JP3430801B2 - Plasma generator and dry etching method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductively coupled plasma generator and a dry etching method using the same. More specifically, the present invention relates to an electrode structure for uniformizing the plasma distribution in the vacuum chamber.

[0002]

2. Description of the Related Art As the integration density of VLSI increases,
As the device size shrinks, so does the device structure. In such a situation, a precise dry etching technique is required to realize a fine wiring pattern and the like. This dry etching is excellent in anisotropy, can precisely control the pattern width, and is desired to have high selectivity with respect to the underlying film. For example, in the etching process of the gate electrode, it is particularly desired to have a high selection ratio with respect to an oxide film, reduction of damage caused by plasma, reduction of contamination by particles, and the like. In addition, it is necessary to secure a high etching rate in order to realize a throughput suitable for mass production while satisfying such various required characteristics. In order to achieve such an object, low-pressure dry etching using a high-density plasma generator that has a uniform plasma distribution and can obtain a relatively low ion energy has been attracting attention. In recent years, as a high-density plasma generator for dry etching, an inductively coupled plasma generator (Ind
uctively Coupled Plasma, I
CP) is being developed. Furthermore, a TCP (Tr
Transformer Coupled Plasma)
Type plasma generators are attracting attention. The TCP-type high-density plasma generator is Lam Rease of the United States.
It is commercially available from rch Corp. and is characterized by a plasma electrode structure.

FIG. 4 schematically shows a TCP type plasma generator. (A) shows the cross-sectional shape of the device, and (B) shows the planar shape. This apparatus includes a vacuum chamber 1 capable of introducing a desired gas. A stage 2 is arranged below the vacuum chamber 1, and a substrate 3 to be processed is provided.
To place. A dielectric plate 4 is mounted on the ceiling portion 1a of the vacuum chamber 1 and is arranged to face the stage 2 with a predetermined space in between. A coil 5 is formed along the outer surface of the dielectric plate 4. The coil 5 is composed of a conductor pattern 6 which is spirally wound. This coil 6 has a high frequency (R
F) Functions as an antenna. A high frequency power supply 7 is connected between the center side terminal and the peripheral side terminal of the coil 5, and supplies high frequency power to the coil 5 to turn the gas introduced into the vacuum chamber 1 into plasma. Further, another high frequency power source 8 is also connected to the stage 2 which functions as a lower electrode.
In such a configuration, a gas for dry etching or the like is introduced around the stage 2 via the supply pipe 9. In addition,
The vacuum chamber 1 is, for example, a turbo molecular pump (not shown)
It can be exhausted. The substrate 3 placed in the vacuum chamber 1 is mechanically fixed to the stage 2. A coolant such as liquid helium is circulated inside the stage 2, and the temperature of the substrate 3 is controlled by cooling the liquid. High-density plasma is inductively generated using the coil 5 that constitutes the RF antenna. The high frequency power (eg 13.56 MHz) applied to the coil 5 is mainly used for controlling the plasma density, and the high frequency power (eg 13.56 MHz) applied to the stage 2 which functions as the lower electrode mainly controls the DC bias. ing. In other words, it controls the ion energy. When dry etching is performed using such an apparatus, for example, a mixed gas of Cl ₂ / O ₂ or Ar is used as a processing gas.

[0004]

However, in the above-described TCP type plasma generator, the structure in which the RF antenna composed of the spiral coil 5 is installed at the position facing the stage 2 with the dielectric plate 4 interposed therebetween. Above, the strength of the RF induction magnetic field is different between the central part and the peripheral part, and the central part tends to be stronger than the peripheral part. For this reason, there is a structural defect that the plasma density and the ion current density in the vicinity of the center are higher than in the vicinity of the periphery, and the spatial distribution of these becomes non-uniform. If the distribution of plasma density becomes non-uniform, the processing accuracy of dry etching is adversely affected. In order to improve this point, a TCP type plasma generator in which the shape of the dielectric plate is modified has been proposed. Yoshida et a
l; 1994 Dry Process Symposs
ium 1-9, P43. This is Figure 5
As shown in FIG. 3, the central portion 4a of the dielectric plate 4 is thicker than the peripheral portion 4b, and the dielectric plate 4 having a convex cross section is incorporated in the frame 1b of the vacuum chamber. Central part 4a
This is an attempt to make the RF induction magnetic field in the central portion relatively weaker than that in the peripheral portion by increasing the thickness of the dielectric plate in the vicinity to increase the capacitance, and consequently to make the plasma density uniform. However, in this method, since the distance between the upper surface of the stage and the lower surface of the dielectric plate is different between the central portion and the peripheral portion, the conductance of the gas filled between them and the electric field of the plasma are adversely affected. For this reason, it is hard to say that it is suitable for increasing the diameter of the plasma generation device corresponding to the increase in the size of the substrate. Therefore, a method for improving this point is desired.

