JP4433614B2 - Etching equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an etching apparatus that etches the entire surface of a wafer or a thin film formed on the surface of a wafer or a specific portion, and more specifically, etching characteristics deteriorate like a large-diameter wafer of 300 mm or more and a wafer peripheral region. The present invention also relates to an etching apparatus capable of obtaining uniform etching characteristics for a process.
[0002]
[Prior art]
In a semiconductor manufacturing process, particularly in a dry etching apparatus using plasma, how to uniformly process a wafer is an important point from the viewpoint of etching characteristics.
Here, the uniform etching means that the etching rate, the etching selectivity, and the etching shape are as equal as possible over the entire surface of the wafer.
On the other hand, it is said that the most suitable method for achieving uniform etching is to make the plasma density, electron temperature, radical composition, electric field (bias), magnetic field, and pressure directly above the surface of the wafer to be etched uniform. ing.
However, what is difficult to realize is the composition of the gas used for etching. Even if all the etching parameters are made uniform in the wafer plane, etching non-uniformity in the peripheral area of the wafer is inevitable. That is, in the central region of the wafer, since the periphery is surrounded by the object to be etched, the consumption of the etchant is intense, and the production of a bi-product that is a product at the time of etching increases. On the other hand, in the peripheral area of the wafer, a phenomenon opposite to that in the central area occurs.
[0003]
Therefore, in the conventional etching apparatus, as shown in FIG. 4, at a place on the lower electrode 2 located on the outer periphery of the wafer 3 placed on the lower electrode (wafer stage) 2 in the vacuum reaction chamber 1. An annular focus ring 4 is provided, and the phenomenon described above is alleviated by the focus ring 4 to improve etching uniformity.
Further, the focus ring 4 has a rectangular cross-sectional shape shown in FIG. 5 or a step-like vertical cross-sectional shape shown in FIG. 6 so that the outside of the wafer 3 does not become a simple space. Is used. The focus ring 4 is made of a material that actively consumes an etchant, such as a wafer, or has electrical continuity, or the focus ring 4 is stepped as shown in FIG. Thus, the etching gas flow is made to have a stagnation to provide an etching uniformity effect.
In FIG. 4, 5 is an upper electrode provided in the upper part of the vacuum reaction chamber 1, and 6 is a gas ejection shower plate provided on the lower surface of the upper electrode 5.
[0004]
[Problems to be solved by the invention]
However, even in the conventional etching apparatus as described above, the effect of mitigating the above phenomenon due to the difference in the composition of the etching gas is small, and in addition to the introduction of gas from the upper part of the vacuum reaction chamber 1 as shown in FIG. Even if the configuration is such that the etching gas is introduced from the side portion, the desired relaxation effect cannot be realized.
In addition, in the etching apparatus having a structure in which the etching gas is introduced from the side surface portion of the vacuum reaction chamber 1, the distance from the side wall portion of the vacuum reaction chamber to the outer peripheral region of the wafer is considerable, so the effect of introducing the gas from the side surface is also limited. There is. Further, when the distance from the side wall of the vacuum reaction chamber to the outer peripheral region of the wafer is narrow, there are problems that the exhaust characteristics of the vacuum reaction chamber are deteriorated and the etching uniformity is deteriorated.
[0005]
Accordingly, the present invention has been made to solve the above-described problems, and etching that can obtain uniform etching characteristics even for an etching process in which uniformity of a large-diameter wafer and a wafer peripheral region is difficult to be obtained. An object is to provide an apparatus.
[0006]
In order to achieve the above object, an etching apparatus according to the present invention includes a vacuum reaction chamber, a wafer stage installed in the vacuum reaction chamber, on which a wafer is placed, and an etching gas from above with respect to the wafer on the wafer stage. In the apparatus for converting the etching gas ejected from the first gas ejecting means into plasma with high-frequency power and etching the wafer with the plasma-activated active gas, the wafer stage A focus ring provided facing the outer periphery of the wafer mounted on the wafer, a gas passage formed in a ring shape over the entire length of the focus ring inside the focus ring, and a predetermined direction in the circumferential direction of the focus ring And one end communicates with the gas passage and the other end is the focus ring. Comprising a plurality of gas ejection holes which are opened inward, characterized in that it comprises a second gas ejection means for ejecting an etching gas toward the center from the outer periphery of the wafer.
