JP2921137B2 - Method of forming insulating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device having an insulating film, and more particularly to a method for manufacturing a semiconductor device having an insulating film on a step portion, for example, an electrode or a wiring, on a semiconductor device substrate by ECR (Electron Cyclotron) plasma CVD. The present invention relates to a technique for forming an insulating film. According to the present invention, an ECR plasma CVD apparatus to which an ECR plasma CVD method is applied is provided with a microwave generation window on an axis, an axially symmetric plasma generation chamber for converting introduced gas into plasma, and a coaxial surrounding of the plasma generation chamber. A coil that forms an electron cyclotron resonance magnetic field region with microwaves in the plasma generation chamber and a plasma extraction window provided on the side of the plasma generation chamber facing the microwave transmission window and communicates with the plasma generation chamber. And a reaction chamber in which a film formation substrate is disposed.

[0002]

2. Description of the Related Art As an interlayer insulating film or a passivation film (surface protective film) of a semiconductor integrated circuit, a thermal CV which uses heat energy to excite gas molecules as a raw material of an insulating film is usually used.
An oxide film, a nitride film, and the like formed by the D method or a high frequency plasma CVD method in which gas molecules are excited by plasma discharge by applying a high frequency voltage are used. However, in recent years,
As the integration and densification of semiconductor devices advance and the structural dimensions such as wiring spacing and wiring width shift to the submicron region, high quality insulating films are required, and the above-mentioned film formation is required. Various approaches other than the method have been attempted. As one of them, an ECR plasma CVD method capable of forming a low-temperature film and forming an insulating film excellent in acid resistance and denseness has been developed.

In this ECR plasma CVD method, a gas is introduced into a magnetic field having a predetermined intensity, and a microwave having a frequency corresponding to the magnetic field intensity is incident on the gas, whereby the energy of the microwave is resonantly absorbed by accidental electrons. The plasma generated at high density by absorbing energy even to electrons that multiply by ionization of gas molecules due to collision of accidental electrons that have gained energy, is introduced on the substrate together with the reaction gas to form a film. is there.

Here, when an insulating film is formed on a step on a substrate (for example, an uneven surface formed by electrodes or wirings formed on the substrate), the insulating characteristics are improved or a multilayer structure is formed. In order to be able to form, it is necessary to perform a flattening process. As a method for forming an insulating film that can be flattened without special need for this flattening process and has good step coverage on the substrate, a high-frequency bias is applied to the substrate, and the self-bias effect of the substrate is applied. There is known a bias sputtering method in which a negative potential is generated on the surface of a substrate to perform etching and deposition simultaneously. The application of the high-frequency bias can be performed also in the ECR plasma CVD method, and thereby, improvement in step coverage of the insulating film and improvement in film quality are expected.

FIG. 5 shows a structural example of an ECR plasma CVD apparatus to which the present invention is applied as an apparatus to which the ECR plasma CVD method is applied. Forming the insulating film by the apparatus of FIG. 5, when the insulating film is, for example, a SiO ₂ film, by a coil 4 surrounding the plasma generation chamber 5 formed axisymmetrically coaxially, a microwave frequency plasma generating chamber 5 After forming an electron cyclotron resonance magnetic field area surface (hereinafter abbreviated as ECR area surface or ECR surface) of the plasma generation chamber
Within 5 while O ₂ gas _is introduced from the first gas introduction system 3, the microwave oscillated by the microwave source (not shown) through the waveguide 1, by transmitting microwave transmission window 2 plasma generating chamber 5 by introducing into, and ionization degree of ionization higher O ₂ gas in the ECR region the vicinity generate O ₂ gas plasma, and guides into the reaction chamber 6 along a divergent magnetic field to the plasma coil 4 is formed, Second gas introduction system 7
The SiH ₄ gas as a reactive gas is introduced into the reaction chamber 6 from the O ₂ gas plasma by decomposing and activating, SiO ₂ on the substrate
This is done by depositing molecules.

