JPH07326750A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to control the threshold voltage of a transistor without inflicting an adverse effect on the characteristics of the transistor by a method wherein an insulating film containing carbon is formed between a gate insulating film, which is formed on a substrate, and a gate electrode, the film-forming condition at the time of formation of the insulating film is changed and the concentration of the carbon being contained in the insulating film is controlled. CONSTITUTION:An oxide film 12 is formed on the surface of a semiconductor substrate 11 and a BPSG film 13 is formed on the surface of the film 12. Then, a polycrystalline silicon film 14 is formed on the surface of the film 13. A resist mask 15 is formed on the surface of the film 14 and the film 14 and the film 13 are etched in order using this mask 15 as a mask to form a gate electrode. The film-forming condition of the film 13 within this gate electrode is changed and the concentration of carbon being contained in the film 13 is controlled. Thereby, the threshold voltage of a transistor 4 can be controlled without inflicing an adverse effect on the characteristics of the transistor 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and its manufacturing method, and more particularly to a field effect transistor and its manufacturing method.

[0002]

2. Description of the Related Art The threshold voltage of a field effect transistor is important in the characteristics of the device, and it has been practiced to control this threshold voltage to a desired value. Factors that determine the threshold voltage include the thickness of the gate insulating film, the amount of charge in the gate insulating film, and the type and concentration of impurities in the impurity region formed in the semiconductor substrate. It is difficult to control the amount of electric charge in the desired value during the manufacturing process of the semiconductor device. Further, the impurity concentration in the semiconductor substrate and the film thickness of the gate insulating film also affect characteristics other than the threshold voltage, and are therefore limited to a certain value.

As a method of controlling the threshold voltage of a field effect transistor, a channel doping method is mainly used. This channel doping method is a method in which impurities such as B and P are ion-implanted into the channel region on the surface of the semiconductor substrate to change the impurity concentration on the surface of the semiconductor substrate.

A method of manufacturing a gate electrode in the case of manufacturing an N-channel field effect transistor on a P-type silicon substrate using this channel doping method will be described below with reference to the drawings. First, as shown in FIG. 5A, an oxide film 112 is formed on the surface of the semiconductor substrate 111. Next, the oxide film 112 other than on the channel formation planned region
A resist mask 113 is formed on the surface, and using this as a mask, B is ion-implanted 114 into the semiconductor substrate 111 with a predetermined acceleration energy and a predetermined dose amount, and the channel region 1 is formed.
The impurity concentration of 15 is controlled. In this step, the threshold voltage of the field effect transistor is determined.

Subsequently, as shown in FIG. 5B, the oxide film 1
A polycrystalline silicon film is formed on the surface 12 and patterned to form a gate electrode 116. Using this gate electrode 116 as a mask, P ions are implanted into the semiconductor substrate 111 to form an N-type diffusion region, one of which is the source region 11
7 and the other is the drain region 118. Through the above steps, the manufacturing process of the gate electrode of the field effect transistor using the channel doping method is completed.

[0006]

The channel doping method for the field effect transistor described above has the following problems. The first problem is that impurity atoms such as B and P are accelerated as ions with high energy and are directly implanted into the semiconductor substrate, so that the implanted ions disturb the arrangement of Si constituting the semiconductor substrate. Then, a crystal defect is generated. This crystal defect causes a leak current.

A second problem is that heat treatment at 1000 ° C. or higher is performed in order to activate the impurity ions implanted by ion implantation in the semiconductor substrate, but with the miniaturization and high integration of the device. For example, the distance between the source and drain is narrowed, and the region where these impurity regions are formed is also a shallow region of the semiconductor substrate. When high-temperature heat treatment is performed, re-diffusion of impurities occurs, and This may cause a junction leak current in other formed elements or between elements.

In the conventional method of manufacturing a semiconductor device by the channel doping method, which is performed to control the threshold voltage as described above, crystal defects, re-diffusion of impurities, etc. occur,
Finally, there is a problem in that the characteristics required for the device as a product may not be obtained in some cases. Therefore, it is an object of the present invention to provide a semiconductor device capable of controlling the threshold voltage without adversely affecting the characteristics of the transistor and a manufacturing method thereof.

