JPS6333826A - Low pressure oxidizing apparatus - Google Patents

Abstract

PURPOSE:To form a uniform thickness oxide film in a surface with good controllability of the film by performing the thermal oxidation of a semiconductor wafer by feeding O2 gas sufficient for an oxidation under lower pressure than an atmospheric pressure from an O2 gas supplying mechanism with a flow meter into a furnace. CONSTITUTION:Gas sufficient for an oxidation is temporarily transferred to a gas tank 11 with a flow meter in response to the thickness of the film to be oxidized from an O2 gas cylinder 50, a plurality of wafers 51 set on a boat 52 are inserted into a furnace 21, the furnace is closed and with a cover 23. Then, the temperature of the furnace is raised to 1000 deg.C, and the furnace is evacuated by a pump 31 or the like. When the pressure (vacuum degree) in the furnace becomes sufficiently low, dry O2 gas is fed from the talk 11 through an O2 gas inlet tube 12, and the O2 gas pressure is matched to a predetermined value in the furnace by regulating the flow rate. The predetermined pressure is frequently approx. 0.1 atm as a standard. Simultaneously, O2 gas is fed from a gas tank 41 with a flow meter through an organic contaminant preventing O2 gas tube 42 to an exhaust tube 32, and an oxide film is completely formed after a predetermined time is elapsed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a low-pressure oxidation device for semiconductor wafers, and in particular to a device for forming a thin thermal oxide film with good uniformity and controllability. Used as manufacturing equipment.

(Prior Art) Semiconductor wafer oxidation technology is one of the main technologies for semiconductor device manufacturing. Among these, the dry (H2O-free) 02Fa conversion method is used for forming a thin and high quality oxide film such as a gate oxide film of an MO8 structure. This is a high-temperature oxidation furnace (furnace core tube) for silicon wafers.
In this process, a 5i02 film is formed on the wafer surface by reacting with oxygen gas (02 gas) that does not contain moisture.

Conventional methods include normal-pressure oxidation, in which the pressure of 02 gas in the furnace is approximately equal to atmospheric pressure, and high-pressure oxidation, in which the pressure of 02 gas is increased using a nearly sealed reaction tube. be. Among these, the normal pressure oxidation method is generally used. In this oxidizer, as schematically shown in FIG. 2, a certain amount of dry 02 gas 4 is supplied into the tube from the left end of the furnace core tube 1, which is regulated by a flow JLii2, a needle valve 3, etc. This 02 gas reacts with the silicon wafer 86 heated to about 000 DEG C. to 1200 DEG C. by the heater 5 to form a 5i02 film on its surface.

After this, the remaining 02 gas is released into the atmosphere. o
The supply of the two gases is continued until the end of oxidation. In the prior art, the thickness of the oxide film is controlled by controlling the wafer temperature, the oxidation time, the partial pressure of the 02 gas mixed with the carrier gas, etc.

(Problems to be Solved by the Invention) As devices become more integrated, the required thickness of the thermal oxide film becomes thinner. There are problems with thickness uniformity and controllability. On the other hand, the diameter of wafers has been increased in order to improve productivity, and as a result, the uniformity and controllability of the 7t' film have become increasingly difficult, which has become an important problem.

An object of the present invention is to provide a semiconductor wafer oxidation apparatus that can produce a thin oxide film on a semiconductor wafer with good controllability, and can produce a highly uniform oxide film with a film thickness that meets a target value and has small in-plane variations. The goal is to provide the following.

[Structure of the Invention] (Means for Solving the Problems) The present invention comprises: (a) a first O22 gas supply structure equipped with a flowmeter that supplies a certain amount of O2 gas sufficient for oxidizing semiconductor wafers; , (b) an oxidation furnace for thermally oxidizing the surface wafer in an O2 gas atmosphere of, for example, 0.5 atm to 0.0001 atm lower than atmospheric pressure; and (C) an oxidation furnace for thermally oxidizing the O2 gas in the oxidation furnace. Exhaust mechanism for maintaining low pressure, (d
) A second 02 gas supply mechanism that supplies 02 gas to the exhaust pipe of the exhaust mechanism to prevent contamination from the exhaust mechanism.

(Function) Thermal oxidation of semiconductor wafers is carried out at a pressure lower than atmospheric pressure.
By flowing sufficient 02 gas for oxidation into the furnace from the 02 gas supply mechanism with a flow meter, the oxide film can be formed with good controllability.
It can be formed to have a uniform film thickness within the surface. Generally 02
When the pressure of the gas is reduced from normal pressure, the force acting between molecules becomes negligible, and the 02 molecules begin to move without exerting any force on each other. As a result, the density and energy of O2 molecules reaching the wafer surface are almost independent of the wafer position, and it is presumed that in-plane uniformity of the oxide film can be obtained. Furthermore, in order to perform low-pressure oxidation, an exhaust mechanism is essential to maintain low pressure, but foreign matter with high vapor pressure in the exhaust mechanism can diffuse into the furnace.
Although the oxide film on the wafer is contaminated, it has been found through trials that contamination can be effectively prevented by flowing the 02 gas from the second 02 gas supply mechanism to the exhaust pipe of the exhaust mechanism.

(Example) An example of the present invention will be described with reference to the drawings. Fig. 1 is a schematic configuration diagram of a low-pressure oxidation apparatus of the present invention.

