JPH05102067A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a semiconductor device in which an irregular FET threshold value Vth is suppressed by accelerating diffusion of baron by fluorine in a gate (SiO2) oxide film in an activating heat treatment after boron fluoride BF2 ions are implanted in the method for manufacturing a MOSFET of a polysilicon gate. CONSTITUTION:Chlorine (Cl) is previously introduced into a gate (SiO2) oxide film before boron fluoride ions are implanted. A first method comprises the steps (a)-(f): of (a) thermally oxidizing a silicon semiconductor substrate 1 to form an SiO2 film 3, (b) forming a polysilicon electrode 4A, (c) implanting chlorine in the electrode by an ion implanting method, (d) thermally diffusing the implanted chlorine in the film 3, (e) ion implanting boron fluoride (BF2) in the electrode 4A, and (f) activating to heat treat the ion implanting to suppress diffusion of boron by the chlorine in the SiO2 film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor devices such as ICs and LSIs, and more particularly to polysilicon gate MOSs.
The present invention relates to a method for manufacturing a field effect transistor (FET).

[0002]

2. Description of the Related Art A MOSFET has a SiO ₂ gate oxide film formed by thermally oxidizing a silicon semiconductor substrate (wafer), and a polysilicon or amorphous silicon gate electrode formed thereon. In a semiconductor device using a MOSFET, a complementary MOS (C
A MOS) structure is adopted from the advantage of low power consumption operation, and a P-type region (source / drain region) is formed by ion implantation of boron (B) to form a P-channel MOSFET. This ion implantation causes the gate electrode to be doped with boron. In addition, boron may be ion-implanted into polysilicon (amorphous silicon) due to the conductivity of the gate electrode.

In the past, since the gate electrode was relatively thick, the implanted boron did not penetrate through the gate electrode to reach the gate oxide film. With the recent trend toward higher integration and miniaturization of semiconductor devices, the gate electrode film thickness has become thinner. When it becomes thin, there is a problem that the implanted boron penetrates the gate electrode and reaches the gate oxide film.
Therefore, the mass of boron ions to be ion-implanted is increased, that is, boron fluoride (a compound of boron and fluorine) such as BF and BF ₂ is ion-implanted, so that ion implantation in the polysilicon film of the gate electrode is prevented. By making the distance shorter, the problem of punch-through can be avoided.

[0004]

In the ion implantation of boron fluoride, in the activation heat treatment after the ion implantation, fluorine in the gate (SiO ₂ ) oxide film promotes the diffusion of boron,
It has been found that there is a problem that the threshold voltage Vth of the MOSFET is different (varies) for each FET.

An object of the present invention is to propose a method of manufacturing a semiconductor device in which the above-mentioned threshold variation is suppressed.

[0006]

[Means for Solving the Problems] Basically, chlorine (Cl) is introduced in advance in a gate (SiO ₂ ) oxide film before boron fluoride ion implantation, thereby suppressing boron diffusion and suppressing threshold voltage. The present inventors have found that the variation is also suppressed, and arrived at the present invention. The above-mentioned object is achieved by the following three kinds of manufacturing methods which are different in the method of introducing chlorine into the SiO ₂ film.

The first method is steps (a) to (f): (a) a step of thermally oxidizing a silicon semiconductor substrate to form a SiO ₂ film, (b) a polysilicon electrode on the SiO ₂ film And (c) injecting chlorine into the polysilicon electrode by an ion implantation method.
A heat treatment step of diffusing into the SiO ₂ film, a step of implanting boron fluoride into the polysilicon electrode by ion implantation of (e) boron fluoride (BF ₂ ), and a heat treatment of activation of (f) ion implantation. And a step of suppressing the diffusion of boron by chlorine in the SiO ₂ film, the method for manufacturing a semiconductor device.

