JPH1065152A - Manufacturing method for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the punch-through of boron from a p+ gate in the forming method of a diffused layer of a surface channel type fine semiconductor element and to try to stabilize the threshold. SOLUTION: An oxygen leakage layer 5 is provided at the formation time of a polysilicon film 4 which is to be a gate electrode and then BF2 is implanted, making its peak position on the level lower than the oxygen leakage layer, so as to reduce the fluorine concentration in a gate oxide film 3 by making this oxygen leakage layer 5 segregate the fluorine which has been led in the polysilicon film 4. Through these procedures, the acceleration of the boron diffusion by fluorine in the gate oxide film 3 can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a surface channel type MOS transistor.

[0002]

2. Description of the Related Art A surface channel type MOS structure is considered to be advantageous in consideration of suppression of a short channel effect and improvement of a driving force with miniaturization of a MOSFET. Therefore, as a method of doping impurities, a method of doping simultaneously by ion implantation into the gate electrode and the source / drain diffusion layers is generally used. The current trend is to form the gate oxide film as thin as possible.
If boron is used at the time of ion implantation into the MOS, the diffusion layer is formed deeply by channeling, and boron is implanted into the channel region through the gate electrode and the gate oxide film, causing fluctuations in the threshold value. Is a problem. For this reason, a method is generally used in which channeling is suppressed by using BF2 ions, which are molecular ions, to prevent these problems.

However, when BF2 ions are implanted, fluorine is introduced at the same time as boron, and this fluorine has a property of being easily captured in an oxide film or crystal defects by thermal diffusion. It is known that the presence of the fluorine ions in the oxide film has an effect of promoting the diffusion of boron in the oxide film. Therefore, if a large amount of fluorine is present in the gate oxide film during the activation heat treatment after the implantation of BF2 during the formation of the pMOS, boron in the gate electrode will pass through the gate oxide film.

As a measure for suppressing this problem, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. -10-2067 proposes a method of suppressing the diffusion of boron from a gate electrode doped by BF2 ion implantation by introducing chlorine into a gate oxide film. This method aims at suppressing the promotion of boron diffusion of fluorine by introducing chlorine to reduce fluorine bonding in the gate oxide film.

Japanese Patent Application Laid-Open No. 7-122746 discloses that an oxide film 8 is formed on a gate electrode 3 before ion implantation as shown in FIG. 5 in order to prevent fluorine from entering the gate electrode during BF2 ion implantation. By depositing the BF2 ions within the oxide film 8 after the deposition, the concentration of fluorine implanted into the gate polysilicon 3 can be reduced. Therefore, entry of fluorine into the gate electrode during the activation heat treatment is suppressed, and the threshold voltage is stabilized.

[0006]

However, in the method disclosed in Japanese Patent Laid-Open No. Hei 5-102,067, since chlorine is introduced into the gate oxide film, the threshold voltage is affected by the fixed charge of chlorine itself. Instability and the reliability of the gate oxide film may be adversely affected.

In the method disclosed in Japanese Patent Application Laid-Open No. 7-122746, since the amount of fluorine to be implanted and the amount of B to be introduced are also reduced, the boron concentration in the gate electrode is reduced, and the layer resistance is increased. In addition, a problem of a reduction in driving force due to depletion of the gate electrode occurs. Immediately after polysilicon is deposited to avoid this problem, phosphorus is implanted into the NMOS region, boron is implanted into the PMOS region, and ion implantation is performed using a resist as a mask.
Means for preventing the intrusion of fluorine into the gate and at the same time sufficiently lowering the resistance by sufficiently doping the gate electrode are also described. The number has increased significantly.

In order to realize high speed and low power consumption of LSI, it is necessary to improve the performance of semiconductor elements.
In order to suppress the short channel effect accompanying the miniaturization of the OS type transistor, a surface channel type MOSFET must be formed.

Accordingly, an object of the present invention is to provide a method for establishing a gate electrode forming technique of a MOS transistor for suppressing penetration of boron from a p + gate electrode and improving operation stability and reliability. Is to provide.

