JP2976442B2 - Method of forming insulating film - Google Patents

Description

The present invention relates to a method for forming an insulating film, and more particularly, to a method for forming an insulating film.
The present invention relates to a method for forming an insulating film on a surface in contact with a substrate having a step or a semiconductor substrate by a bias ECR plasma CVD method, which has reduced stress and has improved adhesion to a step.

SUMMARY OF THE INVENTION The present invention is a method for forming an insulating film in contact with a semiconductor substrate having a step, wherein the insulating film is formed by a bias ECR plasma C
By forming the SiO ₂ film as the first step and then forming the SiN _x film as the second step by the VD method, it is possible to form an insulating film having high adhesion to the step portion. For example, it is possible to improve the adhesion to the inner wall of the trench in the trench isolation, and to reduce the leak current.

[Prior Art] The bias ECR plasma CVD method is becoming an important technology capable of meeting the demand for the planarization of an interlayer film, as the degree of integration of devices increases in the future. That is, the bias ECR plasma CVD method can form high-density plasma at low pressure,
It has the advantage of being able to grow a film at high speed even on grooves and steps with a high aspect ratio, and to remove excess film by applying RF bias to the wafer and to form a planarized insulating film in the same device. is there. In addition, since the CVD method uses low-temperature plasma, low-temperature growth is possible.

This type of bias ECR plasma CVD method is disclosed in
The one described in JP-A-63-80538 is known. This technology uses silane (SiH ₄ ) gas and oxygen (O ₂ ) gas as reaction gases, etches and deposits a SiO ₂ film while flattening it, and applies a bias voltage to the substrate,
By using an inert gas having a larger mass than argon (Ar), the etching rate in the horizontal direction is increased, and the time required for the planarization process is reduced.

In recent years, research and development to take advantage of the characteristics of such a bias ECR plasma CVD method, for example, to form a trench in an element isolation region and bury an insulating film such as SiO ₂ in the trench by the bias ECR plasma CVD method. Is being done.

[Problems to be Solved by the Invention] However, in such a conventional method for forming an insulating film, Si is used as a reactive gas for bias ECR plasma CVD.
Although H ₄ and O ₂ are used, the stress of the deposited insulating film is relatively large, so that defects may be induced in the base crystal by heat treatment applied during the device formation process after filling the trench,
There is a problem that cracks are easily generated in the embedded film.

The present invention has been made in view of such conventional problems, and is intended to reduce the stress of an insulating film embedded in a step.

[Means for Solving the Problems] The present invention is a method for forming an insulating film in contact with a semiconductor substrate having a step, and in forming the insulating film, compressive stress is reduced by a bias ECR plasma CVD method as a first step. After forming a SiO ₂ film having a bias EC
The solution is to relax the compressive stress of the SiO ₂ film by forming a SiN _X film having a tensile stress by the R plasma CVD method.

[Operation] In the present invention, after forming the SiO ₂ film, the silicon nitride film (SiN _x ) is formed, so that the compressive stress of the SiO ₂ film is relaxed by the tensile stress of the SiN _X film, and the silicon substrate is moved toward the substrate. Prevent stress. For this reason, for example, the leakage current in the trench portion is reduced, and the trench with a high aspect ratio can be embedded.

EXAMPLES Hereinafter, details of a method for forming an insulating film according to the present invention will be described based on examples shown in the drawings.

(First Embodiment) FIGS. 1A to 1C are cross-sectional views showing steps of a first embodiment of the present invention.

First, as shown in FIG. 1A, a trench 1a as a step is formed on the surface of a silicon substrate 1 as a base by using a lithography technique and a dry etching technique, and then the inner wall surface of the trench 1a and the silicon substrate 1 are formed. Thermal oxidation is performed on the surface to form an oxide film 2 having a thickness of about 100 to 200 °.

Next, as a first step, as shown in FIG. 1B, using a silane (SiH ₄ ) gas and a dinitrogen oxide (N ₂ O) gas as a reaction gas, a bias ECR plasma CVD method is performed to form an insulating film. A first SiO ₂ film 3 is formed to a thickness of about 500 to 3000 °. Conditions for this bias ECR plasma CVD method include Si
The H ₄ gas flow rate is 20 SCCM, the N ₂ O gas flow rate is 40 SCCM, and the pressure is 5
× 10 ^-3 Torr, microwave power 800W, RF bias 300W
Set to.

Next, as a second step, as shown in FIG. 1C, bias ECR plasma CVD is performed by replacing the reaction gas with SiH ₃ gas, oxygen (O ₂ ) gas, and argon (Ar) gas, thereby forming a second SiO ₂ gas. The film 4 is buried and flattened. Note that this bias ECR
The plasma CVD conditions were as follows: SiH ₄ gas flow rate was 20 SCCM, O ₂ gas flow rate was 4 SCCM, argon gas flow rate was 10 SCCM, pressure was 5 × 10 ^-3 Torr, microwave power was 800 W, and RF bias was
Set to 300W.

Primary SiO ₂ film 3 described above are those capable sake of about 1 × 10 ⁹ dyne / cm ² or lower stressed, secondary SiO ₂ film 4
Even if the stress is relatively high, about 2 × 10 ⁹ dyne / cm ² , it is possible to prevent the stress from being applied from the primary SiO ₂ film 3 to the silicon substrate 1 side.

The SiO ₂ film of the trench 1 thus formed (first
Since the secondary SiO ₂ film 3 and the secondary SiO ₂ film 4) can be reduced in stress as a whole, even after the heat treatment performed in the device forming process, defects occur in the crystal of the silicon substrate 1 or the SiO ₂ film No cracks occur on the surface.