[0009]

According to the present invention, in order to control the threshold voltage of a field effect transistor, carbon (hereinafter referred to as a “gate”) is formed between a gate insulating film formed on a semiconductor substrate and a gate electrode. An insulating film containing C) is formed. The concentration of C contained in the film is controlled by changing the film forming conditions when forming the insulating film. This C can function as an electric charge, and the amount of electric charge of the insulating film is changed by controlling the concentration of C contained in the insulating film. The action of this charge controls the threshold voltage of the field effect transistor to a desired value.

[0010]

According to the present invention, it is possible to control the threshold voltage of a field effect transistor without causing crystal defects or re-diffusion of impurities in the semiconductor substrate and adversely affecting the characteristics of the device. Becomes

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, as a typical example thereof, a method of manufacturing a field effect transistor which constitutes a large scale integrated circuit will be described.

As shown in FIG. 1A, an oxide film 12 having a thickness of 100 angstrom is formed by thermal oxidation on the surface of the semiconductor substrate 11 on which the memory cell portion (not shown) is already formed. Next, BPSG (Boron doped Phospho Silica) having a film thickness of 100 angstrom is formed on the surface of the oxide film.
te Glass) film 13 is formed. Next, a polycrystalline silicon film 14 having a film thickness of 4000 angstrom is formed on the surface of the BPSG film 13 by the LPCVD method.

The BPSG film 13 is formed by LPCVD (Low Pressu
A film is formed by a re chemical vapor deposition (deposition) method, and TEOS (tetraethoxysilane), PH3 (phosphine), TMB (trimethylborate), and oxygen are introduced into an apparatus under a reduced pressure of about 1 degree to 600 degrees Celsius. By. The doping amount of B and P introduced into the BPSG film can be controlled to a desired value by changing the conditions such as the flow rate ratio of the introduced gas.

However, if the amount of P introduced is too large, BP
Since there is a problem of moisture absorption in the SG film, it is desirable that the amounts of B and P dopants are about 7% for P and 4% for B with respect to the total weight of the introduced gas.

In the film of the formed BPSG film 13, T
An organic substance, which is a component of EOS, is contained, and C is contained in the BPSG film 13. Since C functions as a constant electric charge, the electric charge by the C has an effect of lowering the threshold voltage in the N-channel field effect transistor. By controlling the concentration of C contained in the BPSG film, It is possible to control the threshold voltage of the field effect transistor.

FIG. 2 shows the deposition temperature of the BPSG film and B
The relationship between the concentrations of C contained in the PSG film 13 is shown. The oxygen partial pressure at this time was constant at 0.17 torr, and the flow rate of each introduced gas was TEOS 100 cc / se.
c, PH3 180cc / sec, TMB12cc / se
c and oxygen were 100 cc / sec.

FIG. 3 shows the relationship between the oxygen partial pressure during the formation of the BPSG film and the concentration of C contained in the BPSG film 13. The oxygen partial pressure is a value for the introduced gas, and the flow rate of the introduced gas excluding oxygen such as TEOS at this time is the same as that in the case of FIG. The film forming temperature is constant at 600 degrees Celsius.

According to these, the concentration of C contained in the BPSG film decreases as the film forming temperature increases, and the concentration of C contained in the BPSG film increases by increasing the flow rate of oxygen. It can be seen that is decreasing. Therefore, the concentration of C contained in the BPSG film can be controlled by the film forming conditions of the BPSG film, for example, the film forming temperature and the partial pressure ratio of oxygen to be introduced.

FIG. 4 shows the relationship between the concentration of C contained in the BPSG film and the threshold voltage. According to this, it is understood that the threshold voltage is lowered by increasing the concentration of C. Therefore, the threshold voltage can be controlled to a desired value by changing the film forming conditions of the BPSG film based on FIGS. 2 and 3 and controlling the concentration of C contained in the BPSG film. Becomes

Subsequently, as shown in FIG. 1B, a resist mask 15 is formed on the surface of the polycrystalline silicon film 14, and the polycrystalline silicon film 14 and the BPSG film 1 are used as a mask.
A gate electrode is formed by etching 3 sequentially.

