JPH09134914A - Formation of element isolation region - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved LOCOS (local oxidation of silicon) method, which suppresses the generation of a bird's beak and can enhance the flatness of the surfaces of element isolation regions. SOLUTION: This method forms an antireflection pattern 13a consisting of a silicon nitride film on a substrate 11 consisting of silicon via a pad oxide film 12, introduces fluorine ions and oxidation ions in the surface layer of the substrate 11 by an ion-implantation using the pattern 13a as a mask, then, performs a heat treatment of the substrate 11 and oxidizing and fluorinate selectively the surface layer parts, which are exposed through the pattern 13a, of the substrate 11 to form element isolation regions 16 consisting of a silicon fluorooxide film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an element isolation region on the element formation surface side of a substrate in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, element isolation regions are formed between element formation regions on a substrate surface made of silicon by, for example, the following LOCOS (Local Oxidation of Silicon) method. In the LOCOS method, first, an anti-oxidation pattern made of silicon nitride is formed on a substrate via a pad oxide film by a lithography method and an etching process that follows. The anti-oxidation pattern is formed so as to cover the element formation region of the substrate. Next, a thermal oxidation process is performed on the surface of the substrate using the anti-oxidation pattern as a mask. As a result, an oxide film is grown on the surface layer portion of the substrate exposed from the oxidation prevention pattern, and an element isolation film made of the oxide film is formed.

By forming the element isolation region by the LOCOS method or various improved LOCOS methods improved from the LOCOS method, formation of a parasitic MOSTr between elements arranged on both sides of the element isolation region is prevented. it can. Then, the element isolation capability can be improved by increasing the values of the isolation region width and the isolation film thickness.

[0004]

However, in the above-described method for forming the element isolation region, since the oxide film is partially grown on the surface of the substrate, the surface of the substrate becomes uneven. Then, for example, when lithography for forming a wiring pattern on the substrate is performed in a step after the element isolation region is formed, a notch due to the interference of exposure light is formed in the shoulder of the convex step of the element isolation region. A resist pattern having (constriction) is formed. Therefore, the wiring pattern formed by etching using this resist pattern as a mask also has a notch. Then, as the wiring pattern becomes finer, the influence of the notch on the wiring pattern becomes larger, and the pair may be broken. Therefore, in order to miniaturize the semiconductor element, it is required to reduce the thickness of the element isolation region to reduce the step difference on the substrate surface.

On the other hand, in order to achieve high integration of the semiconductor device, it is necessary to narrow the width of the element isolation film and widen the area occupied by the element formation region. However, in order to provide the element isolation region with a certain element isolation capability, there is a trade-off relationship between the width of the isolation region made of an oxide film and the film thickness. Must be secured. This is one of the factors that prevent miniaturization of semiconductor elements and high integration of semiconductor devices.

Further, when the element isolation region is formed by the LOCOS method, a transition region called bird's beak is formed between the element isolation region and the element formation region. The fact that the bird's beak portion narrows the effective element formation width and the effective element isolation width is also a factor that hinders high integration of the semiconductor device.

[0007]

Therefore, a method of forming an element isolation region according to the present invention for solving the above-mentioned problems is a method for forming a surface layer of a substrate by ion implantation using an antioxidation pattern formed on the substrate as a mask. At least one of fluorine ions and oxygen ions is introduced into the substrate, and then the substrate is heat-treated. As a result, the surface layer of the substrate is oxyfluorinated or oxidized to form an element isolation region made of an oxyfluoride film or an oxide film.

In the method of introducing fluorine ions into the surface layer of the substrate, an element isolation region made of an oxyfluoride film is formed on the surface of the substrate. This oxyfluoride film has a lower dielectric constant than the oxide film. Therefore, as compared with the case where the element isolation region made of an oxide film is formed, the film thickness required to prevent the parasitic MOS becomes thinner. Therefore, the step difference on the substrate surface is reduced and the bird's beak in the element isolation region is also reduced.

Further, in the method of introducing oxygen ions, since the heat treatment is performed in a state where the oxygen ions are introduced with good selectivity to the surface portion of the substrate exposed from the oxidation prevention pattern in advance, the oxide film is formed in the heat treatment. It is not necessary to diffuse oxygen to the surface layer of the substrate in order to grow the element isolation region consisting of. Therefore, as compared with the case where oxygen is diffused in the surface layer of the substrate by the thermal oxidation process to form the element isolation region made of an oxide film, good selectivity is maintained, that is, the oxygen ion implantation region is oxidized. As a result, an element isolation region is formed. Therefore, it is possible to obtain the element isolation region in which the spread of the oxidized region (bird's beak) due to the diffusion of oxygen is suppressed.

