JP3194062B2 - Method of forming thermal oxide film - Google Patents

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 a thermal oxide film, and more particularly to a method for manufacturing a gate and capacitor insulating film, in which an oxide thin film is formed on a surface of a substrate to be processed, which is a semiconductor substrate, by an oxidation method. The present invention relates to a method for forming a thermal oxide film for forming a film.

[0002]

2. Description of the Related Art Conventionally, a thermal oxidation method has been adopted as a method for forming an oxide film on the surface of a substrate to be processed (also referred to as a wafer or a work) which is a semiconductor substrate. This is a method in which the substrate to be processed is heated at a temperature of about 1000 ° C. in an oxidizing atmosphere to oxidize the surface of the substrate to be processed, and has an advantage that an oxide film having good film quality can be obtained.

In recent years, as semiconductors have become more highly integrated, it has become necessary to reduce the thickness of an oxide film formed on the surface of a substrate to be processed, and film forming conditions have become stricter.

As an apparatus for forming a thin film by an oxidation method or a CVD (Chemical Vapor Deposition) method capable of coping with such severe film formation conditions, the present applicant has previously disclosed in Japanese Patent Laid-Open No.
In Japanese Patent Application Laid-Open No. 3-241936, a substrate to be processed such as a Si wafer or a Ga-As wafer is placed and sealed in a process tube through an outlet on one side, and the surface of the substrate to be processed is filled with a gas introduced into the process tube. A substrate to be processed into a process tube provided with a gas inlet and a vacuum exhaust port in front of the outlet and a means for physically cleaning the substrate to be processed, wherein a thin film is formed by chemically reacting the components. We have proposed a furnace for oxidation and CVD, in which a closed chamber for insertion and removal of a gas is connected. Then, the substrate to be processed, such as a Si wafer, placed in a quartz boat at an interval in a laminated manner into the process tube is inserted into and taken out of the process tube through a sealed chamber. A reaction gas such as SiH _{4 is} introduced from a gas inlet while heating the processing substrate, and a thin film, ie, CVD, on the surface of the processing target substrate by a chemical reaction of the reaction gas.
A thin film is formed by the method.

FIG. 2 shows an example of a sequence (system) for forming an oxide film on the surface of a substrate to be processed by the above apparatus.
It will be described according to. First, after loading a substrate to be processed, which is placed in a stacked state at an interval on a boat, into a closed chamber,
The sealed chamber by a vacuum pumping system for example 1 × 10 ^{- 4} Pa
Evacuate to a degree (step 1). Subsequently, the boat is transported into the process tube, that is, moved (step 2). The inside of the process tube is always 1 × 10
^- are evacuated to about ⁴ Pa, also, for example, 80
It is kept at a temperature of 0 ° C. After the substrate to be processed is transported into the process tube, the temperature raised to, for example, 1000 ° C. in the process tube and (Process 3), after a certain time Maho lifting said temperature (Process 4), the process tube to Oxidation treatment (process 5) is performed by introducing oxygen.
Further, an annealing process (process 6) is performed on the substrate to be processed for a predetermined time. Thereafter, the temperature in the process tube is lowered to, for example, 800 ° C. (Step 7), and the boat is transferred from the process tube into the closed chamber, that is, moved (Step 8). The pressure is restored (step 9), and the substrate to be processed is carried out of the closed chamber together with the boat.

[0006]

However, when the surface of the substrate to be processed is oxidized in the above-mentioned sequence (system), the surface of the substrate to be processed is naturally oxidized at a high temperature until the thermal oxidation treatment of the surface of the substrate and in a vacuum state. There has been a problem that the surface of the substrate to be processed is roughened due to a phenomenon such as a reaction between the oxide film and the substrate to be processed or a reaction between the substrate and the remaining trace impurities in the process tube.

Further, there is a problem that this surface roughening phenomenon occurs not only in a vacuum state but also in an atmosphere of an inert gas such as argon (Ar) or nitrogen (N ₂ ) at a high temperature.

