JP2002076134A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thin gate oxide film and a thick gate oxide film in one step for forming the gate oxide film. SOLUTION: A sacrifice oxide film 32 is formed at the surface of each element forming region 14a, 14b on a substrate 10. Subsequently, by implanting nitrogen into the element forming region 14a for forming elements having the thin gate oxide film via the sacrifice oxide film 32, a shallow nitrogen implantation part 38 is formed at the upper part of a well 16a of this element forming region 14a (fig. 2 (1)). Next, after the sacrifice oxide film 32 is etched and removed, a substrate 10 is heated in an oxidizing atmosphere, and the surfaces of wells 16a, 16b are oxidized. As a result, the thin gate oxide film 40 is formed in the element forming region 14a having the nitrogen implantation part 38. The thick gate oxide film 42 is formed in the element forming region 14b where nitrogen has not been implanted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor, and more particularly to a semiconductor device having a different gate oxide film thickness, such as a semiconductor device performing a logical operation or a semiconductor device performing a memory operation. The present invention relates to a method for manufacturing a semiconductor device formed on a substrate.

[0002]

2. Description of the Related Art Recently, a semiconductor device in which semiconductor elements performing different types of operations are mixed on the same substrate (one chip) is often provided. Here, the semiconductor elements that perform different types of operations refer to semiconductor elements that perform different types of operations, such as a semiconductor element that performs a logical operation and a semiconductor element that performs a memory operation. A semiconductor device in which semiconductor elements that operate differently in this way coexist is
It is common to form a gate oxide film having a different thickness for each type of semiconductor device that operates differently.

For example, a thin gate oxide film suitable for high-speed operation is formed on a semiconductor element which operates at a high speed such as a logic operation, and reliability is emphasized on a semiconductor element which performs a memory operation requiring reliability. A thick gate oxide film is formed.

FIG. 4 is a schematic view showing a main part of a process for explaining a conventional method for manufacturing the above-described semiconductor device. In FIG. 4, as shown in (1), impurities are implanted into the upper portion of a substrate 10 made of a silicon wafer, and wells 16 (16
a, 16b,...). After that, the surface of the substrate 10 is LOCOS (Local Oxidation).
is selectively oxidized by silicon of silicon (Si), and an element isolation region 12 made of thick silicon dioxide (SiO ₂ ) is provided to form a plurality of element formation regions 14 (14a, 14b,...).
…) Is formed. Further, the substrate 10 is heated in an oxidizing atmosphere to oxidize the element formation region 14, and an oxide film 18 is formed on the surface of the well 16. The wells 16a, 16
b may be the same conductivity type or different conductivity types.

Next, a photoresist is applied on the substrate 10 and is exposed and developed to be patterned.
As shown in (2), the oxide film 18 in the element formation region 14a where the semiconductor element having the thin gate oxide film is formed is exposed, and the oxide film 18 in the element formation region 14b where the semiconductor element having the thick gate oxide film is formed. A resist film 20 covering 18 is formed.

Next, using the resist film 20 as a mask,
The oxide film 18 in the element formation region 14a for forming a semiconductor element having a thin gate oxide film is removed by wet etching, leaving the oxide film 18 only in the element formation region 14b for forming a semiconductor element having a thick gate oxide film. The resist film 20 is removed (see FIG. 4C). Then, the substrate 1
0 is heated again in an oxidizing atmosphere to form a new oxide film (gate oxide film) 22 on the surface of an element forming region 14a where a semiconductor element having a thin gate oxide film is to be formed, and a semiconductor element having a thick gate oxide film. The oxide film 18 in the element formation region 14b for forming the gate oxide film is further grown to a thick oxide film (gate oxide film) 26 composed of the oxide film 18 formed earlier and the oxide film 24 grown this time.

Thereafter, a step of forming a normal MOS transistor is performed, and a MOS transistor (not shown) as a semiconductor element is formed in the element forming region 14a and the element forming region 14b. Thereby, the element forming region 14a
A MOS transistor having a thin gate oxide film 20 for performing a logical operation is formed, and a MOS transistor having a thick gate oxide film 26 in element formation region 14b for performing a memory operation is formed.

[0008]

However, the conventional thin gate oxide film 22 and thick gate oxide film 26 described above are used.
It is necessary to cover the initially formed thin oxide film 18 with a resist film 20 once, and then to perform a peeling and cleaning process of the resist film 20. Therefore, when the thick gate oxide film 26 is formed, not only does it have a two-layer structure, but the previously formed oxide film 18 is exposed to the cleaning liquid, and is deteriorated due to the formation of irregularities on the surface and the reliability. descend.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages of the prior art, and an object of the present invention is to enable a thin gate oxide film and a thick gate oxide film to be formed in a single step of forming a gate oxide film. The purpose is. Another object of the present invention is to improve the reliability of a gate oxide film.

