JP2000340561A - Method for forming film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a silicon nitride film as an insulation film, suitable for further shrinkage with the stress of the film itself which is suppressed by changing the flow ratio of a silane system gas and ammonium gas. SOLUTION: Ammonium gas is supplied through two ammonium nozzles 26A, 26B for setting the inside atmosphere of a treatment vessel 8 to an ammonium atmosphere. When the inside of the treatment vessel 8 is turned into an ammonium atmosphere, the ammonium gas is supplied continuously, and at the same time, a flow-controlled monosilane gas is supplied through a silane series nozzle 22 together with N2 gas, a carrier gas, into the treatment container 8 and then a film formation processing is started. In this film formation processing, two kinds of gases are supplied simultaneously. By changing the ratio of the flow of the monosilane gas and the flow of the ammonium gas, the refractive index of a silicon nitride film to be deposited, hence the stress of the film can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a silicon nitride film.

[0002]

2. Description of the Related Art Generally, in order to form a semiconductor integrated device, as an insulating film in the device, SiO ₂ ,
PSG (Phospho Silicate Glass)
s), P (plasma) -SiO, P (plasma) -Si
N, SOG (Spin On Glass), Si ₃ N ₄
(Silicon nitride film) or the like is used. Among them, Si ₃ N ₄
Because the film has high insulation and high dielectric constant,
For example, it tends to be frequently used as a sidewall, a capacitor film, an etching stopper or the like in a device. Generally, in order to form a silicon nitride film on the surface of a semiconductor wafer, thermal CVD is performed using a silane-based gas such as monosilane (SiH ₄ ) or dichlorosilane (SiH ₂ Cl ₂ ) and an ammonia (NH ₃ ) gas as a deposition gas. (Chemical
A method of forming a film by Vapor Deposition is known.
It is performed in a high temperature range of about ° C.

[0003]

By the way, based on the conventional design rules in which the degree of miniaturization is not so severe,
Although the latter film forming method described above did not cause any particular problem,
As the degree of miniaturization and integration has recently become more advanced and the device design rules have become more stringent, disadvantages have become apparent. For example, as described above, as the device design rules become stricter, the adhesion area between the silicon nitride film used as the insulating film and the underlying layer becomes smaller, and as a result, silicon nitride on the underlying layer becomes smaller due to the stress of the film itself. There has been a problem that the adhesion strength of the film is reduced, the silicon nitride film is peeled off, and a huge leak current exceeding an allowable amount flows.

For example, a stoichiometric ratio of 3: formed by flowing a flow rate of ammonia gas to a silane-based gas at least 5 times 3:
The stress of a silicon nitride film close to 4 (Si ₃ N ₄ ) is 1
× 10 ¹⁰ dyne / cm ² or more. The junction where the above-mentioned huge leak current flows is, for example, as shown in FIG. 4, a silicon nitride film insulating layer covering the entire gate electrode GE formed on the surface of a semiconductor wafer W made of a silicon substrate via a gate oxide film G. As seen in the layer I, a huge leakage current due to the stress of the silicon nitride film insulating layer I is induced at the junction J between the insulating layer I and the wafer surface. The present invention has been devised in view of the above problems and effectively solving them. An object of the present invention is to provide a film forming method capable of manufacturing a silicon nitride film as an insulating film corresponding to further miniaturization by suppressing stress of the film itself.

[0005]

The present inventors have conducted intensive studies on the stress of the silicon nitride film. As a method of reducing the stress, it is only necessary to control the refractive index of the silicon nitride film. The present invention has been made based on the finding that one method of changing the rate is to control the flow rate ratio of the film forming gas. The invention defined in claim 1 is a film forming method for forming a silicon nitride film on the surface of a processing object using a silane-based gas and an ammonia gas, wherein a flow rate ratio of the silane-based gas and the ammonia gas is adjusted. By changing the stress, the stress of the silicon nitride film is controlled.

