JPH04255223A - Formation method of insulating film - Google Patents

Abstract

PURPOSE:To form a fine oxide insulating film with few defects. CONSTITUTION:A silicon substrate 12 preoxidation-cleaned up is arranged in a reaction furnace 14. Next, H2 gas as a reducing gas led in the reaction furnace 14 is RF plasma discharged to remove a natural oxide film and impurities on the substrate 12. Next, O2 gas as an oxidizing gas is led in the reaction furnace 14 while holding the substrate in the reaction furnace 14 as it is so that the O2 gas may be RF discharged to form a thermal oxide film on the substrate 12. At this time, the substrate 12 is heated by an infrared ray lamp 18. On the other hand, since the O2 gas is activated by the RF plasma discharging step while heating the substrate 12 by infrared ray irradiation so as to efficiently accelerate the reaction between the substrate constituent Si and the oxide gas component atom O, the uncoupled bond of substrate constituent Si can be reduced thereby enabling said purpose to be attained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating film.

0002

[Prior Art] Silicon integrated circuits formed using cutting-edge technology, especially MOS (Metal Oxide S)
In semiconductors, an extremely thin oxide film is used as the gate oxide film. In particular, 1.0 μm
In a submicron MOS device having a gate length of the following, an oxide film having a film thickness of, for example, 100 Angstroms or less is used, and by reducing the film thickness in this way, the gain is improved. An example of a conventional method for forming an oxide film is the one disclosed in the document: "MOSLSI Manufacturing Technology, Edited by Iwao Tokuyama and Tetsuichi Hashimoto, Nikkei McGraw-Hill, 1985, p. 65."

[0003] In the method disclosed in this document, first,
The cleaned substrate is placed in a quartz tube heated to 800 to 1200° C. in an electric furnace. Thereafter, an oxidizing gas for forming an oxide film is introduced into the quartz tube. As the oxidizing gas, for example, dry oxygen gas, a mixed gas of oxygen and hydrogen, a gas obtained by atomizing hydrochloric acid and mixing it with oxygen gas, etc. are used. By leaving the substrate in the quartz tube for a time and temperature appropriate to the desired thickness of the oxide film, an oxide film with a uniform thickness is formed on the surface of the substrate.

0004

[Problems to be Solved by the Invention] However, in the method disclosed in the above-mentioned literature, the film thickness is 100A°.
When forming the following thin oxide film, it was difficult to control the film thickness. Therefore, when forming a thin oxide film as described above, a method of heating the quartz tube to 800°C or less (hereinafter referred to as
A method of diluting oxygen gas with nitrogen gas to reduce the oxidation rate (hereinafter referred to as a diluted oxidation method) must be used.

However, when forming a silicon oxide film on a silicon substrate, the low temperature oxidation method has the disadvantage that the interface between the substrate and the oxide film becomes rough. Furthermore, the dilute oxidation method has the disadvantage that nitrogen segregates at the interface between the substrate and the oxide film, resulting in generation of new, undesired interface levels. Furthermore, with both low-temperature oxidation and diluted oxidation methods, it is difficult to obtain a dense oxide film, and unpaired bonds of silicon atoms and distorted Si-O-Si bonds, for example, occur at the interface between the substrate and the oxide film and in the oxide film. Since there are a lot of them, there is a drawback that the interface level becomes high. Therefore, if a gate insulating film of a MOS type field effect transistor is formed by a low temperature oxidation method or a diluted oxidation method, various problems arise due to these defects.

For example, a fine MO with a gate length of 1 μm or less
In an S-type field effect transistor, when hot electrons generated in the channel region enter the gate oxide film, they cause unpaired bonds between silicon atoms in the oxide film and distorted Si-
The O--Si bond traps these hot electrons, and this trap generates a new interface level. As a result, there are problems in that the threshold voltage of the MOS field effect transistor fluctuates and the transfer conductance decreases. In addition, when performing a breakdown voltage test on a MOS field effect transistor, it is found that dangling bonds between silicon atoms and strained Si
There is a problem in that the -O--Si bond is broken and a new interface level is generated in the gate oxide film, resulting in dielectric breakdown in the field effect transistor.

