is applied
M and the pause time (pause) of the DRAM according to the conventional method.
Figure 2 shows a comparison of the yield of the characteristics .
Illustrative methods are shown as methods of the invention) . The horizontal axis represents the lot division of the conventional method and the method of the first reference example, and the vertical axis represents the pause yield of each lot. From the figure, before
In the DRAM to which the method of the first reference example is applied, a high-quality capacitor oxide film with little leakage current or the like is obtained, and the stored charge retention characteristics are improved.

A DRAM having a trench-type capacitance memory cell structure
For also obtained the same effect by applying the method of the second embodiment.

Next , after a CVD film is formed as in the present invention.
Without implanting hydrogen ions into the CVD film
A description will be given of a second reference example in which a manufacturing method in which heat treatment is performed in an original atmosphere is applied to manufacture of a floating gate of an EPROM.

FIG. 3 is a sectional view of a main part of the structure of the EPROM.
FIG. 4 is a cross-sectional view during the manufacturing process. First, a thin first thermal oxide film 23 is formed on the surface of an island-shaped element region surrounded by a field oxide film 30 on a P-type silicon substrate 31.
Next, a first polycrystalline Si film 27 having a thickness of 100 nm serving as a floating gate is formed thereon by a low-pressure CVD method.
Next, heat treatment is performed in a 100% H ₂ atmosphere at 1200 ° C. for 90 seconds. Next, after doping this polycrystalline Si film 27 with phosphorus,
Thermal oxidation is performed to form a second thermal oxide film 26 having a thickness of 50 nm. Next, a second polycrystalline Si film 22 serving as a control gate is deposited on the entire surface (see FIG. 4).

Next, a second polycrystalline Si is formed by photolithography.
Film 22, second thermal oxide film 26, first polycrystalline Si film 27
Then, the first thermal oxide film 23 is sequentially etched to form a control gate 32, a second gate oxide film 36, a floating gate 37, and a first gate oxide film 33 as shown in FIG. Note that an oxide film may be deposited on the first polycrystalline Si film instead of the second thermal oxide film 26 obtained by thermally oxidizing the first polycrystalline Si film 27. Next, N-type impurities are ion-implanted using these laminated films as a mask, and heat treatment is performed to form N ⁺ drain regions 34 and N ⁺ source regions 35, and a post-oxide film 38 is formed on the outer surface of the laminated films. Next, a passivation film (for example, a PSG film) 39 is deposited on the entire surface, a contact hole is opened by selective etching, and an Al—Si film is further deposited on the entire surface, and then patterned to form a drain electrode 40 and a source electrode. Forming an electrode 41,
The EPROM shown in FIG. 3 is obtained.

The EPROM has an N ⁺ drain region 34.
This is a device in which a positive high voltage is applied to the floating gate 37 and the control gate 32 to inject electrons into the floating gate 37 for writing. The injected electrons need to be accumulated in the floating gate 37 for a long period of time. The leakage of the stored charges is often determined by the quality of the second gate oxide film 36.

FIG. 5 shows a comparison of the product yield between an EPROM to which the method of the second embodiment is applied and an EPROM according to the conventional method .
The method is shown as the method of the present invention ). It is considered that the difference in yield between the two methods is mainly due to the difference in quality of the second gate oxide film 36.

As described above, the metal impurities in the polycrystalline Si, particularly in an excessive amount, tend to precipitate at the crystal grain boundaries, and such metal atoms cause outward diffusion due to the grain boundary diffusion. Heat treatment is effective. In such a case, it is desirable that the heat treatment be performed at a temperature of 1100 ° C. or more and 3 minutes or less.

It is needless to say that, for example, even for a polycrystalline Si CVD film formed at a low temperature, the electrical characteristics can be improved by "baking" by the high-temperature, short-time main heat treatment.

[0028] Next withstand voltage of the oxide film polycrystalline Si film was formed by thermal oxidation, by applying the method of Reference Example, Reference Example (FIG. 6 which is improved as shown in FIG. 6
Is shown as the method of the present invention ). Figure (a)
In the method of the reference example , the same figure (b) is based on the conventional method, and the horizontal axis is the electrolytic strength (MV / c
m), and the vertical axis indicates the sample frequency indicating the withstand voltage limit.
It can be seen from the figure that the application of the method of the reference example significantly improves the breakdown voltage. This is because although polycrystalline Si immediately after being formed by the CVD method has fine irregularities on the surface due to the influence of grain boundaries, the above irregularities are flattened by heat treatment in a high temperature atmosphere of 1100 ° C. or more. Has contributed.

