Plasma Etching Apparatus

TECHNICAL FIELD

The present invention relates to a plasma etching apparatus for etching the surface of a substrate, such as a silicon substrate, a glass substrate and the like, with a plasma generated from an etching gas.

BACKGROUND ART

As an apparatus for plasma etching a silicon substrate, conventionally, the apparatuses disclosed in the Japanese Unexamined Patent Application Publication Nos. 2006-80504 (prior-art example 1) and 2006-60089 (prior-art example 2) are known.

As shown in FIG. 6, a plasma etching apparatus 101 of the prior-art example 1 has a cylindrical chamber 102 having a plasma generating space 109 defined at the upper side and a processing space 110 defined at the lower side, a coil 103 disposed on the outside of the chamber 102 corresponding to the plasma generating space 109 in such a manner that it winds around the chamber 102, RF power supply means 104 for supplying RF power to the coil 103, etching gas supply means 105 for supplying an etching gas into the plasma generating space 109, a platen 106 which is disposed in the processing space 110 and on which a substrate is to be placed, RF power supply means 107 for supplying RF power to the platen 106, and exhaust means 108 for exhausting the gas within the chamber 102.

In this plasma etching apparatus 101, an inductive electric field is generated in the plasma generating space 109 by applying RF power to the coli 103, plasma is generated from an etching gas supplied into the plasma generating space 109 due to this inductive electric field, and a substrate K on the platen 106 is etched by the generated plasma.

On the other hand, as shown in FIG. 7, a plasma etching apparatus 201 of the prior-art example 2 has a chamber 202, which is similarly formed in a cylindrical shape, comprising a small-diameter portion 202a at the upper side and a large-diameter portion 202b at the lower side. A coil 203 is disposed on the outside of the small-diameter portion 202a in such a manner that it winds around the small-diameter portion 202a, and the inside of the small-diameter portion 202a is defined as a plasma generating space 209. The inside of the large-diameter portion 202b is defined as a processing space 210, and a platen 206 on which a substrate is to be placed is disposed in the processing space 210.

RF power supply means 204 supplies RF power to the coil 203, and on the other hand, RF power supply means 207 supplies RF power to the platen 206. Further, etching gas supply means 205 supplies an etching gas into the plasma generating space 209, and exhaust means 208 exhausts the gas within the chamber 202.

According to this plasma etching apparatus 201, similarly to the plasma etching apparatus 101 of the prior-art example 1, an inductive electric field is generated in the plasma generating space 209 by applying RF power to the coil 203, plasma is generated from an etching gas supplied into the plasma generating space 209 due to this inductive electric field, and a substrate K on the platen 206 is etched by the generated plasma.

Patent Literature

Patent document 1: Japanese Unexamined Patent Application Publication No. 2006-80504.

Patent document 2: Japanese Unexamined Patent Application Publication No. 2006-60089.

SUMMARY OF THE INVENTION
Technical Problem

By the way, in recent years, a substrate to be processed has increased in size and therefore there has been a demand for a plasma etching apparatus capable of etching the entire surface of such a large-sized substrate uniformly.

However, when such a large-sized substrate is processed by the above conventional plasma etching apparatus 101 or 201, there are problems as described below.

That is, with respect to the plasma etching apparatus 101, since the plasma generating space 109 is large, the plasma etching apparatus 101 can be structurally easily adapted to a relatively large substrate. However, if the chamber 102 is made larger and the plasma generating space 109 is made larger corresponding to the increase of the size of the substrate K, the in-plane density Pm of the plasma generated in the plasma generating space 109 has a concave density distribution in which the density is high at the portion close to the coil 103 and is low at the central portion, and this density distribution acts on the substrate K as it is. Therefore, the surface of the substrate K is not etched uniformly.

Particularly, at the periphery portion of the substrate K, the etching rate is higher than that at the central portion thereof even if the in-plane density Pm of the plasma is uniform, and therefore the etching is apt to proceed fast. Therefore, in a case where the in-plane density Pm of the plasma has a concave density distribution as described above, the etching at the periphery portion of the substrate K proceeds faster and it is not possible to etch the entire surface of the substrate K uniformly.

