JPH08274090A - Method for forming insulation film - Google Patents

Abstract

PURPOSE: To form an insulation film composed of silicon nitride or silicon oxynitride at a low temperature with less damage, by taking in gas containing nitrogen, and making it vapor-phase-react with evaporated silicon or silicon mono-oxide. CONSTITUTION: A substrate 18 by a silicon semiconductor substrate is arranged in a chamber 10, and SiO powder is put on a Ta boat as a container 13, and the chamber 10 is evacuated by a vacuum pump 15. When the pressure inside the chamber 10 is 1×10<-6> Torr, SiO of a material 14 is heated to the extent of not evaporating by causing a current to flow into the Ta boat, and water adsorbed by the SiO powder is discharged. After that, the Ta boat is once cooled, and a current is caused to flow into the container 13 again taking in ammonia gas from an inlet 22 to evaporate SiO. And silicon material composed of SiO evaporated and gas containing nitrogen i.e., an ammonia gas are vapor- phase-reacted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating film forming method, for example, an insulating film forming method applied to various semiconductor devices.

[0002]

2. Description of the Related Art In a semiconductor device, it is necessary to form a good quality insulating film for various purposes. For example, in an insulated gate field effect transistor (MIS transistor), a gate insulating film is formed on a semiconductor substrate.

As this type of insulating film, a silicon substrate is used as a semiconductor substrate, and a SiO ₂ film formed by thermally oxidizing the surface is often used. SiO ₂ by thermal oxidation
Since the film has extremely good interface characteristics, that is, low interface state density, it is not limited to the gate insulating film of the MIS transistor, and is one of the basic technologies of the current semiconductor process.

Further, for example, Si used for an interlayer insulating film, etc.
As another method of forming the O ₂ film, a high temperature thermal CVD (Chem
ical Vapor Deposition) method.

[0005]

The SiO ₂ film formed by the above-mentioned thermal oxidation or high temperature thermal CVD method has excellent electric characteristics, but it is 1 when the film forming temperature is by thermal oxidation.
All require extremely high temperatures of 000 ° C. or higher, and 600 ° C. or higher in the case of the thermal CVD method.

Therefore, for example, in the case of forming a thin film transistor on a glass substrate, it is not possible to apply the above-described method of forming an insulating film accompanied by high temperature heating in the manufacture of a device required to be formed by a low temperature process.

On the other hand, as a method of forming a SiO ₂ film at a low temperature, there is a plasma CVD method. This plasma CVD
As for the method, a mixed gas of SiH ₄ , N ₂ O and O ₂ is RF
(Radio Frequency) It can be decomposed by discharge and the SiO ₂ film can be deposited at a low temperature of 300 ° C. or lower. Therefore, this method can be applied even if the substrate on which the insulating film is formed has a low heat resistance such as a glass substrate.

In this plasma CVD method, however, high-energy ions and electrons impact the surface on which the insulating film is formed in order to generate high-energy plasma during film formation, which damages the surface. Therefore, by this method, for example, M
When the gate insulating film of the IS transistor is formed, there is a problem that the semiconductor surface is damaged at the time of forming the film, and good transistor characteristics such as good current-voltage characteristics cannot be obtained.

In order to solve the above-mentioned problems, the present inventors have made use of silicon monooxide (SiO) in an oxygen atmosphere.
And a method of forming a SiO ₂ film without using plasma was proposed (Japanese Patent Application Nos. 5-17609 and 6-232117). By this method, a good insulator-semiconductor interface can be formed at a low temperature without damaging the surface on which an insulating film such as a semiconductor is formed.

However, in the insulating film formed by this method, that is, the SiO ₂ film, Si by thermal oxidation is used.
As compared with the O ₂ film, there is a problem that a positive charge trap level due to oxygen deficiency is likely to occur. In addition, SiO ₂ by thermal oxidation
There is a problem that the withstand voltage becomes smaller than that of.