Further, in the method of introducing the fluorine ions and the oxygen ions, the element isolation region having a lower dielectric constant than that of the oxide film is formed while maintaining good selectivity. From this, it is possible to reduce the step difference on the substrate surface by thinning the element isolation region, reduce the bird's beak in the element isolation region, and suppress the spread of the oxidized region (bird's beak) due to oxygen diffusion. A separation area is obtained.

[0011]

Embodiments of the present invention will be described below. 1 (1) to 1 (3) are cross-sectional process diagrams showing a first embodiment in which the element isolation region forming method of the present invention is applied to the LOCOS method. First, the first embodiment will be described with reference to these drawings. Will be explained. As shown in FIG. 1A, the substrate 11 forming the element isolation region is made of, for example, silicon. First, in the first step, a pad oxide film 12 having a film thickness of 20 nm is formed on the surface of the substrate 11 by a humid oxidation method such as a pyrogenic oxidation method. Here, as an example, the film formation is performed with the oxidation temperature set to 850 ° C. Next, LP-CVD (Low Pressure-Chemical Va
A silicon nitride film 13 having a film thickness of 150 nm is formed on the pad oxide film 12 by the pore deposition method.

Next, a resist pattern 14 is formed on the silicon nitride film 13 by a lithography method, and then RIE (Reac) using this resist pattern 14 as a mask.
The pad oxide film 12 and the silicon nitride film 13 on the substrate 11 are etched by the tive ion etching method. As a result, the oxidation prevention pattern 13a made of a silicon nitride film is formed on the substrate 11 with the pad oxide film 12 interposed therebetween. The anti-oxidation pattern 13a is formed so as to cover the element formation region 11a of the substrate 11.

Next, in a second step shown in FIG. 1B, oxygen ions (O ⁺ ) and fluorine ions (F ⁺ ) are formed in the surface layer of the substrate 11 by ion implantation using the resist pattern 14 as a mask. To introduce. Here, the amorphous silicon oxide layer 15 having a certain depth in the depth direction is formed on the surface layer portion of the substrate 11 by introducing oxygen ions into the substrate 11 in plural times with different implantation energies. To do. Therefore, for example, in the first stage, the implantation energy is 150 to 200 keV and the implantation dose is 0.4 × 10.
Ion implantation of ^{18 to} 1.6 × 10 ¹⁸ ions / cm ² is performed, and in the second step, implantation energy = 100 to 150 keV and implantation dose amount = 0.4 × 10 ^{18 to} 1.6 × 10 ¹⁸ ions / cm 2.
Ion implantation of ² . Fluorine ions are implanted at a dose of 1 × 10 ^{14 to} 5 × 10 ¹⁵ ions / cm ² at an implantation energy of 40 to 120 keV so that a range distance is provided inside the amorphous silicon oxide layer 15. Ion implantation is performed. The ion implantations may be performed in any order.

Next, in a third step shown in FIG. 1C, after removing the resist pattern (14), a heat treatment is performed at 1000 to 1200 ° C. in a diluted humidified oxygen (O ₂ ) atmosphere.
Do ~ 2 hours. As a result, crystallization of the amorphous silicon oxide layer (15) into which the fluorine ions have been introduced is advanced, and the element isolation region 16 made of silicon oxyfluoride (SiOx Fy) is formed on the surface layer of the substrate 11.

Here, since the heat treatment of the substrate 11 is performed with oxygen ions introduced in advance, it is not necessary to diffuse oxygen to the surface layer of the substrate 11 by this heat treatment. Therefore, as compared with the case where oxygen is diffused into the surface layer of the substrate 11 by the thermal oxidation process to form the element isolation region made of an oxide film, the element isolation region 1 is maintained with good selectivity.
6 are formed. Therefore, the growth of the bird's beak 17 is suppressed, the effective element formation width w with respect to the width W of the anti-oxidation pattern 13a is expanded, and the anti-oxidation pattern 13 is formed.
The effective element separation width w ₁ with respect to the opening width W _{1 of} a can be expanded.