Further, the high plasma density at the periphery portion of the substrate K causes a problem that when a deep hole, for example, is formed in the substrate K, as shown in FIG. 8, the periphery of the entrance of a hole 300 is etched by a high density of ions and thereby the entrance is formed into a tapered shape and the surface thereof becomes rough because of sputtering, which results in deterioration of etching shape.

On the other hand, with respect to the plasma etching apparatus 201, the volume of the plasma generating space 209 is small and therefore it is possible to generate high-density plasma even if the RF power applied to the coil 203 is low, and the in-plane density Pm of the plasma has a convex density distribution. Therefore, although it is possible to etch the entire surface of the substrate K uniformly when the substrate K is a relatively small, if only the processing space 210 is made larger corresponding to the increase of the size of the substrate K without changing the plasma generating space 209, it is difficult to cause the plasma generated in the plasma generating space 209 to act on the periphery portion of the substrate K, and therefore, also in this case, it is not possible to etch the entire surface of the substrate K uniformly.

Alternatively, if the plasma generating space 209 is also made larger corresponding to the increase of the size of the substrate K, a problem similar to that in the case of the plasma etching apparatus 101 described above is caused.

The present invention has been achieved in view of the above-described circumstances, and an object thereof is to provide a substrate processing apparatus capable of etching the entire surface of a substrate uniformly even if the substrate is large-sized and capable of preventing a deterioration of shape caused by ions.

Solution to Problem

The present invention, for solving the above-described problem, relates to a plasma etching apparatus comprising:

a non-conductive chamber which comprises a cylindrical body portion, a top plate for closing the top of the body portion, and a bottom plate for closing the bottom of the body portion, and which has a plasma generating space defined in an upper region in the body portion and a processing space defined below the plasma generating space;

a coil disposed on the outside of a portion of the chamber corresponding to the plasma generating space in such manner that it winds around the chamber;

a platen which is disposed in the processing space in the chamber and on which a substrate to be processed is to be placed;

processing gas supply means for supplying a processing gas into the plasma generating space in the chamber;

power supply means for coil for supplying RF power to the coil;

power supply means for platen for supplying RF power to the platen; and

a plasma density adjusting member which comprises a cylindrical member having an opening at the top and an opening at the bottom, and the upper end portion of which is fixed on an inner wall of the chamber between the plasma generating space and the platen, and which adjusts the in-plane density of a plasma generated in the plasma generating space and guides the plasma to a substrate on the platen, wherein

- the body portion forming the plasma generating space is formed to have an inner diameter larger than the outer dimension of the substrate, and
  - the plasma density adjusting member is made of a conductive material grounded and is formed in a funnel shape the lower end portion of which has an inner diameter smaller than the inner diameter of the upper end portion thereof and than the inner diameter of the body portion forming the plasma generating space.

According to this plasma etching apparatus, first of all, RF power is applied to the coil by the power supply means for coil. Thereby, an inductive electric field is generated in the plasma generating space in the chamber. Under this condition, when a processing gas is supplied into the plasma generating space by the processing gas supply means, plasma is generated from the supplied processing gas due to the inductive electric field.

The in-plane density of the plasma thus generated has a concave density distribution in which the density is high at the periphery portion which is close to the coil and the density is low at the central portion.

The plasma having such a concave density distribution flows downward and flows through the cylindrical plasma density adjusting member having an opening at the top and an opening at the bottom, reaches a substrate placed on the platen which is positioned below the plasma density adjusting member, and etches the surface of the substrate.

Since the plasma density adjusting member is formed in a funnel shape the lower end portion of which has an inner diameter smaller than the inner diameter of the upper end portion thereof and than the inner diameter of the body portion forming the plasma generating space, the in-plane density of the plasma which has an extremely concave density distribution is equalized or is adjusted to have a somewhat convex density distribution in reverse by flowing the plasma through the plasma density adjusting member, after which the plasma reaches the substrate.