The present invention addresses such problems and provides a method for forming an insulating film of good quality which can be formed at low temperature and with low damage, and which has few oxygen vacancies and a sufficient withstand voltage. It is provided.

[0012]

The present invention is based on silicon Si.
Alternatively, a first step of heating and evaporating silicon monooxide (SiO) and a first step of introducing a gas containing nitrogen are performed.
The second step of vapor-phase reacting silicon Si or silicon monooxide (SiO) vaporized in the above step with nitrogen is used to obtain an insulating film of silicon nitride (SiN) or silicon oxynitride (SiON). To be formed on the surface to be formed.

[0013]

According to the above configuration of the present invention, Si or Si
By heating and evaporating O and reacting it with a gas containing nitrogen in a gas phase, an insulating film made of SiN or SiON is formed at a low temperature, so that a high-quality insulating film can be formed at a low temperature.

[0014]

EXAMPLES Before describing the examples of the present invention, an outline of the method for forming an insulating film of the present invention will be described. In the method for forming an insulating film of the present invention, a first step of heating and vaporizing Si or SiO, and a gas containing nitrogen is introduced to cause Si or SiO vaporized in the first step to undergo a gas phase reaction with nitrogen. In the second step, an insulating film made of SiN or SiON is formed on the target formation surface.

In the above-described method for forming an insulating film according to the present invention,
The following conditions may be mentioned as preferable forming conditions.
Raw material Si or Si that is the evaporation source in the first step
O has a ratio of oxygen to silicon in the range of 0 to 1.8.
Preferably there is. Beyond 1.8, SiO ₂Close to
If it becomes, the temperature to evaporate becomes high, and if it is not high, it will evaporate.
It gets harder.

Nitrogen used for the gas phase reaction in the second step
The gas containing ^-Five-10^-2torr
It 10^-2When the gas pressure is higher than torr, the characteristics are excellent.
It becomes difficult to form an insulating film,^-FiveGas pressure lower than torr
If so, nitrogen will not be combined in a sufficient amount.

The temperature of the surface on which the insulating film is formed is 0 to 9
The range is 00 ° C. The temperature is set so that the substrate is not damaged, although it depends on the material of the substrate on which the film is formed and the underlying substrate and other conditions.

By using nitrogen atomized by plasma discharge or the like for the gas phase reaction in the second step, the nitriding reaction is more likely to occur.

Since the reaction rate of nitrogen with respect to silicon is smaller than the reaction rate of oxygen with respect to silicon, when the oxygen / nitrogen ratio in the SiON film is controlled by the oxygen / nitrogen partial pressure ratio in the reaction gas, the oxygen / nitrogen partial pressure ratio O By setting / N to 0 to 2, a good SiN film or SiON film can be obtained.

An example of the method for forming an insulating film according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of a film forming apparatus for carrying out the method for forming an insulating film according to the present invention. First, this apparatus will be described with reference to FIG.

In the vacuum chamber 10, a film forming raw material (evaporation source) 14 for an insulating film, a container 13 for accommodating SiO powder in this example, and a Ta boat in this example are arranged. This container 13
Is provided with a heating means 12 for evaporating the raw material 14 to turn it into a gas phase. The heating means 12 is configured to heat the container 13 itself, which is, for example, a Ta boat, by energizing it. Then, in this container 13, that is, in the Ta boat, SiO
Add powder and heat it. At this time, although not shown, for example, a similar Ta film having a through hole with a diameter of 0.5 mm is formed.
The lid 16 made of
Prevents iO powder from jumping out due to bumping.

A substrate 18 such as a silicon semiconductor substrate having a surface on which an insulating film is to be formed is arranged above the container 13 in the chamber 10 so as to face the container 13. A shutter 20 is provided between the container 13 and the base 18.

A vacuum pump 15 for evacuating the chamber is connected to the chamber 10. Further, an inlet 22 for the supply gas is provided on the upper side surface of the chamber 10.

