Method for manufacturing semiconductor device

ABSTRACT

A provided method for manufacturing the semiconductor device includes the steps of: forming a trench in a silicon substrate on which a silicon oxide film and a silicon nitride film are sequentially stacked; oxidizing the silicon substrate by an oxidation method of not forming nearly at all a silicon oxide film on a surface of the silicon nitride film, to form a silicon oxide film on the surface of the trench and perform pullback etching on the silicon nitride film; and performing rounding oxidation by using radical oxidation to round an edge of the surface of the trench. Therefore, it is possible to perform pullback etching on the nitride film, even in case of performing rounding oxidation by using radical oxidation.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Best mode of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings based on the principle described above. The description is made specifically with reference to the embodiments.

The following will describe a semiconductor device manufacturing method according to the embodiment of the present invention with reference to FIGS. 1A-1I and FIG. .

First, as shown in FIG. 1A, a silicon oxide film having a film thickness of 5-20 nm is formed by thermal oxidation on a silicon substrate , on which silicon oxide film , a silicon nitride film having a film thickness of 120-140 nm is then formed by CVD (Chemical Vapor Deposition) method and stacked sequentially.

Next, as shown in FIG. 1B, after a resist film (not shown) is formed except on an element isolation forming region, allocated to form an element isolation region, on the silicon substrate , using the resist film (not shown) as a mask, the silicon nitride film and the silicon oxide film which are present on the an element isolation forming region are selectively etched off by anisotropic etching; and then, using the silicon nitride film as a mask, the silicon substrate is selectively etched off by plasma etching plasma to thus form a trench therein having a depth of about 300 nm. It is to be noted that a width of the trench is determined arbitrarily in accordance with a desired property.

Next, as shown in FIG. 1C, by performing pre-pullback oxidation in accordance with the “oxidation method of forming a silicon oxide film having a film thickness of about 2 nm by dry oxidation at a film formation temperature of about 700° C.” described in a paragraph of the principle, a silicon oxide film having a film thickness of about 2 nm is formed only on a surface of the trench . The dry oxidation method is performed in an oxidizing atmosphere containing 100% oxygen. In this case, as described in the paragraph of the principle, a silicon oxide film is not formed nearly at all on a surface of the silicon nitride film . Therefore, it is not necessary to perform etching processing as pre-pullback processing subsequently.

Next, as shown in FIG. 1D, using a resist film (not shown) as a mask, the silicon nitride film is pullback etched by isotropic etching using hot phosphoric acid, to form therein an opening having a width W1 larger than a width W2 of the trench and is pulled back by about 20 nm. During this etching, the silicon oxide films and are also etched slightly off simultaneously.

Next, as shown in FIG. 1E, rounding oxidation by use of radical oxidation for rounding an edge of the trench in the silicon substrate is performed to form a silicon oxide film having a film thickness of about 20 nm on the surface of the trench . That is, the silicon oxide film having the thinner film in thickness (about 2 nm) already formed on the surface of the trench is transformed into the silicon oxide film having the greater film in thickness (about 20 nm). By thus utilizing radical oxidation, a conventional overhung rounded shape such as shown in FIG. 8 is improved, to mitigate irregularities in film thickness of the edge of the trench in order to provide a constant film thickness as shown in FIG. . Since radical oxidation has a high degree of oxidation behavior, during this oxidation, the silicon nitride film is also oxidized considerably on its surface simultaneously, to form a silicon oxide film having a film thickness of 15-18 nm. However, pullback etching is already completed, so that the silicon oxide film , if any, has no adverse effects.

Next, as shown in FIG. 1F, a buried silicon oxide film made of a silicon oxide film is formed by CVD throughout the surface. The buried silicon oxide film is specifically buried in such a manner as to completely cover an inside surface of the trench through the silicon oxide film present on the surface of the silicon nitride film .

Next, as shown in FIG. 1G, the buried silicon oxide film is polished by CMP (Chemical Mechanical Polishing) method so as to be thinner using the silicon nitride film as a stopper layer. Subsequently, as shown in FIG. 1H, the silicon nitride film is etched off using hot phosphoric acid. Next, as shown in FIG. 1I, the silicon oxide film is selectively etched off to thereby form an element isolation region .