[0006]

SUMMARY OF THE INVENTION ECR plasma CVD
Since the insulating film formed by the method has a bias in the density and energy of the plasma reaching the substrate at the time of film formation, the insulating film formed by this method has poor uniformity of film thickness and film quality. There are drawbacks, such as a lack of adaptability to a fine structure and a stability of insulation characteristics due to the high integration of the semiconductor device, and a lack of coverage of steps such as wiring.

An object of the present invention is to provide an ECR plasma CVD.
Without any substantial structural changes or cost increases,
An object of the present invention is to provide a method for forming an insulating film capable of forming an insulating film having a uniform thickness and film quality.

[0008]

According to the present invention, there is provided, in accordance with the present invention, an axially symmetric plasma generation chamber having a microwave transmission window on an axis for converting introduced gas into plasma, An ECR including a coil for forming an electron cyclotron resonance magnetic field region surface with microwaves in a plasma generation chamber coaxially surrounding the generation chamber, and a reaction chamber in communication with the plasma generation chamber and in which a substrate on which a film is to be formed is disposed. Plasma C
An insulating film forming method for forming an insulating film on a film formation substrate using a VD apparatus, wherein a geometric center of the coil is
The coil was arranged so that the surface of the microwave transmission window on the side of the plasma generation chamber inside space was on the opposite side of the plasma generation chamber interior space, and the coil passed through the microwave transmission window through the electron cyclotron resonance magnetic field area. In the method for forming an insulating film, in which the insulating film is formed by applying a high-frequency bias to a substrate on which the film is to be formed at a peak value position of the electric field strength of the microwave,
° C, gas pressure of 1 × 10 ^{-4 to} 5 × 10 ^-3 torr, and microwave power incident on the plasma generation chamber of 250 to 45.
0 W, the high frequency bias power applied to the film formation substrate is 60
An insulating film is formed at 0 to 1000 W. Here, it is preferable that the position of the peak value of the electric field intensity of the microwave on which the electron cyclotron resonance magnetic field region surface is formed be the first peak position of the microwave transmitted through the microwave transmission window.

[0009]

The plasma generated in the plasma generation chamber flows onto the substrate along the lines of magnetic force due to the magnetic field intensity gradient of the divergent magnetic field formed by the coil surrounding the plasma generation chamber which is symmetrical with respect to the axis. An attempt is made to form a thin film thickness distribution on the edge side. On the other hand, a high-frequency bias is applied to the substrate, and a negative bias potential is generated on the surface of the substrate, and the electric field due to this potential is directed toward the peripheral wall of the reaction chamber. Attempts to attract ions in the plasma toward the substrate more strongly at the peripheral edge. As a result, an insulating film having a more uniform thickness is formed on the surface of the substrate, and ions are accelerated by the negative potential on the surface of the substrate. It is considered that a dense film is formed by forming the film.

Further, by forming the ECR region surface of the coil at the peak value of the electric field intensity of the microwave transmitted through the microwave, the energy of the microwave for absorbing gas molecules into the ionizing electrons increases. High-density plasma is generated near the surface of the region, and near the peak value of the microwave, the width of the electric field region close to the peak value is large in the axial direction. The ECR area surface exists within this width, and the plasma is uniformly formed in the radial direction of the plasma generation chamber, and the application of the high frequency bias makes the plasma density reaching the substrate uniform in the radial direction of the substrate. Can be. In addition, since the geometric center of the coil is located on the opposite side of the plasma transmission chamber interior space from the surface of the microwave transmission window on the plasma generation chamber interior space side, the magnetic field formed by the coil is generated at any position in the plasma generation chamber. Since the plasma diverges in the direction of the plasma extraction window, the plasma in the plasma generation chamber does not go to the microwave transmission window, the damage of the microwave transmission window is prevented, and stable operation of the apparatus becomes possible.

