JPH0645593A - Manufacture of transistor - Google Patents

Abstract

(57) [Summary] [Structure] By introducing ozone and oxygen ions generated by plasma discharge of oxygen gas into the film forming apparatus, carbon compounds existing in the film forming apparatus and on the substrate surface are removed. Formed on the substrate surface by introducing hydrogen ions and hydrogen fluoride generated by introducing hydrogen ions and fluorine gas generated by discharging hydrogen gas into the film forming apparatus. And a step of removing the removed natural oxide film. [Effect] Carbon compounds existing in the film forming apparatus and on the surface of the substrate are oxidized by ozone or oxygen ions and are changed into gases such as carbon monoxide and carbon dioxide. Impurity contamination in the membrane device can be reduced. Further, the silicon oxide film can be etched with fluorine ions to remove the natural oxide film formed on the substrate surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a transistor, and more particularly to a method for manufacturing a transistor which can be manufactured by a low temperature process.

[0002]

2. Description of the Related Art In recent years, by using a glass substrate, a device which requires a thin film transistor to be formed on a large area such as a display device or an image sensor has been manufactured by a low temperature process of about 600.degree. ing. However, at a temperature of about 600 ° C., when the gate oxide film is formed, the conventional semiconductor process, that is, the thermal oxidation method cannot be performed. Therefore, the gate oxidation by the low pressure CVD method, the plasma CVD method, or the deposition method such as sputtering is performed. A film is being formed.

[0003]

In a conventional method for manufacturing a semiconductor device, an unstable natural oxide film is formed on the surface of the semiconductor layer immediately after the semiconductor layer is formed, and it is very difficult to avoid this. In particular, low pressure CVD method, plasma CVD method,
Alternatively, when a deposition method such as sputtering is used, a natural oxide film will be formed at the interface between the semiconductor layer and the gate oxide film. Therefore, there has been a problem that the interface state density and the fixed surface charge density increase, which may cause an increase in the threshold voltage of the transistor and a decrease in the field effect mobility.

Further, generally, in a semiconductor manufacturing apparatus, a small amount of carbon-based impurities mainly caused by oils and fats used in exhaust pumps are present and adhere to the surface of the semiconductor layer, so that It is possible to make the characteristics unstable. The present invention has been made in view of the above problems, and removes carbon-based impurities existing in the film forming apparatus and on the surface of the semiconductor layer, and also removes the natural oxide film formed on the surface of the semiconductor layer. It is an object of the present invention to provide a method for manufacturing a transistor capable of achieving the above.

[0005]

According to the present invention, ozone and oxygen ions generated by plasma discharge of oxygen gas are introduced into a film forming apparatus so as to exist in the film forming apparatus and on the surface of a substrate. And a step of removing the carbon compound, and by introducing into the film-forming apparatus the fluorine ions and hydrogen fluoride produced by introducing hydrogen ions and fluorine gas produced by the discharge of hydrogen gas. And a step of removing a natural oxide film formed on the surface of the substrate, a method of manufacturing a transistor is provided.

That is, the present invention relates to the surface treatment step of forming the gate insulating film in the process of forming the transistor. The film forming apparatus used in the present invention is not particularly limited as long as it is an apparatus normally used for forming a film, but for example, the film forming apparatus 10 as shown in FIG. 2 is used. it can.
The film forming apparatus 10 is mainly composed of a substantially cylindrical film forming chamber 11 formed of stainless steel and a plasma chamber 12 connected to a lower portion thereof and formed of a quartz tube. A substrate holder 13 having a heater (not shown) embedded therein is disposed on the upper wall of the film forming chamber 11, and the substrate 1 is placed on the substrate holder 13. In addition, two exhaust ports 14 are formed on the upper wall end portion on a substantially diagonal line. Further, the first gas nozzle 15 is arranged at a position facing the mounted substrate 1 in a substantially central portion of the film forming chamber 11, and a gas introduction port of the first gas nozzle 15 is formed. It extends to the outside of the membrane chamber 11. As the gas introduced from the first gas nozzle 15, a raw material gas which does not need to be decomposed by plasma can be directly introduced into the film forming chamber 11.
Further, below the first gas nozzle 15, there is a plasma chamber 12
And a second gas nozzle 16 for introducing the source gas excited in the plasma chamber 12 is formed.
Further, in order to excite the raw material gas introduced into the plasma chamber 12, a coil 17 for oscillating plasma is arranged in the outer peripheral portion of the plasma chamber 12, and the coil 17 is connected to a high frequency power supply 18.

