JP2002025924A - Blank baking method of heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blank baking method of a heat treatment furnace whereby metallic contamination in a reaction tube of a heat treatment furnace can be reduced in an efficient and sufficient manner. SOLUTION: In this blank baking method of the heat treatment furnace having a reaction tube, oxidizing gas is supplied to the reaction tube of the heat treatment furnace to perform first heat treatment at 900 to 1350 deg.C, and then, non-oxidized gas is supplied thereto to perform second heat treatment at 900 to 1350 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for baking a heat treatment furnace having a reaction tube for heat treating a silicon wafer, and more particularly to a method for baking a heat treatment furnace capable of reducing metal contamination in a shorter time than conventional methods. Regarding the baking method.

[0002]

[Related Art] Generally, in a heat treatment furnace (diffusion furnace) used for heat treatment of a silicon wafer, a reaction tube (a quartz tube, a SiC tube, etc.) into which the wafer is introduced is exchanged, other members are exchanged, and a contaminated wafer is introduced. It is known that the level of metal contamination of the furnace deteriorates due to, for example, remodeling work and an irregular work such as a power failure. When a product wafer is heat-treated using a heat treatment furnace having a deteriorated level of metal contamination, the wafer is contaminated with metal, which causes a problem of deteriorating device characteristics to be manufactured.

Conventionally, as a method of reducing metal contamination in a heat treatment furnace, N ₂ , N ₂ , and N ₂ , after etching the surface of a reaction tube lightly using an HF-based chemical solution or without etching.
A method has been adopted in which baking (heat treatment without loading a wafer) is repeated at a high temperature while flowing a gas such as H ₂ , Ar, or O ₂ . However, it is empirically known that this method requires a great deal of time to recover the metal contamination level of the wafer.

[0004] In addition, the dry baking method described in Japanese Patent Application Laid-Open No. 5-144802 discloses a baking method using a cleaning gas of the same type as the process gas. This is a technique to discharge metal contaminants during baking. However, even if this technique is used, the metal contamination in the reaction tube is below an allowable level (for example, the contamination concentration of the heat-treated wafer is 2%).
(× 10 ¹⁰ atoms / cm ³ or less) still required a great deal of time.

[0005]

[Problems to be Solved by the Invention] As the allowable level of metal contamination required for future wafers becomes more and more severe,
In the conventional empty baking method, in addition to the problem that the time required for the empty baking is too long, the production throughput is reduced and the cost is inevitably increased, and in addition, there is a problem that the metal contamination level is not sufficiently reduced. Was.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of baking a heat treatment furnace that can efficiently and sufficiently reduce metal contamination of a reaction tube of the heat treatment furnace. Aim.

[0007]

In order to solve the above-mentioned problems, the present invention comprises a two-stage heat treatment process for baking, and as a first step, baking in an oxidizing atmosphere at a high temperature (900 to 1350 ° C.). Then, as a second step, baking is performed in a non-oxidizing gas atmosphere at a high temperature (900 to 1350 ° C.). As a result, metal contamination can be reduced in a shorter time than before. This is because, in the first step, the furnace is annealed in an oxidizing atmosphere to form an oxygen compound on the surface of a member such as a tube or a boat, the metal is taken into the oxygen compound, and then the non-oxidizing gas is used. It is considered that the amount of metal contamination is reduced in a short time by removing (etching) the oxygen compound by annealing in an atmosphere. If the heat treatment temperature is lower than 900 ° C., metal contamination cannot be reduced. If the heat treatment temperature exceeds 1350 ° C., the load on the apparatus increases, and conversely, metal contamination may increase.

The preferred heat treatment conditions of the present invention are as follows: the first and second heat treatment temperatures are 1150-1250 ° C.
The heat treatment time at the heat treatment temperature is at least 4 hours each, for a total of 20 to 40 hours. This ensures that the metal contamination level is 2 × 1
It can be set to 0 ¹⁰ atoms / cm ³ or less. Ar is suitable as the non-oxidizing gas in the second heat treatment.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
As will be described, it is needless to say that this embodiment can be variously modified without departing from the technical idea of the present invention.

The heat treatment furnace preferably used in the present invention is a resistance heating type heat treatment furnace, which is a batch furnace capable of processing a large number of wafers at a time. Generally, a vertical furnace and a horizontal furnace are known. Have been. Such a heat treatment furnace has a reaction tube into which a wafer to be heat-treated is introduced, and this reaction tube is generally made of quartz or silicon carbide (SiC).

As shown in FIG. 1, in the present invention,
As a first step, the temperature is raised to a temperature of 900 ° C. to 1350 ° C. while introducing an oxidizing gas into the reaction tube, and a first heat treatment is performed for a predetermined time. As the oxidizing gas, 100
% O ₂ gas, N ₂ gas containing O ₂ gas or water vapor, an inert gas, or a mixed gas of H ₂ and O ₂ (so-called pyrogenic oxidation) can be used. After reaching the target temperature, the oxidizing gas can be introduced.

Next, as a second step, the gas introduced into the reaction tube is switched from an oxidizing gas to a non-oxidizing gas, and the
A second heat treatment is performed at a temperature of 0 ° C. to 1350 ° C. for a predetermined time. As a non-oxidizing gas, an inert gas such as Ar or He;
Although N ₂ gas, H ₂ gas or a mixed gas thereof can be used, Ar is preferable since it is a safe and inexpensive gas which has a high metal oxide etching action and is safe.

