JPH06120150A - Thin film treatment - Google Patents

Abstract

PURPOSE:To perform a surface treatment being high in uniformity by forming a thin film in a temperature region excepting the boundary temperature region between a temperature for attaining an amorphous state and that for attaining a polycrystalline state. CONSTITUTION:A treated atmosphere in a reaction tube 2 is heated by a heater 13 so that the temperature of the center part of a wafer boat 5 is 580 deg.C and below for attaining an amorphous state or 60 deg.C and over for attaining a polycrystalline state. After that, the inside of the reaction tube 2 is loaded with the wafer boat 5, which contains e.g. 100 wafers W arranged at 4.76mm pitch, from a lower opening by a ramp 4. Then, the inside of the reaction tube 2 is brought to a predetermined degree of vacuum, a film-forming gas containing the main component of a thin film is introduced from a second gas introduction tube 62 into an inner cylinder 22, air is discharged from the reaction tube 2 so that the inside of the reaction tube is put under 0.4Torr pressure, and film forming is performed while the wafer boat 5 is rotated. Thus, the uniformity of smoothness of the surface of the thin film is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film processing method.

[0002]

2. Description of the Related Art In a semiconductor device, a polysilicon film is widely used including an electrode layer of DRAM and is indispensable as a highly reliable material. Here, with the high integration of semiconductor devices, the structure of the device has become complicated, and strict requirements have been placed on the characteristics of the oxide film and electrode film, or the film thickness. Therefore, the polysilicon film is also required. It is necessary to further improve the uniformity of film thickness and the uniformity of impurity concentration within the same wafer and between wafers.

Under the circumstances, various improvements have been made to the structure of the processing apparatus and the gas supply method. On the other hand, the number of processed sheets per batch is increasing in order to improve mass productivity. For example, when a polysilicon film is formed by a vertical heat treatment apparatus and a compound layer containing impurities, for example, a POCl ₃ layer is formed on the surface of the polysilicon film, and then a heat treatment is performed to obtain a polysilicon film in which impurities in the compound layer are diffused, It is difficult to obtain in-plane uniformity (uniformity between wafers having different height positions) and uniformity between different batches with respect to the film thickness and impurity concentration of the silicon film, which is one of the causes of lowering the yield of wafers. .

The present invention has been made under the above circumstances, and an object thereof is to form a layer containing impurities to be diffused or to perform etching on the surface of a thin film when performing surface treatment of the thin film. The present invention aims to provide a thin film processing method capable of performing highly uniform surface treatment on the same target object and between different target objects.

[0005]

The present invention focuses on the fact that the surface treatment of a thin film as described above depends on the surface state of the thin film, and the amorphous state and the polycrystalline state of the main components of the thin film are When mixed, it was understood that the surface smoothness of the thin film was different even in the same batch because the solid state was non-uniform. This is a method for forming a thin film in a temperature range outside the boundary temperature range.

More specifically, the present invention provides a method of supplying a film-forming gas containing a main component of a thin film to an atmosphere to be processed to form a thin film on an object to be processed, and then processing the surface of the thin film. In Table ₁ , the upper limit of the temperature at which all or substantially all of the main components of the thin film are in an amorphous state is T ₁ , and the lower limit of the temperature at which all or substantially all of the main components of the thin film are in the polycrystalline state is T _2. The thin film forming step is performed by setting the temperature of the atmosphere to be processed to T ₁ or lower or T ₂ or higher.

When the thin film is made of silicon, the thin film forming step is performed by setting the temperature of the atmosphere to be processed to 5
The temperature is set to 80 ° C or lower or 610 ° C or higher.

[0008]

For example, a silane-based gas is supplied to the atmosphere to be treated, and the temperature of the atmosphere to be treated is 620 ° C. or higher or 5
When a film is formed on the object to be processed with the temperature set at 80 ° C. or lower, a thin film in a polycrystalline state at a temperature of 620 ° C. or higher or in an amorphous state at a temperature of 580 ° C. or lower is obtained. The surface of each of these thin films has a uniform solid phase, so that the smoothness of the surface is good. Therefore, for example, a compound layer containing impurities or an impurity layer is formed on the surface of the thin film, and then the impurities are diffused into the thin film. In this case, the uniformity of the impurity concentration in the thin film between the objects to be processed is high, or even when the surface of the thin film is etched, highly uniform surface treatment can be performed between the objects to be processed.