The substrate used in the present invention is not particularly limited as long as it is a substrate for forming a transistor. For example, when forming a thin film transistor, an insulating substrate such as a glass substrate that is usually used as a substrate for forming a thin film transistor can be used. Then, on the insulating substrate, it is preferable to deposit a semiconductor thin film of amorphous silicon, polysilicon, or the like by about 50 to 150 nm by a known method, for example, a CVD method or the like to form a region to be a channel portion. . When forming a transistor such as a MOS, a semiconductor substrate such as a silicon substrate can be used. In the present invention, the substrate, in the case of a thin film transistor, includes a semiconductor thin film formed on an insulating substrate.

In the present invention, it is preferable that the substrate on which the semiconductor thin film is formed or the semiconductor substrate is placed on the substrate holder in the film forming apparatus and is evacuated to 5 × 10 ⁻⁷ Torr or less. Further, when introducing ozone and oxygen ions generated by plasma discharge of oxygen gas into the film forming apparatus,
Oxygen gas is first introduced into the plasma chamber. In this case, the oxygen gas is preferably introduced at a flow rate of about 10 to 500 sccm. The pressure in the plasma chamber is 0.1 to 1
About Torr is preferable. The time for treatment with ozone and oxygen ions generated by plasma discharge of oxygen gas is preferably about 5 to 15 minutes. Further, the high frequency power applied to the oscillation coil during plasma discharge is 50 to 15
0 W is preferable.

When hydrogen ions and hydrogen fluoride generated by introducing hydrogen ions and fluorine gas generated by the discharge of hydrogen gas are introduced into the film forming apparatus, the hydrogen gas first forms plasma. Introduced into the room. In this case, hydrogen gas is introduced at a flow rate of about 10 to 500 sccm, excited and introduced into the film forming chamber. The pressure of the plasma chamber at this time is preferably about 0.1 to 1 Torr.
Further, the fluorine gas, which is directly introduced into the film forming chamber at the same time as the introduction of hydrogen ions, is preferably introduced at a flow rate of about 2 to 50 sccm. Then, by reacting these hydrogen ions with fluorine gas, fluorine ions and hydrogen fluoride are generated. The time for treatment with fluorine ions and hydrogen fluoride in the film forming apparatus is preferably about 1 to 5 minutes.

Further, after performing these treatments, an oxide film to be a gate insulating film is subsequently formed on the surface of the substrate.
At that time, similarly to the above, by introducing oxygen gas, ozone and oxygen ions are generated, and at the same time, the silane gas can be directly introduced into the film formation chamber at a flow rate of about 1 to 20 sccm to form an oxide film. . Although the thickness of the oxide film in this case is not particularly limited, it is preferably about 80 to 120 nm when forming a thin film transistor.

After forming the gate insulating film, the gate electrode, the source / drain regions, the interlayer insulating film, and the like are formed by a known method to manufacture a transistor.

[0012]

According to the above method, since ozone and oxygen ions generated by plasma discharge of oxygen gas are introduced into the film forming apparatus, the carbon present in the film forming apparatus and on the surface of the substrate by ozone or oxygen ions is introduced. The compound is oxidized and converted into a gas such as carbon monoxide or carbon dioxide. Then, the gas in the film forming apparatus is removed by evacuating the gas such as carbon monoxide or carbon dioxide generated in the film forming apparatus, and the impurity contamination in the film forming apparatus by the carbon compound is reduced. .