As described above, the in-plane uniformity of the film thickness and quality of the insulating film formed on the substrate is improved. By controlling the high frequency bias, it is possible to improve the step coverage and flatness of the electrodes and wirings. The operation when the ECR region surface is formed at the first peak value of the electric field intensity of the microwave transmitted through the microwave transmission window, and the film forming conditions such as the substrate temperature and the gas pressure are set as described above. The operation in this case will be described in the embodiment section together with the structure of one embodiment of the ECR plasma CVD apparatus to which the above-described insulating film forming method is applied.

[0012]

FIG. 1 shows an embodiment of an ECR plasma CVD apparatus to which an insulating film forming method according to the present invention is applied. In the drawing, the same members as those in FIG. 5 are denoted by the same reference numerals. This device differs from the device of FIG.
As described in detail below, the geometric center of the coil 4 is located at a position sufficiently away from the surface of the microwave transmission window 2 on the side of the space inside the plasma generation chamber toward the side opposite to the space inside the plasma generation chamber. And the lower end surface of the coil is the microwave transmitting window 2
The point is that the coil is arranged so as to be located near the first peak value position of the electric field strength of the microwave transmitted through the substrate, and the high frequency power supply 11 is connected to the substrate table 10 on which the substrate 9 is mounted.

When the device is formed in this manner and the current flowing through the coil 4 is adjusted to form the ECR region surface near the lower end surface of the coil, which is the first peak value position of the electric field intensity of the microwave, the ECR region surface Can be formed on a relatively flat surface, so that the ECR region surface can exist within the axial width of the region near the peak value of the microwave electric field intensity. Further, once the plasma is formed in the plasma generation chamber, the peak value of the electric field intensity of the microwave attenuates in the traveling direction of the microwave. Forming the ECR region surface at a position where the electric field intensity reaches the peak value first is also effective for increasing the film forming speed.

Therefore, the ECR plasma CVD shown in FIG.
Table 1 shows the film forming conditions when forming an SiO ₂ film using the apparatus.
Various characteristics of the SiO ₂ film when set as described below will be described below. Note that, compared to the conventional normal film forming conditions, the film forming conditions are higher in the high frequency bias power (RF power) applied to the substrate than the microwave power input into the plasma generation chamber.
The feature is that is increased. That is, under these film forming conditions, the difference between the microwave power and the high frequency bias power is caused by the ratio between the pulse width and the pulse period of the power applied in a pulse shape, that is, the difference in the duty. By increasing the duty of power, a dense film can be formed.
When the insulating film is a SiN film, the insulating film is formed by changing the flow ratio of the N ₂ gas to the SiH ₄ gas from the gas flow ratio shown in this table.

[0015]

[Table 1]

As can be seen from FIG.
Formed by the incoming divergent magnetic field _TwoThe film thickness depends on the substrate
Radially outwardly. This is
Reflects bias of plasma density generated in plasma generation chamber 3
It is considered that the Si formed according to the present embodiment
O_TwoIn the film, a uniform film thickness is reached up to the outer periphery of the substrate.
Have. To apply a high frequency bias to the substrate 8
More uniform plasma density and sputtering
The surface is flattened by the effect, and unevenness is reduced
It seems to be due to.

FIG. 4 shows the distribution of the etching rate when the SiO ₂ film is etched with BHF (buffer hydrofluoric acid, a solution obtained by diluting 50% hydrofluoric acid with water). The in-plane uniformity of the etching rate of the SiO ₂ film formed under the film forming conditions of the present embodiment is extremely excellent as compared with the case where the SiO ₂ film is formed by the conventional divergent magnetic field. In addition, the etching rate is slower than before, and the film quality is improved as a whole. This is considered to be due to the fact that ions in the plasma collide with the substrate due to the application of the high-frequency bias under the film forming conditions of the present embodiment, thereby forming a denser film than before.

As described above, the in-plane uniformity of both the film thickness and the film quality can be improved, and the film quality itself can be improved as compared with the prior art.

