JPH09330921A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device which is improved in yield and leak characteristic by reducing the size of a strain field by relieving stresses at both end sections of a field oxide film formed on the surface of a silicon substrate by the LOCOS(local oxidation of silicon) method and preventing the concentration of heavy metal contaminant atoms to both end sections of the field oxide film and a method for manufacturing the device. SOLUTION: At the time of forming a field oxide film 6 by selectively oxidizing the surface of a silicon substrate 1, nitrogen 7 is injected into the substrate 1 at both edge sections of the oxide film 6 in the pre-process or post-process of the selective oxidation and a silicon nitride film 8 is formed at the boundary between the oxide film 8 and the substrate 1 by causing a reaction between the nitrogen 7 and silicon. When the film 8 is formed, the stress between the oxide film 6 and substrate 1 is offset and the stresses at both edge sections of the oxide film 6 are relieved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 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 and a manufacturing method thereof in which the yield reduction and the leakage characteristic deterioration of the semiconductor device caused by the element isolation insulating film are improved. .

[0002]

2. Description of the Related Art As a method for electrically separating elements formed on a semiconductor substrate, there is a conventional method as 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 to form an oxide film 2 on the surface of the silicon substrate 1. After that, a silicon nitride film 3 is formed on the oxide film 2 by the 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 by 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 separate elements. Form an area. In order to prevent electrical inversion, ions having the same conductivity type as the silicon substrate 1, for example, boron in the case of the silicon substrate 1 having p-type conductivity, is implanted into this region using the silicon oxide film 2 as a mask. , Boron ion implantation layer 5 is formed. Further, as shown in FIG. 3C, the resist 4 is stripped off and the silicon nitride film 3 is used as a mask to thermally oxidize a region to be an element isolation, thereby forming a thick silicon oxide film for element isolation. A field oxide film 6 is formed. The field oxide film 6 and the ion-implantation layer 5 for preventing inversion immediately below the field oxide film 6 make it possible to separate adjacent transistors without deteriorating the characteristics.

[0003]

[Problems to be Solved by the Invention] Such LOCOS
In the method of forming the element isolation insulating film by the method, the silicon nitride film 3 is used as a mask to thermally oxidize the silicon substrate 1 in the region to be the element isolation, and the field oxide film 6 which is a thick silicon oxide film for element isolation is formed. When the film 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 the difference in thermal expansion coefficient between the field oxide film 6 and the silicon substrate 1. On the other hand, Fe introduced into the silicon substrate 1 due to line contamination during the manufacturing process of the semiconductor device,
Heavy metal contaminant atoms such as Cu and Ni tend to collect in the stress-induced strain field. Then, these heavy metal contaminating atoms form a deep level in the energy forbidden band in the silicon crystal, and become carriers and recombination centers. As a result, the leak current of the PN junction increases, which deteriorates the hold characteristic in the DRAM, for example. Further, recent semiconductor devices must be miniaturized to operate the element with a minute current, but the yield is reduced due to the leakage current due to the contaminating atoms. This problem becomes more serious as the element isolation region becomes narrower with the miniaturization of the element and the stress generated in the silicon substrate 1 increases.

The object of the present invention is to reduce the strain field by relaxing the stress at both ends of the field oxide film in the silicon substrate formed by the LOCOS method, and to collect heavy metal pollutant atoms at both ends of the field oxide film. It is an object of the present invention to provide a semiconductor device and a manufacturing method thereof, in which the above is prevented, the yield is improved, and the leak characteristic is improved.

[0005]

According to the present invention, there is provided a semiconductor device comprising:
A silicon nitride film is formed at the interface between the field oxide film and the silicon substrate at both edges of the field oxide film formed of a thick silicon oxide film on the surface of the silicon substrate.

Further, according to the manufacturing method of the present invention, at least the field oxidation is performed in the step of selectively oxidizing the surface of the silicon substrate to form a field oxide film made of a thick silicon oxide film and in the step before or after this selective oxidation. The method includes the steps of injecting nitrogen into the silicon substrate at both edges of the film and reacting the nitrogen with silicon to form a silicon nitride film at the interface between the field oxide film and the silicon substrate.

