JP2629615B2 - 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 forming an element isolation region by a selective oxidation method.

[0002]

2. Description of the Related Art As a method of forming an element isolation region, conventionally, an oxidation resistant mask such as a silicon nitride film is applied to a region other than the element isolation formation region, and then oxidized in an oxidizing atmosphere. The so-called LOC that forms a film
The OS method (selective oxidation method) has been used.

However, in the method of manufacturing a semiconductor device having an element isolation region by the LOCOS method, a so-called bird's beak is formed by invasion of an oxidizing species below the mask, so that the required area of the element isolation region is increased accordingly.
This hinders high integration of semiconductor devices.

As one method for suppressing the bead bark, ion implantation is performed in advance in an element isolation formation region.
A method has been proposed which utilizes accelerated oxidation due to secondary defects generated near a depth given by an average range of implanted ions (hereinafter referred to as Rp). Hereinafter, the bird's beak reduction method will be described with reference to the drawings.

FIGS. 3 (a) to 3 (d) show Japanese Patent Application Laid-Open No. 62-16 / 1987.
5A to 5C are cross-sectional views in a process order for describing a method of forming an element isolation oxide film disclosed in Japanese Patent No. 5951. First, as shown in FIG. 3A, a pad oxide film 2 is formed on a semiconductor silicon substrate 1 by a thermal oxidation method, and then a mask silicon nitride film 3 serving as an oxidation resistant mask is formed on the pad oxide film 2. I do. Next, as shown in FIG. 3B, a photoresist pattern 4 is formed by ordinary photolithography so as to open an element isolation formation region, and a mask silicon nitride film 3 is formed.
Is removed by etching. Subsequently, arsenic is implanted using this photoresist pattern as a mask. At this time, the energy is selected such that the average range Rp of the ions is substantially equal to the thickness of the pad oxide film 2. For example, in the case of a 22 nm pad oxide film 2, arsenic ions are supplied at 40 keV and 5 × 10 ^15.
Inject under the condition of cm ^-2 . By performing ion implantation so that the peak of the ion concentration coincides with the substrate surface, accelerated oxidation is caused when the field oxide film 5 is formed in the subsequent low-temperature selective oxidation step, thereby reducing bird's beak. Things. At this time, the pad oxide film 2 in the area opened by the photoresist pattern 4 can be removed as shown in FIG. After removing the photoresist pattern 4, field oxidation is performed (FIG. 2D). The mask silicon nitride film 3 and the pad oxide film 2 are sequentially removed to complete an element isolation region.

Further, the mask silicon nitride film 3 is formed in the same manner.
A method of forming a LOCOS structure by performing selective oxidation only by a secondary defect by ion implantation without using a semiconductor device is disclosed in
It is disclosed in JP-A-2-165950.

Japanese Patent Application Laid-Open No. 60-101947 discloses that argon ions are replaced with 30 keV instead of arsenic ions.
Injected in the case of 1 × 10 ¹⁵ cm ^-2 , and Rp
A method has also been proposed in which field oxidation is performed using accelerated oxidation caused by a secondary defect introduced in the vicinity to reduce bird's beak.

[0008]

In the conventional method of manufacturing a semiconductor device described above, the implantation energy is set so that Rp comes to the surface of the semiconductor substrate. By utilizing the secondary defects caused by the ion implantation, accelerated oxidation is performed to suppress bird's beak.

However, 2 generated near this Rp
The secondary defects are not easily reduced in the heat treatment step, and the subsequent step includes an oxidation step called a field oxidation step. Therefore, the secondary defects do not shrink, but conversely grow and remain below the element isolation region. When the grown crystal defect is applied to the active region of the element, there is a problem that the critical characteristic of the semiconductor device is deteriorated such as an increase in junction leakage current.

Further, Japanese Patent Application Laid-Open No. Sho 62-165951,
In the conventional method for manufacturing a semiconductor device disclosed in Japanese Patent Application Laid-Open No. Sho 62-165950, ion implantation for causing accelerated oxidation is performed using arsenic ions. Arsenic is an electrically active impurity in silicon, and there is a problem that arsenic is diffused by a heat treatment in a later step and characteristics of a semiconductor device are changed.

An object of the present invention is to provide a method of manufacturing a semiconductor device which can suppress occurrence of bird's beak during selective oxidation and does not involve an increase in junction leakage current.

[0012]

According to the method of manufacturing a semiconductor device of the present invention, when forming an element isolation region by a selective oxidation method, inactive ions are implanted into a semiconductor silicon substrate at a relatively high energy and the Rp of the inert ion is increased. Is selectively oxidized to a position less than the depth of the ion-implanted region given by. As the inert ion, a silicon ion, a carbon ion, or a germanium ion is preferably used.

[0013]

When a high energy inert ion is implanted, silicon vacancies are generated from the substrate surface to a position of about Rp. These vacancies are formed by recoil of silicon which should originally be at lattice points during ion implantation by the implanted ions. These holes function as so-called sink positions for absorbing interstitial silicon generated during selective oxidation, and the oxidation rate in the depth direction becomes higher than the oxidation rate in the horizontal direction, thereby reducing bird's beak.

By implanting inert ions with relatively high energy, secondary defects occur at a depth of about Rp, but secondary defects do not occur in the silicon region consumed by selective oxidation. Therefore, unlike the conventional example, there is no problem that defects grow during selective oxidation and the junction leakage current increases.

In addition, since electrically inactive ions are selected as the ions to be implanted, there is no problem that the characteristics of the semiconductor device fluctuate even if the ions implanted in the heat treatment in a later step diffuse.