Further, since it is generally known that fluorine ions etch a silicon film and a silicon oxide film, etching utilizing plasma decomposition of carbon tetrafluoride (CF ₄ ) is widely used. However, when this method is applied, carbon remains on the surface of the silicon film, so that a clean interface cannot be formed. Therefore, by introducing hydrogen ions and hydrogen fluoride, which are generated by introducing hydrogen ions and fluorine gas, which are generated by the discharge of hydrogen gas, into the film forming apparatus, the natural formed on the substrate surface is introduced. The oxide film is removed. This is because hydrogen ions are formed by plasma decomposition of hydrogen and fluorine ions are formed by reacting the hydrogen ions with fluorine to etch the silicon oxide film.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a transistor according to the present invention will be described with reference to the drawings. First, polysilicon 2 is deposited on the insulating substrate 1 made of glass, for example, by a CVD method so as to have a film thickness of 100 nm to form the polysilicon 2 which will be a channel portion of a transistor (FIG. 1A).

This is mounted on the substrate holder 13 of the film forming apparatus 10 shown in FIG. 2, and once the inside of the film forming apparatus 10 is 5 × 1.
The substrate 1 is heated to 300 ° C. with the heater of the substrate holder 13 while evacuation is performed to 0 ⁻⁷ Torr.
Then, first, oxygen gas is introduced into the plasma chamber 12 at a flow rate of about 100 sccm, and for example, high frequency power of about 100 W is applied to the oscillation coil 17 to form oxygen plasma. Then, ozone and oxygen radicals are introduced into the film forming chamber 11 through the second gas nozzle 16 to remove impurities consisting of carbon compounds existing on the surface of the substrate 1 and in the film forming chamber 11. At this time, the pressure in the plasma chamber 12 is 1
The processing time is about 10 minutes at about Torr. Then, after evacuating to 5 × 10 ⁻⁷ Torr again,
Hydrogen gas is introduced into the plasma chamber 12 at a flow rate of about 100 sccm, and high frequency power of about 100 W is applied to the oscillation coil 17 to form hydrogen plasma. Then, hydrogen radicals are introduced into the film forming chamber 11 through the second gas nozzle 16 and, at the same time, fluorine gas is introduced through the first gas nozzle 15 at a flow rate of about 10 sccm.
The natural oxide film formed on the surface is removed by etching. The processing time at this time is about 5 minutes. After that, oxygen gas is further introduced into the plasma chamber 12 at a flow rate of about 100 sccm to form oxygen plasma, and the film formation chamber 11
Ozone and oxygen ions are introduced into. At the same time, by introducing monosilane from the first gas nozzle 15 at a flow rate of about 2 sccm, an S film having a film thickness of about 100 nm to be a gate insulating film of a transistor is formed on the polysilicon 2.
An iO ₂ film 3 is formed (FIG. 1B).

Next, after taking out the substrate 1 from the film forming apparatus 10, a polysilicon film having a film thickness of about 250 nm is formed on the substrate 1 and patterned into a desired shape to form a gate electrode 44. This is ion-implanted into a self-aligned impurity element at 1 × 10 ¹⁵ ions / cm ² , 40 keV.
The source and the drain of the transistor are formed by implanting and activating the solution to some extent. At the same time, after the resistance of the gate electrode 44 is reduced, the film thickness is 500 nm.
An interlayer insulating film 5 made of a SiO ₂ film is formed (FIG. 1C).

Further, the interlayer insulating film 5 is formed by the usual process.
After forming a contact hole in, a lead electrode 6 made of, for example, aluminum is formed to fabricate a transistor (FIG. 1D). The drain current-gate voltage characteristic of the transistor thus manufactured is shown by a solid line in FIG.

Example 1 An example of an experiment relating to cleaning of a film forming apparatus and a substrate surface by oxygen plasma will be shown. A silicon wafer that has been subjected to RTA cleaning as the substrate 1 is set in the substrate holder 13 and oxygen gas is supplied at a flow rate of 100 sccm in the plasma chamber 1.
2 was introduced to form oxygen plasma, and ozone and oxygen ions were introduced into the film forming chamber 11 through the second gas nozzle 16. The high frequency power for forming plasma is 100 W, the temperature of the substrate 1 is 300 ° C., the pressure of the plasma chamber 12 and the film forming chamber 11 is set to 1 Torr by controlling the exhaust speed,
The treatment was carried out for 10 minutes.