The second method is steps (a) to (f): (a) a step of implanting chlorine into the silicon semiconductor substrate by an ion implantation method, (b) thermal oxidation of the silicon semiconductor substrate to form a SiO ₂ film. forming a, (c) forming a polysilicon electrode on the SiO ₂ film, (d) allowing the injected chlorine is subjected to heat treatment to diffuse into the SiO ₂ film, (e) boron fluoride ( BF ₂ ) ion implantation of boron fluoride into the polysilicon electrode, and (f) ion implantation activation heat treatment to suppress diffusion of boron by chlorine present in the SiO ₂ film. And a method of manufacturing a semiconductor device, the method including:

The third method is the steps (a)-
(E): (a) A step of thermally oxidizing a silicon semiconductor substrate to form a SiO ₂ film, (a) a step of injecting chlorine into the SiO ₂ film by an ion implantation method, and (c) a step on the SiO ₂ film. Forming a polysilicon electrode on the polysilicon layer, (d) implanting boron fluoride into the polysilicon electrode by ion implantation of boron fluoride (BF ₂ ), and (e) performing an activation heat treatment for ion implantation. A method of manufacturing a semiconductor device, comprising a step of suppressing diffusion of boron by chlorine in an SiO ₂ film.

[0010]

In the present invention, by introducing chlorine into the gate (SiO ₂ ) oxide film, the amount of fluorine bonds in the SiO ₂ film can be reduced and the promotion of boron diffusion of fluorine can be suppressed. ..

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings by way of embodiments and comparative examples of the present invention. Example 1 FIGS. 1 to 3 are schematic cross-sectional views of a semiconductor device illustrating a process of manufacturing a MOSFET according to a first method.

As shown in FIG. 1, a silicon single crystal substrate (wafer) 1 is selectively thermally oxidized to form a field oxide film 2. Further, the exposed silicon substrate is thermally oxidized to form a thin SiO ₂ film (gate oxide film) 3 with a thickness of 16 nm, for example. A boron-doped polysilicon film 4 is formed on the oxide films 2 and 3 by the CVD method to have a thickness of 330 nm, for example. Chlorine (arrow A) is implanted into this polysilicon film 4 by an ion implantation method. The implantation conditions are, for example, an acceleration voltage of 60 KeV and a dose of 10 ¹⁶ ions / cm ² . Then, heat treatment is carried out after the ion implantation to diffuse chlorine into the gate oxide film 3. This heat treatment is, for example, 900 ° C. × 120 minutes.

As shown in FIG. 2, the polysilicon film 4 is selectively etched and patterned into a polysilicon electrode 4A according to a normal lithography technique, and the gate (SiO ₂ ) oxide film 3A is left on the polysilicon electrode 4A. , The SiO ₂ film 3 is also etched. Next, boron fluoride (BF ₂ ) (arrow B) is ion-implanted to p-type source region 6 on silicon substrate 1.
And the drain region 7 are formed, and the polysilicon electrode 4A
Boron fluoride is also introduced. The implantation conditions are, for example, an acceleration voltage of 60 KeV and a dose of 3.5 × 10 ¹⁵ ions /
It is cm ² . Then, activation heat treatment after ion implantation is performed. This heat treatment is, for example, 900 ° C. × 15 to 60 minutes.

Next, as shown in FIG. 3, an insulating film (SiO ₂ film) 8 is formed on the entire surface by the CVD method. This insulating film 8
Is selectively etched by lithography technology,
Open contact holes in the source / drain regions. Then, the source electrode 9 and the drain electrode 10 are formed by a normal process to obtain a MOSFET. The threshold voltage V of the P-channel MOSFET manufactured in this way
The th was examined by changing the heat treatment time after the boron fluoride ion implantation, and the results shown in FIG. 4 were obtained. As a comparative example, FIG. 4 shows the threshold voltage Vth of the P-channel MOSFET manufactured as described above without ion implantation of chlorine. Figure 4
As can be seen from the above, the threshold voltage of the MOSFET according to the present invention to which chlorine ions are implanted is more in proportion to the linear heat treatment temperature, and the threshold voltage is stable and has a small variation.

