JPH0766281A - Forming method of element isolating region - Google Patents

Abstract

PURPOSE:To enable a fine element isolating region to be formed by a method wherein a trench and an element isolating region are formed at the same time. CONSTITUTION:A thermal oxide film 2 and an anti-oxidizing film 3 (SiN film) are formed on a silicon semiconductor substrate 1, and the films 3 and 2 located on a part which serves as an element isolating region are so removed as to make the surface of the substrate 1 exposed. Then, the silicon semiconductor substrate 1 is thermally oxidized to form a LOCOS oxide film 4, and the LOCOS oxide film 4 is anisotropically etched using the anti-oxidizing film 3 as a mask. Then, the Si substrate 1 is anisotropically etched to form a trench 5. Next, a non-doped CVD-SiO2 6 is deposited on all the surface, all the surface is etched back until the anti-oxidizing film 3 is exposed, then the anti-oxidizing film 3 is removed, the oxide film 2 is removed by an HF treatment, and thus an NMOS element isolating region is formed by LOCOS and trench.

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.

[0002]

2. Description of the Related Art Development of a large-capacity LSI depends on how to develop a highly integrated circuit within a limited chip area. Such an improvement in the degree of integration is made by miniaturizing the elements constituting the integrated circuit. Further, miniaturization of elements is accompanied by miniaturization of transistors, and miniaturization of element isolation regions is also required.

In general, a method called a selective oxidation (LOCOS) method is used for forming the element isolation region. In this method, after forming a SiN film on a silicon substrate,
This is a method of forming a device isolation region made of a silicon insulating film by patterning in a photolithography process to remove the SiN film in the device isolation region and selectively oxidizing the exposed silicon substrate surface.

[0004]

Due to the reduction of the element isolation region, the following matters have become problems. S during selective oxidation
Due to the stress of the iN film, the field oxide film does not grow sufficiently in the narrow element isolation region, and the field oxide film is thinned (FIG. 1). Even if an opening of 0.2 μm or less is formed in the photolithography or etching process, as is apparent from FIG. 1, the film thickness of the LOCOS oxide film in the element isolation region becomes 60% or less, and sufficient isolation capability cannot be obtained. Is coming. Also, the separation characteristics can be improved by increasing the impurity concentration under the LOCOS oxide film.
If the impurity concentration is too high, there is a problem that the junction breakdown voltage becomes low. Another problem is that the Si substrate is oxidized to the region covered with the SiN film during the selective oxidation, the silicon oxide film called bird's beak spreads, and the element region is narrowed.

As a technique for suppressing bird's beak, a technique for forming a sidewall beside a SiN film (Japanese Patent Laid-Open No. 4-127433)
No.). However, in the technique of forming the sidewall, the opening width at the time of selective oxidation is reduced by the sidewall width as the pattern is miniaturized, and thus the LOCOS oxide film in the element isolation region is likely to be thinned. . A trench isolation method (Japanese Patent Laid-Open No. 2-198153) is known as an element isolation method that solves the problems of the LOCOS method. In this method, a trench is formed in the Si substrate by anisotropic etching, and an oxide film or the like is embedded to perform etch back. Since no oxidation is performed, the element region can be determined according to patterning, and the film thickness can be secured even in a narrow isolation region.

However, since the entire surface is etched back when the trench is filled, it is difficult to fill a wide isolation region other than the trench. As a method of solving this, there is a method of forming a wide isolation region by a LOCOS method and a narrow isolation region by a trench, but the photo process is required twice. There is also a method of forming a LOCOS oxide film and a trench in a self-aligned manner (US Pat. No. 5096848, Japanese Patent Laid-Open No. 3-24554), but the process is complicated.

[0007]

Thus, according to the present invention, an oxide film and an anti-oxidation film are formed in this order on a silicon substrate, and then an oxide film in a portion where a device isolation region is to be formed and a portion where a trench is to be formed are formed. The oxidation preventing film is removed until the substrate is exposed, and the substrate is thermally oxidized to form a locos oxide film at the portion where the formation is to be formed, and then selectively the locos is formed until the substrate where the trench is to be formed is exposed. The oxide film is removed by anisotropic etching, and the silicon substrate in the part where the trench is to be formed is selectively anisotropically etched to form a recess, and then silicon oxide is deposited on the entire surface, followed by an etchback process. A method for forming an element isolation region, characterized in that a trench and an element molecule region are simultaneously formed by removing the antioxidant film and the oxide film after exposing There is provided.

