JPH104140A - Method for forming interlayer insulating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interlayer insulating film forming method capable of preventing sludge composed of oxides of impurities, etc., in the interlayer insulating film from being produced on the surface of the interlayer insulating film after reflow. SOLUTION: A first-layer BPSG film 3 and a second-layer BPSG film 4 are formed successively by atmospheric CVD for example on a semiconductor substrate 1 having a pattern 2. The concentrations of B and P of the first-layer BPSG film 3 are made higher than those of B and P of the second-layer BPSG film 4. Next, after causing the BPSG films 3, 4 to reflow and flattening the surface by performing heat treatment at 800-900 deg.C in a nitrogen gas atmosphere in a vacuum CVD furnace, an SiO2 film 5 is formed as a protective film on the BPSG film 4 by vacuum CVD successively. After this, the semiconductor substrate 1 is take out from the vacuum CVD furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an interlayer insulating film, and more particularly, to a method suitable for forming an interlayer insulating film whose surface is flattened by so-called reflow.

[0002]

2. Description of the Related Art In a semiconductor device, an interlayer insulating film below a metal wiring, whose surface can be flattened by reflow by heat treatment, is often used. One type of such an interlayer insulating film is boron phosphorus silicate glass (Boro-p
There is a hosphosilicate glass (BPSG) film.

In this BPSG film, the concentration of B and P is often increased to improve the reflow performance. In the manufacture of a semiconductor device, after forming this BPSG film on a substrate by a chemical vapor deposition (Chemical Vapor Deposition, CVD) method, 800 to 9
By performing a heat treatment at a high temperature of 00 ° C., the BPSG film is reflowed and its surface is flattened.

[0004]

However, the above-mentioned conventional method for forming an interlayer insulating film has the following problems. That is, after the BPSG film is reflowed at a high temperature as described above, when the substrate is taken out of the CVD furnace, the surface of the BPSG film is exposed to the atmosphere, so that the oxygen in the atmosphere is removed from the BPSG film. It reacts with boron (B) and phosphorus (P) to produce BPO _{4 and the} like,
It occurs as a precipitate on the surface of the PSG film. Further, even when such precipitates are not generated immediately after the reflow, the precipitates are generated on the surface of the BPSG film if left in the air thereafter.

[0005] When precipitates are formed on the surface of the BPSG film in this manner, in the step of forming metal wiring on the BPSG film, processing defects occur, and problems such as short-circuiting of the metal wiring occur.

A similar problem is that BPSG is used as an interlayer insulating film.
This can occur not only when a film is used but also when another interlayer insulating film containing impurities is used.

Therefore, an object of the present invention is to prevent the formation of precipitates such as oxides of impurities contained in the interlayer insulating film on the surface of the interlayer insulating film when left in the air after reflow or after that. It is an object of the present invention to provide a method for forming an interlayer insulating film that can prevent such a problem.

[0008]

In order to achieve the above object, a method of forming an interlayer insulating film according to the present invention comprises the steps of forming an interlayer insulating film containing impurities on a substrate, and performing a heat treatment on the interlayer insulating film. The method is characterized by including a step of flattening the surface by reflowing the film and a step of forming a protective film on the interlayer insulating film without exposing the surface of the interlayer insulating film to the atmosphere.

In the present invention, typically, the heat treatment and the formation of the protective film are continuously performed using the same chemical vapor deposition reactor, preferably a reduced pressure chemical vapor deposition reactor. in this case,
The heat treatment is preferably performed under reduced pressure or normal pressure in an inert gas atmosphere, for example, a nitrogen gas atmosphere.

In the present invention, the interlayer insulating film is most typically a boron phosphorus silicate glass (BPSG) film, but when exposed to the atmosphere after reflow, impurities contained therein contain oxygen in the atmosphere. Any other interlayer insulating film, such as a phosphosilicate glass (PSG) film, a boron silicate glass (BSG) film, an arsenic silicate glass (AsSG) film, or the like, may be used as long as a precipitate is generated on the surface by reacting with the substrate. You may.