The first step and the second step are the most efficient in terms of time if they are continuously performed only by switching the introduced gas. However, since this is not a heat treatment performed by charging a product wafer, the temperature is not changed during this time. There is no problem with raising and lowering. In addition, by putting only the wafer boat on which the product wafer is placed into the reaction tube, the wafer boat can be heat-treated (empty-baked) simultaneously with the reaction tube.

The heat treatment time may be appropriately set in accordance with the target contamination level, but it must be 2 × 10
^In order to reduce the pressure to ¹⁰ atoms / cm ³ or less, both the first and second heat treatments are performed at a temperature of 1150 ° C. or more, and the heat treatment time at the heat treatment temperature is set to at least 4 hours each.
What is necessary is just to make it 20 hours or more in total. In this case, considering the durability of the quartz tube and the SiC tube and the time required for raising and lowering the temperature, the heat treatment temperature is preferably 1250 ° C. or less, and the total heat treatment time is about 40 hours, so that the contamination level becomes almost constant. However, even if the heat treatment is performed further, the effect is not so much obtained.

[0015]

The present invention will be described below with reference to examples.
It goes without saying that these examples are shown by way of illustration and should not be construed as limiting.

Example 1 and Comparative Example 1 UL-260-10H manufactured by Tokyo Electron Co., Ltd. (reaction tube made of quartz) was used as a heat treatment furnace, and 100% O ₂ was used as a first step.
After the heat treatment in an atmosphere at 1150 ° C. for 4 hours, the introduced gas was switched to 100% Ar,
Heat treatment was performed at 150 ° C. for 4 hours. At this time, a monitor wafer for monitoring the level of metal contamination is put into the reaction tube, and after the heat treatment is completed, the wafer is taken out. Metal contamination (here Fe) by wafer contamination monitoring system)
The level was measured.

After that, another monitor wafer is loaded,
Furthermore, a second step heat treatment (100% Ar atmosphere, 1
After the addition of (150 ° C., 4 hours), the experiment for measuring the contamination level was repeated in the same manner, and the transition of the contamination level in the reaction tube every 4 hours of the additional heat treatment was observed. The results are shown in FIG. 2 as Example 1. As a comparison, an experiment was performed under the same conditions as above except that the heat treatment in the first step was also performed in a 100% Ar atmosphere at 1150 ° C. for 4 hours, and the transition of the contamination level was observed. This is shown as Example 1.

From the results shown in FIG. 1, in the case of Comparative Example 1, which corresponds to the conventional baking method, the reduction of metal contamination is moderate.
Even if the number of times of annealing is repeated, 5 × 10 ¹⁰ (atoms / c
m ³ ). On the other hand, in the case of Example 1 corresponding to the dry baking method of the present invention, the metal contamination level rises extremely once after the oxidizing heat treatment, but then rapidly decreases, and at the time of the total annealing time of 20 hours, the metal contamination level is reduced. It is reduced to 1 × 10 ¹⁰ (atoms / cm ³ ) or less, which is the lower limit of detection (the lower limit at which the reliability of data is guaranteed).

At this time, the reason why the metal contamination level once rises can be considered to be a process in which the metal taken in the oxygen compound formed in the furnace is etched by Ar annealing and released into the atmosphere. Then, it is considered that metal contamination is greatly reduced after the oxygen compound is exhausted.

(Examples 2 to 5 and Comparative Example 2) In order to investigate the effective temperature range in the baking method of the present invention, an experiment similar to that in Example 1 (repetition of heat treatment in an oxygen atmosphere + heat treatment in an Ar atmosphere) was conducted. The first and second heat treatment temperatures were set at five levels, namely, 850 ° C. (Comparative Example 2), 900 ° C. (Example 2), 1000 ° C. (Example 3), 1100 ° C. (Example 4), and 1150 ° C. Example 5) was carried out, and the transition of the contamination level was observed (FIG. 3). As a result, 850 ° C.
Although there is almost no effect, at 900 ° C. or higher, a tendency is observed that the Fe concentration in the furnace decreases. Therefore, it is considered that the effective temperature of the present method is 900 ° C. or more.

[0021]

As described above, according to the method for baking a heat treatment furnace according to the present invention, the level of metal contamination in the heat treatment furnace can be significantly reduced in a short time.

[Brief description of the drawings]

FIG. 1 is a process chart showing the steps of the method of the present invention in principle.

FIG. 2 is a graph showing the relationship between heat treatment time and Fe concentration in Example 1 and Comparative Example 1.

FIG. 3 is a graph showing the relationship between the heat treatment time and the Fe concentration in Examples 2 to 5 and Comparative Example 2.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F004 AA15 BA02 BA19 BB19 DA00 DA22 DA23 DA24 DA25 DA26 DB00 EA34 5F045 AA20 AC11 AC15 AC16 AC17 AD13 AD14 AD15 AD16 AD17 BB14 EB06

Claims (3)

[Claims] 1. A method for baking a heat treatment furnace having a reaction tube, wherein an oxidizing gas is introduced into the reaction tube of the heat treatment furnace.
A baking method for a heat treatment furnace, comprising: performing a first heat treatment at a temperature of 00 to 1350 ° C, and then introducing a non-oxidizing gas to perform a second heat treatment at a temperature of 900 to 1350 ° C. 2. The method according to claim 1, wherein the first and second heat treatment temperatures are set to 115.
The method according to claim 1, wherein the heat treatment is performed at a temperature of 0 to 1250C and the heat treatment time at the heat treatment temperature is at least 4 hours each, for a total of 20 to 40 hours. 3. The method according to claim 1, wherein the non-oxidizing gas is Ar.