[0007]
In the etching apparatus of the present invention, the etching gas can be jetted from the second gas jetting means independent of the first gas jetting means to the peripheral area of the wafer. This makes it possible to obtain uniform etching characteristics even for an etching process in which uniformity of a large-diameter wafer and a wafer peripheral region is difficult to obtain.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a dry etching apparatus showing an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part showing an example of a focus ring used in the dry etching apparatus according to an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of the main part showing another example of the focus ring used in the dry etching apparatus according to the embodiment of the present invention.
[0009]
In FIG. 1, a dry etching apparatus includes a vacuum reaction chamber 12 for etching a wafer 10, a circular lower electrode (constituting a wafer stage according to the claims) 14 installed in the vacuum reaction chamber 12, and An annular focus ring 16 provided at the upper surface portion 141 of the lower electrode 14 facing the outer periphery of the wafer 10 placed on the lower electrode 14, and an upper electrode 18 provided at the upper part in the vacuum reaction chamber 12 A shower plate 20 for gas ejection (corresponding to the first gas ejection means described in the claims) provided on the lower surface of the upper electrode 18 is provided. Further, a known air-core coil (not shown) is installed on the outer periphery of the vacuum reaction chamber 12.
The wafer 10 placed on the lower electrode 14 is held by an electrostatic chuck or a mechanical chuck (both not shown) provided on the lower electrode 14. Further, the focus ring 16 is configured to be mounted on the upper surface portion 141 of the lower electrode 14 or held by screwing or the like.
[0010]
The shower plate 20 includes a plurality of different etching gas sources, for example, gas sources such as O ₂ , Ar, C ₄ F ₈ , CO, etc., for adjusting the flow rate and gas composition of the gas supplied to the shower plate 20. The flow rate control valves 22-1 to 22-4 (corresponding to the flow rate control means of the first gas ejection means described in claims) are connected via a gas supply path 24.
Further, a UHF power source 26 that generates, for example, 27 MHz electromagnetic waves is connected between the upper electrode 18 including the shower plate 20 and the ground, and a high frequency of, for example, 800 kHz is connected between the lower electrode 14 and the ground. A bias power supply 28 is connected.
The frequency of the UHF power source 26 and the frequency of the high frequency bias power source 28 are not limited to the values described above.
[0011]
The focus ring 16 is made of a material mainly composed of silicon, aluminum, stainless steel, silicon oxide, aluminum oxide or the like, and its vertical cross-sectional shape is rectangular as shown in FIG. 14 have substantially the same thickness up to the upper surface of the wafer 10 placed on the substrate 14.
As shown in FIGS. 1 and 2, a gas passage 161 is formed in a ring shape over the entire length of the focus ring 16, and one end of the focus ring 16 is in contact with the lower electrode 14. A plurality of gas ejection holes 162 that are communicated with 161 and have the other end penetrating the focus ring 16 and opened obliquely upward with respect to the center of the focus ring 16 are formed in the circumferential direction of the focus ring 16 at a predetermined interval. ing.
In this embodiment, the number of gas ejection holes 162 is four or more.
[0012]
Further, as shown in FIG. 3, the vertical cross-sectional shape of the focus ring 16 includes a portion 16 </ b> A lower than the height up to the upper surface of the wafer 10 placed on the lower electrode 14, and a portion 16 </ b> B higher than the height up to the upper surface of the wafer 10. In this high portion 16B, a plurality of gas ejection holes 162 opened in the horizontal direction with respect to the center of the focus ring 16 are formed in the circumferential direction of the focus ring 16 with a predetermined interval therebetween. Each gas ejection hole 162 communicates with a gas passage 161 formed at a contact surface portion with the lower electrode 14.
The gas passage 161 is supplied to the peripheral region of the wafer 10 from a plurality of different types of etching gas sources, for example, gas sources such as O ₂ , Ar, C ₄ F ₈ , and CHF ₃ through the gas passage 161 and the gas ejection holes 162. The flow rate control valves 30-1 to 30-4 (corresponding to the flow rate control means of the second gas ejection means described in the claims) 30-1 to 30-4 for adjusting the gas flow rate and the gas composition are provided via the gas supply path 32. It is connected.
The gas passage 161 including the focus ring 16 and the gas ejection hole 162 constitute the second gas ejection means described in the claims.
