JPH0364912A - Hydrogen burning oxidative diffusion furnace - Google Patents

Abstract

PURPOSE:To form a uniform and highly reliable oxide film without causing deformation of the wall of a quartz tube for a long period by a method wherein the upstream part of the quartz tube is bent in L-shape, and hydrogen is burnt by introducing it vertically upward in the quartz tube. CONSTITUTION:A horizontal type hydrogen burning oxidative diffusion furnace, equipped with a furnace core tube 21 consisting of a quartz reaction tube having one end bent in L-shape, is composed of a uniform heat tube 22 provided surrounding the furnace core tube, heaters 24 divided into three parts and provided at the outside of the uniform heat tube 22 in the upstream, middle stream part and down stream part, a hydrogen introducing hole 23 and an oxygen introducing hole 25 provided on the edge part of a furnace core tube which is bent in L-shape, and a burning region 26 formed on the part which is bent in L-shape. In the above-mentioned fuel burning region, hydrogen is burnt under presence of oxygen, the semiconductor wafer 7 placed on a boat 6 is oxidized by the generated high temperature steam in the furnace core tube. The hydrogen and oxygen necessary for oxidation of hydrogen fuel are into the section located at vertically upper part in the furnace through introducing holes 23 and 25 respectively. According to the above-mentioned constitution, a uniform oxide film can be formed at high speed without increasing the overall length of the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a hydrogen-burning oxidation diffusion furnace, and particularly to the structure of the entry portion thereof.

(Prior Art) An internal combustion oxidation furnace for oxidizing the surface of a semiconductor wafer in a steam atmosphere, as shown in FIG. A tail pipe 2 attached to one end and an introduction pipe 3 arranged at the bottom of the tail pipe 2
and a heating means 4 disposed outside the core tube 1. Oxygen is introduced from the tail tube 2 and hydrogen is introduced from the introduction tube 3, and these are reacted in the combustion zone 5 at the entrance. This system generates water vapor and oxidizes the semiconductor wafers 7 placed on the boat 6.

In this device, when steam is generated in the combustion zone 5, reaction heat is generated and the temperature becomes high, which causes problems such as deterioration of the core tube and bending of the tail tube 3. Further, since the temperature is higher upstream, the oxidation rate of the wafer in the upstream area increases, resulting in a problem of poor uniformity.

In order to solve this problem, the heating means outside the furnace tube 1 is adjusted to lower the temperature in the upstream part, but since the reaction heat is not always constant, the desired temperature profile cannot be achieved. It was difficult to obtain.

Therefore, there is a method of increasing the distance between the combustion region 5 and the wafer 7 to reduce the effect of reaction heat, and to prevent deformation of the hydrogen introduction pipe 3 and the tapered part of the tail pipe 2, which are easily affected by reaction heat. Another method is to lengthen the hydrogen introduction pipe 3. However, in the former method, the length of the furnace core tube is often predetermined depending on the shape of the furnace, and there is a problem that it cannot be increased unnecessarily. In addition, in the latter method, the combustion flame is long in the axial direction, so extending the hydrogen introduction tube has little effect, and there is a limit to the length of the reactor core tube, so in the end it is necessary to move the combustion point closer to the wafer. Become.

In this way, in reality, this did not provide a fundamental solution and was insufficiently effective.

Now, in the semiconductor process, the diameter of wafers is increasing, and 5-inch to 6-inch wafers are now mainstream. In the case of a 5-inch diffusion furnace, the inner diameter of the core tube is around 180 mm, so the distance between the combustion point and the inner wall is 90+ at short distances.
+v, the current situation is that it is only possible to move about 20 cm toward the center of the combustion flame.

Therefore, in order to solve the above-mentioned problems, as shown in FIG. An external combustion oxidation furnace was devised (Japanese Patent Laid-Open No. 57-19
Publication No. 4522).

This method has the advantage that the influence of reaction heat can be reduced because the combustion section and the furnace core tube are provided apart from each other. However, it is necessary to heat the combustion section and the reactor core tube with separate heaters, and because the shape is complicated, cleaning and handling of the reactor core tube is difficult, and the cost of the equipment also increases. .

(Problem to be solved by the invention) As described above, in conventional hydrogen-burning oxidation diffusion furnaces, the distance from the combustion point to the furnace wall is small in the internal combustion type, and the reaction heat can deform the tail pipe or the core tube. In addition to
Since the distance between the combustion point and the wafer is close and it is not possible to obtain a uniform temperature profile, there is a problem that the uniformity of the oxide film deteriorates.