The silicon oxyfluoride forming the element isolation region 16 is a material having a lower dielectric constant than silicon oxide. From this, the threshold voltage (Vth) for forming the parasitic MOSTr in the element isolation region 16 formed of the silicon oxyfluoride is higher than the threshold voltage of the element isolation region made of silicon oxide. Become. Therefore, it is possible to obtain a predetermined element isolation capability with a thinner film thickness t as compared with the element isolation region made of silicon oxide. Therefore, as compared with the method of forming the element isolation region made of silicon oxide, the bird's beak of the element isolation region 16 is suppressed small, and the step difference on the surface of the substrate 11 is reduced to prevent the occurrence of a notch during photolithography. Will be possible.

In the first embodiment, fluorine ions and oxygen ions are introduced into the surface layer of the substrate 11. But the second
In the process, only oxygen ions may be introduced to the surface of the substrate 11. In this case, the element isolation region 1 made of silicon oxide
6 is formed, the film thickness of the element isolation region 16 is set to be thicker than that in the first embodiment to secure the element isolation ability. In the above-mentioned forming method, the element isolation region 16 can be formed with good selectivity maintained, and the effective element formation width w and element isolation width w by suppressing the expansion of the bird's beak 17 can be achieved as in the first embodiment. w ₁ can be expanded.

In the second step, only fluorine ions may be ion-implanted. In this case, in the second step, high-concentration ion implantation of about 5 × 10 ⁵ ions / cm ² is performed with an implantation energy such that fluorine ions are introduced near the surface of the substrate. In addition, in the third step, 10 in an oxidizing atmosphere.
The heat treatment at 00 ° C. is performed in a short time within 1 hour. With the above-described formation method, the element isolation region 16 made of silicon oxyfluoride can be formed, and the element isolation having a thinner film thickness t can be formed as compared with the element isolation region made of silicon oxide as in the first embodiment. The region 16 can be formed to prevent the occurrence of notches during photolithography.

In each of the above-described first embodiments, at the time of ion implantation in the second step, boron ions (B ⁺ ) for forming the inversion prevention layer are formed at a position deeper than the implantation depth of fluorine ions and oxygen ions. May be introduced. By performing such ion implantation, an inversion prevention layer having a high p-type impurity concentration is formed along the periphery of the element isolation region 16.

Next, FIGS. 2 (1) to 2 (4) are views for explaining a second embodiment of the method of forming an element isolation region of the present invention. First, the claims will be described with reference to these drawings. A second embodiment to which the method described in No. 3 is applied will be described. Next, FIG.
(1) to (3) are SWAMI (side wall masked) which is an improved LOCOS method for the method of forming the element isolation region of the present invention.
It is a cross-sectional process drawing which shows 2nd Embodiment applied to the isolation) method, and 2nd Embodiment is described below using these figures. The same components as those in the first embodiment will be described with the same reference numerals.

First, in the first step shown in FIG. 2A, as in the first embodiment, the oxidation prevention pattern 13a made of silicon nitride is formed on the substrate 11 via the pad oxide film.
After forming, the surface layer of the substrate 11 is continuously etched by about 50 to 100 nm using the resist pattern 14 as a mask.

Next, in the second step shown in FIG. 2 (2), oxygen ions are introduced into the surface layer of the substrate 11 by ion implantation, as in the second step of the first embodiment, so that amorphous silicon oxide is formed. The layer 15 is formed, and the amorphous silicon oxide layer 15 is formed.
Fluorine ions are introduced so that the range is within. However, the maximum value of the implantation energy of oxygen ions may be set smaller than that in the case of the first embodiment, and the width of the amorphous silicon oxide layer 15 formed thereby in the depth direction may be made shallow. As in the first embodiment, only oxygen ions or fluorine ions may be introduced.

Further, here, the boron ions (B ⁺ ) for forming the inversion prevention layer are introduced at a position deeper than the implantation depth of fluorine ions and oxygen ions by ion implantation using the same resist pattern as a mask. good. In this case, for example, oxygen ions are introduced to form the amorphous silicon oxide layer 15, and then boron ions are introduced by ion implantation. In this case, ion implantation is performed with an implantation energy of 200 keV and a dose amount of 2 × 10 ¹³ ions / cm ² .
After that, ion implantation for introducing fluorine ions is performed in the same manner as described in the first embodiment.