SUMMARY OF THE INVENTION An object of the present invention is to provide an insulating film forming method that solves the above-mentioned conventional problems and can form an insulating film with better film quality than the conventional method.

[0008]

[Means for Solving the Problem] In order to achieve this object, the insulating film forming method of the present invention includes a step of introducing a substrate cleaning gas into a reactor in which a substrate is installed, and a step of introducing a substrate cleaning gas into a reactor in which a substrate is installed. a step of cleaning the substrate by plasma discharge;
The method includes a step of introducing an insulating film forming gas into the reactor while holding the cleaned substrate in the reactor, and a step of forming an insulating film on the substrate while RF discharging the insulating film forming gas. Features.

[0009]

[Operation] According to such a forming method, a substrate cleaning gas is introduced into a reactor in which a substrate is installed, and the substrate is cleaned by RF plasma discharge of this gas. Then, an insulating film forming gas is introduced into the reactor while the cleaned substrate is held in the reactor, and an insulating film is formed on the substrate while causing RF plasma discharge of this gas.

Therefore, since cleaning of the substrate and formation of the insulating film are performed continuously in the same reactor, the insulating film can be formed on the substrate in an extremely clean state.

[0011] Furthermore, since the insulating film forming gas is activated by RF plasma discharge, the reaction between the constituent atoms of the insulating film forming gas and the atoms constituting the substrate is promoted and carried out efficiently, resulting in dense and defect-free formation. It is possible to form an insulating film with less

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are merely shown schematically to the extent that the invention can be understood, and therefore the invention is not limited to the illustrated examples.

Referring to FIG. 1, an example of the structure of an insulating film forming apparatus suitable for carrying out the present invention will be described. FIG. 1 is a diagram schematically showing the overall configuration of an insulating film forming apparatus.

The insulating film forming apparatus 10 shown in FIG.
a reactor 14 in which a reactor 14 is installed, and an electrode section for plasma discharge consisting of a first electrode member 161 and a second electrode member 162 for RF plasma discharge of the substrate cleaning gas and oxidizing gas supplied into the reactor 14. 16, and a heating section 18 for heat-treating the substrate 12 placed in the reactor 14.

The reactor (heating furnace) 14 is composed of a main body 141 having a recess a and a lid member 142 having a recess b, and the lid member 142 is removably attached to the main body 141 via an airtight member 20, for example, a rubber packing. . When the inside of the reactor 14 is evacuated, the airtight maintaining member 20 is pressed and held between the main body 141 and the lid member 142, so that the inside of the reactor 14 can be kept airtight. For example, stainless steel is used as the material for forming the main body 14a and the lid member 14b.

The heating section 18 is composed of a lamp that emits infrared light. It consists of a film 161b.

Although the forming material and forming method are not limited, for example, a quartz plate is used as the transparent member 161a, In2O3 is laminated on the transparent member 161a by sputtering, and a transparent conductive layer consisting of an In2O3 layer with a layer thickness of about 10 μm is formed. A film 161b is formed. The material for forming the transparent conductive film 161b includes SnO2, Cd2SnO4, ZnO, and SnO.
2-Sb, In2O3-Sn, and any other suitable material suitable for RF discharge can be used. Further, as a method for forming the transparent conductive film 161b, an electron beam evaporation method, an ion beam sputtering method, a CVD method, or any other suitable method can be used.

A measuring device 26 for measuring the surface temperature of the substrate 12, for example, a device called an optical pyrometer, and a susceptor as a second electrode member 162 are provided at the bottom of the recess a of the main body 141. An insulator 22 is provided between the second electrode member 162 and the main body 141 to provide electrical insulation therebetween. Then, one side of the second electrode member 162 is inserted into the recess a which is inside the main body 141.
The other side of the second electrode member 162 is extended to the outside of the main body 141 , and this extended portion is electrically connected to the RF power source 24 .

Furthermore, the transparent member 161a is made of a transparent conductive film 161.
b faces the second electrode member 162, and the main body 1
41 in a detachable manner. Wiring is provided so that the transparent conductive film 161b and the RF power source 24 are electrically connected in this locked state.