[0005]

Means for Solving the Problems The following means have been taken in order to solve the above-mentioned problems of the conventional technology. That is, the plasma generator according to the present invention includes a vacuum chamber into which a desired gas can be introduced. A stage is arranged below the vacuum chamber, and a substrate to be processed can be placed on the stage. Further, a dielectric plate is mounted on the ceiling of the vacuum chamber, and is arranged so as to face the stage via a predetermined space. A coil is formed along the outer surface of the dielectric plate. This coil consists of a spiral conductor pattern. A high frequency power source is connected between the center side terminal and the peripheral side terminal of the coil, and the high frequency power is supplied to the coil to turn the gas in the vacuum chamber into plasma. Characteristically, the area of the conductor pattern located in the central portion of the coil is enlarged as compared with the conductor pattern located in the peripheral portion. That is , the conductor pattern located at the center of the coil has a flat plate shape. The coil passing around the spiral is the ratio of the inner diameter of the center portion is set to 0.4 or less with respect to the outer diameter. In addition,
The conductor pattern located at the core is made disk-shaped, while
The coiled conductor pattern located around the
The width is gradually reduced toward the outside. The TCP type plasma generator having such a configuration can be used for dry etching of the substrate surface, for example. In some cases, as a protective film, a substance scattered from the inner surface of the dielectric plate due to plasma irradiation is applied to the side wall of the uneven pattern formed in the process of selectively and anisotropically dry-etching the surface of the substrate. Dry etching can be performed while depositing.

According to the present invention, the shape and thickness of the spiral conductor pattern are changed between the central portion and the peripheral portion of the coil which constitutes the RF antenna. For example, the conductor pattern is formed in a continuous disk shape in the vicinity of the central portion, and is formed in a discrete shape in the vicinity of the peripheral portion. As a result, the area of the conductor pattern located in the central portion can be enlarged as compared with the conductor pattern located in the peripheral portion. In this way, by increasing the area of the conductor pattern in contact with the dielectric plate in the central portion, the capacitive coupling in the central portion is made larger than that in the peripheral portion. Due to this capacitive coupling, the RF induction magnetic field in the vicinity of the central portion is reduced as compared with that in the peripheral portion, so that a substantially uniform plasma density distribution can be obtained in the vacuum chamber. That is, the same effect can be obtained by adjusting the coupling capacitance, which is realized by changing the thickness of the dielectric plate in the conventional example shown in FIG. 5, but by changing the installation area of the RF antenna on the dielectric plate in the present invention. ing. In the conventional method, since the thickness of the dielectric plate is changed, the cross section thereof has a convex shape, whereas in the present invention, the dielectric plate itself has a constant thickness. Therefore, it is possible to generate a uniform plasma even with a large diameter without adversely affecting the gas conductance, the plasma electric field, and the like. It should be noted that the range of the central portion for enlarging the conductor pattern area may be appropriately optimized depending on the structure of the substrate and the content of the treatment. Generally, it is preferable to set the ratio of the inner diameter of the central portion to the outer diameter of the coil to 0.4 or less. As the number of turns of the coil increases with the increase in the diameter of the plasma generator, the induction magnetic field near the center becomes stronger, so that it is necessary to expand the range for increasing the area of the conductor pattern. However, if the ratio of the inner diameter of the central portion to the outer diameter of the coil exceeds 0.4, the function of the RF antenna itself is adversely affected.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing an inductively coupled plasma generator according to the present invention. (A)
Shows schematically the cross-sectional shape of the present apparatus, and (B) also schematically shows the planar shape of the present apparatus. Note that FIG.
The parts corresponding to those of the conventional plasma generator shown in FIG. As shown in the figure, the plasma generator includes a vacuum chamber 1. A desired gas can be introduced into the vacuum chamber 1 through a gas supply pipe 9. A stage 2 is arranged below the vacuum chamber 1, and a substrate 3 to be processed is provided.
Can be placed. This stage 2 functions as a lower electrode and is connected to a high frequency power source 8. Although not shown, a cooling mechanism is incorporated inside the stage 2. A dielectric plate 4 made of quartz or the like is mounted on the ceiling portion 1a of the vacuum chamber 1, and is arranged to face the stage 2 with a predetermined space in between. A coil 5 is formed along the outer surface of the dielectric plate 4 and functions as an RF antenna. This coil 5 is a conductor pattern 6 which is spirally wound.
It consists of a and 6b. A high frequency power supply 7 is connected between the center side terminal and the peripheral side terminal of the coil 5, and the coil 5
The high-frequency power is supplied to the chamber to turn the gas in the vacuum chamber 1 into plasma. The area of the inner conductor pattern 6a located in the central portion of the coil 5 is enlarged as compared with the outer conductor pattern 6b located in the peripheral portion. Specifically, the conductor pattern 6a located at the center has a flat plate shape. On the other hand, the conductor patterns 6b located in the peripheral portion are discretely formed along the radial direction of the coil 5. The ratio of the inner diameter d of the central portion to the outer diameter D of the spirally wound coil 5 is set to 0.4 or less.
If it exceeds this range, the function of the coil 5 as an RF antenna becomes insufficient. As described above, in the present embodiment, by making the vicinity of the center of the coil 5 into a flat plate shape (specifically, a disk shape), the area where the inner conductor pattern 6a is in contact with the dielectric plate 4 is expanded to increase the coupling capacitance. There is. As a result, the RF induction magnetic field near the center is reduced to obtain a substantially uniform plasma density distribution in the vacuum chamber 1.