After the element isolation region is formed, as in the case of an ordinary semiconductor device manufacturing method, desired elements such as MOS transistors (not shown) are formed in each of semiconductor regions (active regions) which are insulated and isolated from each other by the element isolation region , thereby completing an LSI (Large Scale Integration).

Thus, according to the semiconductor device manufacturing method of the present embodiment, by forming the trench in the silicon substrate on which the silicon oxide film and the silicon nitride film are stacked sequentially; then oxidizing the silicon substrate using the oxidation method, hereby forming a silicon oxide film only on the surface of the trench , without forming nearly at all a silicon oxide film on the surface of the silicon nitride film , after this pullback etching processing of the silicon nitride film follows; and then performing rounding oxidation by use of radical oxidation to round the edge of the surface of the trench , it is possible to use the pullback etching proceeding and the radical oxidation method in combination with each other, thereby improving a degree of the buried silicon oxide film being buried and also well forming a round shape of the edge of the trench .

Therefore, it is possible to perform pullback etching on the silicon nitride film while performing rounding oxidation by use of radical oxidation.

It is apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention. For example, although the dry oxidation method of forming the silicon oxide film only on the surface of the trench without forming nearly at all the silicon oxide film on the surface of the silicon nitride film has been exemplified as being conducted in an oxidizing atmosphere containing 100% oxygen, the present invention is not limited thereto; for example, it may be conducted in an oxidizing atmosphere in which oxygen is diluted by an inert gas such as nitrogen or argon. This approach is effective in adjusting a film formation rate of the silicon oxide film despite that in this case the film formation rate is decreased due to a decrease in concentration of oxygen in the atmosphere.

Further, the dry oxidation method of forming a silicon oxide film only on the surface of the trench without forming nearly at all a silicon oxide film on the surface of the silicon nitride film can provide almost the same effects under conditions of a temperature range of 600-750° C. and a film thickness range of 1-4 nm irrespective of the temperature conditions and the film thickness described in the embodiments. Further, although the embodiments have been described in an example where the buried silicon oxide film is buried into the trench to thus form the element isolation region , a silicon nitride film in place of the silicon oxide film or any other insulating material such as a silicon oxide film to which an impurity such as boron or phosphorus is added may be buried.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1C are process diagrams for showing in sequence a method for manufacturing a semiconductor device according to an embodiment of the present invention;

FIGS. 1D-1F are continued process diagrams for showing in sequence the method for manufacturing the same semiconductor device;

FIGS. 1G-1I are further continued process diagrams for showing in sequence the method for manufacturing the same semiconductor device;

FIG. 2 is a partial diagram for showing schematically a minute part of a semiconductor device manufactured by the same method according to the same embodiment;

FIG. 3 is a graph for showing a relationship between an etching time (horizontal axis) of a silicon nitride film and an etched amount (vertical axis) thereof for explaining a principle of the present invention;

FIGS. 4A-4C are process diagrams for showing in sequence a conventional method for manufacturing a semiconductor device (a first conventional technology);

FIGS. 4D-4G are continued process diagrams for showing in sequence the conventional method for manufacturing the semiconductor device (the first conventional technology);

FIGS. 5A-5D are process diagrams for showing in sequence another conventional method for manufacturing a semiconductor device (a second conventional technology);

FIGS. 5E-5H are continued process diagrams for showing in sequence the other conventional method for manufacturing the semiconductor device (the second conventional technology);

FIGS. 6A-6C are process diagrams showing in sequence still another conventional method for manufacturing a semiconductor device (a third conventional technology);

FIGS. 6D-6F are continued process diagrams for showing in sequence still the other conventional method for manufacturing the same semiconductor device (the third conventional technology);

FIG. 7 is an illustration for outlining a disadvantage of the conventional semiconductor device manufacturing method;

FIG. 8 is an illustration for outlining a disadvantage of the conventional semiconductor device manufacturing method; and

FIGS. 9A-9B are illustrations for outlining a disadvantage of the conventional semiconductor device manufacturing method.