Example 2 In the process described above with reference to FIG. 1, after forming the field oxide film 2 and before forming the thin oxide film 3, chlorine is ion-implanted to dope the silicon substrate 1. The injection conditions at this time are, for example, an acceleration voltage of 60 KeV.
And the dose amount is 10 ¹⁶ ions / cm ² . Then, if the thin oxide film (SiO ₂ gate oxide film) 3 is formed by performing the thermal oxidation process, chlorine is introduced into the gate oxide film. In this case, the thermal treatment after the ion implantation also serves as the thermal oxidation treatment, so that it does not have to be performed. Then, the MOSFET is manufactured according to the manufacturing process in Example 1.

Example 3 In the process described above with reference to FIG. 1, after forming the thin oxide film 3, chlorine is ion-implanted into the oxide film 3.
The implantation conditions at this time are the same as in the case of Example 1. Also in this case, since chlorine is introduced into the thin oxide film (SiO ₂ gate oxide film) 3, heat treatment after ion implantation need not be performed. Then, according to the manufacturing process in Example 1, MOSF
We will make an ET.

[0017]

As described above, according to the present invention,
By introducing chlorine into the gate oxide film in advance, a gate (Si, which is generated by ion implantation of boron fluoride (BF, BF ₂ ),
O ₂ ) The amount of fluorine bonds in the oxide film is reduced, and accelerated diffusion of boron can be suppressed. Then, variations in the threshold voltage of the MOSFET can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a semiconductor device in a MOSFET manufacturing process.

FIG. 2 is a schematic cross-sectional view of a semiconductor device in the process of manufacturing a MOSFET.

FIG. 3 is a schematic cross-sectional view of a manufactured semiconductor device (MOSFET).

FIG. 4 is a graph showing the relationship between the threshold voltage of MOSFET and the temperature of heat treatment after boron fluoride ion implantation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 3 ... Thin SiO ₂ film 3A ... Gate oxide film 4 ... Polysilicon film 4A ... Polysilicon gate electrode 6 ... Source region 7 ... Drain region 9 ... Source electrode 10 ... Drain electrode A ... Chlorine B ... Boron fluoride

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/336 29/784

Claims (3)

[Claims] 1. The following steps (a) to (f): (a) a step of thermally oxidizing the silicon semiconductor substrate (1) to form a SiO ₂ film (3), (a) the SiO ₂ film (3) On top of polysilicon electrode (4A)
A step of forming chlorine, (c) a step of implanting chlorine into the polysilicon electrode (4A) by an ion implantation method, (d) a step of performing a heat treatment for diffusing the implanted chlorine into the SiO ₂ film (3), E) The step of implanting boron fluoride into the polysilicon electrode (4A) by ion implantation of boron fluoride (BF ₂ ), and (f) the activation heat treatment of ion implantation, to remove chlorine in the SiO ₂ film. A method of manufacturing a semiconductor device, comprising the step of suppressing the diffusion of boron. 2. The following steps (a) to (f): (a) A step of implanting chlorine into the silicon semiconductor substrate by an ion implantation method, (a) Thermal oxidation of the silicon semiconductor substrate to form a SiO ₂ film. A step, (c) a step of forming a polysilicon electrode on the SiO ₂ film, (d) a step of performing a heat treatment for diffusing the injected chlorine into the SiO ₂ film, (e) a boron fluoride (BF ₂ ). Ion implantation of boron fluoride into the polysilicon electrode, and (f) ion activation activation heat treatment to inhibit chlorine existing in the SiO ₂ film from diffusing boron. A method of manufacturing a semiconductor device. 3. The following steps (a) to (e): (a) a step of thermally oxidizing a silicon semiconductor substrate to form a SiO ₂ film, (b) chlorine injection into the SiO ₂ film by an ion implantation method. A step, (c) a step of forming a polysilicon electrode on the SiO ₂ film, (d) a step of implanting boron fluoride into the polysilicon electrode by ion implantation of boron fluoride (BF ₂ ), and (o) ) A method of manufacturing a semiconductor device, comprising a step of performing an activation heat treatment for ion implantation to suppress chlorine diffusion in the SiO ₂ film.