[0010]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention is directed to a method of manufacturing a semiconductor device in which semiconductor elements having gate oxide films having different thicknesses are formed on the same substrate. In the manufacturing method, of the substrate,
A step of implanting nitrogen into a region where a semiconductor element having a thin gate oxide film is to be formed; and a step of growing an oxide film on a surface of the substrate.

According to the present invention having the above-described structure, nitrogen is implanted into a region where a semiconductor element having a thin gate oxide film is formed, and then the substrate surface is oxidized. The oxidation speed is lower than the oxidation speed in the region where nitrogen is not implanted, and oxide films (gate oxide films) having different thicknesses can be easily formed in the same oxidation treatment time. That is, gate oxide films having different thicknesses can be simultaneously formed in one gate oxide film forming step. In addition, since no resist film or the like is formed, the gate oxide film is not exposed to a cleaning solution or the like, so that a single-layer thick oxide film can be obtained, and a highly reliable thick gate oxide film can be obtained. In addition, since nitrogen is implanted in the region where the thin gate oxide film is formed, nitrogen atoms are present in the thin gate oxide film and the substrate under the thin gate oxide film, and resistance to electric stress due to long-term use is improved. A highly reliable semiconductor element can be formed.

The implantation of nitrogen may be performed by nitrogen ion implantation or by exposing the substrate to a plasma of nitrogen gas or ammonia gas.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for manufacturing a semiconductor device according to the present invention will be described below with reference to the drawings. Note that the same reference numerals are given to the portions corresponding to the portions described in the above-described related art, and the description thereof is omitted.

FIGS. 1 and 2 are main part process diagrams for describing a method of manufacturing a semiconductor device according to a first embodiment of the present invention. First, as shown in FIG. 1A, impurities are implanted into an upper portion of a substrate 10 made of a silicon wafer in the same manner as in the prior art to form a plurality of wells 16 to be active regions. Next, as in the conventional case, a silicon nitride film (Si ₃ N ₄ film) 30 is deposited on the entire upper surface of the substrate 10 and the silicon nitride film 30 is etched to remove a portion of the silicon nitride film 30 corresponding to the element isolation region. Then, the exposed portion is selectively oxidized by heating the substrate 10 in an oxidizing atmosphere, and an element isolation region 12 made of a thick oxide film (silicon dioxide film) is provided at the boundary of the well 16 on the substrate surface to form a plurality of element formation regions 14. Form.

Then, after the silicon nitride film 30 is removed by etching, the substrate 10 is again heated and oxidized in an oxidizing atmosphere, and as shown in FIG. A thin sacrificial oxide film 32 for preventing damage due to ion implantation is formed.
Next, a photoresist is applied to the entire upper surface of the substrate 10 and patterned to expose an element formation region 14a where a semiconductor element having a thin gate oxide film is to be formed, as shown in FIG. A resist film is formed to cover an element forming region b where a semiconductor element having an oxide film is to be formed.

Next, the whole of the substrate 10 is irradiated with nitrogen ions (N ⁺ ) 36 from above the substrate 10 to form a semiconductor element which is not covered with the resist film 34, that is, has a thin gate oxide film. Well 16a in region 14a
Then, nitrogen ions 36 are implanted through the sacrificial oxide film 32,
A shallow nitrogen implanted portion 38 is formed in the surface layer of the well 16a. Note that the concentration of nitrogen in the nitrogen injection section 38 may be about several% in atomic%.

Thereafter, as shown in FIG. 2A, the resist film 34 is peeled off, removed, and washed. Further, the substrate 1
Then, as shown in FIG. 2B, the surface of the sacrificial oxide film 32 is etched and removed. next,
The substrate 10 is heated again in an oxidizing atmosphere, and the surface of each well 16 is oxidized to form gate oxide films 40 and 42. At this time, since the nitrogen injection portion 38 into which nitrogen is injected is provided in the surface layer of the well 16a, the oxidation rate of silicon is lower than that of the well 16b into which nitrogen is not injected.
Therefore, a thin gate oxide film 40 is formed in the well 16a, and a thick gate oxide film 42 is formed in the well 16b.

That is, in one step of forming a gate oxide film, an element formation region 14a having a thin gate oxide film 40 and an element formation region 14b having a thick gate oxide film 42 are obtained by the same oxidation treatment time. Can be Therefore, by forming a semiconductor element (MOS transistor) in these element formation regions 14a and 14b, a semiconductor element having a thin gate oxide film 40 and a semiconductor element having a thick gate oxide film 42 can be formed. . The gate oxide films 40 and 42 may be formed by dry oxidation using dry oxygen or wet oxidation using water vapor.

In the embodiment, a thick gate oxide film can be formed in one oxidation step, and the element forming region 14 where the thick gate oxide film 42 is formed can be formed.
Since there is no need to provide a resist film on b, deterioration of the gate oxide film due to removal and cleaning of the resist film can be prevented, a highly reliable gate oxide film can be obtained, and the reliability of the semiconductor device can be improved. be able to. The thin gate oxide film 40 provided in the element formation region 14a is
8 is formed by oxidizing, since nitrogen atoms are present in the gate oxide film 40 and the upper part of the well 16a, resistance to electric stress due to long-term use is improved,
It is possible to suppress the level of the reduction in the life due to the thinning of the gate oxide film 40.