Furthermore, the external combustion method has problems in that the system is complicated and expensive.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydrogen combustion oxidation diffusion furnace that has a simple structure and is capable of forming a high-quality film.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in a first aspect of the present invention, in a horizontal hydrogen combustion oxidation diffusion furnace equipped with a quartz tube for oxidizing and diffusing semiconductor wafers in an oxygen and hydrogen atmosphere, the upstream portion of the quartz tube is shaped into an L-shape. The tube is bent so that hydrogen is introduced vertically upward into the quartz tube and combusted.

Further, in the second aspect of the present invention, a heat insulating material is provided in a part of the upstream portion of the quartz tube, and hydrogen and oxygen are supplied upstream of the region where the heat insulating material is provided to form a combustion point. The steam generated at the combustion point is configured to be sent to the reaction section downstream of the quartz tube, and the temperature at the combustion point is lower than the temperature at the reaction section.

(Function) According to the first configuration, the distance from the combustion point to the tube wall is the sum of the length of the bent portion and the tube diameter, so the tube wall is affected by the effect of reaction heat (combustion heat). It becomes possible to prevent deterioration such as alteration.

Furthermore, since the distance between the combustion point and the wafer can be increased, it is possible to form a highly uniform oxide film.

Furthermore, in the second aspect of the present invention, the area around the combustion section and the area around the reaction section are insulated via a heat insulating material, and the temperature of the reaction section is configured to be higher than the temperature of the combustion section. , the temperature in the upstream part of the reaction part does not become higher due to the temperature of the combustion part, and the temperature profile of the reaction part can be kept uniform, making it possible to form a highly uniform oxide film with good film quality. becomes.

(Example) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

In this internal combustion oxidation furnace, one end of the core tube is bent into an L-shape, hydrogen and oxygen are introduced vertically upward from this tip to generate steam, and this high-temperature steam is guided into the tube. It is characterized by a large distance between the combustion point and the furnace core tube.

As shown in FIG. 1, there is a furnace core tube 21 consisting of a quartz reaction tube with one end bent into an L-shape, a soaking tube 22 arranged so as to surround the furnace core tube 21, and an outside of the soaking tube. The heater 24 is divided into three parts, an upstream part, a midstream part, and a downstream part, and a hydrogen introduction hole for introducing hydrogen is provided at the end of the L-shaped core tube. 23 and an oxygen introduction hole 25 for introducing oxygen are provided, and a combustion region 26 is formed in this L-shaped bent portion.

In this combustion region, hydrogen is heated and combusted in the presence of oxygen to generate high-temperature steam, and this steam is placed on the boat 6 inside the core tube 21. The processed semiconductor wafer 7 is then oxidized.

In such an internal combustion oxidation diffusion furnace, hydrogen and oxygen necessary for hydrogen combustion oxidation are introduced into the furnace through the introduction holes 23 and 25, respectively.

Here, the distance between the combustion point and the inner wall of the core tube was 60 cm.

As a result of hydrogen combustion oxidation using this internal combustion oxidation diffusion furnace, the hydrogen flow rate X was 15 (j) /l111n),
When the oxidation temperature was 900° C. and the oxygen flow rate was 20 (N 2 /m1n), reliability could be maintained without deformation even after use for more than 2000 hours.

Incidentally, in the case of the conventional horizontal diffusion furnace shown in FIG. 7, similar experiments were conducted and the furnace core tube was found to be deformed after about 200 hours of use.

Let's consider this effect.

First, in such a diffusion furnace, the center of the furnace is 90
Since it is heated to about 0°C to 1000°C, the temperature at the introduction section is also around 800°C. The ignition point of hydrogen is 500℃
˜600° C., this temperature is sufficient for combustion, and hydrogen burns completely in the presence of oxygen.

Since the hydrogen introduced in this way is completely combusted,
At a sufficient distance from the point of combustion, it is equal to the average temperature in the furnace.

Here, if the pressure is 1 atffl and hydrogen is introduced at a rate of X1 per minute, the heat of combustion of hydrogen is 33°9
kcal/g, so the calorific value per second is x
/1344(wool/5ee) x 3380G(c
al/mol) x 2 (g/mol) x 4.18 (J
/cat) -210,8x (J/5ee).

Considering the shape of the region that is isothermal (T), at 1 atffl, the mean free path is about several A,
Hydrogen molecules are thought to spread in almost all directions.

Therefore, as shown in FIG. 2(a), a hemispherical shape with a radius r from the tip of the introduction hole is considered to be an isothermal region (combustion region) with a temperature T. FIG. 2(b) is a diagram showing the relationship between the distance from the combustion point and the temperature.

It is now assumed that combustion is progressing and is in an equilibrium state, and that the ambient temperature is t-1270 (K) based on actual measurement results.

The mass of water vapor remaining per unit time in the isothermal region m-219.5V/T (g/see) (m-1
8n-18PV/RT, P-1, R-0°082), and the reaction heat Q is Q=mc(T-t) (where C is the specific heat of water vapor, c-1,854(J/kg ).) Therefore, T
= (Q/me)+t Substituting into such arithmetic expression, the temperature T in the isothermal region is 15
In order to make it less than or equal to 00, Va must be 53ρ. At this time, the radius will be approximately 300 Ill. Therefore, it is necessary to design it at least 30 ctn apart from the introduction hole. However, since it will be somewhat longer in the direction of the combustion axis, additional allowance must be made. Furthermore, since the place where deformation is most likely to occur is in the direction of the combustion axis, which is more than twice as far away as the shortest distance, it is thought that it is necessary to estimate twice the radius mentioned above. It is extremely difficult to achieve long distances with conventional horizontal furnaces.

On the other hand, with the above structure, the distance between the combustion point and the wafer or inner wall of the core tube can be made 3 to 4 times larger than in the horizontal furnace shown in FIG. 7 without changing the length of the furnace. It is believed that the hydrogen flow rate can be increased without worrying about deformation of the core tube or tail tube, and the oxidation rate can be further increased.

Furthermore, increasing the oxidation rate requires increasing the hydrogen flow rate, making this condition even more severe.

As described above, according to the hydrogen combustion oxidation diffusion furnace of the embodiment of the present invention, it is possible to form a uniform oxide film at high speed without increasing the overall length of the furnace.

As a modification of the present invention, as shown in FIG. 3, a second oxygen introduction hole 25s for introducing oxygen in the horizontal direction of the furnace tube may be added to the bent portion of the furnace tube.

In this structure, the temperature of the steam is lowered by the oxygen introduced horizontally from the second oxygen introduction hole 25s, so that the thermal load on the reactor core tube can be further reduced.

Further, as shown in FIG. 4, the main reaction section 31 and the vertical section 32 of the introduction section may be divided into a detachable structure.

This makes cleaning easier.

Further, other embodiments of the present invention will be described.

In this hydrogen-burning oxidation diffusion furnace, the outside of a region separated by a predetermined distance from one end of the furnace core tube 41 covered with a soaking tube 42 and a heater 43 is covered with a heat insulating material, and this outside portion is covered with a tail tube. 40, in which combustion of hydrogen is caused, and heat is transferred from the reaction section to the tail tube and the core tube only by conduction. In addition, this tail pipe part 40 is exposed from the soaking tube. The other parts have the same structure as the conventional hydrogen combustion type oxidation diffusion furnace shown in FIG.

As shown in FIG. 5, this hydrogen-burning oxidation diffusion furnace includes a tail pipe part 40 formed integrally with the quartz tube and having one end tapered and constituting an oxygen introduction pipe 44 at the tip of the quartz tube. At the same time, a tail pipe 45 as a hydrogen introduction pipe is arranged so that its tip is located near this introduction port, thereby forming a combustion point O. The reaction section is a reactor core tube 4 made of quartz.
1, and a soaking tube 4 arranged so as to surround this furnace core tube 41.
2 and a heater 43 arranged outside the heat equalizing tube and divided into three parts: an upstream part, a midstream part, and a downstream part, and a heat insulating material is provided outside the boundary with the tail pipe part. 48 are arranged.

In the combustion region of the tail tube, hydrogen is heated and combusted in the presence of oxygen, producing high-temperature steam. A semiconductor wafer 47 placed thereon is oxidized.

Here, the furnace core tube had an inner diameter of 180φ and a wall thickness of 4 mm, and the distance X from the combustion point 0 to the heat insulating material 48 was 50 cm. The heaters in the midstream and downstream parts of the furnace tube are set to have a temperature of 900°C, while the heaters in the upstream part are set to have a slightly lower temperature in consideration of the heat from the combustion part.

As a result of hydrogen combustion oxidation using this internal combustion oxidation diffusion furnace, when the hydrogen flow rate was 15 (Q/m1n), the oxidation temperature was 900°C, and the oxygen flow rate was 10 (1/ff1in), the temperature profile of the reaction part was is uniform, making it possible to form an oxide film with extremely good film quality, and
It was possible to maintain reliability without causing deformation even after being used for many hours.

In addition, here, the flow rate ratio of hydrogen flow rate and oxygen flow rate is 1.33:
1, and the stoichiometry (hydrogen:oxygen-
2=1), the oxygen flow rate is increased. This is not only because it is dangerous if unburned hydrogen remains, but also because an oxide film formed in a slightly oxygen-rich atmosphere has a higher dielectric strength voltage and a lower defect rate. This is because by increasing the oxygen flow rate compared to stoichiometry, there are oxygen molecules that do not participate in the reaction.
This seems to be because the overall heat capacity increases and temperature rise is suppressed.

Further, at this time, the temperature of the combustion region was 800 to 850°C. The water vapor produced by combustion here is
As it flows into the region where the wafer 47 is present, it is gradually heated to a predetermined temperature.

As described above, according to this hydrogen combustion type oxidation diffusion furnace, the combustion region of hydrogen and oxygen is maintained higher than the ignition point to cause self-ignition, and the outside of the boundary between the combustion region and the reaction section is It is coated with a heat insulating material and is configured so that the temperature during combustion is lower than that of the reaction zone, making it possible to flatten the temperature profile inside the furnace and to form an oxide film with a uniform thickness within the batch. It becomes possible. In addition, since the water vapor temperature can be lowered, the temperature distribution in the upper and lower portions is created and the in-plane uniformity is improved.

In addition, when performing a process at a low temperature (800 degrees Celsius), an auxiliary heater 50 is installed around the tail pipe as shown in FIG.
may be placed. This heater heats the tail pipe to 700℃ at most.
Since the purpose is to maintain a certain level, it does not need to be very large.

This is to prevent the temperature of the tail pipe from becoming lower than the ignition point of hydrogen (600°C) even when performing a process at a low temperature (800°C).

Note that a thermocouple 51 may be provided to monitor the temperature of the combustion region, and the auxiliary heater 5o may be driven only when this temperature falls below a predetermined temperature.

In this way, by arranging the auxiliary cod 0 in the tail pipe section as a separate body from the heater of the reaction section, it becomes possible to apply it to a wider range of processes.

〔Effect of the invention〕

As explained above, according to the first hydrogen combustion oxidation diffusion furnace of the present invention, the upstream portion of the quartz tube is bent into an L shape, and hydrogen is introduced vertically upward into the quartz tube and combusted. , it is possible to form a uniform and highly reliable oxide film over a long period of time without deforming the tube wall.

Further, according to the second hydrogen-burning oxidation diffusion furnace of the present invention, a heat insulating material is provided at the boundary between the periphery of the combustion part and the periphery of the reaction part, and the temperature of the reaction part is higher than the temperature of the combustion part. Since the temperature profile of the reaction section can be kept uniform, it is possible to form an oxide film with good film quality and high uniformity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a hydrogen combustion oxidation diffusion furnace according to an embodiment of the present invention;
Figures 2(a) and 2(b) are diagrams showing the isothermal region (combustion region) of temperature T, diagrams showing the relationship between distance from the combustion point and temperature, and Figures 3 to 6, respectively. 7 and 8 are diagrams respectively showing other embodiments of the present invention, and FIGS. 7 and 8 are diagrams showing conventional hydrogen combustion oxidation diffusion furnaces, respectively. 1... Furnace core tube, 2... Tail tube, 3... Introductory tube, 4...
... Heating means, 5... Combustion area, 6... Boat, 7
... semiconductor wafer, 11 ... furnace core tube, 15 ... combustion section, 21 ... furnace core tube, 22 ... soaking tube, 23 ...
・Hydrogen introduction hole, 24...Heater, 25...Oxygen introduction hole, 25s...Second oxygen introduction hole, 26...Combustion area, 31...Main reaction part, 32...Vertical Mold part, 40・
... Tail pipe part, 41 ... Furnace core tube, 42 ... Soaking tube, 4
3... Heater, 44... Introductory pipe, 45... Tail pipe,
46...Boat, 47...Semiconductor wafer, 48...
- Insulation material, 50... Auxiliary heater, 51... Thermocouple.

Claims (2)

[Claims] (1) In a horizontal hydrogen combustion oxidation diffusion furnace equipped with a quartz tube for oxidizing and diffusing semiconductor wafers in an oxygen and hydrogen atmosphere, the upstream portion of the quartz tube is bent into an L shape, and hydrogen is introduced vertically upward into the quartz tube from the end. A hydrogen-burning oxidation diffusion furnace characterized in that the hydrogen combustion oxidation diffusion furnace is introduced into the furnace for combustion. (2) In a horizontal hydrogen combustion oxidation diffusion furnace equipped with a quartz tube for oxidizing and diffusing semiconductor wafers in an oxygen and hydrogen atmosphere, a heat insulating material is provided in a part of the upstream portion of the quartz tube, and this heat insulating material is provided. Hydrogen and oxygen are supplied upstream of the region to form a combustion point, and water vapor generated at this combustion point is sent to the reaction section downstream of the quartz tube, and the temperature of the combustion point is A hydrogen combustion oxidation diffusion furnace characterized in that the temperature is lower than that of the reaction section.