Further, although, as described above, the density of the plasma generated in the plasma generating space is high at the periphery portion thereof, that is, the ion density is also high there, since the plasma density adjusting member of the present invention is made of a conductive material grounded, a high density of ions existing at the periphery portion of the plasma is neutralized by contacting with the plasma density adjusting member while the plasma passes through the plasma density adjusting member, and thereby the ion density at the periphery portion is reduced.

Therefore, it is possible to improve the above-described problem that a high density of ions causes deterioration of etching shape.

It is noted that an object of the present invention is to etch the entire surface of a substrate uniformly even if the substrate is large-sized, that is, to equalize the etching rate throughout the entire surface of a substrate. According to the knowledge of the inventors of the invention, it is necessary, for achieving the above object, that the in-plane density of the plasma has a gradual concave density distribution or a gradual convex density distribution depending on various conditions such as mask opening ratio of substrate, substrate size etc. By using the above plasma density adjusting member and appropriately setting the length thereof and the inner diameter of the lower end portion thereof, the in-plane density of the plasma can be adjusted to have such a density distribution. As a result thereof, it is possible to etch the entire surface of the substrate uniformly.

It is noted that it is preferable to provide, in the plasma etching apparatus, a cylindrical core member at the central portion of the top plate, which core member hangs downward from the top plate to form the plasma generating space in a doughnut shape.

When thus configured, it is possible to reduce the volume of the plasma generating space and thereby to generate high-density plasma by supplying a relatively low RF power to the coil. Therefore, it is possible to enhance energy efficiency.

Furthermore, it is preferable that the core member is made of a non-conductive material. When the core member is made of a conductive material and is provided, ions in the plasma generated in the plasma generating space disappear, and, as a result thereof, the plasma density is reduced. When the core member is made of a non-conductive material, it is possible to prevent the reduction of the plasma density.

Advantageous Effects of Invention

According to the plasma etching apparatus of the invention, the in-plane density of plasma can be adjusted to become in a most suitable state by flowing the plasma through said plasma density adjusting member, and, as a result thereof, it is possible to etch the entire surface of a substrate uniformly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view of a plasma etching apparatus according to one embodiment of the present invention;

FIG. 2 is an illustration for explaining an etching shape obtained when trench etching is performed by the plasma etching apparatus according to the embodiment;

FIG. 3 is a sectional view of a plasma density adjusting member according to the embodiment;

FIG. 4 is a graph relating to an etching rate when etching is performed after adjusting the plasma density using the plasma density adjusting member according to the embodiment;

FIG. 5 is a graph relating to etching rates when etching is performed after adjusting the plasma density using the plasma density adjusting member according to the embodiment;

FIG. 6 is a front sectional view of a plasma etching apparatus according to a prior-art example;

FIG. 7 is a front sectional view of a plasma etching apparatus according to a prior-art example; and

FIG. 8 is an illustration for explaining an etching shape obtained when trench etching is performed by the plasma etching apparatus according to one of the prior-art examples.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferable embodiment of the present invention will be described on the basis of the drawings.

As shown in FIG. 1, a plasma etching apparatus 1 of the embodiment has a chamber 2 comprising a lower body portion 3, an upper body portion 7, a bottom plate 4, an intermediate plate 5, and a top plate 8. The lower body portion 3, the upper body portion 7, the bottom plate 4, the intermediate plate 5 and the top plate 8 are each made of a non-conductive material (for example, ceramics), and the upper body portion 7 and the lower body portion 3 are formed in a cylindrical shape.

The bottom plate 4 is fixed on the lower end portion of the lower body portion 3 and the intermediate plate 5 is fixed on the upper end portion of the lower body portion 3, and the lower body portion 3, the bottom plate 4 and the intermediate plate 5 form a processing space 6.