FIG. 3 is an explanatory view of a main part of a method for manufacturing a semiconductor device according to the second embodiment. In the second embodiment, the element forming region 14 where the thin gate oxide film 40 is formed is formed.
The injection of nitrogen into a is performed by plasma. That is, similar to the first embodiment, FIG.
By performing the steps of (1) and FIG. 1B, a sacrificial oxide film 32 is formed on the surface of the well 16. Thereafter, the resist film 34 covering the element formation region 14b for forming the semiconductor element having a thick gate oxide film is exposed by exposing the sacrificial oxide film 32 in the element formation region 14a for forming the semiconductor element having a thin gate oxide film. (See FIG. 1 (3)).

Next, the substrate 10 provided with the resist film 34
Is disposed, for example, in the plasma processing apparatus 50 shown in FIG. The plasma processing apparatus 50 includes a vacuum chamber 52
And a high frequency power supply 5
4 is provided with a discharge electrode 56. In the plasma processing apparatus 50, a processing stage 58 facing the discharge electrode 56 is provided at a lower portion in the vacuum chamber 52.
The processing stage 58 is configured such that the substrate 10 is disposed on the upper surface, serves as one discharge electrode, and is grounded. In the vacuum chamber 52, a nitrogen gas (N ₂ ) or an ammonia gas (N
H ₃ ) 60 is provided, and an exhaust port 64 to which a vacuum pump (not shown) is connected is provided, and an exhaust gas 66 is sucked by the vacuum pump.
Exhaust can be done.

The substrate 10 by the plasma processing apparatus 50
Nitrogen is implanted as follows. First, as described above, the substrate 10 provided with the resist film 34 is disposed on the processing stage 58. Thereafter, the inside of the vacuum chamber 52 is evacuated to a predetermined degree of vacuum by a vacuum pump, and then a nitrogen gas or an ammonia gas 60 is introduced into the vacuum chamber 52 from the gas inlet 62. Then, a high-frequency voltage is applied between the discharge electrode 56 and the processing stage 58 by the high-frequency power source 54, and a discharge is generated between the two to turn the nitrogen gas or ammonia gas 60 into plasma. As a result, the substrate 10 is filled with nitrogen gas or ammonia gas 6
The plasma particles exposed to the zero plasma and collided with the element forming region 14a where the resist film 34 is not provided penetrate into the well 16a via the sacrificial oxide film 32, and form a nitrogen implanted portion 38 above the well 16a.

After performing the plasma processing for a predetermined time in this manner, the steps shown in FIGS. 2A to 2C are performed in the same manner as after the plasma injection in the first embodiment. Thus, as in the first embodiment, a thin gate oxide film 40 is formed in the element formation region 14a, and a thick gate oxide film 42 is formed in the element formation region 14b. Also, according to the second embodiment, the same operation and effect as those of the first embodiment can be obtained. Further, in the second embodiment, since the energy of the plasma colliding with the substrate 10 is small, the nitrogen implantation depth can be made shallower than in the first embodiment, and the operation of the semiconductor element is less affected. can do.

[0024]

As described above, according to the present invention, gate oxide films having different thicknesses can be obtained in one step, and the reliability of the gate oxide film can be improved.

[Brief description of the drawings]

FIG. 1 is a view showing a part of a process chart for explaining a main part of a method for manufacturing a semiconductor device according to a first embodiment of the present invention;

FIG. 2 is a part of a process diagram illustrating a main part of the method for manufacturing the semiconductor device according to the first embodiment of the present invention, and is a diagram illustrating a process subsequent to FIG. 1;

FIG. 3 is a process diagram illustrating a main part of a method for manufacturing a semiconductor device according to a second embodiment of the present invention, and is a diagram illustrating a process of implanting nitrogen into a substrate.

FIG. 4 is a process chart for explaining a method of manufacturing a conventional semiconductor device.

[Explanation of symbols]

 10 Substrates 14a, 14b Device forming regions 16a, 16b Wells 18, 32 Sacrificial oxide film 36 Nitrogen ions 38 Nitrogen implants 40, 42 Gate Oxide film 50 Plasma processing device

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device in which semiconductor elements having gate oxide films having different thicknesses are formed on the same substrate, wherein a region of the substrate where a semiconductor element having a thin gate oxide film is formed is formed. Injecting nitrogen,
Growing an oxide film on the surface of the substrate. 2. The method according to claim 1, wherein the nitrogen implantation is performed by nitrogen ion implantation. 3. The method according to claim 1, wherein the nitrogen is implanted by exposing the substrate to plasma of nitrogen gas or ammonia gas.