[0009]

EXAMPLE FIG. 1 is a vertical cross-sectional side view showing an example of a film forming apparatus for carrying out the method of the present invention. The heating furnace 1 is installed on a base plate 10, and is provided with a heater 13 on the inner peripheral surface of a heat insulating layer 12 laminated on the inner surface of a metal plate 11 so as to surround a reaction tube described later.

In the heating furnace 1, there is provided an outer cylinder 21 made of, for example, quartz and having a closed upper end, and an inner cylinder 22 concentrically arranged in the outer cylinder 21, made of, for example, quartz. A reaction tube 2 having a double tube structure that forms an atmosphere to be processed is provided.

The outer cylinder 21 and the inner cylinder 22 are respectively held at their lower ends by a cylindrical manifold 3 made of stainless steel or the like, and the manifold 3 is fixed in a state of being inserted into the opening of the base plate 10. Has been done. A cap portion 31 for hermetically sealing the opening is provided at the lower end opening of the manifold 3 so as to be openable and closable.

A rotating shaft 32, which is rotatable in an airtight state by, for example, a magnetic seal, is inserted through a central portion of the cap portion 31, and a lower end of the rotating shaft 32 is connected to a rotating mechanism (not shown) of the lifting table 4. In addition, the upper end is fixed to the turntable 33. A wafer boat 5 is mounted on the upper side of the turntable 33 via a heat insulating cylinder 34, and the wafer boat 5 can accommodate, for example, 150 semiconductor wafers W stacked at a predetermined interval. ing.

The elevating table 4 moves up and down along the elevating shaft 41 to load and unload the wafer boat 5 into the reaction tube 2.

On the lower side surface of the manifold 3, a film forming gas such as monosilane (SiH ₄ ) gas or disilane gas (Si ₂ H ₆ ) gas is mixed with a carrier gas such as helium gas and introduced into the reaction tube 2. A first gas introduction pipe 61 and a second gas introduction pipe 62 for insertion are inserted, and these gas introduction pipes 61 and 62 are connected to a common gas supply source (not shown). The first gas inlet pipe 61 is bent upward in an L-shape so that the gas outlet is located above the wafer boat 5, and the second gas inlet pipe 62 has a gas outlet at the wafer outlet. Similarly, the boat 5 is bent in an L-shape so as to be located near the lower end thereof.
By forming the film-forming gas introduction pipe into a long and short structure, the film-forming gas can be supplied to each wafer W on the wafer boat 5 more uniformly.

On the lower side surface of the manifold 3,
A third introducing pipe 7 for mixing a doping gas such as phosphine (PH ₃ ) with a carrier gas such as helium gas and introducing the mixed gas into the reaction tube 2 is horizontally installed.

On the other hand, on the upper side surface of the manifold 3,
An exhaust pipe 8 connected to a vacuum pump (not shown) is connected for discharging the processing gas from the gap between the outer cylinder 21 and the inner cylinder 22 to set the inside of the reaction tube 2 to a predetermined reduced pressure atmosphere.

Next, an embodiment of the method of the present invention using the above-mentioned film forming apparatus will be described. First, the heater 13 heats the atmosphere to be treated in the reaction tube 2 so that the temperature of the central portion (the central portion in the vertical direction) of the wafer boat 5 becomes 620 ° C. The wafer boat 5 accommodating 100 wafers W is loaded at a pitch of, for example, 4.76 mm from the section by the elevating table 4.

Next, the inside of the reaction tube 2 has a predetermined degree of vacuum, for example, 1 ×.
After evacuation to 10 ⁻³ Torr, 100% monosilane gas, which is a film forming gas containing the main component of the thin film, is supplied from the second gas introduction pipe 62 (shorter gas introduction pipe) for 180 S.
It is introduced into the inner cylinder 22 at the flow rate of CCM and the reaction tube 2
The interior is evacuated to a pressure of 0.4 Torr, and film formation is performed for 10 minutes while rotating the wafer boat 5 at a rotation speed of 3 rpm, for example.

Subsequently, the supply of the monosilane gas is stopped, and in order to discharge the gas (monosilane gas) in the reaction tube 2, a vacuum pump (not shown) connected to the exhaust pipe 8 evacuates the gas for about 30 seconds.

Then, from the third gas introducing pipe 7, for example, phosphine gas, which is a doping gas, is replaced with helium gas.
The mixed gas diluted to 0% was introduced into the inner cylinder 22 at a flow rate of 100 SCCM, and the inside of the reaction tube 2 was 0.5 Torr.
The gas is evacuated so that the pressure becomes, and the treatment is performed for 1 minute, for example.