A plurality of heating units 18, for example, tungsten-halogen lamps, are provided in the recess b of the lid member 142 so as to face the second electrode member 162. A first electrode member 16 through which infrared light passes between the heating section 18 and the second electrode member 162
1, the infrared light from the heating section 18 can reach the substrate 12 installed on the second electrode member 162.

By using a lamp that emits light in a wavelength range that can efficiently heat the substrate 12,
The substrate 12 can raise the substrate temperature to a set temperature (for example, 1100° C.) in a short time, and at the same time prevents the substrate temperature from becoming locally high or low, and removes the natural oxide film and impurities. The entire area can be heated almost evenly.

Further, in FIG. 1, reference numerals 28 and 32 indicate a vacuum evacuation means and a gas supply section installed for the insulating film forming apparatus 10.

These evacuation means 28 and gas supply section 3
Although the configuration of 2 is not limited to what will be described below, the evacuation means 28 is configured from, for example, a turbo molecular pump 281 and a rotary pump 282. The turbo molecular pump 281 is then connected to the reactor 14 via the pressure regulating valve 30, and the rotary pump 282 is further connected to the turbo molecular pump 281.

The gas supply unit 32 is also connected to, for example, a reducing gas source 321 that supplies a reducing gas as a substrate cleaning gas.
, an oxidizing gas source 322 that supplies an oxidizing gas used to form an insulating film, such as a thermal oxide film, on the substrate 12, and a source 322 for preventing the formation of a natural oxide film on the substrate 12 installed in the reactor 14. and an inert gas source 321 that supplies inert gas used for this purpose. These gas sources 321, 3
22 and 323 are connected to the inside of the reactor 14 through gas introduction pipes 34, valves 36a and 36d are provided between the reactor 14 and the reducing gas source 321, and
Valves 36b and 36d are provided between the reactor 14 and the oxidizing gas source 322, and a valve 36c is provided between the reactor 14 and the inert gas source 323. The valves 36a, 36b, and 36c are valves for opening and closing the respective gas introduction pipes, and the valve 36d is a valve for evacuating the inside of the reactor 34. Note that the inert gas source 323 may not be provided.

Next, referring to FIG. 1, an example of forming an insulating film, such as a thermal oxide film, using the above-mentioned insulating film forming apparatus 10 will be described.

First, a silicon substrate is prepared as the substrate 12, and pre-oxidation cleaning is performed as conventionally done. Note that the pre-oxidation cleaning does not necessarily have to be performed.

Next, the lid member 142 and the first electrode member 161
is removed from the main body 141, the substrate 12 is placed on the second electrode member 162, and the rear cover member 142 and the first electrode member 161 are sequentially attached to the main body 141.

In order to prevent the oxidation of the substrate 12 from proceeding in the reactor 14 (therefore, the formation of a natural oxide film in the reactor 14), the valve 36c is opened before the substrate 12 is installed. Then, an inert gas such as nitrogen gas is introduced into the reactor 14 in advance. At this time, in order to prevent reducing gas and oxidizing gas from being introduced into the reactor 14, the valve 3
6a and 36b are closed. Note that it is not necessary to introduce an inert gas.

After the lid member 142 and the first electrode member 161 have been attached, the introduction of the inert gas is stopped, and the exhaust means 28 is activated to evacuate the inside of the reactor 14. This evacuation is performed by closing the valves 36c and 36d, then operating the turbo molecular pump 281 and rotary pump 282, and gradually opening the pressure regulating valve 30. In order to improve the cleanliness inside the reactor 14, preferably 1×1
It is preferable to form a high vacuum of 0-6 Torr or less in the reactor 14.

After this evacuation, the valves 36a and 36
d and introduce a reducing gas such as hydrogen H2 gas into the reactor 14.
to be introduced within. At this time, since the natural oxide film on the substrate 12 and the impurities on the substrate 12 are removed in a reduced pressure state in the reactor 14, the inside of the reactor 14 into which the reducing gas has been introduced is brought into a reduced pressure state. Therefore, while introducing the reducing gas, the pressure regulating valve 30 is operated to adjust the degree of opening of the valve and the flow rate of the reducing gas. These adjustments are made so that the pressure inside the reactor 14 is, for example, about 1×10 −2 Torr. The gas flow rate is normally adjusted using a gas flow rate adjusting means (not shown) such as a flow meter.