[0013]
In the etching apparatus configured as described above, the wafer 10 is removed from a gas source such as O ₂ , Ar, C ₄ F ₈ , and CO while the wafer 10 is placed on the lower electrode 14 in the vacuum reaction chamber 12. A gas optimal for etching is selected by the flow control valves 22-1 to 22-4, and a mixed gas whose flow rate and composition are adjusted is supplied to the shower plate 20, and O ₂ , Ar, C ₄ F ₈ , A gas optimal for etching the wafer 10 is selected from a gas source such as CHF ₃ by the flow rate control valves 30-1 to 30-4, and a mixed gas whose flow rate and composition are adjusted is passed through the gas passage 161 and the gas ejection holes 162. Supply to the peripheral area of the wafer 10. Then, the inside of the empty reaction chamber 12 is evacuated by an evacuation device (not shown), an electromagnetic wave from the UHF power supply 26 is supplied to the upper electrode 18 and activated by an interaction with a magnetic field applied by an air core coil (not shown). A gas plasma is generated.
In this state, a high frequency bias voltage is applied to the wafer 10 from a high frequency bias power supply 28 connected to the lower electrode 14, thereby drawing the active gas in the plasma into the wafer surface for etching.
[0014]
In this embodiment, the direction of the etching gas ejected from the gas ejection hole 162 of the focus ring 16 toward the peripheral region of the wafer 10 is determined by the direction of the opening of the gas ejection hole 162, and the initial velocity of the ejection gas Depends on the diameter of the gas ejection hole 162.
Further, the relationship between the diameter of the gas ejection hole 162 and the initial velocity is approximately as shown in the following equation.
The flow rate F determined by the flow rate control valves 30-1 to 30-4 is F = k1γβ- ² . Here, k1 is a constant, γ is a pressure, and β is a diameter of the gas ejection hole.
From this equation, the pressure is determined, and the initial speed S is S = k2γ. However, k2 is a constant.
[0015]
In the etching apparatus shown in this embodiment, when the silicon oxide film on the surface of the wafer 10 is etched, the frequency of the UHF power source 26 of the upper electrode 18 is 27 MHz, the power is 2.5 kW, and the high frequency bias power source 28 of the lower electrode 14 is used. The frequency is 800 kHz, the power is 2 kW, and the pressure in the vacuum reaction chamber 12 is 100 mTorr.
Then, the type and flow rate of the etching gas supplied to the shower plate 20 are C ₄ F ₈ : 20 sccm, O ₂ : 50 sccm, Ar: 500 sccm, and the type and flow rate of the etching gas supplied to the focus ring 16 are CHF ₃ : ₃ sccm, C ₄ F ₈ : ₂ sccm, O ₂ : 10 sccm, Ar: 250 sccm.
[0016]
In such an embodiment, CHF ₃ gas that contributes to the deposition property of the inner surface of the etched portion is ejected from the focus ring 16 to the peripheral region of the wafer 10, and the O ₂ gas that acts as the opposite of the deposition component. The ratio of C ₄ F ₈ gas that greatly contributes to the etching rate is lowered from the shower plate 20 side.
[0017]
In this way, the etching gas is ejected from the central region and the peripheral region of the wafer 10 by separate gas ejection systems, and the flow rate and composition of the introduced gas are changed, so that the focus ring 16 moves toward the peripheral region of the wafer 10. With respect to the flowing gas, the ratio of the etchant whose composition is excessive in the peripheral area of the wafer can be lowered, and the deposition gas for correcting the influence of the biproduct which is insufficient in the peripheral area of the wafer can be increased. .
According to such an embodiment, uniform etching characteristics can be obtained even for an etching process in which it is difficult to obtain uniformity of a large diameter wafer of 30 mm or more and a wafer peripheral region.
[0018]
In addition, while using the same vacuum reaction chamber 12, it is possible to process different processes such as contact and etch back that greatly change the uniformity of the central region and the peripheral region of the wafer. In this case, in addition to the method of changing the composition of the gas from the focus ring 16, there is also a method of using a plurality of types of focus rings in which the gas ejection direction and the initial ejection speed are changed.
Furthermore, in a process where deposits tend to adhere to the wafer periphery and the focus ring itself, by flowing unreacted virgin gas from the vicinity of the wafer outer periphery, the deposition performance on the wafer periphery and focus ring can be reduced, and etching by the deposit is possible. Stopping can be prevented and the frequency of cleaning the focus ring can be reduced.