A description will be given below according to the forming method of the present invention. First, an oxide film and an antioxidant film are formed on a silicon substrate. As a method for forming the oxide film, a known method such as a thermal oxidation method, a CVD method or a sputtering method can be used, and the film thickness thereof is preferably 25 to 150Å. The antioxidant film may be, for example, SiN or the like, and the formation method thereof is PCVD.
Method, LPCVD method, etc., and the film thickness is 500-
2500Å is preferred.

Next, using the resist pattern formed by one photolithography process as a mask, the oxide film and the oxidation prevention film in the portions to be the element isolation regions and trenches are removed by etching. Here, if it is necessary to flatten the surface after oxidizing the element isolation region, the silicon substrate may be further etched by 100 to 1000 Å. A known method can be used as the etching method, and examples thereof include wet etching, ion etching, and plasma etching.

Next, the resist pattern is removed, and the temperature is 900 ° C.
As described above, preferably, the silicon substrate is oxidized by performing thermal oxidation at 1000 ° C. or higher, and a LOCOS oxide film is formed in a film thickness of 1000 to 5000 Å in the element isolation region and the trench portion. At the time of this oxidation, the oxidant also diffuses under the oxide film, so that the so-called bird's beak so-called lateral protrusion of the oxide film occurs at the ends of the element isolation region and the trench portion. Due to this overhang, the LOCOS oxide film has a structure in which the film thickness gradually decreases toward the end. Here, instead of the LOCOS oxide film formed by the LOCOS method, a polybuffer LOCOS method and a sidewall L are used.
A film formed by the OCOS method or the like can also be used.

Next, the LOCOS oxide film is etched by anisotropic etching. For anisotropic etching, plasma etching, reactive ion etching (RI
A known method such as the method E) can be used. As the etching gas, it is preferable to use a gas such as CF ₄ + H ₂ which has a higher etching rate for the LOCOS oxide film than that for silicon. By such etching, the LOCOS oxide film is etched. Since the LOCOS oxide film is thinner in the trench portion than in the element isolation region, the silicon substrate in the trench portion is exposed earlier.

By changing the etching gas when the silicon substrate in the trench portion is exposed in this way, the silicon substrate can be selectively anisotropically etched to open the trench. Examples of the etching gas that can be used at this time include chlorine-based (Cl ₂ or the like) or bromine-based (HBr or the like) gas, and the depth of the trench is 1000 to 30.
00Å is preferred.

In order to prevent sidewall inversion, an impurity concentration of 1 × 10 ¹³ to 1 × 10 ¹⁴ ion is applied to the trench.
It is preferable to implant into the sidewall of the trench with s / cm ² implantation energy of 50 to 150 kev. Further, a thermal oxide film having a film thickness of 100 to 1000 Å may be formed in order to recover the damage at the time of etching and control the Si / SiO ₂ interface.

Next, a silicon oxide film is formed on the entire surface by the CVD method. The thickness of this silicon oxide film is at least ½ of the minimum trench width, and is preferably 1000 to 5000Å. After forming this silicon oxide film, hydrofluoric acid solution or RI
The entire surface is etched back by using a constant velocity etch back with E or the like to expose the antioxidant film. Instead of the above silicon oxide film, a polysilicon film or an amorphous silicon film may be formed, and a silicon oxide film obtained by performing an oxidation process after etching back may be used.

Next, if the antioxidant film and the oxide film are removed by solvent treatment, element isolation using a LOCOS oxide film and a trench together can be formed. The solvent used here includes phosphoric acid when the antioxidant film is SiN, and HF or the like for the oxide film. The formation method of the present invention can be applied to any semiconductor device that requires element isolation.
It can be applied to various devices such as OS, PMOS and CMOS.

[0016]

Since the thinning of the LOCOS oxide film is utilized, the element isolation region formed by the LOCOS oxide film and the element isolation region formed by the trench can be simultaneously formed in a self-aligned manner, and the photolithography process can be performed only once.

[0017]

EXAMPLES Example 1 A thermal oxide film 2 of 100 Å and an antioxidant film 3 (SiN film) of 1200 Å were formed on a silicon semiconductor substrate 1, and then a lithographic pattern formed by a single photolithography process was used as a mask. The anti-oxidation film 3 and the oxide film 2 which are to be element isolation regions are removed until the substrate 1 is exposed, and then the substrate 1 is flattened to have a flat surface after LOCOS oxidation.
0Å Further etching.