Thus, for example, the stress of the silicon nitride film used as the insulating film can be set to a substantially desired value. In this case, as defined in claim 2, the flow rate ratio (ammonia gas / silane-based gas) is:
By setting the thickness within the range of about 0.2 to about 1.5, it is possible to provide a silicon nitride film with less stress corresponding to a stricter design rule as an insulating film. The invention defined in claim 3 is a film forming method for forming a silicon nitride film on a surface of a processing object using a silane-based gas and an ammonia gas, wherein the silicon nitride film is formed by changing a refractive index of the silicon nitride film. Control the stress of the silicon nitride film. Thereby, for example, the stress of the silicon nitride film used as the insulating film can be set to a substantially desired value. In this case, the refractive index is set within a range of approximately 2.0 to approximately 2.5 when the film forming temperature is approximately 650 ° C., so that the design is more severe. It is possible to provide a silicon nitride film with less stress corresponding to the rule as an insulating film.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a film forming method according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing an example of a film forming apparatus for performing a film forming method according to the present invention. The film forming apparatus 2 has a vertical processing container 8 having a double-tube structure made of quartz and including an inner cylinder 4 and an outer cylinder 6. The processing space S in the inner cylinder 4 accommodates a quartz wafer boat 10 as a holder for holding the object to be processed, and the wafer boat 10 has a semiconductor wafer W as the object to be processed. Are held in multiple stages at a predetermined pitch. The wafer boat 10 is mounted via a rotatable heat retaining tube 14 on a cap 12 that opens and closes a lower portion of the processing container 8, and is moved into the processing container 8 from below by a liftable elevator 16. It is made removable. A manifold 18 made of, for example, stainless steel is joined to an opening at the lower end of the processing container 8, and various film-forming gases of which flow rates are controlled are supplied to the manifold 18.
A gas supply system 20 for introducing the gas into the inside is provided.
More specifically, since two kinds of film forming gases are used for forming the silicon nitride film, that is, a monosilane gas and an ammonia gas as the silane-based gas, the silane in which the silane-based gas is introduced is System nozzle 2
2 and ammonia nozzle 26 for introducing ammonia gas
A and 26B are provided to penetrate, respectively. Incidentally, dichlorosilane may be used as a silane-based gas mixed with monosilane or instead of monosilane. Here, in order to prevent the ammonia concentration on the downstream side (upper side in the figure) in the gas flow direction in the processing vessel 8 from excessively decreasing,
A plurality, in the illustrated example, two ammonia nozzles 26 whose gas outlets are dispersed along the gas flow direction
A and 26B are provided. That is, the gas outlet of one ammonia nozzle 26A is disposed near the bottom of the processing vessel 8, and the gas outlet of the other ammonia nozzle 26B is
The processing container 8 is located at a substantially central portion in the height direction.

[0008] The monosilane gas is sent by N ₂ gas as a carrier gas. Accordingly, the respective film forming gases supplied from the respective nozzles 22 and 26A rise in the processing space S in the inner cylinder 4 and merge with the additional ammonia gas introduced from the other ammonia nozzle 26B on the way.
It is turned down at the ceiling and flows down in the gap between the inner cylinder 4 and the outer cylinder 6 and is discharged. An exhaust port 28 to which a vacuum pump or the like is connected is provided on the bottom side wall of the outer cylinder 6. Further, a heat insulating layer 30 is provided on the outer periphery of the processing container 8, and a heater 32 is provided as a heating means inside the heat insulating layer 30 to heat the wafer W positioned inside to a predetermined temperature. ing. Here, the entire size of the processing container 8 is, for example, 8
Inch, the number of wafers held in the wafer boat 10 is 1
Assuming that the number is about 20 (about 100 product wafers and about 20 dummy wafers), the diameter of the inner cylinder 4 is approximately 260 to
About 270 mm, the diameter of the outer cylinder 6 is approximately 275 to 285 mm
The height of the processing container 8 is about 1280 mm.