Next, the dry etching method using the plasma generator shown in FIG. 1 will be described in detail with reference to FIG. (A) shows the sectional structure of the substrate before the dry etching treatment, and (B) schematically shows the sectional structure of the substrate after the dry etching treatment. As shown in the figure, the substrate 3 uses an 8-inch size silicon wafer 31 as a base material. The surface of the silicon wafer 31 is covered with a base film 32 made of SiO ₂ . On top of that, a PolySi film 33 and a WSi _x film 34 are formed in two layers. Furthermore, a photoresist 35 which is patterned in advance into a predetermined shape is formed thereon.

The substrate 3 shown in (A) was placed on the stage 2, a processing gas was introduced into the vacuum chamber 1, and the coil 5 was supplied with electric power to turn the gas into plasma and irradiate the substrate 3. As a result, as shown in (B), the WSi _x film 34 and the PolySi film are formed using the photoresist 35 as a mask.
The film 33 could be anisotropically dry-etched. 8
A good anisotropic shape was uniformly obtained over the entire surface of the inch wafer 31. In this dry etching process, 2
The processing conditions are switched in two stages corresponding to the layers 34 and 33. In the first stage, a mixed gas of Cl ₂ / O ₂ was used as a gas species and was introduced into the vacuum chamber 1 at a flow rate ratio of 85/15 sccm. The pressure in the vacuum chamber 1 was set to 10 mTorr. The high frequency power supplied from the high frequency power supply 7 is 150
Set to 0 Watt. RF applied to the stage 2 side
The bias was set to 100 Watt. The temperature of the substrate 3 was kept at 50 ° C. In the subsequent second stage, the same mixed gas of Cl ₂ / O ₂ was used as the gas species and introduced into the chamber 1 at a flow rate ratio of 85/15 sccm. The pressure in the vacuum chamber 1 was set to 10 mTorr. The high frequency power supplied to the coil 5 is set to 1500Watt, and the RF applied to the stage 2 is set.
The bias was set to 20 Watts. The temperature of the substrate 3 was also maintained at 50 ° C. In this example, as shown in (B),
A substance (SiOx) scattered from the inner surface of the dielectric plate 4 by plasma irradiation is used as a protective film on the side wall 36 of the uneven pattern formed in the process of selectively and anisotropically dry etching the surface of the substrate 3. Dry etching is performed while depositing. The side wall protective film has an effect of suppressing a chemical reaction between the side wall 36 and plasma to prevent side etching or the like. As a result, it is possible to limit the dimensional conversion difference between the pattern of the photoresist 35 and the uneven pattern that has been dry-etched infinitely.

FIG. 3 is a schematic sectional view showing another embodiment of the TCP type plasma generator according to the present invention. Parts corresponding to those in the embodiment shown in FIG. 1 are designated by corresponding reference numerals to facilitate understanding. This embodiment is particularly 3
It is a large plasma generator designed for 00 mm size wafers. In this example, the inner conductor pattern 6a located in the central portion has a disk shape, while the outer conductor pattern 6b located in the peripheral portion has a shape arranged discretely in the radial direction. In addition, a flat plate-shaped intermediate conductor pattern 6c is wound around the inner conductor pattern 6a having a disc shape. In other words, the width of the conductor pattern of the coil 5 is gradually reduced from the inside to the outside. In this example, the range including the inner conductor pattern 6a and the intermediate conductor pattern 6c is the central portion, and the inner diameter thereof is represented by d. On the other hand, the outer diameter dimension of the coil 5 is represented by D. Preferably, the d / D ratio is set to 0.4 or less.