By carrying out such a treatment, a silicon layer and a phosphorus adsorption layer are formed in this order on the surface of the wafer W. Here, in the above-described process, instead of setting the temperature of the atmosphere to be processed in the step of forming the silicon layer, in this example, the temperature of the center part of the wafer boat 5 to 620 ° C.,
Five settings of 610 ° C., 600 ° C., 595 ° C., 590 ° C., and 580 ° C. were set, and the silicon layer and the phosphorus adsorption layer were formed in this order on the surface of the wafer W under exactly the same conditions.
If the positions of the wafers W placed at the top, center, and bottom of the wafer W group on the wafer boat 5 are the top portion, the center portion, and the bottom portion, respectively, the wafers W located at these three locations are The relationship between the temperature in the film forming process and the phosphorus adsorption amount (phosphorus adsorption layer amount) was investigated, and FIG.
The results shown in are obtained. Graphs indicated by □, Δ, and ◯ in FIG. 2 correspond to the top portion, the center portion, and the bottom portion, respectively.

As can be seen from the results of FIG. 2, 580-6
Under the temperature condition set between 10 ° C, the wafer boat 5
The adsorption amount of phosphorus varies greatly depending on the height position of the upper wafer W, but under the temperature conditions of 580 ° C., 610 ° C. and 620 ° C., the respective height positions of the wafer W (top portion,
The amount of phosphorus adsorbed at the center and bottom is uniform.

Further, on the high temperature side of the temperature range of the silicon layer forming process set as described above, the pressure in the reaction tube 2 is set to 0,6 Torr and 0,8 Torr, and the phosphorus adsorption amount between the surfaces ( When the variations among the top portion, the center portion, and the bottom portion) were examined, the results shown in FIGS. 3A and 3B were obtained. As can be seen from these results, the amount of phosphorus adsorbed between the surfaces is uniform when the temperature of the film forming step is 620 ° C., but the variation is large at 610 ° C.
On the other hand, as shown in FIG. 2, the pressure in the reaction tube 2 is 0.4 To
In the case of rr, the adsorption amount of phosphorus was uniform at the temperature of 610 ° C., but considering together with the results of FIG. 3 and FIG.
It is considered that when the temperature is 620 ° C. or higher, the surface state of the wafer becomes stable and the uniformity of the surface smoothness is improved, and the surface-to-surface uniformity of the adsorption amount of phosphorus can be secured.

This phenomenon is presumed as follows. That is, the surface is in an amorphous state at a temperature of 580 ° C. or lower in the film forming step of the silicon layer, and is in a polycrystalline state at 620 ° C. or higher. Here, the amorphous silicon film has a smooth surface state, while the polysilicon film has fine unevenness, but the unevenness is good, and therefore these two states coexist in the temperature range of 580 to 620 ° C. It is presumed that the surface of the silicon layer becomes non-uniform for each wafer and the adsorption amount of phosphorus varies. The temperature is 6
The surface of the silicon layer at 00 ℃ and 620 ℃ is S
When observed by an EM photograph, the former has a difference in surface flatness, but the latter has a uniform surface smoothness, and this result also confirms that the above inference is correct.

From the above, in order to make the surface condition of the silicon layer uniform between the surfaces, it is necessary to set the film forming temperature to 580 ° C. or lower or 620 ° C. or higher. When phosphorus is adsorbed, the amount of phosphorus adsorbed between the surfaces can be made uniform. Therefore, when phosphorus is diffused from the phosphorus adsorption layer into the silicon layer thereafter, the uniformity of the phosphorus concentration between the surfaces can be ensured. You can On the other hand, if the adsorption amount of phosphorus is non-uniform, the phosphorus concentration varies among the surfaces.

When the film forming rates of the silicon layer were measured at the temperatures of 580 ° C. and 620 ° C., respectively, they were 5 Å / min and 25 Å / min. Therefore, from the viewpoint of improving the throughput,
It is a good idea to set the temperature of the film forming step to 620 ° C. or higher. The film formation rate measurement time is the total time from the start of film formation of the silicon layer to the end of formation of the phosphorus adsorption layer.

Then, the temperature of the film forming step is set to 620 ° C. to form a silicon layer as in the above-mentioned embodiment, and thereafter, exhaustion,
After each step of forming the phosphorus adsorption layer, the supply of the phosphine gas is stopped and the gas in the reaction tube 2 is discharged by, for example, 3
The vacuum is evacuated for about 0 seconds, and then monosilane gas is supplied from the first gas introduction pipe 61 and the second gas introduction pipe 62 respectively for 10 seconds.
The film is introduced into the inner cylinder 22 at a flow rate of 0 SCCM and 80 SCCM, and the reaction tube 2 is evacuated to a pressure of 0.4 Torr, and film formation is performed for 10 minutes, for example. After that, the inside of the reaction tube 2 is evacuated for about 30 seconds as described above.