Inlet port 22 for the supply gas to the chamber 10.
A mass flow controller (MFC) 21 is installed in front of the chamber 1 and controls the introduction amount of nitrogen supply gas such as ammonia gas.
The partial pressure of nitrogen gas in 0 is controlled. Also, chamber 1
Inside 0, a vapor deposition rate measuring device 23 for monitoring the vapor deposition rate made of, for example, a quartz oscillator is provided.

Next, an example of carrying out the method of the present invention by the above-mentioned film forming apparatus will be described.

First, a substrate 18 made of a silicon semiconductor substrate was placed in the chamber 10, and SiO powder was placed on a Ta boat as a container 13. And chamber 10
The inside was evacuated by the vacuum pump 15. Chamber 10
When the degree of vacuum inside was 1 × 10 ⁻⁶ torr, an electric current was passed through the container 13, that is, the Ta boat to heat the SiO 2 as the raw material 14. First, heating is performed to the extent that SiO does not evaporate, and Si
A gas such as water (H ₂ O) adsorbed on the O powder was released.
Then, after cooling the container 13, that is, the Ta boat, while introducing ammonia gas from the introduction port 22,
An electric current was applied to the container 13 again. Then, the shutter 20 was opened, and SiO was evaporated at a speed of 10 nm / min.

The evaporation temperature of SiO is lower than that of SiO ₂ and depends on the oxygen content. Good evaporation was obtained when the composition ratio of oxygen and silicon (O / Si) was in the range of 0 to 1.8.

A vaporized silicon raw material made of SiO and a gas containing nitrogen, that is, ammonia gas in the first embodiment, are caused to undergo a gas phase reaction. By doing so, silicon oxynitride (SiON) is generated, and this S
The iON was deposited and adhered on the surface of the substrate 18, and the insulating film 24 made of SiON was formed on the surface of the substrate 18.

An aluminum electrode was formed on the insulating film 24 to produce an Al gate MIS capacitor. To evaluate the characteristics of this Al gate MIS capacitor, CV
(Capacitance-Voltage) characteristics were investigated.

By evaluating the CV characteristics, chemical bonds (eg, cutting of Si—O, Si—OH, etc.) at the interface between the base 18 made of a silicon semiconductor substrate and the insulating film 24, the base 18 and the insulating film 24 are formed. The generation of fixed charges and interface potential in the insulating film 24 due to movement (injection) of holes during the period can be evaluated.

FIG. 2 shows the CV characteristics of the insulating film 24 when the flow rate of ammonia gas was set to 0 sccm, 2 sccm, and 5 sccm without ammonia. The horizontal axis in FIG. 2 indicates the voltage applied to the gate electrode (unit:
Volts), and the vertical axis represents capacitance (relative value).

It is shown that as the gradient of the CV characteristic is gentler, more interface states are formed and more charges are trapped in the defects near the interface. Obtained C-
Since the V characteristic has a steep slope, it can be seen that the insulating film 24 obtained in this example is an insulating film with very few defects.

In the absence of ammonia gas, the curve of the CV characteristic was largely shifted to the minus gate electrode side, but the shift became small by introducing ammonia gas, and it was slight when the flow rate was 5 sccm. However, a shift to the positive side was observed. Ammonia is SiO
It shows that the positive charge trap level density can be controlled by the amount of ammonia by reacting with SiON to form SiON.

When an insulating film was formed in the same manner by using nitrogen gas instead of the ammonia gas used in the above-mentioned embodiment, the same result (the negative shift is reduced) was obtained for the CV characteristic. It was

In the above-mentioned embodiment, an example in which an insulating film made of silicon oxynitride (SiON) is formed by using silicon oxide (SiO) as a silicon raw material, silicon (Si) is used as a silicon raw material. Even when an insulating film made of silicon nitride (SiN) is formed, it is possible to form an insulating film having similar characteristics.

Although the above-described embodiment is an example using a gas containing nitrogen in a molecular state, an insulating film can be formed by a similar reaction using nitrogen in an atomic or ionic state. An example is shown below.

