JP3055465B2 - 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 LOCOS (Local
The present invention relates to a semiconductor device having an element isolation insulating film using an Oxidation of Silicon method, and more particularly to a semiconductor device in which the yield reduction and leakage characteristic deterioration of a semiconductor device caused by the element isolation insulating film are improved and a method of manufacturing the same. .

[0002]

2. Description of the Related Art As a method of electrically isolating elements formed on a semiconductor substrate, a conventional method is shown in FIG.
An element isolation insulating film by the OCOS method has been proposed. In FIG. 3A, the silicon substrate 1 is oxidized by a thermal oxidation method, and an oxide film 2 is formed on the surface of the silicon substrate 1. Thereafter, a silicon nitride film 3 is formed on the oxide film 2 by a CVD method, and a resist 4 is applied on the silicon nitride film 3. Next, as shown in FIG. 3B, the resist 4 is patterned using a lithography technique, and the silicon nitride film 3 in the opening is removed by an etching method using the patterned resist as a mask to perform element isolation. Form an area. In order to prevent electrical inversion, ions of the same conductivity type as the silicon substrate 1, for example, in the case of the silicon substrate 1 having p-type conductivity, are implanted into this region using the silicon oxide film 2 as a mask. Then, a boron ion implantation layer 5 is formed. Further, as shown in FIG. 3C, the resist 4 is peeled off and the region to be element-isolated is thermally oxidized using the silicon nitride film 3 as a mask, thereby forming a thick silicon oxide film for element isolation. A certain field oxide film 6 is formed. The field oxide film 6 and the ion implantation layer 5 immediately below the field oxide film 6 for preventing inversion make it possible to separate adjacent transistors without deteriorating the characteristics.

[0003]

SUMMARY OF THE INVENTION Such a LOCOS
In the method of forming the element isolation insulating film by the method, the silicon oxide film 3 is used as a mask to thermally oxidize the silicon substrate 1 in a region where element isolation is to be performed, thereby forming a field oxide film 6 which is a thick silicon oxide film for element isolation. Is formed, a large stress is generated in the silicon substrate 1 in contact with both ends of the field oxide film 6 due to a difference in thermal expansion coefficient between the field oxide film 6 and the silicon substrate 1. On the other hand, during the semiconductor device manufacturing process, Fe introduced into the silicon substrate 1 due to line contamination,
Heavy metal contaminants, such as Cu and Ni, tend to collect in stress induced strain fields. These heavy metal contaminant atoms form a deep level in the energy forbidden band in the silicon crystal, and serve as a carrier generation and recombination center. As a result, the leakage current of the PN junction increases, and, for example, the hold characteristics of the DRAM deteriorate. Further, recent semiconductor devices have to be miniaturized and the element must be operated with a very small current. However, the yield is reduced due to a leak current caused by contaminant atoms. This problem becomes more serious as the element isolation region becomes narrower as the element becomes finer, and the stress generated in the silicon substrate 1 increases.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce a stress field at both ends of a field oxide film on a silicon substrate formed by a LOCOS method, thereby reducing a strain field, and collecting heavy metal contaminant atoms at both ends of the field oxide film. It is an object of the present invention to provide a semiconductor device in which the yield is improved by preventing such a phenomenon and the leak characteristic is improved, and a method of manufacturing the same.

[0005]

According to a manufacturing method of the present invention, a step of selectively oxidizing a surface of a silicon substrate to form a field oxide film made of a thick silicon oxide film, and at least a step of performing field oxidation after the selective oxidation. Nitrogen is injected into the silicon substrate at both edges of the oxide film, and the nitrogen is reacted with silicon to form a silicon nitride film at the interface between the field oxide film and the silicon substrate. And a step of forming a laminated structure composed of the silicon oxide film.

[0006]

For example, as a first manufacturing method of the present invention, a step of forming a silicon oxide film on a main surface of a silicon substrate, a step of forming a silicon nitride film on the silicon oxide film, and a step of forming the silicon nitride film Patterning an element isolation region, implanting nitrogen ions into the silicon substrate in the opening region, and thermally oxidizing the surface of the silicon substrate in the opening region to form a field oxide comprising a thick silicon oxide film. includes a step of forming a film, a silicon nitride film is formed on the interface between the field oxide film and the silicon substrate by nitrogen and the ion implantation simultaneously with the formation of the field oxide film, the silicon substrate and the front
Laminated structure comprising the silicon nitride film and the silicon oxide film
Forming structure . Further, as a second manufacturing method, a step of forming a silicon oxide film on a main surface of a silicon substrate, a step of forming a silicon nitride film on the silicon oxide film, and an element isolation by patterning the silicon nitride film Opening a region, thermally oxidizing the silicon substrate in the opening region to form a field oxide film made of a thick silicon oxide film, and ion-implanting nitrogen into the silicon substrate through the field oxide film. Forming a silicon nitride film at the interface between the field oxide film and the silicon substrate with the nitrogen implanted by heat treatment;
Recon substrate, the silicon nitride film, and the silicon oxide film
Forming a laminated structure composed of

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a first embodiment of the present invention in the order of steps. However, only the step of forming an element isolation insulating film on a silicon substrate is shown here. First, in FIG. 1A, the surface of a silicon substrate 1 is oxidized by a thermal oxidation method to form a silicon oxide film 2 on the surface of the silicon substrate 1. Thereafter, a silicon nitride film 3 is formed on the silicon oxide film 2 by a CVD method, and a resist 4 is applied on the silicon nitride film 3. Thereafter, the resist 4 is patterned using a lithography technique, and the silicon nitride film 3 in the opening is removed by etching using the patterned resist as a mask, thereby forming a region for element isolation. Thereafter, ions of the same conductivity type as the silicon substrate 1, for example, boron in the case of the silicon substrate 1 having p-type conductivity, are used as masks for the silicon oxide film 2 to prevent electrical inversion in this region. To form a boron ion implanted layer 5.
In the case of a silicon substrate 1 having n-type conductivity, phosphorus or arsenic is implanted.

Next, as shown in FIG. 1B, a silicon oxide film 2
Is used as a mask, and nitrogen 7 is ion-implanted. The ion implantation condition of nitrogen 7 depends on the thickness of a field oxide film to be formed later, but its acceleration energy is set to be shallower than that of the boron ion implantation layer 5 for preventing inversion. Incidentally, in the ion implantation for preventing the inversion, the acceleration energy is set so that the boron ion implantation layer 5 having the maximum ion concentration is formed at the bottom of the field oxide film formed thereafter. By making the range of the ion implantation of the nitrogen 7 shallower than the range of the implantation of the inversion preventing ions in this way, the silicon substrate 1 at both ends of the opening of the silicon oxide film 2 can be formed without impairing the inversion preventing effect. It becomes possible to introduce nitrogen ions therein.

Next, as shown in FIG. 1C, the resist 4 is peeled off, and the silicon nitride film 3 is used as a mask to thermally oxidize the surface of the silicon substrate 1 in a region where element isolation is to be performed. A field oxide film 6, which is a silicon oxide film for element isolation of the film, is formed. During this thermal oxidation treatment,
A silicon nitride film 8 is formed at the interface between the edges of both ends of the field oxide film 6 and the silicon substrate 1.
And a stacked structure of silicon nitride film 8 and field oxide film 6 is formed.

As described above, when the field oxide film 6 is formed by thermally oxidizing the region to be element-isolated on the silicon substrate 1 by the LOCOS method, stress is generated due to a difference in thermal expansion coefficient between silicon and the silicon oxide film. . In particular, a large stress is generated at both edges of the field oxide film 6.
As the nature of the stress generated in this case, a compressive stress acts on the field oxide film 6 and a tensile stress acts on the silicon substrate 1. However, at the same time as field oxide film 6 is formed, silicon nitride film 8 is formed on silicon substrate 1 at the interface with field oxide film 6, and stress is also generated on silicon substrate 1 by silicon nitride film 8. . The nature of the stress generated in this case is such that a tensile stress is generated in the silicon nitride film 8 and a compressive stress is generated in the silicon substrate 1, which is opposite to the case where the field oxide film 6 is formed on the silicon substrate 1. is there. Therefore,
Both ends of the field oxide film 6 are nitrided to form a silicon substrate 1
Forming a laminated structure of silicon oxide film 8 and silicon oxide film 8 and field oxide film 6 makes it possible to cancel the stress generated at the heterogeneous interface between field oxide film 6 and silicon substrate 1. It is possible to reduce the stress at the edge.

Therefore, in the field oxide film 6 manufactured as described above, that is, in the element isolation insulating film, the stress at both edges is relaxed.
As a result, the heavy metal is removed from the device active layer region of the semiconductor device without collecting the heavy metal at both edge portions of the field oxide film 6, and a high-performance and high-yield semiconductor device with improved leakage characteristics can be manufactured. It becomes possible.

FIG. 2 is a sectional view showing a second embodiment of the present invention in the order of manufacturing steps. First, FIG. 2A shows that a silicon oxide film 2, a silicon nitride film 3, and a resist 4 are formed on a silicon substrate 1 and a region where element isolation is to be performed is formed on the silicon substrate 1, similarly to the first embodiment. This shows a state in which boron ions 5 of the same conductivity type as the silicon substrate 1 are implanted into the silicon substrate 1 to prevent electrical inversion. Next, as shown in FIG.
Is peeled off and the silicon substrate 1 in a region to be element-isolated is thermally oxidized using the silicon nitride film 3 as a mask, thereby forming a field oxide film 6 which is a thick silicon oxide film for element isolation.

Next, as shown in FIG. 3C, nitrogen 7 is ion-implanted using the field oxide film 6 as a mask. The conditions for the ion implantation of nitrogen 7 are such that the acceleration energy is set so that the range is reached at both edges of the field oxide film 6. As a result, nitrogen ions are introduced into the silicon substrate 1 at both edges of the field oxide film 6 without impairing the inversion prevention effect of the inversion prevention ions. Thereafter, a heat treatment is performed by a RTP (Rapid Termal Processing) method to nitride the interface between both edge portions of the field oxide film 6 and the silicon substrate 1, and to form a stack including the silicon substrate 1, the silicon nitride film 8, and the field oxide film 6. Form the structure.

Also in this embodiment, the stress generated when forming the field oxide film 6 and the stress generated simultaneously when the silicon nitride film 8 is formed are mutually opposite stresses. Are canceled out, the stress generated at the heterogeneous interface between the field oxide film 6 and the silicon substrate 1 is cancelled, and as a result, the stress at both edges of the field oxide film 6 can be reduced. As a result, the stresses at the both edges of the field oxide film 6 are relieved, and the heavy metals are removed from the device active layer region of the semiconductor device without collecting the heavy metals at the both edges of the field oxide film 6, and the leakage current is reduced. A high-performance and high-yield semiconductor device having improved characteristics can be manufactured.

[0016]

As described above, according to the present invention, when a field oxide film made of a thick silicon oxide film is formed by selectively oxidizing the surface of a silicon substrate, a step before or after the selective oxidation is performed. Nitrogen is implanted into the silicon substrate at least at both edges of the field oxide film, and the nitrogen is reacted with silicon to form a silicon nitride film at the interface between the field oxide film and the silicon substrate.
The silicon substrate, the silicon nitride film, and the silicon
Since the laminated structure made of the con oxide film is formed, it is possible to manufacture a semiconductor device having an element isolation structure in which stress is relieved at both edges of the field oxide film. As a result, the heavy metal is removed from the device active layer region of the semiconductor device without collecting the heavy metal at both edge portions of the field oxide film, and a high-performance and high-yield semiconductor device with improved leakage characteristics can be manufactured. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a cross-sectional view showing a second embodiment of the present invention in the order of manufacturing steps.

FIG. 3 is a sectional view showing a conventional manufacturing method in the order of manufacturing steps.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 silicon oxide film 3 silicon nitride film 4 resist 5 boron ion implantation layer 6 field oxide film 7 nitrogen 8 silicon nitride film

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/316

Claims (2)

(57) [Claims] 1. A method of manufacturing a semiconductor device, comprising the step of forming a field oxide film made of a thick silicon oxide film by selectively oxidizing a surface of a silicon substrate, wherein at least a field oxide film region edge Nitrogen is injected into a portion of the silicon substrate, and the nitrogen is reacted with silicon to form a silicon nitride film at an interface between the field oxide film and the silicon substrate. The silicon substrate, the silicon nitride film, and the silicon A method for manufacturing a semiconductor device, comprising a step of forming a laminated structure made of an oxide film. 2. A step of forming a silicon oxide film on a main surface of a silicon substrate, a step of forming a silicon nitride film on the silicon oxide film, and a step of patterning the silicon nitride film to open an element isolation region. Forming a field oxide film made of a thick silicon oxide film by thermally oxidizing the silicon substrate in the opening region; ion-implanting nitrogen into the silicon substrate through the field oxide film; Forming a silicon nitride film at an interface between the field oxide film and the silicon substrate with the formed nitrogen, and forming a stacked structure including the silicon substrate, the silicon nitride film, and the silicon oxide film. Semiconductor device manufacturing method.