[0010]

According to the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming polysilicon serving as a gate electrode on a semiconductor substrate via a gate oxide film;
It has been found that when the concentration of fluorine segregated in the gate oxide film is suppressed to 1E14 cm −2 or less at the time of activation heat treatment after ion implantation, boron penetration can be reduced and fluctuation in threshold voltage can be suppressed. Hereinafter, means for solving the problems will be described step by step.

A step of forming a SiO2 film by thermally oxidizing a silicon semiconductor; a step of depositing a polysilicon film on the SiO2 film; a step of providing an oxygen leak layer in the polysilicon film; A pMOS is completed by performing a step of implanting BF2 ions into the film and activating boron by S / D and the BF2 implanted into the gate electrode by an activation heat treatment. In the step, B
Forming a fluorine peak at a depth shallower than the position of the oxygen leak layer at the time of F2 implantation, and forming a crystal formed at the oxygen leak layer and the amorphous layer / polysilicon interface during the activation heat treatment of the introduced impurities. This is a method for manufacturing a semiconductor device including a step of suppressing fluorine taken in a gate oxide film by segregating fluorine into defects.

In the present invention, by reducing the number of fluorine atoms segregating in the gate oxide film, the effect of promoting the diffusion of boron caused by fluorine is reduced, and the penetration of boron is suppressed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process sectional view showing an embodiment of the present invention. FIG. 1A shows that the surface of a silicon substrate 1
This shows a structure in which a field oxide film 2 is selectively formed, and then a gate oxide film 3 is formed on the surface of an element forming region of the substrate. In FIG. 1B, when forming a gate electrode 4 made of non-doped polysilicon on a gate oxide film, an oxygen leak layer 5 is provided in the polysilicon film. This is because oxygen gas is mixed during the growth of polysilicon and the
An oxide film layer as thin as about nm is formed in the polysilicon film.

FIG. 1C shows a general MOS type structure in which a gate electrode 6 is formed by performing patterning using a resist as a mask, and an insulating film 7 is arranged on a gate side wall. Using this gate electrode as a mask, BF2 is doped for 20 k for doping the source / drain region and the gate electrode.
3 × 10 15 cm −2 is implanted with energy of about eV (d). At this time, it is important that the peak of fluorine at the time of BF2 implantation is located in a region shallower than the oxygen leak layer.
The position of the oxygen leak layer is defined in advance during the growth of polysilicon.

The heat treatment for activating the implanted impurities is performed at a high temperature for a short time by lamp annealing. FIGS. 2A and 2B show the profiles of boron and fluorine in the polysilicon film immediately after the BF2 ion implantation and after the activation heat treatment, respectively. Immediately after ion implantation, the peak of fluorine (Rp: projection range) is located on the surface side of the oxygen leak layer, and boron does not penetrate through the gate oxide film even if channeling during ion implantation is considered. 150n film thickness
m. At the time of the activation heat treatment, fluorine has a characteristic that it is easily captured by an oxide film or a crystal defect. Decrease. Further, since fluorine trapped in the oxide film has a property of promoting the diffusion of boron, boron is uniformly distributed in polysilicon as shown in FIG. 2B, and depletion of the gate electrode is reduced. Does not occur.

FIG. 3 shows the fluorine concentration in the gate oxide film and the shift amount of the flat band voltage (Vfb) (shift amount for a sample in which no fluorine is introduced into the gate polysilicon). From this figure, it can be seen that when the fluorine concentration in the gate oxide film is 1 × 10 14 cm −2 or less, the Vfb shift hardly occurs. Therefore, in the present invention, since the fluorine concentration in the gate oxide film can be suppressed to 1 × 10 14 cm −2 or less, the threshold voltage is stable and the variation is small.

A second embodiment will be described with reference to FIG. In FIG. 4, after a field oxide film 2 is selectively formed on the surface of a silicon substrate 1, a gate oxide film 3 and a gate electrode 6 made of non-doped polysilicon are formed on the surface of an element forming region of the substrate. This shows a general MOS type structure, and BF2 is 2
1.times.10@15 cm @ -2 ion implantation is performed at an energy of 0 keV.