FIG. 3 shows a schematic cross-sectional view of another example of a film forming apparatus used in the method for producing an insulating film of the present invention. Also in this case, a container 13 for holding the raw material 14 in the chamber 10, for example, a lid 16 of the container 13 made of Ta boat, Ta or the like, a vacuum pump 15, a heating means 12 for heating the raw material 14 by a heater or the like.
And a plasma generating means 30 by applying, for example, RF (Radio Frequency) harmonics or microwaves is provided and connected in front of the inlet 22 for introducing nitrogen gas.

Also in this case, the inside of the chamber 10 is evacuated by the vacuum pump 15 as in the first embodiment.

The degree of vacuum in the chamber 10 is 1 × 10 ⁻⁶ to
At the time of rr, an electric current was passed through the container 13 or the Ta boat to heat the SiO 2 as the raw material 14. First, heating is performed to the extent that SiO does not evaporate, and water (H ₂ O) adsorbed on the SiO powder is heated.
And so on. Thereafter, the container 13, that is, the Ta boat was once cooled, and then an electric current was supplied to the container 13 again while introducing nitrogen gas from the inlet 22. At this time, the nitrogen gas is applied with microwaves or RF harmonics in the plasma generating means 30 before being introduced from the introduction port 22, and is decomposed by the generated plasma to become nitrogen atoms or nitrogen ions.

This nitrogen atom or nitrogen ion was introduced into the chamber 10 and reacted with SiO to form a SiON film on the substrate 18.

Also in this embodiment, the raw material is silicon Si
Alternatively, the SiN film may be formed by using.

In the above-mentioned embodiment, the resistance heating heater is used as the heating means 12, but other heating methods can be adopted.

For example, as shown in FIG. 4 which is a schematic sectional view of an example of the film forming apparatus, a laser beam 26 can be used as a heating means for the raw material 14. By the laser beam,
Since only Si or SiO of the raw material 14 can be locally heated, the raw material 14 can be evaporated without mixing impurities.

Further, as shown in a schematic sectional view of an example of the film forming apparatus in FIG. 5, the container 13 for containing the raw material 14 is, for example, a ceramic boat, and a heating means 28 for heating by high frequency induction heating is provided on the container 13. You can also in this case,
Container 1 made of ceramic boat by high frequency induction heating
3 is heated to evaporate the raw material 14. Since the ceramic boat is used as the container 13, the metal impurities do not evaporate, and the insulating film can be formed without mixing the metal impurities.

Further, as shown in FIG. 6 which is a schematic sectional view of an example of a film forming apparatus, a heating means 29 such as a heater is provided on the substrate 18, and the substrate 18 is heated by the heating means 29 before the insulating film is deposited. The gas adsorbed on the substrate 18 can be removed by heating. At this time, since the temperature of the base 18 is raised to form the insulating film, a stronger insulating film can be formed.

The film forming apparatus used for forming the insulating film of the present invention is not limited to the above-mentioned embodiment, and various other structures can be adopted without departing from the scope of the present invention.

By the method of forming an insulating film according to the present invention,
Various semiconductor devices with excellent characteristics can be manufactured.

An example of a process of a thin film MIS transistor (TFT) made of polycrystalline silicon using the insulating film according to the present invention as a gate insulating film will be described with reference to the process chart shown in FIG.

First, as shown in the schematic cross-sectional view of FIG. 7A, an amorphous glass substrate 40 is entirely doped with an n-type or p-type impurity such as phosphorus (P) or boron (B). The high-quality silicon film 41d is formed by CVD (chemical vapor deposition) or the like. The amorphous silicon film 41d is pattern-etched to remove the channel formation portion of the MIS transistor to be finally obtained, and the amorphous silicon film 41 is formed over the entire surface including the inside of the removed portion.