When the interlayer insulating film is a boron phosphosilicate glass film, the boron phosphorus silicate glass film
In order to minimize the generation of precipitates on the surface while improving the reflow performance as a whole, it is preferable that the first layer of boron phosphorus silicate glass film and the second layer of boron phosphorus silicate glass film And the concentration of boron and phosphorus in the first layer of boron phosphorus silicate glass film is higher than the concentration of boron and phosphorus in the second layer of boron phosphorus silicate glass film. In this case, the temperature of the heat treatment is typically 800 to 900C.

In the present invention, a silicon nitride film or the like can be used as a protective film in addition to a silicon oxide film. This silicon oxide film typically has a thickness of 600 to
Formed at a temperature of 850 ° C.

In the method of forming an interlayer insulating film according to the present invention having the above-described structure, the surface of the interlayer insulating film is flattened by reflowing by performing a heat treatment.
By forming a protective film on the interlayer insulating film without exposing the surface of the interlayer insulating film to the air, the interlayer insulating film is formed on the surface of the interlayer insulating film after reflow or when left in the air thereafter. It is possible to prevent the generation of precipitates formed of oxides of impurities contained therein.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method of forming an interlayer insulating film according to one embodiment of the present invention. In this embodiment, first, as shown in FIG. 1A, a semiconductor substrate 1 such as a silicon substrate on which a diffusion layer or the like (not shown) is formed in advance.
After the pattern 2 is formed thereon, the first layer BPSG film 3 and the second layer B
The PSG films 4 are sequentially formed. These BPSG films 3, 4
For example, a continuous normal-pressure CVD furnace (not shown)
Is used. As the gas for normal pressure CVD, for example, SiH ₄ or O ₃ -TEOS (Tetra-ethyl-or
tho-silicate) is used. In this case, the first layer B
The B concentration of the PSG film 3 is, for example, 4 to 8% by weight, the P concentration is, for example, 3 to 5% by weight, and the thickness is, for example, 550 nm. The concentration of B and P in the second-layer BPSG film 4 is, for example, 14.5 mol% as a whole, and the thickness is, for example, 50 nm. The pattern 2 is, for example, a gate electrode in the manufacture of a MOS semiconductor device.

Next, as described above, the BPSG films 3, 4
The semiconductor substrate 1 on which is formed is taken out of the continuous atmospheric pressure CVD furnace.

Next, the semiconductor substrate 1 is placed in a vertical reduced pressure CVD furnace shown in FIG. As shown in FIG. 2, in this vertical reduced pressure CVD furnace, a quartz boat 11 on which a semiconductor substrate 1 to be processed is placed is placed in a quartz tube 12. A heater 1 is provided on the outer periphery of the quartz tube 12.
The quartz boat 1 is provided by the heater 13.
1 is to be heated. The inside of the quartz tube 12 is evacuated from its lower part under reduced pressure. Further, a nitrogen gas and a CVD gas are introduced into the quartz tube 12 through a nitrogen gas line 14 and a CVD gas line 15 attached to a lower portion thereof.

Nitrogen gas is introduced at a flow rate of, for example, 20 l / min from a nitrogen gas line 14 into the quartz tube 12 of the vertical type reduced pressure CVD furnace shown in FIG. Heat treatment is performed under normal pressure at a temperature of, for example, 800 to 900 ° C. for, for example, about 30 minutes. Thereby, as shown in FIG. 1B, the BPSG films 3 and 4 are reflowed and the surface is flattened.

Next, in the vertical type low pressure CVD furnace, for example, 600 to 85
BP at a temperature of 0 ° C. and a reduced pressure of, for example, tens to hundreds of Pa
An SiO ₂ film 5 is formed on the SG film 4 as a protective film. The thickness of the SiO ₂ film 5 is, for example, 50 to 100 nm. As the gas for the low pressure CVD, for example,
SiH ₄ / N ₂ O, SiH ₂ Cl ₂ / N ₂ O or TE
OS is used. Si formed by the low pressure CVD method
The O ₂ film 5 has good film quality and is suitable as a protective film.