Next, in order to reduce the concentration of fluorine implanted in the polysilicon, a heat treatment is performed at about 600 ° C. for 5 hours, so that the boron implanted in the diffusion layer is not acceleratedly diffused and implanted. The fluorine diffuses out. At the time of this heat treatment, the condition is that the surface of the gate polysilicon is not covered with the film. By the above process, the fluorine concentration is reduced to 1/3 or less immediately after the implantation. Subsequently, high-temperature short-time annealing is performed by lamp annealing as activation annealing.
At this time, since the fluorine concentration in the polysilicon film has decreased, the concentration of fluorine segregated in the vicinity of the gate oxide film is 1 × 1.
014 cm -2 or less, and the accelerated diffusion of boron in the gate oxide film is not promoted, so that the penetration of boron can be suppressed.

In the third embodiment, similarly to the second embodiment, a field oxide film 2 is selectively formed on the surface of a silicon substrate 1 and then a gate oxide film 3 is formed on the surface of an element formation region of the substrate. And a general MOS type structure in which a gate electrode 4 made of non-doped polysilicon is formed.
Using this gate electrode as a mask, BF2 ions are implanted at 3 * 10 <15> cm <-2> at an energy of 5 keV or less. The diffusion layer during ion implantation and the protective oxide film on the surface of the gate polysilicon are not covered, but the surface is covered with a silicon oxide film or a nitride film serving as a cap after the implantation. This is to prevent the outward diffusion of boron during the activation heat treatment.If the implantation energy is low, most of the impurities are distributed on the outermost surface, and the implantation defects are small and formed only on the surface. Without a cap film, outward diffusion is likely to occur. If boron diffuses outward, the impurity concentration of the diffusion layer and the gate polysilicon decreases, the layer resistance increases, and the driving force decreases. Most of the fluorine in the gate polysilicon is segregated in the oxide film portion on the surface, and the fluorine segregated in the gate oxide film can be reduced to 1 × 10 14 cm −2 or less, so that penetration of boron is suppressed. In this embodiment, since the penetration of boron from the gate oxide film is suppressed and the source / drain diffusion layers can be formed extremely shallow, a high-performance pMOS in which the short channel effect is suppressed can be formed.

[0021]

According to the transistor manufactured by the above-described manufacturing method, the concentration of fluorine segregated in the vicinity of the gate oxide film can be controlled and the enhanced diffusion of boron in the gate oxide film can be suppressed. In addition to preventing fluctuation of the threshold value and obtaining stable device operation, an effect is also obtained regarding long-term reliability.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing a first embodiment of the present invention.

FIG. 2 shows a concentration profile of boron and fluorine in the depth direction of the p-type polysilicon gate of FIG.

FIG. 3 is a diagram showing a relationship between a fluorine concentration in a gate oxide film of FIG. 1 and MOS capacitance characteristics.

FIG. 4 is a sectional view showing a second embodiment of the present invention.

FIG. 5 is a process sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Si substrate, 2 field oxide film 3 gate oxide film 4 polysilicon film 5 oxygen leak layer 6 gate electrode 7 gate side wall 8 BF2 injection region

Claims (6)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: forming a gate electrode on a semiconductor substrate via a gate oxide film; and implanting BF2 ions into the gate electrode. 2. The method according to claim 1, wherein the concentration of fluorine in the gate insulating film is 1 × 1.
2. The method for manufacturing a semiconductor device according to claim 1, wherein the thickness is not more than 014 cm @ -2. 3. The method according to claim 1, wherein the gate electrode is made of polysilicon, and an oxygen leak layer is provided when the polysilicon is formed. 4. The semiconductor device according to claim 3, wherein a peak position of fluorine is formed shallower than said oxygen leak layer when implanting BF2 ions for doping polysilicon as said gate electrode. Manufacturing method. 5. The method according to claim 3, wherein during the activation heat treatment after the implantation of the BF2 ions, fluorine is trapped in the oxygen leak layer to prevent diffusion of fluorine into the gate oxide film. A method for manufacturing a semiconductor device. 6. After the BF2 ions are implanted into the gate electrode, a heat treatment step is performed by annealing at a low temperature for a long time at 600 to 700.degree. C. to diffuse fluorine outward. 2. The method according to claim 1, wherein the concentration of fluorine segregated in the gate insulating film is reduced.