Next, these amorphous silicon films 41 and 4 are formed.
1d is heated by, for example, XeCl excimer laser irradiation to crystallize the amorphous silicon films 41 and 41d, and the impurities are diffused from the impurity-doped film 41d to the silicon film 41 on the film 41d. As shown in FIG. 7B, the polycrystalline silicon film 42 and the doped polycrystalline silicon film 44 of the intrinsic semiconductor portion of the MIS transistor are formed. Next, the doped polycrystalline silicon film 44
Pattern-etching the SiN layer and covering it, as shown in FIG. 7C, as shown in FIG. 7C.
Alternatively, a SiON film is formed as the gate insulating film 48.

Subsequently, as shown in FIG. 7D, the source region 44 is formed of the impurity-doped polycrystalline silicon layer 44.
s and the gate insulating film 48 on the drain region 44d,
A contact hole is opened by etching, an Al film is formed over the entire surface by, for example, a vacuum evaporation method, and pattern etching is performed to form a source electrode 52 and a drain electrode 54.
At the same time, the gate electrode 56 is also formed to form a TFT made of polycrystalline silicon, that is, a MIS transistor.

In forming this MIS transistor,
As described above, since the density of positive charge trap levels in the gate insulating film made of SiN or SiON can be controlled by the flow rate of nitrogen during film formation, a transistor with a low threshold voltage can be manufactured. Further, since the SiN film and the SiON film have a dielectric constant larger than that of SiO ₂ , a transistor having a large drain current can be manufactured.

The above-mentioned embodiment is an example applied to the gate insulating film of the polycrystalline silicon TFT type MIS transistor, but the application of the present invention is not limited to this.
The present invention can be applied to a bulk MIS transistor made of single crystal silicon, a top gate and bottom gate insulating film of an amorphous silicon TFT, an interlayer insulating film, and the like.

Further, SiN formed by the method of the present invention
Alternatively, the SiON film has excellent environmental resistance and is formed at a low temperature, and since plasma or the like is not formed, damage to the surface to be formed can be avoided. Therefore, according to the method of the present invention, a protective insulating film covering the surface of various semiconductor devices can be formed. For example, as shown in the cross-sectional view of FIG. 8, a second conductivity type impurity diffusion layer 51 is formed on a first conductivity type semiconductor substrate 50, and the insulating film 5 is covered therewith.
2 is formed, and the gate electrode 55 is formed on the insulating film between the source electrode 53 and the drain electrode 54 and the source electrode 53 and the drain electrode 54 in the opening of the insulating film 52 on the impurity diffusion layer 51, respectively. In the field effect transistor of, the insulating film 52 and the electrodes 53, 54, 55
It is effective to use it as the protective insulating film 56 formed so as to cover the.

Alternatively, as shown in the sectional view of FIG.
A second conductivity type collector region C, a first conductivity type base region B, and a second conductivity type high-concentration impurity diffused emitter region E are formed on a conductivity type semiconductor substrate 60, and are formed on the respective regions. In the bipolar transistor having the collector electrode 61, the base electrode 62, and the emitter electrode 63 formed thereon, it is effective to use it as the protective insulating film 64 covering the surface of the semiconductor substrate 60.

Further, as shown in the sectional view of FIG.
The second conductivity type impurity diffusion layer 7 is formed on the conductivity type semiconductor substrate 70.
It can also be used as a protective insulating film 73 on the outside of the solar cell 80 in which 1 is formed to form a photodiode PD and a plurality of electrodes 72 are provided on both sides thereof.

The above-described embodiments are only examples of the present invention, and various other configurations can be adopted without departing from the scope of the present invention.

[0058]

According to the above-described method for forming an insulating film of the present invention, an insulating film having the same characteristics as an oxide insulating film by thermal oxidation can be formed without a low temperature process and generation of high energy particles. Can be achieved with low damage. Since damage to the surface on which the insulating film is formed is avoided in this way, good insulating film / semiconductor interface characteristics can be realized, for example, when forming an insulating film on a semiconductor. Further, the insulating film can be formed by a simple process and without any processing on the surface to be formed. Therefore, an insulating film suitable for manufacturing various semiconductor elements can be obtained.