Further, by ejecting the gas from the vicinity of the wafer toward the center of the wafer, it is possible to suppress excessive dissociation of the etching gas, which is suitable particularly when a high etching selectivity is obtained by oxide film etching.
[0019]
In the present invention, as shown in FIG. 1, an optical system 34 that emits light such as a laser and receives light reflected from the processing surface of the wafer 10 is provided in the vacuum reaction chamber 12. The optical signal is taken into the arithmetic processing unit 38 such as a computer through the spectroscope 36 and processed to monitor the etching rate at a plurality of locations including the central region and the peripheral region of the wafer 10, that is, the etching rate and uniformity. By controlling the flow control valves 30-1 to 30-4 according to the result, the gas ejected from the flow control valves 30-1 to 30-4 to the peripheral region of the wafer 10 through the gas ejection holes 162 of the focus ring 16 The flow rate and / or gas composition can be adjusted. As a result, the wafer 10 can be uniformly etched.
[0020]
【The invention's effect】
As described above, according to the etching apparatus of the present invention, uniform etching characteristics can be obtained even for an etching process in which uniformity of a large-diameter wafer of 30 mm or more and a wafer peripheral region is difficult to be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a dry etching apparatus showing an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view of a main part showing an example of a focus ring used in a dry etching apparatus according to an embodiment of the present invention.
FIG. 3 is an enlarged cross-sectional view of a main part showing another example of a focus ring used in a dry etching apparatus according to an embodiment of the present invention.
FIG. 4 is a schematic configuration diagram of a conventional dry etching apparatus.
FIG. 5 is an enlarged cross-sectional view of a main part showing an example of a focus ring used in a conventional dry etching apparatus.
FIG. 6 is an enlarged cross-sectional view of a main part showing another example of a focus ring used in a conventional dry etching apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Wafer, 12 ... Vacuum reaction chamber, 14 ... Lower electrode, 16 ... Focus ring, 161 ... Gas passage, 162 ... Gas ejection hole, 18 ... Upper electrode, 20 ... Shower plate, 22 -1 to 22-4... Flow control valve (flow control means), 26... UHF power supply, 28... High frequency bias power supply, 30-1 to 30-4. ... Optical system 36 ... Spectroscope 38 ... Calculation processing unit.

Claims (6)

A vacuum reaction chamber; a wafer stage that is installed in the vacuum reaction chamber and on which a wafer is placed; and a first gas ejection unit that ejects an etching gas from above to the wafer on the wafer stage, In an apparatus that etches the etching gas ejected from the first gas ejection means with high-frequency power and etches the wafer with the plasma-activated active gas,
A focus ring provided facing the outer periphery of the wafer placed on the wafer stage;
A gas passage formed in a ring shape over the entire length of the focus ring inside the focus ring, and formed at a predetermined interval in the circumferential direction of the focus ring, with one end communicating with the gas passage and the other end Comprising a plurality of gas ejection holes opened inward of the focus ring, and a second gas ejection means for ejecting an etching gas from the outer periphery to the center of the wafer ;
The provided, etching and wherein the. The focus ring has a stepped shape having a portion lower than the height to the upper surface of the wafer and a portion higher than the height to the upper surface of the wafer;
The etching apparatus according to claim 1, wherein the plurality of gas ejection holes are opened in the high portion of the focus ring. 3. The etching apparatus according to claim 1, further comprising a plurality of types of focus rings in which at least one of a gas ejection direction and an initial ejection speed of the gas ejection hole of the second gas ejection means is changed. The first gas ejection means is connected to a plurality of different types of etching gas sources via different flow rate control means, and the composition of the etching gas supplied into the vacuum reaction chamber is controlled by the flow rate control of each flow rate control means. The etching apparatus according to claim 1 , wherein the etching apparatus is adjusted by: The second gas ejection means is connected to a plurality of different types of etching gas sources via different flow rate control means, and the composition of the etching gas to be ejected from the outer periphery to the center of the wafer is controlled by the flow rate control. 3. The etching apparatus according to claim 1 , wherein the etching apparatus is adjusted by controlling the flow rate of the means. 5. The etching apparatus according to claim 4, wherein the etching rate of the central area and the peripheral area of the wafer is monitored, and the flow rate control means of the second gas ejection means is controlled according to the monitoring result.

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