Subsequently, as shown in FIG. 1C, P is ion-implanted into a predetermined region in the semiconductor substrate 11 by using the gate electrode as a mask, and a heat treatment is performed to perform the heat treatment.
And the drain region 17 is formed. Through the above steps, a field effect transistor is manufactured in a large scale integrated circuit. After that, connection with the memory cell portion formed in the previous step is performed, and the manufacturing of the large-scale integrated circuit is completed. Through the above steps, the threshold voltage of the field-effect transistor can be controlled to a desired value without causing the crystal defects and the re-diffusion of impurities, which have been caused by the conventional channel doping method. Become.

In the above embodiment, the BPSG film was used as the LPC.
Although it is formed by the VD method, it can also be formed by the atmospheric pressure CVD method. At that time, the uniformity of the film formed is inferior to that obtained by the LPCVD method, but the growth rate of the film can be increased. The formed film is PSG (Phosph
The same effect as above can be expected with a Silicate Glass) film. Therefore, the BPSG film and the PSG film can be formed in a stack.

Further, although the method of manufacturing the field effect transistor in the large scale integrated circuit is shown in the above embodiment, the present invention can be applied to all field effect transistors, for example, a power MOS-FET.
(Metal Oxide Semiconductor-FET) and the like can also be used for controlling the threshold voltage.

[0024]

According to the present invention, it is possible to control the threshold voltage of a field effect transistor without causing crystal defects or re-diffusion of impurities in the semiconductor substrate and adversely affecting the characteristics of the device. Is possible.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating a manufacturing process according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the film formation conditions for a BPSG film and the C concentration.

FIG. 3 is a diagram showing the relationship between the film forming conditions for the BPSG film and the C concentration.

FIG. 4 is a relationship diagram between the concentration of C and the threshold voltage.

FIG. 5 is a cross-sectional view illustrating a conventional manufacturing process.

[Explanation of symbols]

 11, 111 Semiconductor substrate 12, 112 Oxide film 13 BPSG film 14 Polycrystalline silicon film 15, 113 Resist mask 16, 117 Source region 17, 118 Drain region 114 B ion implantation 115 Channel region 116 Gate electrode

Claims (6)

[Claims] 1. A first insulating film formed on the surface of a semiconductor substrate, a second insulating film containing an organic substance formed in a predetermined region on the surface of the insulating film, and a second insulating film on the surface of the second insulating film. A semiconductor device comprising: a formed conductive film; and a source region and a drain region formed in the semiconductor substrate adjacent to a region immediately below the second insulating film so as to face each other. 2. A first region in a semiconductor substrate, a second region and a third region which are formed in the semiconductor substrate with the first region separated from each other, and at least the semiconductor on the first region. A first insulating film formed on the surface of the substrate, a second insulating film having a predetermined charge amount formed on the first insulating film, and a conductive film formed on the surface of the second insulating film. A semiconductor device having. 3. The semiconductor device according to claim 1, wherein the second insulating film is BPSG (Boron doped Phospho Sili).
cate glass) film or PSG (Phospho Silicate Glas)
s) A semiconductor device comprising a film or the BPSG film and the PSG film. 4. A step of forming a first insulating film on the surface of a semiconductor substrate, a step of forming a second insulating film containing an organic substance on the surface of the insulating film, and a conductive film on the surface of the second insulating film. And a step of processing the second insulating film and the conductive film into a predetermined electrode shape, and the semiconductor substrate by ion implantation using the second insulating film and the conductive film processed into the electrode shape as a mask. And a step of forming an impurity region therein. 5. The method of manufacturing a semiconductor device according to claim 4, wherein the second insulating film is BPSG (Boron doped Phospho Sili).
cate glass) film or PSG (Phospho Silicate Glas)
s) A film or a method of manufacturing a semiconductor device, which is the BPSG film and the PSG film. 6. A channel region in a semiconductor substrate, a source region and a drain region spaced apart in the semiconductor substrate via the channel region, and a channel region formed on the surface of the semiconductor substrate. In a semiconductor device having a field effect transistor having a gate insulating film, a film for controlling a threshold voltage of the field effect transistor is provided on the gate insulating film according to a concentration of carbon contained therein. Characteristic semiconductor device.