Then, each step after the phosphorus adsorption layer forming step,
That is, phosphorus adsorption layer formation → exhaust → silicon layer formation → exhaust 2
Repeated 0 times to obtain a laminate 9 in which silicon layers 91 and phosphorus adsorption layers 92 are alternately laminated as shown in FIG. Thereafter, the inside of the reaction tube 2 is set to 90 in a nitrogen gas (N ₂ gas) atmosphere.
When the laminated body 9 was heated to 0 ° C. and annealed for 60 minutes, the phosphorus concentration was 2 × 10 ²⁰ pieces / C.
A silicon thin film having a thickness of C and a thickness of 4000 Å was obtained.

When the phosphorus concentration inter-plane uniformity (uniformity between the wafers W stacked on the wafer boat 5) of this thin film was examined, it was around 5%, and a good result was obtained. It can be said that this is based on the fact that the surface state of the silicon layer is high in the face-to-face uniformity, and thus the phosphorus adsorption amount is also high in the face-to-face uniformity.

If the silicon layers and the phosphorus adsorption layers are alternately formed as described above and then annealed to obtain a silicon layer doped with phosphorus, a silane-based gas and a phosphine gas are obtained. In-plane uniformity in the film thickness of the thin film is better and the film formation rate is considerably faster than in the case where the film formation is carried out by simultaneously introducing into the reaction tube. Therefore, if the method of the present invention is applied to such a film forming method, it is very effective in practice.

In the above, the present invention can be applied to the case where another surface treatment is performed on the silicon layer. For example, when the POCl ₃ layer is formed on the silicon layer and then phosphorus diffusion is performed, the inter-plane uniformity of the phosphorus concentration is enhanced. In addition, it is possible to improve the surface-to-surface uniformity in the processed state even when the silicon layer is etched.

In the present invention, the main component of the thin film is not limited to silicon.

[0033]

According to the present invention, a thin film is formed in a temperature range in which all or almost all of the main components of the thin film are in an amorphous state or in a temperature range in which all or substantially all of the main components of the thin film are in a polycrystalline state. Therefore, for example, in the case of a silicon film, since the film is formed at 580 ° C. or lower, or 620 ° C. or higher, the thin film surface has high uniformity of smoothness, and the surface condition is always uniform. Alternatively, the surface condition of the thin film is uniform between different batches, and as a result, the surface treatment such as the diffusion of impurities and the etching can be made uniform, and the stable surface treatment can be always performed.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an example of an apparatus used in an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a temperature of a film forming process and a phosphorus adsorption amount.

FIG. 3 is a characteristic diagram showing a relationship between a temperature of a film forming process and a phosphorus adsorption amount.

FIG. 4 is an explanatory diagram showing a laminated body before heat treatment.

[Explanation of symbols]

 1 Heating Furnace 2 Reaction Tube 3 Manifold 4 Lifting Table 5 Wafer Boat 61, 62, 7 Gas Introducing Pipe 8 Exhaust Pipe 91 Silicon Layer 92 Phosphorus Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Okumura 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Tamagawa factory (72) Inventor Reiji Shinna 2-3-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Tokyo Electron Ltd. (72) Inventor Yoshiyuki Fujita 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Electron Ltd. (72) Inventor Hiroshi Suzuki 52, Matsunane, Iwatani, Esashi, Iwate Tokyo Electron Tohoku Co., Ltd.

Claims (2)

[Claims] 1. A method of supplying a film-forming gas containing a main component of a thin film to an atmosphere to be processed to form a thin film on an object to be processed, and then performing a process on a surface of the thin film, When the upper limit of the temperature at which all or substantially all of the main components are in the amorphous state is T ₁ and the lower limit of the temperature at which all or substantially all of the main components of the thin film are in the polycrystalline state is T ₂ , the growth of the thin film is defined. A method for processing a thin film, wherein the film process is performed by setting a temperature of an atmosphere to be processed to T ₁ or lower or T ₂ or higher. 2. A method of forming a thin film of silicon on a target object and then performing a process on the surface of the thin film, wherein the step of forming the thin film comprises setting a temperature of a target atmosphere at 580 ° C.
A method for treating a thin film, which is performed below or at 620 ° C. or higher.