In the processing space 6, a platen 10 is disposed on which a substrate K is to be placed and the platen 10 is lifted up and down by an appropriate lifting mechanism. An RF power supply unit 13 is connected to the platen 10 via a matching unit 14, and RF power is supplied to the platen 10 by the RF power supply unit 13. It is noted that the reference numeral 11 indicates a cover covering the outer peripheral portion of the platen 10 and the reference numeral 12 indicates a support for supporting the lifting of the platen 10.

The lower body portion 3 has an opening 3a for loading and unloading the substrate K and an exhaust port 3b for exhausting the gas within the processing space 6 formed therein. The opening 3a is opened and closed by a shutter mechanism 21, and the exhaust port 3b is connected to an exhaust device 22 and the gas within the processing space 6 is exhausted by the exhaust device 22.

The upper body portion 7 is fixed on the intermediate plate 5 and the top plate 8 is fixed on the upper end portion of the upper body portion 7. On the central portion of the top plate 8, a cup-shaped core member 15 is fixed in such a manner that it hangs downward from the top plate 8. Thus, a doughnut-shaped plasma generating space 9 is formed by the upper body portion 7, the top plate 8 and the core member 15. It is noted that the inner diameter of the upper body portion 7 is larger than the outer diameter of the substrate K.

The intermediate plate 5 has an opening 5a formed therein and a plasma density adjusting member 20 which is formed in a funnel shape having an opening at the top and an opening at the bottom is fixedly provided on the lower surface of the intermediate plate 5. The plasma generating space 9 and the processing space 6 communicate with each other via the opening 5a and the plasma density adjusting member 20. The plasma density adjusting member 20 is positioned between the plasma generating space 9 and the substrate K, and is made of a conductive material (for example, aluminum) and is appropriately grounded. Further, the inner diameter of the lower end portion of the plasma density adjusting member is smaller than the inner diameter of the upper body portion 7.

A coil 16 is disposed on the outside of the upper body portion 7 in such a manner that it winds around the upper body portion 7, and is connected to an RF power supply unit 17 via a matching unit 18. The RF power supply unit 17 supplies RF power to the coil 16.

Further, a supply pipe 19a connecting to an etching gas supply source 19 is connected to the top plate 5, and an etching gas is supplied into the plasma generating space 9 from the etching gas supply source 19.

According to the plasma etching apparatus 1 of the embodiment having the above-described configuration, initially, a substrate K (for example, a silicon substrate) is placed, through the opening 3a, on the platen 10 which is at a lowered position. Subsequently, the platen 10 is lifted up to a processing position and the processing space 6 and the plasma processing space 9 are brought to a negative pressure by the exhaust device 22, and RF power is supplied to the platen 10 from the RF power supply unit 13.

Further, RF power is supplied to the coil 16 from the RF power supply unit 17, and thereby an inductive electric field is generated in the plasma generating space 9. Under this state, an etching gas (for example, SF₆gas) is supplied into the plasma generating space 9 from the etching gas supply source 19 and plasma is generated from the etching gas due to the inductive electric field.

Since the plasma generating space 9 is, as described above, formed in a doughnut shape by the cylindrical core member 15, the volume thereof is small. Further, since only the region close to the coil 16 is defined as the plasma generating space 9, high-density plasma can be generated even when the power applied to the coil 16 is relatively low.

The high-density plasma thus generated flows downward and flows through the plasma density adjusting member 20, and reaches the substrate K positioned below the plasma density adjusting member 20 and etches the surface of the substrate K. It is noted that the in-plane density of the plasma flowing downward from the plasma generating space 9 has a concave density distribution in which the density is extremely high at the periphery portion and is low at the central portion.

While the plasma having such a density distribution passes through the plasma density adjusting member 20, since the plasma density adjusting member 20 is formed in a funnel shape the lower opening of which has an inner diameter smaller than the inner diameter of the upper body portion 7, the plasma is gradually concentrated and the in-plane density thereof is gradually equalized, and thereby the in-plane density of the plasma is adjusted to have a gradual concave density distribution or to have a flat uniform density distribution or to have a gradual convex density distribution, after which the plasma reaches the substrate.