It is an object of the present invention to provide a method for forming a thermal oxide film capable of forming an oxide thin film without solving the above problems and without causing the surface of the substrate to be processed to be rough.

[0009]

According to the present invention, there is provided a method for forming a thermal oxide film, comprising a furnace for oxidizing a substrate to be processed, and a preliminary exhaust chamber connected to the furnace. In a method in which the substrate to be processed is moved from the preliminary exhaust chamber into the furnace while the exhaust chamber is in a reduced-pressure atmosphere, and the substrate is oxidized in the furnace to form a thermal oxide film on the surface of the substrate to be processed, During the process, the oxygen gas is brought to a partial pressure of 10 ^-1 to 10 ^-3 Pa.
Characterized in that it contains the step of maintaining the reduced pressure atmosphere introduced into so that.

[0010]

By maintaining the substrate to be processed under a reduced pressure in a trace oxygen atmosphere, an extremely thin oxide film of several atomic layers grows on the surface of the substrate to be processed. The ultra-thin oxide film prevents the reaction and the roughening of the impurity carbon on the surface of the substrate to be processed with the silicon of the substrate.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for forming a thermal oxide film according to the present invention includes the steps of loading, transporting (moving), unloading, heating, cooling, and temperature stabilization.
Mainly, in the process before and after the thermal oxidation, the process is performed in a vacuum atmosphere by flowing a trace amount of oxygen, for example, about 30 SCCM, in the preliminary exhaust chamber and the furnace of the apparatus.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. In the figure, reference numeral 1 denotes a load-lock type vertical furnace.

The load-lock type vertical furnace 1 comprises a pre-evacuation chamber 2 made of a stainless steel chamber and a furnace 3 made of a quartz tube, and a gate valve 4 connects the pre-evacuation chamber 2 and the furnace 3 to each other. The partition, the atmosphere in the preliminary exhaust chamber 2 and the atmosphere in the furnace 3 can be separated from each other.

A valve 6 is connected to an external vacuum pump or other vacuum exhaust system 5 in order to make the inside of the preliminary exhaust chamber 2 have a predetermined degree of vacuum.
And a gas introduction pipe 7 for introducing, for example, nitrogen (N ₂ ) gas into the preliminary exhaust chamber 2.

In order to make the inside of the furnace 3 a predetermined vacuum, a valve 9 is connected to an external vacuum pump or other vacuum exhaust system 8.
And a gas introduction pipe 10 for introducing, for example, oxygen (O ₂ ) gas into the furnace 3 and a gas introduction pipe 11 for introducing, for example, nitrogen (N ₂ ) gas. Further, a heater 12 made of, for example, a Kanthal wire is arranged outside the furnace 3 to heat the inside of the furnace 3.

After a substrate to be processed 14 such as a Si wafer is placed in layers on a quartz boat 13 at regular intervals, the substrate 14 is loaded into the pre-evacuation chamber 2 and is rotatable so as to advance and retreat. Placed on a freely movable table 15 so that the movable table 15 can be further loaded into the furnace 3 from the preliminary exhaust chamber 2;
Further, after the oxide film is formed on the surface of the substrate to be processed 14, it is carried out from the furnace 3 into the preliminary exhaust chamber 2, and furthermore, can be carried out from the preliminary exhaust chamber 2.

In the drawing, reference numeral 16 denotes an entrance for taking the substrate 14 into and out of the preliminary exhaust chamber 2, and 17 denotes a door for closing the entrance 16.

Next, specific examples of the present invention will be described together with comparative examples.

Embodiment 1 A case where an oxide film is formed on the surface of a substrate 14 to be processed using the load-lock type vertical furnace 1 having the above-described configuration will be described with reference to FIG.

First, a substrate 14 to be processed, which is placed on a quartz boat 13 in a layered manner at a predetermined interval, is carried into the preliminary exhaust chamber 2 from outside the preliminary exhaust chamber 2 through the entrance 16. 1 is placed on the moving table 15 as indicated by the phantom line, and the door 17
After sealing the doorway 16 closed, the vacuum degree of the pre-evacuation chamber 2 1 × 10 in an evacuation system 5 ^- it was set to ³ Pa (Step 1).