Next , the third embodiment will be described. As shown in FIG. 7, a LOCO is
An island-shaped oxide film 72 for element isolation is formed by the S method. Thereafter, a polycrystalline Si film 73 was formed on the entire surface by the CVD method, and then a heat treatment was performed at 1200 ° C. for 10 hours in a 100% H ₂ atmosphere. FIG. 7 shows B inside the substrate after this heat treatment.
FIG. 3 is a cross-sectional view showing the concept of the distribution of MD (micro defects such as oxygen precipitates) 74. Isolation portion is BMD is generated to the vicinity of the island-shaped oxide film 72, there is a gettering effect of metal impurities, in the element active region 75, H ₂
Due to the heat treatment in the atmosphere, the oxygen concentration was significantly reduced.
MD does not occur and does not affect the operation of the device. That is, according to the method of the present invention according to claim 3, such a desirable distribution of BMD can be easily obtained. In this case, since this treatment affects the depth of the diffusion layer, it is necessary to suppress the drive-in heat treatment time before the main heat treatment.

Further, this method does not react with the substrate in a reducing atmosphere when selectively extracting metal impurities in a substrate on which an oxide film is formed and obtaining high-speed outward diffusion of oxygen in the substrate. By forming a polycrystalline Si film or the like, the oxide film on the substrate is not reduced, and high-speed outward diffusion of oxygen becomes possible.

In the step of fabricating the DRAM capacitor of the first reference example, after forming a polycrystalline Si film for the lower layer capacitor electrode, hydrogen ions are implanted into the Si film as in the present invention , and then a reduction at 850 ° C. A decrease in leakage current was observed for capacitors heat-treated in a neutral atmosphere.
It is considered that the dangling bond of Si resulting from the mismatch at the oxide film interface is filled with hydrogen atoms.

[0032]

As described so far, according to the present invention, according to the present invention, by the CVD film is formed, a heat treatment in a reducing atmosphere at 800 ° C. or higher temperature after the hydrogen ion implantation, CVD
The metal impurities taken into the film were removed, and a more reliable oxide film was obtained in the subsequent oxide film forming step.

[Brief description of the drawings]

FIG. 1 is a sectional view of a principal part of a DRAM structure for explaining a first reference example related to the present invention ;

FIG. 2 is a yield comparison diagram of pause times of DRAMs manufactured by the method of the first reference example and the conventional method, respectively.

FIG. 3 is a sectional view of a main part of the structure of an EPROM for explaining a second reference example related to the present invention ;

FIG. 4 is a sectional view showing a manufacturing process of the EPROM shown in FIG. 3;

FIG. 5 is a product yield comparison diagram of EPROMs respectively manufactured by the method of the second reference example and a conventional method.

FIG. 6 is a comparison diagram of the breakdown voltage of an oxide film formed by each of the method of the reference example and the conventional method.

FIG. 7 is a diagram for explaining a third reference example related to the present invention, and shows a distribution of BMD when the third reference example is applied to a substrate on which an element isolation oxide film is formed by a LOCOS method; It is a board | substrate sectional drawing.

[Explanation of symbols]

1, 31 P-type silicon substrate 2 Gate electrode 3 Gate oxide film 4, 34 N ⁺ Drain region 5, 35 N ⁺ Source region 7 Lower capacitor electrode 8 Capacitor oxide film 9 Upper capacitor electrode 32 (22) Control gate (second gate) Crystal Si
33 (23) First gate oxide film (first thermal oxide film) 36 (26) Second gate oxide film (second thermal oxide film) 37 (27) Floating gate (first polycrystalline Si)
Film) 40 drain electrode 41 source electrode 72 island oxide film for element isolation 73 polycrystalline Si film 74 BMD 75 element active region

Claims (1)

(57) [Claims] 1. A method according to claim 1 , wherein hydrogen ions are formed after the CVD film is formed.
Implanting into the CVD film, and then heat-treating the CVD film in a reducing atmosphere at a temperature of 800 ° C. or higher; and forming an oxide film on or on the CVD film. A method for manufacturing a semiconductor device.