Under this reduced pressure state, the RF power source 24 is turned on, and the RF power is set to about 150 W and the discharge time is about 10 minutes, so that the reducing gas is plasma-discharged. The natural oxide film on the substrate 12 is removed mainly by the reducing action of the reducing gas and the etching action by the reducing gas chemically activated by plasma discharge, and the substrate 12 is removed mainly by the etching action of the reducing gas. Carbon and other impurities adhering to the surface are removed. That is, the natural oxide film and impurities are removed by subjecting the reducing gas introduced into the reactor 14 to RF discharge.

Preferably, the heating unit 18 is used to heat the substrate 12 during this plasma discharge, and this heating can increase the amount of native oxide film and impurities removed per unit time.

Reaction products generated during removal of the native oxide film and impurities from the substrate are discharged to the outside of the reactor 14 because the pressure inside the reactor 14 is reduced.

[0034] In order to remove the native oxide film and impurities, a reducing gas is subjected to RF plasma discharge under arbitrary suitable conditions, and then the RF power source 24 is turned off. Then valve 36
A and 36d are closed to stop the introduction of reducing gas. Then, the pressure regulating valve 30 is gradually opened and the reactor 14 is
Evacuate the inside. Preferably, in order to improve the cleanliness inside the reactor 14, a high vacuum of 1×10 −6 Torr or less is preferably formed in the reactor 14 .

After performing this evacuation, the valve 36
b and 36d are opened to introduce an oxidizing gas such as oxygen O2 gas into the reactor 14. At this time, in order to form a thermal oxide film on the substrate 12 in a reduced pressure state in the reactor 14, the reactor 14 into which the oxidizing gas has been introduced is brought into a reduced pressure state. For this reason, the pressure regulating valve 30 is adjusted while introducing the oxidizing gas, and the flow rate of the oxidizing gas is also adjusted. These adjustments are made so that the pressure inside the reactor 14 is, for example, about 1×10 −2 Torr.

Under this reduced pressure state, the RF power source 24 is turned on, and the oxidizing gas is plasma-discharged with an RF power of about 40 W, for example. At or immediately after the start of the discharge, the heating section 18 is turned on to irradiate the substrate 12 with infrared light, thereby heating the substrate 12 to any suitable predetermined temperature. This heating is performed, for example, at a temperature increase rate of 100° C./sec, and while monitoring the substrate surface temperature with the measuring device 26, until the substrate surface temperature (set temperature) reaches 1000° C. and the board 12
about 20℃ while maintaining the substrate surface temperature at approximately 1000℃.
Heat for seconds. When heated in this way, the film thickness is 10
A thermal oxide film with a thickness of 0 to 300 A° (angstroms) can be formed.

The reaction products generated during the formation of the oxide film are removed from the reactor 14 because the pressure inside the reactor 14 is reduced. The RF discharge is stopped at the same time as or after the heating of the substrate is stopped. Further, by arbitrarily setting the gas flow rate of the oxidizing gas, the holding temperature of the substrate surface, the heating time of the substrate, and other heating conditions, it is possible to form an oxide film of any suitable thickness.

[0038] Also, after stopping heating and stopping RF discharge,
Stop introducing oxidizing gas. In order to prevent the oxide film from growing more than necessary, the oxidizing gas in the reactor 14 is replaced with an inert gas such as nitriding gas or nitrogen gas.

For this reason, after stopping heating and RF discharge, the valves 36b and 36d are closed to stop the introduction of oxidizing gas, and the pressure regulating valve 30 is opened to evacuate the inside of the reactor 14. This vacuum evacuation is carried out within the reactor 14 by 1×10-6
It is preferable to form a high vacuum of Torr or less. After this evacuation, the pressure regulating valve 30 is closed to stop the operation of the evacuation means 28, and then the valve 36c is opened to introduce an inert gas into the reactor 14, and the substrate 12 is placed in an inert state in the reactor 14. Hold in gas.

[0040] The surface temperature of the substrate 12 is room temperature (for example, 25°C).
), take out the substrate 12 into the atmosphere,
Post-processing may be performed. Note that it is preferable to hold the substrate 12 in an inert gas and wait for the substrate temperature to drop.
In this way, there is no need to wait for the substrate temperature to drop.