Using the plasma generator shown in FIG.
The substrate was dry-etched as shown in FIG. In this apparatus, a 12-inch size wafer was targeted. As a result of the dry etching, it was possible to form a pattern having a good anisotropic shape on a 12-inch size substrate. This dry etching is also performed in two steps as in the previous example. In the first stage, Cl ₂ is used as a gas species.
A mixed gas of / O ₂ was used and introduced into the vacuum chamber at a flow rate ratio of 450/50 sccm. Vacuum chamber pressure is 10 mT
Set to orr. The high frequency power supplied to the coil is 150
It is 0 Watt. The RF bias applied to the stage is 10
It is 0 Watt. The substrate temperature was set to 50 ° C. In the second stage, a mixed gas of Cl ₂ / O ₂ was used as a gas species, and 4
It was introduced into the vacuum chamber at a flow rate ratio of 50/50 sccm. The pressure in the vacuum chamber is 10 mTorr. The high frequency power applied to the coil is 1500 Watt and the RF bias applied to the stage is 20 Watt. The substrate temperature was controlled at 50 ° C. Although the present invention has been specifically described based on the two embodiments, the present invention is naturally not limited to these embodiments, and does not deviate from the gist of the invention such as a device structure and a substrate structure. It goes without saying that the range can be appropriately selected.

[0012]

As described above, according to the present invention, T
In the CP type plasma generator, the coupling capacitance is increased by making the area near the center of the spiral coil functioning as an RF antenna larger than that near the periphery. This allows
It is possible to reduce the RF induction magnetic field near the center and obtain a substantially uniform plasma density in the vacuum chamber. By adopting the present invention, it is possible to obtain a uniform plasma even if the diameter of the apparatus is increased in response to the increase in size of the substrate, and it is possible to realize dry etching with almost no dimensional conversion difference.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a plan view showing an embodiment of a plasma generator according to the present invention.

2 is a process diagram showing a dry etching method performed using the plasma generator shown in FIG. 1. FIG.

FIG. 3 is a sectional view showing another embodiment of the plasma generator according to the present invention.

FIG. 4 is a cross-sectional view and a plan view showing an example of a conventional plasma generator.

FIG. 5 is a schematic partial cross-sectional view showing an example of a dielectric plate incorporated in a conventional plasma generator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber, 2 ... Stage, 3 ... Substrate, 4 ... Dielectric plate, 5 ... Coil, 6a ... Inner conductor pattern, 6b ... Outer conductor pattern, 7 ... High frequency power supply, 8 ... High frequency power supply, 9
… Gas supply pipe

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/205 C23F 4/00 H05H 1/46

Claims (3)

(57) [Claims] 1. A vacuum chamber into which a desired gas can be introduced, a stage disposed under the vacuum chamber on which a substrate to be processed can be placed, and a predetermined space which is mounted on a ceiling portion of the vacuum chamber. A dielectric plate disposed opposite to the stage via a coil, a coil formed of a spiral conductor pattern formed along the outer surface of the dielectric plate, and a center side terminal and a peripheral side terminal of the coil. A high-frequency power source for supplying a high-frequency power to a high-frequency power source to turn a gas in a vacuum chamber into a plasma, wherein the coil has a conductor located in a central portion as compared with a conductor pattern located in a peripheral portion. The pattern area has been expanded
The coil has a flat plate-shaped conductor pattern located at the center.
The spirally wound coil has a shape corresponding to its outer diameter.
The ratio of the inner diameter of the central part is set to 0.4 or less, and the conductor pattern located in the central part is made into a disc shape,
Is the coil-shaped conductor pattern located around it
The plasma generator is characterized in that the width dimension gradually decreases from the outside toward the outside . 2. A stage, which is arranged in the lower part of the vacuum chamber, a dielectric plate mounted on the ceiling of the vacuum chamber, and a spiral conductor pattern formed along the outer surface of the dielectric plate. A method of performing dry etching using a plasma generator equipped with a coil having a larger area than that of a peripheral portion and a high-frequency power source for supplying power to the coil, wherein And a step of introducing a processing gas into the vacuum chamber,
The irradiation procedure row stomach to irradiate the substrate with plasma the gas Kyoden to said coil, said irradiation means, the conductor pattern in the center Tairabankatachi
Using a coil with a spiral shape, the spirally wound coil is
The ratio of the inner diameter of the center to the outer diameter is 0.4 or less.
The conductor pattern is set below and located in the center.
While having a disk shape, coil-shaped conductors located around it
The width of the electric body pattern decreases from the inside to the outside.
A dry etching method that uses a coil that is thin . 3. A substance scattered from the inner surface of the dielectric plate by plasma irradiation on the side wall of the uneven pattern formed in the process of selectively and anisotropically dry etching the surface of the substrate is used as a protective film. The dry etching method according to claim 2, wherein dry etching is performed while depositing.