[0019]

According to the present invention, the ECR plasma CV
Since the method of forming the insulating film by the method D is the method described above, the following effects can be obtained.

According to the first aspect of the present invention, the position of the ECR region surface coincides with the peak value position of the microwave electric field intensity in the plasma generation chamber, and the axial width of the region near the peak value of the microwave electric field intensity is wide. Even if the ECR area surface has some curvature, the ECR area surface will be present within this width,
High-density plasma is uniformly formed in the radial direction, and this plasma reaches the substrate with uniform density by the divergent magnetic field and the negative bias potential on the substrate surface due to the high frequency bias applied to the substrate. And the film quality itself is also improved by the ion bombardment effect of the negative bias potential on the substrate surface.

Furthermore, since the microwave power applied to the plasma generation chamber is small and the high frequency bias power applied to the substrate is large, adjusting both powers within this set range allows the radius of the film thickness and film quality to be adjusted. It is possible to improve the film quality while controlling the inclination of the direction to eliminate the inclination.

According to the second aspect of the present invention, the surface of the ECR region is formed at the maximum peak value position closest to the microwave transmission window among the peak values of the microwave electric field intensity. And the film forming speed is further improved.

[Brief description of the drawings]

FIG. 1 shows an ECR to which an insulating film forming method according to the present invention is applied.
Longitudinal sectional view showing one embodiment of a plasma CVD apparatus structure

FIG. 2 is an explanatory view showing an insulating film forming method according to the present invention.

FIG. 3 shows a film thickness distribution when an SiO ₂ film is formed according to an embodiment of the film forming conditions under the method of forming an insulating film according to the present invention, in comparison with a case where an SiO ₂ film is formed according to a conventional technique. Diagram showing

FIG. 4 shows an etching rate when an SiO ₂ film is formed under the same film forming conditions as in FIG. 3 under the insulating film forming method according to the present invention, as compared with a case where an SiO ₂ film is formed by a conventional technique. Diagram

FIG. 5 is a longitudinal sectional view showing a structural example of an ECR plasma CVD apparatus to which a conventional insulating film forming method is applied.

[Explanation of symbols]

2 Microwave transmission window 4 Coil 5 Plasma generation chamber 6 Reaction chamber 8 Plasma extraction window 9 Substrate (deposition target substrate) 11 High frequency power supply

Claims (2)

(57) [Claims] 1. An axially symmetric plasma generation chamber having a microwave transmission window on an axis for converting introduced gas into plasma, and an electron cyclotron resonance magnetic field of microwaves in the plasma generation chamber surrounding the plasma generation chamber coaxially. Insulation when an insulating film is formed on a deposition target substrate using an ECR plasma CVD apparatus including a coil forming a region surface and a reaction chamber communicating with a plasma generation chamber and having a deposition target substrate disposed therein. A film forming method, comprising: arranging a coil so that a geometric center of the coil is located on a side opposite to a plasma generation chamber interior space on a surface of the microwave transmission window on a side of the plasma generation chamber interior space; The electron cyclotron resonance magnetic field region surface is formed at the peak position of the electric field intensity of the microwave transmitted through the microwave transmission window, and a high frequency bias is applied to the substrate on which the film is to be formed. In the method of forming the insulating film forming the Enmaku, room temperature to 150 DEG ° C. The temperature of the deposition substrate, the microwave power entering the gas pressure ^{1 × 10 -4 ~5 × 10 -3} torr, the plasma generating chamber From 250 to 450 W, and the high frequency bias power applied to the film formation substrate from 600 to 1000 W
A method for forming an insulating film, wherein an insulating film is formed as W. 2. The method for forming an insulating film according to claim 1, wherein the position of the peak value of the electric field intensity of the microwave on which the electron cyclotron resonance magnetic field region surface is formed is determined by the initial position of the microwave transmitted through the microwave transmission window. A method of forming an insulating film, wherein the peak value is set at a peak value.