Second Embodiment FIGS. 2A to 2C are cross-sectional views showing steps of a second embodiment of the method for forming an insulating film according to the present invention. First, the second
As shown in FIG. A, a trench 1a is formed on the surface of a silicon substrate 1 by using lithography and dry etching techniques, and then thermal oxidation is performed to form an oxide film 2 on the inner wall surface of the trench 1a and the surface of the silicon substrate 1. Is formed to a thickness of about 100 to 200 mm.

Next, as shown in FIG. 2B, a silane (SiH ₄ ) gas and an oxygen (O ₂ ) gas are used as reaction gases, and a bias ECR is used.
Perform plasma CVD in trench 1a and silicon substrate 1
An SiO ₂ film 5 is formed thereon. The conditions for this CVD are SiH
₄ gas flow rate 20SCCM, O ₂ gas 20SCCM, pressure 5 × 10 ^-3
Torr, microwave power was set to 800W and RF bias was set to 300W. After forming the SiO ₂ film 5 with a thickness of about 500~3000Å in this condition, the pressure, by reducing the flow rate ratio remains SiH ₄ was kept microwave power and RF bias to the same conditions, further, SiO ₂ film 5 deposition and planarization biased ECR plasma CVD
(FIG. 2C). In this case, the SiH ₄ gas is
The flow rates of CM and O ₂ gas were 40 SCCM, and the flow rate of argon gas was 10 SCCM.

As described above, the flow ratio of the SiH ₄ gas is reduced stepwise, but the flow ratio of the SiH ₄ gas may be reduced continuously. In other words, if the flow ratio of SiH ₄ is large when the SiO ₂ film covering the inner wall of the trench 1a is formed (the flow ratio of SiH ₄ gas to O ₂ gas is about 1: 1), it is possible to sufficiently reduce stress. It is.

In this embodiment, the argon gas is added, but another inert gas may be added.

Third Embodiment FIGS. 3A to 3C are cross-sectional views showing steps of a third embodiment of the present invention.

First, as shown in FIG. 3A, an oxide film 2 is formed on the inner wall of the trench 1a of the silicon substrate 1 and the surface of the silicon substrate 1 by thermal oxidation.

Next, as a first step, as shown in FIG. 3B, a bias ECR plasma CVD is performed using SiH ₄ gas and O ₂ gas as reaction gases to form an SiO ₂ film 5 with a thickness of about 500 to 3000 °. . This SiO ₂ film 5 has a compressive stress. The conditions of this CVD are as follows: gas flow rate is SiH ₄ / O ₂ = 20/40 SCCM, pressure is 5 × 10
^-3 Torr, microwave power set to 800W, RF bias set to 300W.

Next, as a second step, as shown in FIG. 3C, silicon nitride (SiN _x ) is formed by a bias ECR plasma CVD method.
The film 6 is flattened and formed. The CVD conditions were as follows: the flow rate of the reaction gas was SiH ₄ / O ₂ = 20/60 SCCM, and the pressure was 5 × 10 ⁻³ To
rr, microwave power was set to 800W and RF bias was set to 300W.

The silicon nitride film 6 has a tensile stress,
The compressive stress of the SiO ₂ film is reduced.

In the present embodiment, _two layers of the SiO ₂ film 5 and the SiN _X film 6 are used.
If the layer that adheres to the inner wall of the trench 1a is an SiO ₂ film, a multilayer structure with a silicon nitride film may be used. Also, the SiO ₂ film 5
The step of forming the SiN _X film 6 may be performed continuously by gradually changing the reaction gas. In this case, for example, Si
Maintaining the flow rate of H ₄ gas to 20SCCM, 0SCC O ₂ gas from 40SCCM
By changing to M and simultaneously changing the N ₂ gas from “0” to 60 SCCM, continuous bias ECR plasma CVD becomes possible. When the insulating film is continuously formed as described above, the adhesion between the SiO ₂ film and the SiN _X film is improved as compared with the case where the insulating film is formed in two layers. Further, by controlling the temperature and the like of the silicon substrate 1, it is possible to further improve the film quality.

According to the present embodiment, it is possible to reduce leakage current and the like and to achieve good isolation of trenches even in trenches having a high aspect ratio, as compared with the case where trenches are buried only with the SiO ₂ film.

[Effects of the Invention] As is clear from the above description, according to the method for forming an insulating film according to the present invention, it is possible to reduce the stress of the step portion, particularly the insulating film embedded in the trench, and to reduce the device stress. Defects do not occur in the base crystal even when heat treatment is performed in the formation process, and for example, there is an effect of having good characteristics such as a reduction in leak current. Further according to the invention,
Since an insulating film having high adhesion can be formed on the step portion of the semiconductor substrate, the adhesion to the inner wall of the trench in the trench isolation can be improved, and the leakage current can be reduced.

[Brief description of the drawings]

1A to 1C are cross-sectional views showing steps of a first embodiment of a method for forming an insulating film according to the present invention, and FIGS. 2A to 2C show steps of the second embodiment. Sectional views, FIGS. 3A-3C
FIG. 9 is a cross-sectional view showing a step of the third embodiment. 1 ... silicon substrate, 1a ... trench, 2 ... oxide film,
3 ...... primary SiO ₂ film, 4 ...... secondary SiO ₂ film, 5 ...... SiO ₂
Film 6, SiN _X film.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21 / 316,21 / 318

Claims (1)

(57) [Claims] 1. A method for forming the insulating film in contact with the semiconductor substrate having a step, in forming the insulating film, after forming a SiO ₂ film having a bias ECR plasma CVD process in the compression stress as the first step Bias EC as the second step
A method for forming an insulating film, wherein a compressive stress of the SiO ₂ film is reduced by forming a SiN _X film having a tensile stress by an R plasma CVD method.