In FIG. 4, a mass spectrometer is installed in the film forming chamber 11 to observe the atmosphere inside the film forming chamber 11 before (A), immediately after (B) and after 1 minute of evacuation (C). It was done. The pressure during measurement was 5 × 10 ⁻⁷ Torr before and after the treatment. Before the treatment (A), a signal indicating a carbon compound derived from oils and fats used in an exhaust pump or the like is observed at a mass number of 38 to 44.

Immediately after the treatment (B), signals other than the mass number 44 are decreased. This is because the impurities consisting of carbon compounds existing in the film forming chamber 11 are oxidized by ozone and oxygen ions and changed into gas such as carbon monoxide or carbon dioxide. Therefore, immediately after the treatment, the mass number is 4
Observations show that carbon dioxide in No. 4 is increasing.

After evacuation for 1 minute (C), the signal of mass number 44 also decreased, indicating that the impurities consisting of carbon compounds were removed. In FIG. 5, the Auger electron spectroscopic analyzer is similarly installed in the film forming chamber 11, and changes in the state of the surface of the silicon substrate 1 are observed before (D) and after (E) treatment. A signal indicating that carbon atoms are attached to the surface of the silicon substrate 1 is observed before the treatment (D), but no carbon atoms are observed after the treatment (E).
From this, it can be confirmed that the carbon impurities on the substrate surface are also removed. However, the signal indicating an oxygen atom is increased because the oxidation of silicon is progressing due to ozone and oxygen ions.

Example 2 An example of an experiment relating to removal of a surface oxide film by introducing hydrogen plasma and fluorine will be shown. After performing the process of Example 1,
Hydrogen gas was introduced into the plasma chamber at a flow rate of 100 sccm to form hydrogen plasma, and hydrogen ions were introduced into the film formation chamber 11 through the second gas nozzle 16. Further, fluorine gas was introduced from the first gas nozzle 15 at a flow rate of 10 sccm. The high frequency power that forms plasma is 100
W, substrate temperature is 300 ° C., plasma chamber 12 and film forming chamber 1
The pressure of 1 is 0.5 Tor by controlling the exhaust speed
and treated for 1 minute.

FIG. 6 shows a change in the state of the surface of the silicon substrate 1 observed before (F) and after (G) processing by installing an Auger electron spectroscopic analyzer in the film forming chamber 11. Before the treatment (F), signals of oxygen atoms showing the oxide film on the surface of the substrate 1 are observed, but after treatment (G), the signals of oxygen atoms are not observed at all. From this, it is shown that the natural oxide film existing on the surface of the substrate 1 and the oxide film formed in the process of Example 1 are removed by etching.

Example 3 An example of an experiment concerning cleaning of a film-forming apparatus and a substrate surface by oxygen plasma, removal of a surface oxide film by hydrogen plasma and fluorine introduction, and a silicon oxide film on a silicon wafer after the treatment. The example of the experiment regarding film-forming is shown. Oxygen is introduced into the plasma chamber at a flow rate of 100 sccm to form oxygen plasma, and ozone and oxygen ions are introduced into the film forming chamber 11 through the second gas nozzle 16, and at the same time monosilane is flown from the first gas nozzle 15 at a flow rate of 2 sccm. Introduced in. The high-frequency power for forming plasma was 100 W, the substrate temperature was 300 ° C., the pressure in the plasma chamber 12 and the film forming chamber 11 was 0.1 Torr by controlling the exhaust speed, and the film formation was performed for 12 minutes.
In this method, a silicon oxide film is grown by the reaction of ozone and oxygen ions with monosilane, which is about 4 nm even at a low temperature of 300 ° C., which is about four times as high as the low pressure CVD using normal oxygen and monosilane. A growth rate of min was obtained. In addition, it is considered that there is almost no damage to the substrate surface as compared with normal plasma CVD in which plasma oscillation is performed in the film forming chamber.

A MOS structure was formed from the 100 nm-thick silicon oxide film formed as described above, and the leak current characteristics and the CV curve by the high frequency CV method were measured. FIG. 7 is a diagram showing the leakage current characteristics. The density of the leakage current in a low electric field is about 3 nA / cm ² and the withstand voltage is about 8 MV / cm. It was

FIG. 8 shows the CV curve. As a result of calculating the interface state density from the CV curve, a value of 2 × 10 ¹⁰ / cm · eV was obtained near the center of the band gap of silicon. This indicates that the silicon surface was cleaned by the treatment shown in Examples 1 and 2 and the silicon oxide film was formed thereon.