The first 02 gas supply mechanism 10 consists of a gas tank 11 with a flow meter, a gas inlet @ 12, and a needle valve for adjusting the flow rate, a filter, a dehydrator, etc. (not shown). The 02 gas inlet pipe 12 has a plurality of 02 gas outlets, so that the dry 02 gas flows uniformly to each wafer. The oxidation furnace 20 consists of a furnace 21, a heating and insulation wall surrounding the furnace 21 (indicated by dotted lines) in which a heater 22 is embedded in the inner wall, a furnace lid 23, and the like.

The exhaust mechanism 30 includes a vacuum pump (for example, an oil rotary pump) 3
It consists of 1, an exhaust pipe 32, a booster pump (not shown), and 1 to lap. The second 02 gas supply mechanism 40 includes a gas tank 41 with a flowmeter and a 02 gas tank 41 for preventing organic pollution.
□ Consists of gas introduction pipe 42, etc.

Next, a method of forming an oxide film on a wafer using this low pressure oxidation apparatus will be explained. maf02 gas cylinder 5
From 0, enough gas for oxidation is temporarily transferred to the gas tank 11 with a flow meter, depending on the thickness of the film desired to be oxidized. Next boat 52
A plurality of wafers 51 set in the wafers 51 are inserted into the tray 21, and the lid 23 of the furnace is closed. Next, increase the temperature of the furnace to 1000℃
At the same time, the inside of the furnace is evacuated using a pump 31 or the like.
When the pressure (degree of vacuum) in the furnace becomes sufficiently low, dry 02 gas is flowed from the gas tank 11 with a flow meter through the 02 gas inlet 12. 'a Adjust the 02 gas pressure in the furnace to a predetermined value by adjusting it etc. The predetermined pressure can be from 0.5 atm to o, oooi atm, but the standard pressure is 0.5 atm.
The pressure is often about 1 atm.

At the same time, 02 gas is caused to flow from the gas tank 41 with a flow meter to the exhaust pipe 32 via the 02 gas introduction pipe 42 for preventing pollution. After a predetermined period of time (for example, about one hour) has elapsed in this state, the oxide film formation is finished.

An example of the results of forming an oxide film on a wafer using the low-pressure oxidation apparatus of the present invention will be described. The target thickness of the oxide film on the wafer (the aim value of ilfrJ) is 350X and 45X.
Five pieces of wood (20 pieces in total) were oxidized under each condition using two methods: one using the apparatus of the present invention and the other using a conventional oxidation method for comparison. For each wafer, the film thickness was measured at five points within the plane, and the average I! ! J
The thickness and film variation (dispersion) were determined and the results are shown in Tables 1 and 2. Table 1 shows the case where the target film thickness is 350 mm. The total average film thickness was 319× in the conventional method and 346× in the method of the present invention, which is close to the target value of 350×.

Table 1 Table 2 The average value of variance is also smaller, 0.26 in the present invention, compared to 1.12 in the conventional method. Table 2 shows the case of oxidation with a target film thickness of 450 people, and the results are similar to those in Table 1, the total average film thickness in the present invention is close to the target value, and the average of the variance indicating the variation is also small.

Next, the effect of preventing organic pollution by flowing 02 gas into the exhaust pipe of the exhaust mechanism was investigated.

That is, an analysis of impurities in the film after the oxide film was formed was performed and compared between cases in which the 02 gas was flowed and cases in which the 02 gas was not flowed. The results are shown in FIG. 3, where Q indicates the case where 02 gas was flowed, and . is the case where it was not flowed. As is clear from this, it can be seen that the impurities of Na and C are significantly reduced by flowing 02 gas into the exhaust pipe in the low-pressure oxidation apparatus of the present invention.

Next, the amount of 02 gas used depending on the thickness of the oxide film was investigated in the case of forming an oxide film in the bag packaging of the present invention and in the conventional case. The curve connecting the O marks shown in FIG. 4 shows the results of the present invention, and the * marks show the results of the conventional method. By using the device of the present invention, the amount of gas used can be reduced compared to conventional methods.

[Effects of the Invention] In the low-pressure oxidation apparatus of the present invention, a certain amount of oxygen gas sufficient for oxidation is supplied under low pressure, unlike the conventional oxidation method that uses a large amount of 02 gas at high pressure or normal pressure. By flowing,
As seen in the examples above (see Tables 1 and 2)
It is possible to obtain an oxide film with good controllability and a uniform in-plane thickness.

Furthermore, by flowing 02 gas through the exhaust pipe, organic contamination from the exhaust mechanism can be effectively reduced and a high-quality oxide film can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the low-pressure oxidation equipment of the present invention, Figure 2
This figure is a schematic diagram of a conventional atmospheric pressure oxidation apparatus, FIG. 3 is a diagram showing the effect of reducing organic contamination, and FIG. 4 is a diagram showing the relationship between the use of 02 gas and the film thickness. 10...First 02 gas supply mechanism, 11...Flow■
Gas tank with meter, 20... Oxidation furnace, 30...
Exhaust mechanism, 32... Exhaust pipe, 40... Second 0
2 gas supply structure, 51...semiconductor wafer. 21 Door 1 Flash C (atoms/cc) Figure 3 Oxidation 4 (A) Figure 4

Claims (1)

[Claims] 1 A first oxygen gas supply mechanism equipped with a flow meter that supplies a certain amount of oxygen gas sufficient to oxidize the semiconductor wafer surface to the oxidation furnace; an oxidation furnace for thermal oxidation; an exhaust mechanism for maintaining the pressure of the atmosphere in the oxidation furnace at the predetermined pressure; and an exhaust pipe of the exhaust mechanism for reducing contaminants flowing into the oxidation furnace from the exhaust mechanism. A low-pressure oxidation apparatus for semiconductor wafers, comprising a second oxygen gas supply mechanism that supplies oxygen gas.