Next, the method of the present invention performed using the film forming apparatus configured as described above will be described. First,
A large number of unprocessed semiconductor wafers W are held in multiple stages at a predetermined pitch on the wafer boat 10, and the elevator 16 is driven up in this state, whereby the wafer boat 10 is inserted into the processing container 8 from below, The inside of the processing container 8 is sealed. The inside of the processing container 8 is preheated in advance, and when the wafer W is inserted as described above, the supply voltage to the heater 32 is increased to raise the temperature of the wafer W to a predetermined process temperature, and The inside of the container 8 is evacuated. Then, in order to prevent polycrystalline silicon from adhering to the wafer surface at the initial stage of film formation, first, ammonia gas is supplied from the two ammonia nozzles 26A and 26B to set the inside of the processing chamber 8 to an ammonia gas atmosphere. deep.

When the inside of the processing vessel 8 becomes an ammonia atmosphere in this way, the supply of ammonia gas is continued and the monosilane gas whose flow rate is controlled from the silane nozzle 22 is further mixed with the carrier gas N ₂ gas. 8
And start the film forming process. In this film forming process, two gases, that is, a monosilane gas and an ammonia gas are supplied simultaneously, and a silicon nitride film is deposited on the wafer surface. During the film formation process,
Maintain a predetermined process temperature and process pressure.
Here, as an example of the process conditions, for example, the process temperature is 650 ° C., and the process pressure is 0.35 Torr.

Here, by changing the ratio of the flow rate of the supplied monosilane gas to the flow rate of the ammonia gas, it is possible to control the refractive index of the deposited silicon nitride film, and thus the stress. in this regard,
This will be described in detail with reference to FIG. FIG. 2 is a graph showing the relationship between the flow rate ratio of ammonia gas to monosilane gas and the refractive index. Regarding the film forming conditions, the process temperature is 650 ° C., the process pressure is 0.35 Torr, the flow rate of the monosilane gas is fixed at 200 sccm, and the total flow rate of the ammonia gas is variously changed.

As is clear from this graph, when the supply amount of ammonia gas is small (the silicon nitride film is in a silicon-rich state), the refractive index becomes high near about 2.5, and then increases. As the supply amount of the ammonia gas increases, the refractive index sharply decreases.
When the flow ratio of the ammonia gas is about 2.5, the stoichiometric ratio of the silicon nitride film is 3: 4 (Si ₃ N ₄ ).
, Which is close to 2.0, which is the refractive index at that time.
As described above, the refractive index of the silicon nitride film is controlled within the range of about 2.0 to 2.5 by changing the flow ratio of the ammonia gas to the flow rate of monosilane in the range of 0.2 to 2.5. It becomes possible. In other words, when the nitrogen element in the silicon nitride film is reduced to obtain a silicon-rich composition, the refractive index can be increased accordingly.

In this case, as will be described later, the allowable range of the refractive index with respect to the film stress under the stricter design rule is approximately 2.05 to 2.5. It is preferable to form a silicon-rich silicon nitride film by setting the range of about 0.2 to 1.5. FIG. 3 is a graph showing a change in stress of the silicon nitride film when the refractive index of the silicon nitride film is variously changed based on the above results. Here, as described above, the refractive index of the silicon nitride film is changed to about 2 to 2.5 by variously changing the flow ratio of the ammonia gas to the flow rate of the monosilane gas.

As for the process conditions at this time, the process pressure is 0.35 Torr and the process temperature is 650 ° C.
And 680 ° C. As is clear from this graph, the stress in the silicon nitride film decreases substantially linearly as the refractive index increases, that is, as the silicon-rich state in the silicon nitride film increases. That is, the stress of the silicon nitride film can be controlled by changing the refractive index of the silicon nitride film. Also, the stress can be reduced as the process temperature is increased, but if the temperature is excessively increased, the diffusion state of impurities and the like doped in other films before performing this film formation process changes, and the device becomes less active. It is not preferable to raise the process temperature above 680 ° C. because the characteristics are deteriorated. The lower limit of the process temperature is a limit value at which a silicon nitride film can be formed, for example, 53
It is about 0 ° C.