Comparative Example 1 A comparative example in which the silicon oxide film shown in Example 3 is formed on a silicon wafer without performing the processing shown in Examples 1 and 2 will be shown. The silicon wafer that had been subjected to RTA cleaning was set on the substrate holder 13, and the silicon oxide film was formed in Example 3 without performing the processes shown in Examples 1 and 2. The result of measuring the CV curve of the silicon oxide film having a film thickness of 100 nm in the same manner as in Example 3 is shown by the dotted line in FIG. As is clear from FIG. 8, the silicon oxide film manufactured in Example 3 has a smaller interface state density and better characteristics than the silicon oxide film manufactured in Comparative Example 1.

COMPARATIVE EXAMPLE 2 A transistor in which a silicon oxide film is formed by ordinary plasma CVD without performing the processing of Examples 1 to 3 on the gate insulating film will be described. Transistors were manufactured in the same manner as in the example except that the silicon oxide film was formed by the usual plasma CVD without performing the processes of the examples 1 to 3.

The result of measuring the gate voltage-drain current characteristics of the transistor of Comparative Example 2 in the same manner as in Example is shown by the dotted line in FIG. It was found that the transistor of the example has a larger on-current and a lower threshold voltage than the transistor of the comparative example 2 and has good characteristics.
In this embodiment, the case of forming a thin film transistor has been described, but other transistors,
This is essentially the same when forming a transistor such as a MOS, and the present invention extends to them.

[0030]

According to the manufacturing method of the present invention, since ozone and oxygen ions generated by plasma discharge of oxygen gas are introduced into the film forming apparatus, ozone or oxygen ions are used to form the film forming apparatus and the substrate surface. The carbon compounds present in are oxidized and converted into gases such as carbon monoxide and carbon dioxide. Then, by evacuating the gas such as carbon monoxide and carbon dioxide generated in the film forming apparatus, the gas in the film forming apparatus is removed, and impurity contamination in the film forming apparatus by the carbon compound is reduced. You can

Further, by introducing hydrogen ions and hydrogen fluoride produced by introducing hydrogen ions and fluorine gas produced by the discharge of hydrogen gas into the film forming apparatus, silicon oxide by fluorine ions is produced. The film can be etched to remove the native oxide film formed on the substrate surface. Therefore, the interface state density and the interface fixed charge density can be reduced, and the characteristics of the transistor can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a method of manufacturing a transistor according to the present invention.

FIG. 2 is a schematic cross-sectional view of a film forming apparatus used for forming a silicon oxide film according to an embodiment of the present invention.

FIG. 3 is a graph showing gate voltage-drain current characteristics of transistors manufactured according to Examples of the present invention and Comparative Examples.

FIG. 4 is a graph showing changes in the mass spectrum obtained by measuring the atmosphere in the film forming apparatus before and after performing the process shown in Example 1 of the present invention.

FIG. 5 is a graph showing changes in Auger electron spectrum observed on the surface of a silicon wafer before and after performing the treatment shown in Example 1 of the present invention.

FIG. 6 is a graph showing changes in Auger electron spectrum observed on the surface of a silicon wafer before and after the treatment shown in Example 2 of the present invention.

FIG. 7 is a graph showing leak current characteristics of a silicon oxide film manufactured according to Example 3 of the present invention.

FIG. 8 is a graph showing CV characteristics of a silicon oxide film manufactured according to Example 3 of the present invention.

[Explanation of symbols]

 1 substrate 10 film forming apparatus

Claims (1)

[Claims] 1. A step of removing carbon compounds existing in the film forming apparatus and on the surface of a substrate by introducing ozone and oxygen ions generated by plasma discharge of oxygen gas into the film forming apparatus, By introducing hydrogen ions and hydrogen fluoride generated by introducing hydrogen ions and fluorine gas generated by discharging hydrogen gas into the film forming apparatus, the natural oxidation formed on the surface of the substrate. And a step of removing the film.