Next, opens the gate valve 4, the degree of vacuum 1 × 10 advance evacuation system 8 ^- is maintained at ⁴ Pa, a heater 1
The substrate to be processed 14 is moved into the furnace 3 in which the temperature is set to 800 ° C. in FIG.
After carrying in (step 2) as shown by the solid line, the gate valve 4 was closed.

[0023] At this time, oxygen (O ₂₎ from the gas introducing pipe 10 into the furnace 3 partial pressure 10 of the gas ^{- 1-10 -} introduced so that ³ Pa, the inside of the furnace 3 to a vacuum of trace oxygen atmosphere A very thin oxide film having a minimum thickness of, for example, about 1 to 2 atoms is grown on the surface of the substrate 14 to be processed. This is to prevent the reaction between the substrate 14 and residual impurities such as carbon remaining in the furnace 3 by intentionally growing an extremely thin oxide film on the surface of the substrate 14.

Subsequently, the inside of the furnace 3 is heated by the heater 12 at a heating rate of 8 ° C./min to reduce the temperature of the substrate 14 to be treated to 100 ° C.
The temperature was raised to 0 ° C. (Step 3), and the temperature was maintained for 40 minutes to stabilize the temperature of the substrate 14 (Step 4). During the steps 3 and 4, as in the case of the step 2, a predetermined oxygen partial pressure was introduced into the furnace 3 to prevent the reaction, and the inside of the furnace 3 was maintained at a reduced pressure atmosphere of a trace amount of oxygen.

Next, oxygen (O ₂ ) gas is supplied into the furnace 3 through the gas introduction pipe 10 at a flow rate of 2 for the oxidation treatment of the substrate 14 to be processed.
Oxidation was performed at 0 slm, and while maintaining that state for 1 minute, a thermal oxide film having a thickness of 6 nm was formed on the surface of the substrate to be processed 14 (step 5). During the oxidation treatment (step 5), the pressure in the furnace 3 was maintained at the atmospheric pressure.

Further, while maintaining the substrate 14 at the same temperature for 15 minutes, nitrogen (N ₂ ) gas is introduced into the furnace 3 at the same flow rate to remove the thermal oxide film formed on the surface of the substrate 14. after annealing (step 6), the heating was stopped by the heater 12, the inside of the furnace 3 is an oxygen partial pressure of 10 ^{- 1} ~10 ^{- 3} P
The pressure in the trace oxygen atmosphere of a was reduced, and the temperature in the furnace 3 was lowered to 800 ° C. at a rate of 4 ° C./min (step 7). During the cooling (Step 7), the pressure in the furnace 3 was maintained at the same pressure as during the heating (Step 3).

Subsequently, the gate valve 4 is opened, and the boat 13 in the furnace 3 is carried out into the preliminary exhaust chamber 2 by retreating the moving table 15 as shown by the phantom line in FIG. 1 (step 8). , Gate valve 4
Was closed and the introduction of trace oxygen into the furnace 3 was immediately stopped.

Next, nitrogen (N ₂ ) gas is introduced into the pre-evacuation chamber 2 from the gas introduction pipe 7, and the pressure in the pre-evacuation chamber 2 is restored to the atmospheric pressure (step 9). 15
After cooling to 0 ° C., the door 17 is opened, and the substrate to be processed 14 is moved together with the boat 13 through the entrance 16 into the preliminary exhaust chamber 2.
Removed from inside.

As described above, during step 2 to step 8, the pressure in a trace oxygen atmosphere is reduced, so that the surface of the substrate 14 is covered with oxygen during each step, and the substrate to be processed is Since it does not react with impurities as in the prior art, a high-quality oxide film without roughness is formed on the surface of the substrate to be processed.

The substrate to be processed 14 manufactured in the above steps
A withstand voltage test of the current-voltage characteristics of the thermal oxide film formed on the surface was performed, and the result is shown as a curve A in FIG.