Since the film can be formed even at a low temperature, the insulating film can be formed on a substrate having no heat resistance, for example, a glass substrate.

Further, the semiconductor device using the insulating film according to the present invention as the protective film exhibits excellent environment resistance, and thus can be a device with stable operation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an apparatus for forming an insulating film according to the present invention.

FIG. 2 is a sectional view showing another example of an apparatus for forming an insulating film according to the present invention.

FIG. 3 is a sectional view showing another example of an apparatus for forming an insulating film according to the present invention.

FIG. 4 is a sectional view showing another example of an apparatus for forming an insulating film according to the present invention.

FIG. 5 is a cross-sectional view showing another example of an apparatus for forming an insulating film according to the present invention.

FIG. 6 is a sectional view showing another example of an apparatus for forming an insulating film according to the present invention.

7A to 7D are process diagrams showing a method of manufacturing a polycrystalline silicon thin film transistor using the method for forming an insulating film according to the present invention.

FIG. 8 is a cross-sectional view of an example of an element having an insulating film formed according to the present invention. This is an example used for a field effect transistor.

FIG. 9 is a cross-sectional view of another example of an element having an insulating film formed according to the present invention. This is an example used for a bipolar transistor.

FIG. 10 is a cross-sectional view of another example of an element having an insulating film formed according to the present invention. This is an example used for a solar cell.

[Explanation of symbols]

 10 Chamber 12, 26, 28, 29 Heating Means 13 Container 14 Raw Material 15 Vacuum Pump 16 Lid 18 Base 20 Shutter 21 MFC 22 Inlet 23 Deposition Rate Measuring Device 24 Insulating Film 30 Plasma Generating Means 41 Amorphous Silicon Film 41d Amorphous Silicon film (impurity doped) 42 polycrystalline silicon film 44 polycrystalline silicon film 48 gate insulating film 50, 60, 70 semiconductor substrate 51, 71 impurity diffusion layer 52 insulating film 53 source electrode 54 drain electrode 55 gate electrode 56, 64, 73 Protective Insulating Film 61 Collector Electrode 62 Base Electrode 63 Emitter Electrode 72 Electrode 80 Solar Cell

Claims (10)

[Claims] 1. A first step of heating and evaporating silicon or silicon monooxide, and a gas containing nitrogen is introduced to cause silicon or silicon monooxide evaporated in the first step to undergo a gas phase reaction with nitrogen. A method of forming an insulating film, which comprises forming an insulating film of silicon nitride or silicon oxynitride on a formation surface in the second step. 2. The method for forming an insulating film according to claim 1, wherein the concentration ratio O / Si of oxygen to silicon in the heat-vaporized silicon or silicon monooxide is selected to be 0 to 1.8. . 3. The method for forming an insulating film according to claim 1, wherein the pressure of the gas containing nitrogen in the second step is selected to be 10 ⁻⁵ to 10 ⁻² torr. 4. The method for forming an insulating film according to claim 1, wherein the temperature of the surface on which the insulating film is formed is selected to be 0 to 900 ° C. 5. The method for forming an insulating film according to claim 1, wherein ammonia and nitrogen gas are used as a supply source of the gas containing nitrogen in the second step. 6. The method for forming an insulating film according to claim 3, wherein ammonia and nitrogen gas are used as a supply source of the gas containing nitrogen in the second step. 7. Atomic state nitrogen is used as the nitrogen-containing gas in the second step.
The method for forming an insulating film as described in 1. 8. The atomic state nitrogen is used as the nitrogen-containing gas in the second step.
The method for forming an insulating film as described in 1. 9. The insulating film according to claim 1, wherein the partial pressure ratio (O / N) of oxygen and nitrogen in the gas containing nitrogen in the second step is selected to be 0 to 2. Forming method. 10. The insulating film according to claim 3, wherein the partial pressure ratio (O / N) of oxygen and nitrogen in the gas containing nitrogen in the second step is selected to be 0 to 2. Forming method.