[0016]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view for explaining a first embodiment of the present invention in the order of steps.

First, as shown in FIG. 1A, a pad oxide film 2 having a thickness of 30 nm is formed on a semiconductor silicon substrate 1 by a thermal oxidation method. Next, 200 times by chemical vapor deposition.
A mask silicon nitride film 3 (an oxidation-resistant mask) having a thickness of nm is formed. Next, as shown in FIG. 1B, a photoresist pattern 4 is formed by ordinary photolithography so as to open the element isolation formation region, and the mask silicon nitride film 3 in the element isolation formation region is etched away. Next, using the same photoresist pattern 4 as a mask, ion implantation regions 6a are formed by implanting silicon ions at an energy of 650 keV at a dose of 5 × 10 ¹⁵ cm ⁻² . When silicon ions are implanted at 650 keV, the average range in the silicon is about 1000 n.
m. Next, the photoresist pattern 4 is removed, and 1
As shown in FIG. 1C, a field oxide film 5 of 600 nm is formed by pyrogenic oxidation (hydrogen combustion oxidation) at 000 ° C.

The silicon consumed during this selective oxidation is about 1/2 of the field oxide film, that is, 300 nm.
This is a region sufficiently shallower than Rp of silicon ions. Therefore, the implanted interstitial silicon and secondary defects existing at a depth of about Rp do not reach the field oxide film 5, and the secondary defects do not grow during the field oxidation. Further, when field oxidation is performed under these conditions, the silicon vacancies existing up to about Rp away from the substrate surface act as sinks for absorbing interstitial silicon generated at the time of field oxidation, thereby improving the oxidation rate. The speed is about twice that of the case where silicon ions are not implanted. Since this is limited to the oxidation rate in the depth direction, the oxidation by the oxidizing species penetrating into the lower part of the pad oxide film is not accelerated. Accordingly, the effective bird's beak length is reduced because the field oxidation time is shortened. Specifically, the bird's beak length of the conventional method was about 0.3 μm, but the bird's beak length of the element isolation region (field oxide film 5) manufactured by the method of the embodiment of the present invention was about 0.3 μm.
It was confirmed that it was halved to 15 μm.

Subsequently, by sequentially removing the mask silicon nitride film 3 and the pad oxide film 2 by wet etching, it becomes possible to obtain an element isolation region in which a bird's beak is suppressed.

FIGS. 2A to 2D are cross-sectional views in the order of steps for explaining a second embodiment of the present invention.

First, as shown in FIG. 2A, a pad oxide film 2 having a thickness of 30 nm is formed on a semiconductor silicon substrate 1 by a thermal oxidation method. Next, 200 times by chemical vapor deposition.
A mask silicon nitride film 3 having a thickness of nm is formed. Next, ion implantation regions 6b are formed by implanting silicon ions at an energy of 800 keV at a dose of 5 × 10 ¹⁵ cm ⁻² . Next, as shown in FIG. 2D, a photoresist pattern 4 is formed by ordinary photolithography so as to open over the element isolation formation region, and the mask silicon nitride film 3 in the element isolation formation region is removed by etching. Next, the photoresist pattern 4 is removed and 1000
A field oxide film 5 having a thickness of 600 nm is formed by pyrogenic oxidation.

Subsequently, by sequentially removing the mask silicon nitride film 3 and the pad oxide film 2 by wet etching, it becomes possible to obtain an element isolation region in which a bird's beak is suppressed.

In the first embodiment, silicon ions are implanted only in the element isolation formation region. In this embodiment, ion implantation is performed on the entire surface. Since the purpose of this ion implantation is to introduce silicon vacancies in order to cause accelerated oxidation during field oxidation, it is not particularly necessary to implant only ions below the element isolation formation region. Further, according to the present embodiment, a secondary defect due to ion implantation is generated in a portion having a depth of 1000 nm below the element forming region (region partitioned by the field oxide film 5), and this is so-called gettering for capturing metal impurities and the like. There is an advantage that can be utilized.

In the above embodiment, the case where silicon ions are used as the ion species has been described. However, ions which become electrically inactive in the semiconductor silicon substrate, that is, carbon, germanium, etc., which are homologous elements, are implanted. Has the same effect.

The channel stopper can be formed by performing ion implantation after forming the field oxide film 5.

[0027]

As described above, in the method of manufacturing a semiconductor device according to the present invention, electrically inactive ions are implanted into a region deeper than the depth of silicon consumed by selective oxidation for forming an element isolation region. Since a bird's beak can be suppressed by accelerated oxidation by silicon vacancies generated by this implantation, and secondary defects due to ion implantation can be made to be much lower than the field oxide film, bonding It is possible to avoid performance degradation of device characteristics due to an increase in leakage current.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in a process order for explaining a first embodiment of the present invention.

FIG. 2 is a process order sectional view for explaining a second embodiment of the present invention.

FIG. 3 is a cross-sectional view in a process order for explaining a semiconductor manufacturing method according to a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor silicon substrate 2 Pad oxide film 3 Mask silicon nitride film 4 Photoresist pattern 5 Field oxide film 6, 6a, 6b Ion implantation area

Claims (4)

(57) [Claims] A step of implanting inert ions to a predetermined depth from the surface of the semiconductor silicon substrate and then performing selective oxidation to a position less than the depth to form an element isolation region. A method for manufacturing a semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the inert ions are selectively implanted. 3. The method according to claim 1, wherein inert ions are implanted into the entire surface.
The manufacturing method of the semiconductor device described in the above. 4. The method according to claim 1, wherein the inert ions are silicon ions, carbon ions or germanium ions.