Next, after removing the resist pattern, 9
The LOCOS oxide film 4 was formed by oxidizing the 3500Å silicon semiconductor substrate by thermal oxidation at 00 ° C or higher (Fig. 2).
(B)). Next, the LOCOS oxide film 4 was anisotropically etched using the anti-oxidation film 3 as a mask (about 50 to 60% of the wide isolation region at the time of LOCOS oxide film). The etching gas is a fluorocarbon-based gas (C _M F _N ; m = 1 to 4, n = 2 to
8, eg CHF ₃ , CH ₂ F ₂ , CH ₃ F, etc.) and H ₂
Alternatively, a mixed gas of O ₂ was used. As shown in FIG.
Since the COS film thickness is thin with a narrow opening width, the substrate 1 is exposed in a pattern with an opening width of 0.2 μm or less.

Next, the Si substrate 1 was anisotropically etched to about 3000 Å to form a trench 5 (FIG. 2 (c)).
The etching gas is chlorine (Cl ₂ etc.) or bromine (HB
r etc.) was used. Next, boron ions are added at 30 keV, 3 × 10 5 for implantation to prevent sidewall inversion.
^It was injected into the sidewall of the trench at ¹² ions / cm ² . next,
A thermal oxide film was formed at 900 ° C. or more and 1000 Å in order to recover damage during etching and control the Si / SiO ₂ interface.

Next, non-doped CVD-SiO ₂ 6 (a film thickness of 1/2 or more of the minimum trench width) is deposited on the entire surface (FIG. 2).
(D)), and the entire surface was etched back. When the antioxidant film 3 is exposed, etching back is stopped (FIG. 2 (e)), and then,
If the antioxidant film 3 is removed by solvent treatment (phosphoric acid when the antioxidant film is SiN) and the oxide film 2 is removed by HF treatment, it is possible to form an NMOS element isolation using both LOCOS and a trench (FIG. 2). (F)).

[0021]

Since the thinning of the LOCOS oxide film is utilized, the isolation region by the LOCOS and the isolation region by the trench can be formed in a self-aligning manner, and the photolithography process for determining the element region can be performed only once. good. Therefore, the number of steps can be reduced, and the cost can be reduced.

Poly buffer LO is used for forming the LOCOS oxide film.
When the COS method is used, since the LOCOS is less oxidized to the substrate side with a narrow opening width, the isolation withstand voltage is reduced, but the application of this method does not reduce the isolation withstand voltage. LO
When the sidewall LOCOS method is used for COS formation, the Si opening width is narrowed and the LOCOS is easily thinned. However, when this method is applied, the thinning of the LOCOS does not deteriorate the separation characteristics.

In the trench isolation method, it is difficult to fill the trenches at once because the trench depth is the same in the wide and narrow openings of the element isolation region. However, in this method, since the LOCOS remains at the bottom of the trench with a wide opening width, the depth of the wide opening becomes shallower than that of the narrow opening, and the filling is easier than in the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a film thickness of a LOCOS oxide film and an opening of a silicon substrate.

FIG. 2 is a schematic cross-sectional view of the forming method of the present invention.

[Explanation of symbols]

 1 Silicon Substrate 2 Oxide Film 3 Antioxidation Film 4 LOCOS Oxide Film 5 Trench 6 Silicon Oxide Film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9274-4M H01L 21/94 A

Claims (1)

[Claims] 1. An oxide film and an oxidation preventive film are formed in this order on a silicon substrate, and then the oxide film and the oxidation preventive film in the element isolation region formation planned portion and the trench formation planned portion are removed until the substrate is exposed. By thermally oxidizing the substrate, a locos oxide film is formed in the portion where the formation is to be formed, and then the locos oxide film is selectively removed by anisotropic etching until the substrate in the portion where the trench is to be formed is exposed. Further, the silicon substrate in the portion where the trench is to be formed is selectively anisotropically etched to form a concave portion, then silicon oxide is deposited on the entire surface, and then subjected to an etchback process to expose the antioxidant film. A method for forming an element isolation region, characterized in that the trench and the element molecule region are simultaneously formed by removing the antioxidant film and the oxide film.