For example, as a first manufacturing method of the present invention, a step of forming a silicon oxide film on the main surface of a silicon substrate, a step of forming a silicon nitride film on this silicon oxide film, and a step of forming this silicon nitride film Patterning to open the element isolation region, implanting nitrogen into the silicon substrate in the opening region, and thermally oxidizing the surface of the silicon substrate in the opening region to perform field oxidation of a thick silicon oxide film. A step of forming a film is included, and at the same time as the formation of the field oxide film, a silicon nitride film is formed at the interface between the field oxide film and the silicon substrate by the ion-implanted nitrogen. As a second manufacturing method, a step of forming a silicon oxide film on the main surface of the silicon substrate, a step of forming a silicon nitride film on the silicon oxide film, and a patterning of the silicon nitride film to isolate elements. A step of opening a region, a step of thermally oxidizing the silicon substrate in the opening region to form a field oxide film made of a thick silicon oxide film, and a step of ion-implanting nitrogen into the silicon substrate through the field oxide film. And forming a silicon nitride film at the interface between the field oxide film and the silicon substrate by heat-treated and implanted nitrogen.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1A to 1C are views showing a first embodiment of the present invention in the order of steps. However, only the step of forming the element isolation insulating film on the silicon substrate is shown here. First, in FIG. 1A, the surface of the 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. Then, a silicon nitride film 3 is formed on the silicon oxide film 2 by the CVD method, and a resist 4 is applied on the silicon nitride film 3. After that, the resist 4 is patterned by 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 form a region for element isolation. Then, in order to prevent electrical reversal in this region, 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, boron is used as a mask with the silicon oxide film 2 as a mask. By implanting it into the silicon substrate 1 to form a boron ion implantation layer 5.
In the case of the silicon substrate 1 having n-type conductivity, phosphorus or arsenic is implanted.

Next, as shown in FIG. 1B, a silicon oxide film 2 is formed in the silicon substrate 1 in the region where element isolation is to be performed.
Using as a mask, nitrogen 7 is ion-implanted. The ion implantation condition of nitrogen 7 depends on the thickness of the field oxide film to be formed later, but the acceleration energy is set so as to be shallower than the boron ion implantation layer 5 for preventing the inversion described above. Incidentally, in the implantation of the ions 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 ion implantation of nitrogen 7 shallower than the range of implantation of ions for inversion prevention, the silicon substrate 1 at both ends of the opening of the silicon oxide film 2 is not impaired without impairing the inversion prevention effect. It becomes possible to introduce nitrogen ions into it.

Next, as shown in FIG. 1 (c), the resist 4 is peeled off, and the surface of the silicon substrate 1 in the region where element isolation is to be performed is thermally oxidized by using the silicon nitride film 3 as a mask. A field oxide film 6 which is a silicon oxide film for element isolation of the film is formed. During this thermal oxidation treatment,
The silicon nitride film 8 is formed at the interface between the edge portions of the field oxide film 6 and the silicon substrate 1.
A laminated structure of the silicon nitride film 8 and the field oxide film 6 is formed.

As described above, when the field oxide film 6 is formed by thermally oxidizing the element isolation region on the silicon substrate 1 by the LOCOS method, stress is generated due to the difference in thermal expansion coefficient between silicon and the silicon oxide film. . In particular, large stress is generated at the edges of the field oxide film 6.
As a property 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 when the field oxide film 6 is formed, a silicon nitride film 8 is formed on the silicon substrate 1 at the interface with the field oxide film 6, and the silicon nitride film 8 also causes stress in the silicon substrate 1. . The properties of the stress generated in this case are opposite to those when the field oxide film 6 is formed on the silicon substrate 1 because tensile stress is generated in the silicon nitride film 8 and compressive stress is generated in the silicon substrate 1. is there. Therefore,
Both ends of the field oxide film 6 are nitrided to form the silicon substrate 1
By forming a laminated structure of the silicon nitride film 8 and the field oxide film 6, the stress generated at the different interfaces between the field oxide film 6 and the silicon substrate 1 can be canceled out, and as a result, both ends of the field oxide film 6 can be offset. It is possible to relieve the stress at the edge portion.

Therefore, in the field oxide film 6 thus manufactured, that is, the element isolation insulating film, the stress at the edges of both ends 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 the edges of the field oxide film 6, and a high-performance and high-yield semiconductor device with improved leak characteristics can be manufactured. It will be possible.

FIG. 2 is a sectional view showing a second embodiment of the present invention in the order of manufacturing steps. First, as shown in FIG. 2A, as in the first embodiment, a silicon oxide film 2, a silicon nitride film 3 and a resist 4 are formed on a silicon substrate 1, and an area for element isolation is opened in these. The 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 removed and the silicon nitride film 3 is used as a mask to thermally oxidize the silicon substrate 1 in the region for element isolation, 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 ion implantation conditions of nitrogen 7 are such that the acceleration energy is set so that the range reaches the edge portions on both ends of the field oxide film 6. As a result, nitrogen ions are introduced into the silicon substrate 1 at the edges of both ends of the field oxide film 6 without impairing the inversion prevention effect of the inversion prevention ions. After that, heat treatment is performed by an RTP (Rapid Termal Processing) method to nitride the interface between both end edges of the field oxide film 6 and the silicon substrate 1, and a stack of the silicon substrate 1, the silicon nitride film 8 and the field oxide film 6 is laminated. Form a structure.

Also in this embodiment, the stress generated when the field oxide film 6 is formed and the stress generated when the silicon nitride film 8 is formed at the same time are stresses in mutually opposite directions. Are canceled out, the stress generated at the different interface between the field oxide film 6 and the silicon substrate 1 is canceled out, and as a result, the stress at both edge portions of the field oxide film 6 can be relaxed. As a result, the stress at both edge portions of the field oxide film 6 is relaxed, and 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, resulting in leakage. It is possible to manufacture a high-performance and high-yield semiconductor device with improved characteristics.

[0016]

As described above, according to the present invention, when the surface of a silicon substrate is selectively oxidized to form a field oxide film made of a thick silicon oxide film, in the step before or after the selective oxidation, At least the nitrogen is injected into the silicon substrate at both edges of the field oxide film, and this nitrogen is reacted with silicon to form the silicon nitride film at the interface between the field oxide film and the silicon substrate. It is possible to manufacture a semiconductor device having an element isolation structure in which stress is relieved at both edge portions. As a result, the heavy metal is removed from the device active layer region of the semiconductor device without collecting the heavy metal on both edges of the field oxide film, and a high-performance and high-yield semiconductor device with improved leak characteristics can be manufactured. It will be possible.

[Brief description of drawings]

FIG. 1 is a 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]

 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

Claims (4)

[Claims] 1. A semiconductor device in which a field oxide film made of a thick silicon oxide film is formed on a surface of the silicon substrate to isolate elements formed on the silicon substrate, and both edge portions of the field oxide film are formed. In the semiconductor device, a silicon nitride film is formed at the interface between the field oxide film and the silicon substrate. 2. A method of manufacturing a semiconductor device, comprising the step of selectively oxidizing the surface of a silicon substrate to form a field oxide film made of a thick silicon oxide film, wherein at least field oxidation is performed in a step before or after the selective oxidation. Semiconductor including a step of injecting nitrogen into the silicon substrate at both edge portions of the film and reacting the nitrogen with silicon to form a silicon nitride film at an interface between the field oxide film and the silicon substrate. Device manufacturing method. 3. 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. And ion-implanting nitrogen 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 film made of a thick silicon oxide film. A method of manufacturing a semiconductor device, wherein a silicon nitride film is formed at an interface between a field oxide film and a silicon substrate by the ion-implanted nitrogen at the same time when the film is formed. 4. 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. A step of thermally oxidizing the silicon substrate in the opening region to form a field oxide film made of a thick silicon oxide film; a step of ion-implanting nitrogen into the silicon substrate through the field oxide film; And a step of forming a silicon nitride film at the interface between the field oxide film and the silicon substrate by the generated nitrogen.