CLAIMS

1. A method for manufacturing a semiconductor device comprising, burying an insulating material into a trench formed in a semiconductor substrate to thereby form an element isolation region in order to form a desired element in each of semiconductor regions which are insulated and isolated from each other by said element isolation region, said method comprising: a trench formation step for sequentially forming and stacking an oxide film and a nitride film on said semiconductor substrate, to selectively etch off said nitride film and said oxide film which are present on a region in which said element isolation region is expected to be formed and then selectively etch off said semiconductor substrate using said nitride film as a mask, thus forming said trench; a semiconductor substrate oxidation step for oxidizing said semiconductor substrate by a method of forming an oxide film only on a surface of said trench without forming nearly at all an oxide film on a surface of said nitride film; a nitride film pullback step for performing pullback etching on said nitride film in such a manner that a width of an opening in said nitride film may be larger than a width of an opening of said trench; a radical oxidation step for performing rounding oxidation by use of radical oxidation method to thus round an edge of the surface of said trench; and an insulating material burying step for burying said insulating material into said trench.

2. A method for manufacturing a semiconductor device comprising, burying an oxide into a trench formed in a silicon substrate to thereby form an element isolation region in order to form a desired element in each of semiconductor regions which are insulated and isolated from each other by said element isolation region, said method comprising: a trench formation step for sequentially forming and stacking a silicon oxide film and a silicon nitride film on said silicon substrate, to selectively etch off said silicon nitride film and said silicon oxide film which are present on a region in which said element isolation region is expected to be formed and then selectively etch off said silicon substrate using said silicon nitride film as a mask, thus forming said trench; a silicon substrate oxidation step for oxidizing said silicon substrate by an oxidation method of forming a silicon oxide film only on a surface of said trench without forming nearly at all the silicon oxide film on a surface of said silicon nitride film; a silicon nitride film pullback step for performing pullback etching on said silicon nitride film in such a manner that a width of an opening in said silicon nitride film may be larger than a width of an opening of said trench; a radical oxidation step for performing rounding oxidation by use of radical oxidation to thus round an edge of the surface of said trench; and an oxide burying step for burying said oxide into said trench.

3. The method for manufacturing the semiconductor device according to claim 2, wherein said silicon substrate oxidation step is performed by dry oxidation at 600-750° C., to form said silicon oxide film.

4. The method for manufacturing the semiconductor device according to claim 3, wherein said silicon oxide film is formed so as to have a film thickness of 1-4 nm.

5. The method for manufacturing the semiconductor device according to claim 3, wherein said dry oxidation method is performed in an oxidizing atmosphere containing an oxygen gas.

6. The method for manufacturing the semiconductor device according to claim 5, wherein said dry oxidation is performed in an oxidizing atmosphere in which said oxygen gas is diluted by an inert gas.

7. The method for manufacturing the semiconductor device according to claim 2, wherein said silicon substrate pullback step is performed using hot phosphoric acid.

8. A method for manufacturing a semiconductor device comprising, burying an oxide into a trench formed in a silicon substrate to thereby form an element isolation region in order to form a desired element in each of semiconductor regions which are insulated and isolated from each other by said element isolation region, said method comprising: a trench formation step for sequentially forming and stacking a silicon oxide film and a silicon nitride film on said silicon substrate, to selectively etch off said silicon nitride film and said silicon oxide film which are present on a region in which said element isolation region is expected to be formed and then selectively etch off said silicon substrate using said silicon nitride film as a mask, thus forming said trench; a silicon substrate oxidation step for oxidizing said silicon substrate by a dry oxidation method of forming a silicon oxide film only on a surface of said trench without forming nearly at all the silicon oxide film on a surface of said silicon nitride film; a silicon nitride film pullback step for performing pullback etching on said silicon nitride film in such a manner that a width of an opening in said silicon nitride film may be larger than a width of an opening of said trench; a radical oxidation step for performing rounding oxidation by use of radical oxidation to thus round an edge of the surface of said trench; an oxide burying step for burying said oxide into said trench, and wherein said dry oxidation method is performed under conditions at 600-750° C. in an oxidizing atmosphere containing an oxygen gas.

9. A method for manufacturing a semiconductor device according to claim 8, wherein said dry oxidation method is performed under conditions at 600-750° C. in an oxidizing atmosphere of 100% oxygen gas.

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