Thus, the high-density plasma adjusted as described above acts on the surface of the substrate, and thereby the entire surface of the substrate is etched uniformly.

Further, in the embodiment, a bias potential is applied to the substrate K by applying RF power to the platen 10. Therefore, ions in the plasma are irradiated toward the substrate K, and thereby so-called ion assisted etching is performed.

Since the plasma density adjusting member 20 is made of a conductive material grounded, while the plasma passes through the plasma density adjusting member 20, a high density of ions existing at the periphery portion of the plasma is neutralized by contacting with the plasma density adjusting member 20, and thereby disappears. Therefore, the problem that deterioration of etching shape is resulted from a high density of ions acting on the substrate is solved.

In this connection, FIG. 2 shows the result of the formation of a deep hole in the substrate K using the plasma etching apparatus 1 of the embodiment. As shown in FIG. 2, the entrance of a hole 30 is not formed into a tapered shape and further the surface thereof is not rough.

Further, FIG. 4 shows the result of the etching of a SiO₂film on a silicon substrate of 6 inches, wherein the plasma etching apparatus 1 of the embodiment as shown in FIG. 1 was used, SF₆gas was used as etching gas, the flow rate of the SF₆gas supplied into the plasma generating space 9 was 500 ml/min, the RF power applied to the coil 16 was 2000 W, the RF power applied to the platen 10 was 70 W, and the dimensions of the plasma density adjusting member 20 as shown in FIG. 3, that is, the lower-end inner diameter D₁, upper-end inner diameter D₂and length L thereof were 172 mm, 270 mm and 106 mm, respectively.

As shown in FIG. 4, in the exampled etching, the entire surface of the substrate K could be etched with an extremely high etching-rate uniformity of 15.5 nm/min±3.1%.

Further, FIG. 5 shows the result of the etching when the D₁and the length L of the plasma density adjusting member 20 were set to 165 mm and 86 mm, respectively and the result of the etching when the D₁and the length L of the plasma density adjusting member 20 were set to 242 mm and 86 mm, respectively. As shown in FIG. 5, the etching rate throughout the entire surface of the substrate K was 17.8 nm/min±10.1% when the D₁was 165 mm, and the etching rate throughout the entire surface of the substrate K was 23.9 nm/min±11.1% when the D₁was 242 mm.

As seen from these examples, adjusting the dimensions of the plasma density adjusting member 20 appropriately enables the entire surface of the substrate K to be processed uniformly. Further, as seen from FIG. 4, setting the dimensions of the plasma density adjusting member 20 to the optimum conditions enables the entire surface of the substrate K to be etched with an extremely high uniformity.

It is noted that the core member 15 is preferably made of a non-conductive material. When the core member 15 is made of a conductive material and is provided, ions in the plasma generated in the plasma generating space 9 disappear, and, as a result thereof, the density of the plasma is reduced. When the core member 15 is made of a non-conductive material, it is possible to prevent the reduction of the density of the plasma.

Thus, one embodiment of the present invention has been described. However, a specific embodiment in which the present invention can be implemented is not limited thereto. For example, although the core member 15 is provided in the above embodiment, it is not necessarily provided.

INDUSTRIAL APPLICABILITY

As described above, the plasma etching apparatus of the present invention can be suitably used as a plasma etching apparatus capable of etching the entire surface of a substrate with an extremely high uniformity.

REFERENCE SIGNS LIST

1 Plasma etching apparatus

1 Chamber

3 Lower body portion

4 Bottom plate

5 Intermediate plate

6 Processing space

7 Upper body portion

8 Top plate

9 Plasma generating space

10 Platen

13 RF power supply unit

15 Core member

16 Coil

17 RF power supply unit

19 Etching gas supply source

20 Plasma density adjusting member

Plasma Etching Apparatus

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