Next, the semiconductor substrate 1 is taken out of the vertical vacuum CVD furnace shown in FIG. 2 with the inside thereof being sufficiently filled with nitrogen in advance.

Thereafter, a metal wiring (not shown) made of, for example, aluminum (Al) or an Al alloy is formed on the SiO ₂ film 5.

As described above, according to this embodiment,
The BPSG films 3 and 4 are reflowed by high-temperature treatment in a vertical reduced-pressure CVD furnace to planarize the surface, and subsequently, Si as a protective film is formed in the same vertical reduced-pressure CVD furnace
After the O ₂ film 5 is formed to cover the surfaces of the BPSG films 3 and 4, the semiconductor substrate 1 is taken out of the furnace, so that the surfaces of the reflowed BPSG films 3 and 4 are not exposed to the atmosphere. Therefore, the precipitate composed of BPO ₄ etc. is BP
Generation on the surfaces of the SG films 3 and 4 can be effectively prevented. Further, even when the semiconductor substrate 1 is left in the air after the reflow, the surface of the BPSG films 3 and 4 has
It is possible to prevent the generation of precipitates such as PO ₄ . For this reason, in the subsequent formation process of the metal wiring, it is possible to prevent the occurrence of processing defects, thereby preventing the metal wiring from being defective such as a short circuit.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. .

For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as needed.

In the above-described embodiment, the BP
Although the vertical low-pressure CVD furnace shown in FIG. 2 is used for reflowing the SG films 3 and 4 and forming the SiO ₂ film 5, a horizontal low-pressure CVD furnace may be used instead of the vertical low-pressure CVD furnace.

[0026]

As described above, according to the method for forming an interlayer insulating film according to the present invention, the surface of the interlayer insulating film is planarized by reflowing the interlayer insulating film by performing a heat treatment, and then the surface of the interlayer insulating film is removed. Since the protective film is formed on the interlayer insulating film without being exposed to the air, the impurity contained in the interlayer insulating film is formed on the surface of the interlayer insulating film when left in the air after reflow or afterwards. It is possible to prevent the generation of precipitates such as oxides.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a method of forming an interlayer insulating film according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a vertical reduced-pressure CVD furnace used in a method of forming an interlayer insulating film according to an embodiment of the present invention.

[Explanation of symbols]

1 ... semiconductor substrate, 3, 4 ... BPSG film, 5 ...
・ SiO ₂ film

Claims (9)

[Claims] A step of forming an interlayer insulating film containing impurities on a substrate; a step of performing a heat treatment to reflow the interlayer insulating film to planarize the surface; Forming a protective film on the interlayer insulating film without exposure. 2. The method for forming an interlayer insulating film according to claim 1, wherein the heat treatment and the formation of the protective film are continuously performed using the same chemical vapor deposition furnace. 3. The method for forming an interlayer insulating film according to claim 1, wherein the heat treatment and the formation of the protective film are continuously performed using the same low-pressure chemical vapor deposition furnace. 4. The method for forming an interlayer insulating film according to claim 1, wherein said interlayer insulating film is a boron phosphorus silicate glass film. 5. The boron phosphorus silicate glass film comprises a first layer of boron phosphorus silicate glass film and a second layer of boron phosphorus silicate glass film. 5. The method for forming an interlayer insulating film according to claim 4, wherein the concentration of phosphorus and phosphorus is higher than the concentration of boron and phosphorus of the second layer boron phosphorus silicate glass film. 6. The method for forming an interlayer insulating film according to claim 1, wherein said heat treatment is performed under reduced pressure or normal pressure in an inert gas atmosphere. 7. The method according to claim 4, wherein the temperature of the heat treatment is 800 to 900 ° C. 8. The method according to claim 1, wherein the protective film is a silicon oxide film. 9. The method according to claim 1, wherein the silicon oxide film is formed at a temperature of 600 to 850 ° C.
9. The method according to claim 8, wherein the temperature is set at a predetermined temperature.
The method for forming an interlayer insulating film according to the above.