As mentioned above, in this embodiment, the substrate 1
A reducing gas is introduced into the reactor 14 in which the substrate 12 is installed, and the natural oxide film and impurities on the substrate 12 are removed by subjecting the reducing gas to RF plasma discharge. By cleaning the substrate 12 in the reactor 14 in this way, cleaning the substrate 12 and forming a thermal oxide film on the substrate 12 can be performed continuously in the same reactor 14. Therefore, an oxide film can be formed on the substrate 12 that is kept clean.

Furthermore, as mentioned above, in this embodiment, the inside of the reactor 14 was evacuated to a high vacuum or reduced in pressure in order to improve the cleanliness inside the reactor 14. There is a limit to the removal of impurities such as substances, and therefore some impurities remain in the reactor 14, albeit in a small amount. However, in this embodiment, since the oxide film is formed by oxidation by rapid heating, the probability that impurities remaining in the reactor 14 will contaminate the oxide film during the formation (growth) of the oxide film can be extremely reduced.

Therefore, a clean oxide film can be formed on the substrate 12 that is kept in a clean state, and therefore a highly reliable oxide film with few defects can be formed, for example, for gate oxidation of submicron MOS devices. A suitable oxide film can be formed using the film.

Further, in this embodiment, when forming a thermal oxide film, the oxidizing gas is activated by RF plasma discharge, and in parallel with this, the substrate 12 is heated by infrared irradiation. Therefore, the reaction between the substrate constituent atoms Si and the oxidizing gas component atoms O is promoted and carried out efficiently. As a result, the substrate constituent atoms S
It is possible to reduce the number of uncombined elements of i, so it is extremely dense (
The substrate 12 is an insulating film SiO2 with high density) and few defects.
can be formed into Furthermore, since the growth rate of the insulating film SiO2 can be increased, the insulating film SiO2 with a desired thickness can be formed in a shorter time.

[0045] In the above-mentioned embodiments, specific configurations, materials, and numerical conditions were cited and explained in order to deepen the understanding of the present invention, but these specific conditions are only examples, and the present invention is based on these specific conditions. It is not limited. Therefore, the structure, shape, arrangement position, dimensions, forming material, temperature, and other conditions of each component can be changed as desired.

[0046]

[Effects of the Invention] As is clear from the above explanation, according to the insulating film forming method of the present invention, a substrate cleaning gas is introduced into a reactor in which a substrate is installed, and this gas is subjected to RF plasma discharge. Clean the board. Then, an insulating film forming gas is introduced into the reactor while the cleaned substrate is held in the reactor, and an insulating film is formed on the substrate while causing RF plasma discharge of this gas.

Therefore, since cleaning of the substrate and formation of the insulating film are performed continuously in the same reactor, the insulating film can be formed on the substrate in an extremely clean state.

Furthermore, since the insulating film forming gas is activated by RF plasma discharge, the reaction between the constituent atoms of the insulating film forming gas and the atoms constituting the substrate is promoted and carried out efficiently, resulting in dense and defect-free formation. It is possible to form an insulating film with less

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a configuration example of an insulating film forming apparatus suitable for use in implementing the present invention.

[Explanation of symbols]

10: Insulating film forming device 12: Substrate 14: Reactor 16: Plasma discharge electrode part 18: Heating part 321: Reducing gas 322: Oxidizing gas

Claims (4)

[Claims] 1. A step of introducing a substrate cleaning gas into a reactor in which a substrate is installed, a step of cleaning the substrate by causing an RF plasma discharge in the substrate cleaning gas, and a step of introducing a substrate cleaning gas into a reactor in which the substrate is installed. An insulating film forming method comprising the steps of: introducing an insulating film forming gas into the reactor while the substrate is maintained at a temperature of Method. 2. The insulating film forming method according to claim 1, wherein the substrate cleaning gas is a reducing gas. 3. The insulating film forming method according to claim 1, wherein the insulating film forming gas is an oxidizing gas and a thermal oxide film is formed as the insulating film. 4. The insulating film forming method according to claim 1, wherein the insulating film is formed by heating the substrate with an infrared lamp.