The withstand voltage test was carried out when the substrate to be processed was a P-type substrate, the surface orientation (100) was mirror-finished with a specific resistance of 1 to 10 Ωcm, and the thickness of the thermal oxide film was 6 nm.

Comparative Example 1 A substrate to be processed was produced in the same manner as in Example 1 except that the atmosphere in Steps 2, 3, 4, 6, 7, and 8 was changed to a reduced pressure state without trace oxygen. A thermal oxide film was formed on the surface of.

Then, a withstand voltage test of the current-voltage characteristics of the thermal oxide film formed on the surface of the substrate to be processed manufactured by the conventional method was performed under the same conditions as in the first embodiment, and the results are shown in FIG. As shown.

As is apparent from FIG. 3, in the case of the first embodiment of the present invention, the leak current starts to increase (rise) when the applied voltage is 8 MV / cm, whereas in the case of the first comparative example,
When the applied voltage was about 7 MV / cm, the leak current started to increase. As a result, it was confirmed that the insulating property of the surface of the substrate to be processed was improved in the method of the present invention.

In the first embodiment, the depressurized state of the trace oxygen atmosphere is set in the steps 2 to 8. However, the present invention is not limited to this. Depending on the degree of vacuum in the furnace, the degree of vacuum in the furnace 3 and the like, the reduced pressure state of the trace oxygen atmosphere may be localized in the steps 3 to 6.

In the first embodiment, the atmosphere in the furnace 3 is only oxygen during the oxidation process (step 5). However, the present invention is not limited to this. An atmosphere in which N ₂ ) gas, hydrogen (H ₂ ) gas, and halogen gas are added at about 1 to 95 at% to oxygen gas may be used.

In addition, the method of the present invention is not limited to the formation of a thermal oxide film on the surface of a substrate to be processed.
Oxidation) and the like, a protective effect on the surface of the substrate to be processed can be obtained in the same manner as described above even when used in a film forming process of a CVD oxide film or a silicon nitride film.

[0038]

According to the method for forming a thermal oxide film of the present invention, the steps of transporting, raising and lowering the temperature other than the step of oxidizing the substrate to be processed are performed under reduced pressure in a trace oxygen atmosphere. As a result, the surface of the substrate to be processed is protected by an ultra-thin oxide film of about several atomic layers grown by a trace amount of oxygen, and a high-quality and stable thermal oxide film can be formed on the surface of the substrate to be processed. effective.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of one example of an apparatus for performing a method for forming a thermal oxide film of the present invention;

FIG. 2 is a process chart showing one example of a method for forming a thermal oxide film of the present invention;

FIG. 3 is a characteristic diagram showing a relationship between a leak current of a thermal oxide film and an applied voltage in an example of the present invention and a comparative example.

[Explanation of symbols]

2 Preliminary exhaust chamber, 3 Furnace, 4 Gate valve, 5, 8 Vacuum exhaust system, 10, 11
Gas inlet pipe, 12 heater, 14
Substrate to be processed.

Continued on the front page (72) Inventor Kafumi Ota 523 Yokota, Yamatake-cho, Yamatake-gun, Chiba Pref. Japan Vacuum Engineering Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 8 / 12,16 / 44 H01L 21 / 31,21 / 316

Claims (1)

(57) [Claims] An apparatus comprising a furnace for oxidizing a substrate to be processed and a preliminary exhaust chamber connected to the furnace, wherein the substrate to be processed is preliminarily kept in a state where the furnace and the preliminary exhaust chamber are in a reduced pressure atmosphere. In the method of moving from the exhaust chamber into the furnace and performing oxidation treatment in the furnace to form a thermal oxide film on the surface of the substrate to be processed, the oxygen gas is subjected to a partial pressure of 10 ^-1 to 10 ^-3 during a process other than the oxidation process. P
a method for forming a thermal oxide film, the method including a step of maintaining a reduced-pressure atmosphere introduced so as to be a .