The allowable range of stress under the recent stricter design rule is about 5 × 10 ⁹ dyne / cm ^2. To satisfy this, the allowable range of the refractive index when the film forming temperature is around 650 ° C. Is preferably set within a range of approximately 2.2 to 2.4. The film formation temperature is 680 ° C.
In the case of (1), it is preferable that the allowable range of the refractive index is set within a range of about 2.1 to 2.4. As described above, the stress of the silicon nitride film having a stoichiometric ratio of 3: 4 (Si ₃ N ₄ ) is about 1.0 × 10 ¹⁰ dyne / cm ² . Incidentally, the more the composition of the silicon nitride film is made to be rich in silicon,
Although the insulating property of the silicon nitride film itself tends to decrease and the leak current tends to gradually increase, the insulating property is sufficiently maintained within the above-described ranges of the flow rate of ammonia gas and the refractive index.

The above-mentioned batch type processing container is merely an example, and the processing container of any size or any number of processing containers can be used as long as the gas flow ratio and the refractive index are maintained. The method of the present invention can also be applied to the method. Further, although the film forming apparatus having a double-tube structure is described here, the present invention can also be applied to a film forming apparatus having a single-tube structure. Further, the method of the present invention is not limited to a batch type film forming apparatus capable of forming a film on a large number of semiconductor wafers at a time as described above, and the semiconductor wafer is mounted on a mounting table (support) in a processing container. The present invention can also be applied to a single-wafer type film forming apparatus that performs a film forming process one by one by lamp heating or heater heating. The object to be processed is not limited to a semiconductor wafer, but can be applied to an LCD substrate, a glass substrate, and the like.

[0017]

As described above, according to the film forming method of the present invention, the following excellent functions and effects can be exhibited. By changing the flow ratio of the silane-based gas and the ammonia gas, or by changing the refractive index of the film itself, the stress of the silicon nitride film can be controlled to a desired value. Therefore, by controlling the stress of the silicon nitride film and setting it within a desired range, it is possible to provide a silicon nitride film having excellent adhesion even under more strict design rules and capable of preventing film peeling.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a film forming apparatus for performing a film forming method according to the present invention.

FIG. 2 is a graph showing the relationship between the flow ratio of ammonia gas to monosilane gas and the refractive index.

FIG. 3 is a graph showing a change in stress of the silicon nitride film when the refractive index of the silicon nitride film is variously changed.

FIG. 4 is a view showing a silicon nitride film insulating layer covering the entire gate electrode formed on the surface of the semiconductor wafer via a gate oxide film.

[Explanation of symbols]

 2 Film forming apparatus 4 Inner cylinder 6 Outer cylinder 8 Processing vessel 10 Wafer boat (holding tool) 20 Gas supply system 22 Silane-based nozzle 26A, 26B Ammonia nozzle 34 Silicon nitride film W Semiconductor wafer (workpiece)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kanako Saito 52, Matsunagae, Iwayado, Esashi-shi, Iwate Prefecture Inside the Tohoku Office of Tokyo Electron Tohoku Co., Ltd. Address Tokyo Electron Tohoku Co., Ltd. Tohoku Office F-term (reference) 4K030 AA06 AA13 AA18 BA40 CA04 CA12 JA05 JA06 JA10 LA01 LA11 LA15 5F058 BA04 BC08 BF04 BF23 BF30 BF37 BJ01

Claims (4)

[Claims] 1. A film forming method for forming a silicon nitride film on a surface of an object to be processed using a silane-based gas and an ammonia gas by changing a flow ratio of the silane-based gas and the ammonia gas. A film forming method, wherein the stress of the silicon nitride film is controlled. 2. The film forming method according to claim 1, wherein the flow rate ratio (ammonia gas / silane-based gas) is set within a range of about 0.2 to about 1.5. 3. A method for forming a silicon nitride film on a surface of an object using a silane-based gas and an ammonia gas, wherein the silicon nitride film is formed by changing a refractive index of the silicon nitride film. A film forming method characterized in that stress is controlled. 4. The film forming method according to claim 3, wherein said refractive index is set within a range of about 2.0 to about 2.5 when the film forming temperature is around 650 ° C. .