Next, as shown in FIG. 2C, after removing the resist pattern (14), the second pad oxide film 21 having a film thickness of 15 nm is formed on the substrate 1 in the same manner as the first step.
A film is formed on the first pad oxide film 21 so as to cover the entire surface thereof, and a silicon nitride film having a film thickness of 30 nm is further formed on the second pad oxide film 21. Then, the silicon nitride film and the second pad oxide film 21 are etched by RIE to remove the second pad oxide film 21 and the silicon nitride film only on the oxidation prevention pattern 13a, the pad oxide film 12, and the side wall of the substrate 11. leave. As a result, the second oxidation prevention pattern 13a made of silicon nitride is formed on the side wall.

Next, in a third step shown in FIG. 2 (4), heat treatment is performed in the same manner as in the first embodiment to form the element isolation region 16 made of silicon oxyfluoride or silicon oxide, and the element concerned. An inversion prevention layer 23 formed by diffusing boron is formed along the lower surface of the isolation region 16.

Since the formation method is a method to which the SWAMI method is applied, the substrate 1 is different from the first embodiment.
(1) The step difference on the surface is further reduced, and the elongation of the bird's beak is further suppressed. From this, the prevention effect of the photolitho notch is further enhanced, and
It is possible to further increase the effective element formation width with respect to the width of the oxidation prevention pattern and the effective element isolation width with respect to the opening width of the oxidation prevention pattern.

[0027]

As described above, according to the present invention, thermal oxidation treatment is performed after introducing fluorine ions into the surface layer of the substrate by using the anti-oxidation pattern as a mask, so that the acid fluoride having a dielectric constant lower than that of the oxide film is obtained. Forming an element isolation region made of a chemical film,
This makes it possible to reduce the film thickness of the element isolation region and reduce the step difference on the substrate surface. Therefore, it is possible to improve the lithography accuracy on the substrate on which the element isolation region is formed. Further, it is possible to suppress the bird's beak to a small size and expand the effective element formation region and the element isolation region.

In addition, the method of performing the heat treatment after introducing oxygen ions into the surface layer of the substrate has better selectivity than the method of forming oxygen by diffusing oxygen into the surface layer of the substrate by thermal oxidation treatment. It is possible to form the element isolation region while keeping it, and it is possible to obtain the element isolation region in which the bird's beak is suppressed small. Therefore, it is possible to expand the effective element formation region and the element isolation region.

Further, in the method of performing the heat treatment after introducing the fluorine ions and the oxygen ions into the surface layer of the substrate, the element isolation region having the low dielectric constant can be formed with good selectivity. Therefore, as above. It is possible to improve the lithographic accuracy on the substrate on which the element isolation region is formed, and suppress bird's beak to a small size to expand the effective element formation region and the element isolation region.

[Brief description of the drawings]

FIG. 1 is a sectional process view showing a first embodiment.

FIG. 2 is a sectional process view showing a second embodiment.

[Explanation of symbols]

 11 substrate 13a oxidation prevention pattern 16 element isolation region

Claims (3)

[Claims] 1. A first step of forming an antioxidant pattern on a substrate, a second step of introducing fluorine ions into a surface layer of the substrate by ion implantation using the antioxidant pattern as a mask, and an oxidizing atmosphere. A third step of heat-treating the substrate therein to selectively oxyfluoride the surface layer portion of the substrate exposed from the anti-oxidation pattern to form an element isolation region made of an oxyfluoride film. A method for forming an element isolation region, comprising: 2. A first step of forming an anti-oxidation pattern on a substrate; a second step of introducing oxygen ions into a surface layer of the substrate by ion implantation using the anti-oxidation pattern as a mask; And a third step of performing a heat treatment to selectively oxidize the surface layer portion of the substrate exposed from the oxidation prevention pattern to form an element isolation region made of an oxide film. Method. 3. A first step of forming an antioxidant pattern on a substrate, and a second step of introducing fluorine ions and oxygen ions into the surface layer of the substrate by ion implantation using the antioxidant pattern as a mask. A third step of performing a heat treatment on the substrate to selectively oxyfluoride the surface layer portion of the substrate exposed from the anti-oxidation pattern to form an element isolation region made of an oxyfluoride film,
A method for forming an element isolation region, comprising: