JPH0774120A - Heat treatment method - Google Patents

Abstract

PURPOSE:To obtain thin and high quality oxide films and suppress surface defects and, further, obtain excellent impurity concentration profiles when a number of semiconductor wafers are simultaneously subjected to a heat treatment. CONSTITUTION:A number of wafers W are mount on the ring-shaped mount table of a wafer boat 4. The inside temperature of a reaction tube 1 is preset, for instance, at 400 deg.C and the wafer boat 4 is brought into the reaction tube 1 and then the inside temperature of the reaction tube 1 is elevated to a treatment temperature, for instance, with a speed of 100 deg./min. As the loading of the wafers are performed under a low temperature and then the inside temperature of the reaction tube 1 is elevated with a high speed, in an oxidation treatment, the growth of a low quality oxide film is suppressed and, in a diffusion treatment, as a difference between the thermal history to which the wafers W in the upper side of the wafer boat and the thermal history to which the wafers W in the lower side of the wafer boat is small, excellent impurity concentration profiles can be obtained on the respective wafers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for oxidizing or diffusing an object to be processed such as a semiconductor wafer.

[0002]

2. Description of the Related Art During the manufacturing process of semiconductor devices,
Oxidation treatment that oxidizes the surface of silicon at high temperature to obtain an insulating film (oxide film), or diffusion treatment that heats a silicon layer with an impurity layer formed on the surface to thermally diffuse the impurities into the silicon layer. There is.

As a heat treatment apparatus for performing this kind of oxidation and diffusion, a vertical furnace has been widely used instead of a horizontal furnace because it has little air entrainment. A conventional example of an oxidation process performed using a vertical heat treatment apparatus will be described with reference to FIG. 9. A large number of wafers are supported on a wafer boat at four points, respectively, and are stacked one on top of the other. A mixed gas atmosphere of ₂ (nitrogen) gas and O ₂ (oxygen) gas and lower than the processing temperature, for example, about 800 ° C.
Then, the wafer is loaded (the wafer boat is loaded into the reaction tube). Then, after the lower end opening of the reaction tube is sealed by the lid, the inside of the reaction tube is heated at a processing temperature of, for example, 900 to 1100 ° C. at a rate of 10 ° C./min, and is maintained at this temperature for a predetermined time and the surface of the silicon film is maintained. After forming the oxide film, the temperature is lowered to 800 ° C. at a rate of about 2 ° C./minute, and then the wafer is unloaded (the wafer boat is unloaded from the reaction tube).

To describe the diffusion of impurities, in this process, a wafer in which impurity ions such as As ions are implanted on the surface of a silicon layer is heated to a temperature of 900 to 1000 ° C., for example.
In the above heating atmosphere and N ₂ gas atmosphere, As ions are diffused in the silicon layer, and when the vertical heat treatment apparatus is used, it is performed in the same manner as in the case of oxidation except that the gas atmosphere in the reaction tube is different.

[0005]

First, the problem in the case of oxidation will be described. Since a cold wafer and a wafer boat are carried into the reaction tube at the time of wafer loading, the temperature inside the reaction tube is lowered from 800 ° C to about 700 ° C. To do. However, since the wafer is rapidly exposed to such a high temperature from the loading chamber, the radiant heat of the heater around the reaction tube causes the temperature of the peripheral edge side of the wafer to become higher than that of the central side, and the thermal strain causes a fault called slip on the wafer surface. Warpage occurs.

Further, when the surface of the silicon layer contacts O ₂ at a temperature lower than the processing temperature, an oxide film having poor film quality, that is, a low withstand voltage grows. However, as described above, the wafer is placed in a temperature region lower than the processing temperature. When exposed for a long time by raising the temperature at a slow rate of 10 ° C./min, an oxide film of poor film quality intervenes under the original oxide film of good film quality,
As a whole, the film quality deteriorates. In the reaction tube, O ₂
Can be avoided if N is not supplied, but N
_If only ₂ gases are used, silicon is nitrided and the surface is roughened. Therefore, O ₂ gas is necessary to prevent nitriding.

Since the device pattern is becoming finer and thinner in recent years, the oxide film is very important for obtaining a large capacitance when a capacitive insulating film of, for example, a CMOS is obtained by oxidation treatment. Therefore, it is necessary to reduce the thickness, and therefore the inclusion of an oxide film of poor film quality formed in an atmosphere at a processing temperature or lower leads to a reduction in yield.

Furthermore, since the wafer on the top side of the wafer boat is exposed to a high temperature in the O ₂ gas atmosphere for a longer time than the wafer on the bottom side during wafer loading, the degree of oxide film formation depends on the upper and lower positions of the wafer boat. There is a possibility that this variation will be reflected in the device as well.

The problem of diffusion processing will be described below.
With the miniaturization of devices, the diffusion depth of impurities such as As in the silicon layer tends to become shallower in order to form a shallow pn junction. On the other hand, the concentration profile of impurities in the silicon layer is greatly affected by thermal history, so that the concentration profile of the wafer varies depending on the height position of the wafer boat. That is, 800 wafer boats
If the wafer is rapidly loaded into or unloaded from the reaction tube at a temperature as high as ℃, not only the above-described slips may occur on the wafer but also the wafer may be cracked.
Unloading should be done gently. However, the wafer located on the upper side of the wafer boat is exposed to a high temperature atmosphere in the reaction tube for a long time, and a large thermal history is received, so that the impurity concentration near the surface is small and the concentration gradient in the depth direction becomes gentle, As a result, there is a problem that a uniform diffusion process cannot be performed on each wafer W in the wafer boat.

The present invention has been made under such circumstances, and an object thereof is to provide a heat treatment method capable of forming a good quality oxide film.

Another object of the present invention is to provide a heat treatment method capable of making the impurity concentration profiles uniform among the objects to be processed.

[0012]

According to a first aspect of the present invention, a large number of objects to be processed are mounted on a holder and carried into a reaction tube, and a processing gas is supplied into the reaction tube under a heating atmosphere to be processed. In the method of oxidizing the surface of, the temperature inside the reaction tube is set to a temperature below which rapid growth of the natural oxide film can be suppressed, the holder equipped with the object to be treated is carried into the reaction tube, and then the inside of the reaction tube is The feature is that the temperature is rapidly raised to the processing temperature.

According to a second aspect of the present invention, a large number of objects to be processed having an impurity layer formed on the surface of a silicon layer are mounted on a holder and carried into a reaction tube, and impurities in the impurity layer are removed from the silicon layer under a heating atmosphere. In the method of diffusing into the reaction tube, the temperature inside the reaction tube is set to a temperature at which the thermal history of the object to be treated is small or less, the holder equipped with the object to be treated is carried into the reaction tube, and then the temperature inside the reaction tube is raised to the treatment temperature. Is characterized by.

According to a third aspect of the present invention, in a method of mounting a large number of non-processed objects on a holder, carrying in the reaction tube, and heat-treating the object to be processed, the holder provided with the object to be processed is provided in the reaction tube. When carrying in, the holder provided with the object to be processed is set in the reaction tube in a state where the temperature in the reaction tube is set to a temperature below the temperature at which unnecessary growth of an oxide film on the surface of the object to be processed is suppressed. A heat treatment method characterized by carrying in.

The invention of claim 4 is the invention of claim 1, 2 or 3.
In the invention of, the temperature inside the reaction tube is set to 600 ° C or lower,
It is characterized in that the holder on which the object to be processed is mounted is carried into the reaction tube.

According to a fifth aspect of the invention, in the first, second, third or fourth aspect of the invention, the temperature in the reaction tube is raised at 50 ° C./min or more after the holder is carried into the reaction tube. To do.

The invention of claim 6 is the invention of claim 1, 2, 3, 4
In the invention of 5 or 5, the holder is characterized by including a ring-shaped mounting table for holding the peripheral edge of the object to be processed.

[0018]

When performing the oxidation or diffusion treatment on the object to be processed, if the temperature at the time of loading the object to be processed is set as in the invention of claim 4, for example, the occurrence of slips on the object to be processed is prevented. In addition, it is possible to prevent the growth of a natural oxide film having poor film quality even if the loading takes time. For example, if the object to be processed is placed on a ring-shaped mounting table and heated at a high speed, for example, at a rate of 50 ° C./minute or more, the temperature of the object to be processed can be increased while maintaining high in-plane temperature uniformity. Moreover, since it can pass through the temperature range where the natural oxide film with poor film quality is formed in a short time,
A high quality oxide film can be obtained.

Further, if the temperature of the heat history of the object to be processed is set to be small as in the second aspect of the present invention, the object to be processed on the upper side and the object to be processed on the lower side of the holder at the time of loading. Since the difference in thermal history is small, uniform diffusion processing can be performed regardless of the vertical position.

[0020]

EXAMPLE FIG. 1 is a diagram showing the overall structure of a vertical heat treatment apparatus for carrying out the film forming method of the present invention. In FIG. 1, reference numeral 1 denotes a cylindrical reaction tube made of, for example, quartz and having an open lower end, and a heating section 2 is arranged around the reaction tube 1. In this heating unit 2, for example, as shown in FIG. 2 and FIG. 3, a plurality of heating blocks arranged along the circumferential direction while repeatedly bending the resistance heating wire 22 vertically are arranged on the inner peripheral surface of the heat insulating body 21. Consists of As the resistance heating wire 22, for example, molybdenum disilicide (MoSi ₂ ) can be used, and according to this, the inside of the reaction tube 2 is 50 to 100 ° C. /
The temperature can be raised at a high rate of temperature increase.

A processing gas supply pipe 31 connected to a gas supply source (not shown) is provided so as to project into the reaction pipe 2.
Its tip extends to a position facing the ceiling surface of the reaction tube 2. Further, the reaction tube 2 is provided with an exhaust pipe 33 connected to a vacuum pump 32.

On the lower side of the reaction tube 1, there is provided a lid body 11 mounted on an elevating table 12, and this lid body 1 is provided.
1 has a role of airtightly closing the lower end opening of the reaction tube 1 at the upper limit position. A wafer boat 4 which is a holder is mounted on the lid body 11 via a heat retaining cylinder 3.

As shown in FIG. 3, the wafer boat 4 has four columns 41 made of quartz arranged in the circumferential direction, for example, a ring-shaped placing table 42 made of a material having a large heat capacity, for example, quartz rings, which are spaced vertically from each other. The wafer W is mounted on each ring-shaped mounting table 42 with the peripheral edge of the wafer W being held in contact with the mounting table 42. The ring-shaped mounting table 42 has a peripheral edge slightly higher than the surface of the wafer W so that the heat rays from the heating unit 2 are not directly radiated to the peripheral edge of the wafer W, and the thickness of the mounting table 42 is greater than that of the inner peripheral side from the outer peripheral side. Is configured to be larger.

Between the lower end of the heating section 2 and the reaction tube 1, an intake passage 52 that opens to the outside of the apparatus via a shutter 51 or communicates with the air supply fan 5 is provided around the reaction tube 1, for example. Four nozzles are provided at the tip of the intake passage 52. Further heating section 2
An exhaust port 54 communicating with the exhaust duct 53 is formed on the upper surface of the exhaust duct 53. The exhaust duct 53 has a shutter 56 that rotates about a support shaft 55 as a fulcrum for opening and closing the exhaust port 54, and a heat exchanger. 57 and an exhaust fan 58 are provided in this order from the upstream side. The intake passage 52 and the exhaust duct 53 are provided in the reaction tube 1 after the film formation on the wafer W is completed.
It constitutes a forced cooling means for forcibly cooling the inside.

Next, an embodiment of the heat treatment method of the present invention using the above heat treatment apparatus will be described with reference to FIG. First, the temperature inside the reaction tube 1 is set to 400 ° C., and a mixed gas of O ₂ gas and N ₂ gas is allowed to flow through the reaction tube 1, and, for example, 30 wafers W to be processed are placed on the wafer boat 4. Then, the elevating table 12 is lifted at a speed of, for example, 200 mm / min to be loaded into the reaction tube 1 through the lower end opening. However, some of the upper and lower wafers W are used as dummy wafers.

Next, the temperature in the reaction tube 1 is set to 100 ° C., for example.
For example, the temperature is raised from 850 ° C. to 900 ° C. at a rate of / minute.
Although the set temperature in the reaction tube 1 is 400 ° C., the actual temperature in the reaction tube 1 once drops to, for example, about 300 ° C. when the cold wafer W and the wafer boat 4 are loaded, and then rises. Becomes Subsequently, O ₂ gas and HCl gas were introduced into the reaction tube 1 at 10 l / min and 1 respectively.
It is supplied at a flow rate of liter / min to perform an oxidation treatment, and as shown in FIG.
An oxide film 102 of about 200 angstrom is formed.
For the oxidation treatment, 100% O ₂ gas may be used, and it is not limited to the dry oxidation as in this example, but SiO ₂ may be used.
Wet oxidation using gas and HCl gas may be used.

After the oxidation treatment, the heating section 2 is turned off, the shutters 51 and 56 of the forced cooling means are opened, and the exhaust fan 57 is operated, thereby heating from the nozzle 50 of the intake pipe 52 to the exhaust port 54. Air is allowed to flow along the inner peripheral surface of the portion 2 to cool the inside of the reaction tube 1. In this way, the inside of the reaction tube 1 is cooled to 400 ° C. at a rate of 50 ° C./minute, and then the wafer W is unloaded.

According to such an embodiment, since the temperature in the reaction tube 1 at the time of loading is set to a temperature as low as 400 ° C., the thermal stress on the wafer W is small, and therefore, surface defects called slip and so on. The warp can be suppressed. Then, the temperature of the wafer W passes through the temperature region lower than the processing temperature at a high temperature of 100 ° C./minute, and the time during which the wafer W is exposed to the low temperature is shortened. Therefore, the growth of an oxide film having poor film quality is suppressed. It is possible,
As a result, a thin and high-quality oxide film can be obtained. Further, during loading and unloading, the wafer located on the upper side of the wafer boat is exposed to the heating atmosphere for a longer period of time, but since the set temperature in the reaction tube 1 at that time is low, the degree of growth of the oxide film is different. There is little, and therefore process variations between wafers are suppressed.

As the resistance heating wire 22 of the heating portion 2, a material having a high heating efficiency, for example, molybdenum disilicide is used.
After the loading, the inside of the reaction tube 1 is heated to the processing temperature at a speed as high as 100 ° C./minute, so that the throughput is high.

Since the peripheral portion of the wafer W is held by the ring-shaped mounting table 42 made of, for example, quartz, which has a large heat capacity, a part of the heat of the peripheral portion of the wafer W is held by the mounting table 4.
2 and the thickness of the mounting table 41 increases from the inner peripheral side toward the outer peripheral side. Therefore, when the temperature of the wafer W is raised and lowered, even if the temperature raising / lowering rate is increased, the wafer W is increased. The temperature distribution in the radial direction can be made uniform. As described above, since the wafer W is loaded at a low temperature and the in-plane temperature uniformity is high when the temperature is raised, it is possible to suppress the occurrence of slip and warp in the wafer W also from this point.

Here, the thickness of the natural oxide film on the surface of the wafer W when the inside of the reaction tube 1 was set to a 100% O ₂ gas atmosphere and the wafer boat was raised at a speed of 200 mm / min to perform loading was measured. For each temperature within 1 (400 ° C, 600
C., 800.degree. C.), the results shown in FIG. 6 were obtained. However, the white frame is the top part of the wafer boat, the shaded frame is the center part, and the halftone frame is the film thickness at the bottom part. By connecting the film thickness at each temperature from this figure, the film thickness of the natural oxide film at a certain temperature of 400 to 800 ° C. can be predicted, and the wafer W is sequentially exposed to the heating atmosphere from the one located at the upper side during loading. However, if the temperature is 600 ° C. or lower, preferably 400 ° C. or lower, it is presumed that the growth of an oxide film having poor film quality can be suppressed.

Next, an embodiment in which the present invention is applied to an impurity diffusion process will be described. First, as a wafer to be processed, a wafer in which impurities such as As (arsenic) ions are implanted into the surface of a silicon layer is used. . Also in this case, for example, 30 wafers including dummy wafers are placed on the wafer boat 4 and loaded in the same manner as in the case of the oxidation process, and then the inside of the reaction tube 1 is heated at a rate of 100 ° C./min, for example, 900.
As shown in FIG. 6, As atoms are diffused into the silicon layer 104 from the impurity layer as shown in FIG. 6 while the temperature is raised to ˜1000 ° C. and N 2 gas is supplied into the reaction tube 1 at a flow rate of, for example, 10 l / min. The diffusion layer 105 is formed.

According to such an embodiment, there is an effect that the slip and warp of the wafer can be suppressed as in the case of the oxidation treatment described above, and further, an effect that the As concentration profile is uniform between the wafers. is there. That is, during loading and unloading, the wafer located on the upper side of the wafer boat 4 is in the reaction tube 1 for a longer period of time and receives a larger amount of heat, but the temperature in the reaction tube 1 during loading and unloading is 400 Since the temperature is set to 0 ° C., the thermal history of the wafer at this temperature is small, and therefore the difference in thermal history between the upper wafer and the lower wafer is also small.

After the loading, the upper wafer and the lower wafer are uniformly heated, so that the impurity concentration profiles are eventually aligned between the wafers, and the concentration profiles are as shown by the solid line in FIG. In addition, the impurity concentration in the surface portion of the silicon layer 104 is high and the diffusion depth is shallow, so that a shallow pn junction can be obtained. It should be noted that the dotted line in the figure is an example of a bad concentration profile when the temperature of the reaction tube during loading and unloading is set to 800 ° C. It is understood that the concentration profile can be improved by the method of the present invention. It Here, considering the suppression of the growth of the natural oxide film at the time of loading and the suppression of the variation of the concentration profile due to the position of the wafer on the wafer boat, the set temperature of the reaction tube at the time of loading is preferably 600 ° C. or lower.

Further, the following experiment was conducted to investigate the influence of the temperature decrease rate in the reaction tube after annealing on the diffusion of impurities. That is, as described above, for a wafer in which As is ion-implanted on the surface thereof, 1
Annealing is performed for 1 minute in a heating atmosphere of 000 ° C. and an N ₂ gas atmosphere, and then the temperature lowering rate in the reaction tube is set to 60.
When the SIMS profiles were set at 2 ° C./min and 2 ° C./min equivalent to those of the normal furnace, the diffusion depth when the temperature was lowered from the SIMS profile at 2 ° C./min was
It was found that the temperature was almost double that when the temperature was lowered at 60 ° C / min. Further, when a similar test was conducted on a wafer in which BF ₂ was implanted instead of As, the same result was obtained.

Further, the active carrier concentration of the silicon surface portion into which As has been injected is 1.3 × 10 ²⁰ atoms / cm ³ when the temperature is lowered at 2 ° C./min, and when the temperature is lowered at 60 ° C./min. Is 2.0 × 10 ²⁰ atoms / cm ³
The former is 35% less than the latter. Therefore, it is understood from these results that the diffusion depth of impurities can be made shallow by increasing the temperature lowering rate after annealing.

[0037]

According to the invention of claim 1, 3 or 4, since the temperature in the reaction tube is lowered at the time of loading the object to be processed, the thermal strain is small, and therefore, the defects on the surface of the object to be processed can be suppressed. Further, it is possible to suppress the growth of an oxide film having poor film quality at the time of loading.

By increasing the temperature in the reaction tube at a high speed after loading the object to be treated as in the fifth aspect of the invention, it is possible to suppress the growth of an oxide film having a poor film quality, and thus a thin and high-quality oxide film. Can be obtained and can be processed with high throughput. Further, in this case, if the ring-shaped mounting table is used as in the invention of claim 6, a high uniformity in the in-plane temperature distribution can be obtained at the time of temperature increase and temperature decrease, and the thermal strain of the object to be processed can be suppressed.

Further, according to the invention of claim 2, 3 or 4, the thermal history of the object to be processed at the time of loading is small, so that a good impurity concentration profile can be obtained, and it is independent of the vertical position of the holder. A uniform diffusion process can be performed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a perspective view showing an example of a heating unit of the heat treatment apparatus.

FIG. 3 is a vertical sectional view showing an example of a holder of the heat treatment apparatus.

FIG. 4 is an explanatory diagram showing the steps in the example of the method of the present invention and the temperature in the reaction tube in a corresponding manner.

FIG. 5 is an explanatory diagram showing the state of oxidation of the surface of a semiconductor wafer.

FIG. 6 is a characteristic diagram showing the relationship between the thickness of the native oxide film and the temperature of the reaction tube during loading.

FIG. 7 is an explanatory diagram showing another example of the surface of the semiconductor wafer.

FIG. 8 is a characteristic diagram showing a concentration profile of impurity atoms.

FIG. 9 is an explanatory diagram showing the steps in the conventional method and the temperature in the reaction tube in association with each other.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tube 2 Heating part 22 Resistance heating wire 4 Wafer boat 42 Ring-shaped mounting table 52 Intake pipe 54 Exhaust port 58 Exhaust fan W Semiconductor wafer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomoyuki Obe 1-24-1 Machiya, Shiroyama-machi, Tsukui-gun, Kanagawa Tokyo Electron Tohoku Co., Ltd. Sagami Business Office (72) Inventor Hiroshi Ikekawa ▲ Aki ▼ Tsukui, Kanagawa 1-2-141 Machiya, Shiroyama-machi, Gunma Inside the Sagami Works, Tokyo Electron Tohoku Co., Ltd. (72) Inventor Ken Nakao 1-241, Machiya Shiroyama-machi, Tsukui-gun, Kanagawa Tokyo Electron Tohoku Co., Ltd.

Claims (6)

[Claims] 1. A method for oxidizing a surface of an object to be treated by loading a large number of objects to be treated into a reaction tube, carrying the same into a reaction tube, and supplying a processing gas into the reaction tube under a heating atmosphere. It is characterized by setting the temperature below a temperature at which rapid growth of a natural oxide film can be suppressed, carrying in a holder equipped with an object to be processed into the reaction tube, and then rapidly raising the inside of the reaction tube to the processing temperature. Heat treatment method. 2. A method for diffusing impurities of an impurity layer into a silicon layer in a heating atmosphere, wherein a large number of objects to be processed having an impurity layer formed on the surface of a silicon layer are mounted on a holder and carried into a reaction tube. The feature is that the inside of the reaction tube is set to a temperature at which the thermal history of the object to be processed is smaller than or equal to a temperature, the holder equipped with the object to be processed is carried into the reaction tube, and then the temperature inside the reaction tube is rapidly raised to the processing temperature. Heat treatment method. 3. A method for providing a large number of non-processed objects on a holder, carrying in the reaction tube, and heat-treating the object to be processed, wherein when carrying the holder equipped with the object to be processed into the reaction tube, In a state in which the temperature in the reaction tube is set to a temperature at which the growth of an unnecessary oxide film on the surface of the object to be processed can be suppressed, the holder provided with the object to be processed can be carried into the reaction tube. Characterizing heat treatment method. 4. The heat treatment method according to claim 1, wherein the inside of the reaction tube is set at 600 ° C. or lower, and the holder on which the object to be processed is mounted is carried into the reaction tube. 5. The heat treatment method according to claim 1, wherein the temperature inside the reaction tube is raised at 50 ° C./min or more after the holder is carried into the reaction tube. 6. The heat treatment method according to claim 1, wherein the holder is provided with a ring-shaped mounting table for holding the peripheral edge of the object to be processed.