JP2012222270A - Etching apparatus and etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching apparatus and an etching method which allow improvement of in-plane uniformity of etching under high pressure, and suppression of reduction in the etching rate.SOLUTION: The etching apparatus comprises: a vacuum chamber 11 in which a substrate S is loaded; a lower electrode 25 on which the substrate S is placed; an upper electrode 12 opposed to the lower electrode 25 over a plasma generation space PL; a high frequency power source 26 connected with the lower electrode 25; a gas inlet 12a for supplying an etching gas into the vacuum chamber 11; and an air exhaustion-system control part C2 for regulating the pressure inside the vacuum chamber 11. The high frequency power source 26 supplies the lower electrode 25 with a high frequency power of a VHF frequency band. The air exhaustion-system control part C2 regulates the pressure inside the vacuum chamber 11 to fall between 50 and 150 Pa inclusive. The inter-electrode distance L between the lower electrode 25 and the upper electrode 12 is between 50 and 100 mm inclusive.

Description

  The present invention relates to an etching apparatus and an etching method.

  As the high frequency discharge plasma used in the etching process, there are mainly capacitively coupled plasma (CCP) and inductively coupled plasma. Among them, an etching apparatus equipped with a capacitively coupled plasma source is used in a manufacturing process for processing a large area substrate such as a solar cell, for example, because it can easily generate a uniform discharge over a wide area.

  FIG. 8 shows an example of a conventional capacitively coupled plasma etching apparatus. The etching apparatus 100 has a grounded vacuum chamber 101, and a plasma generation space PL is provided in the vacuum chamber 101. A grounded upper electrode 102 is provided above the plasma generation space PL, and an etching gas is supplied from the gas supply system 104 to the upper electrode 102 through the gas supply port 103. The gas introduced into the upper electrode 102 is supplied into the vacuum chamber 101 from a shower plate provided on the lower surface of the upper electrode 102. The gas in the vacuum chamber 101 is maintained in a predetermined pressure range by driving an exhaust system 106 such as a pump connected to the exhaust port 105.

  In the vacuum chamber 101, a support base 107 made of an insulating material is provided. A lower electrode 108 is disposed on the support base 107 so as to face and be parallel to the upper electrode 102. The lower electrode 108 has a plane on which the substrate S is placed, and a high frequency power source 110 is connected to the lower electrode 108 through a matching unit 109. When performing the etching, plasma is generated using the etching gas as a raw material by supplying high-frequency power to the lower electrode 108 while supplying the etching gas into the vacuum chamber 101.

  On the other hand, it is known that a capacitively coupled plasma source generally has a lower density of plasma that can be generated than an inductively coupled plasma source. For this reason, the distance L between the electrodes of the etching apparatus 100 is usually kept at a distance smaller than 50 mm in order to improve the plasma density.

  However, if the distance L between the electrodes is reduced, when an etching gas is introduced into the plasma generation space PL, the ease of gas flow in the direction from the gas supply port 103 toward the exhaust port 105 is reduced. Gas tends to stay in the center. As a result, the plasma density in the plasma generation space PL is high at the center of the substrate and decreases as it goes from the center to the outside in the radial direction of the substrate. When the gradient of the plasma density is generated along the radial direction of the substrate S in this way, the in-plane uniformity of the etching rate at the central portion and the edge portion of the substrate S is deteriorated, and the uniformity of the etching shape is adversely affected.

  On the other hand, in Patent Document 1, when performing silicon etching using a resist as a mask, the shower head is surrounded directly under the shower head in order to solve the problem that the etching rate is high at the center of the substrate and low at the edge. Providing such an annular protrusion has been proposed. By forming the annular convex portion, the conductance of the gas flow discharged from the gas supply hole is reduced, the pressure at the substrate edge portion is increased, and the pressure gradient in the space is suppressed. In addition, by forming the gas supply holes concentrated in the center of the shower head, the amount of etchant generated at the upper center is reduced, the etching rate at the center of the substrate is lowered, and the in-plane uniformity is improved. ing.

JP2007-227829

  However, when the conditions such as the pressure in the vacuum chamber change, the in-plane etching characteristics change greatly. For example, when an etching apparatus having a conventional configuration is used and etching is performed under a relatively high pressure, for example, 50 Pa or more and 150 Pa or less, the inventors have found that the etching rate is low at the center of the substrate and high at the edge. Yes. This is presumably because the gas stays too much in the central portion of the plasma generation space PL, resulting in recombination of electrons and positive ions in the plasma in the central portion, and the process of reducing the active species proceeds. Therefore, when etching is performed under high pressure, if an annular convex portion is formed so as to surround the shower head with respect to the etching apparatus 100 of the conventional configuration, gas supply is performed not only at the substrate edge but also at the central portion of the substrate. The gas flow from the port 103 toward the exhaust port 105 is further reduced, which causes a further decrease in the etching rate at the center of the substrate.

  The present invention has been made in view of the above problems, and an object thereof is to provide an etching apparatus and an etching method capable of improving in-plane uniformity under high pressure and suppressing a decrease in etching rate. There is to do.

  In order to solve the above-mentioned problems, the invention according to claim 1 includes a vacuum chamber that accommodates a substrate, a first electrode on which the substrate is placed, and a plasma generation space with respect to the first electrode. A second electrode opposed via the first electrode, a high-frequency power source connected to the first electrode, a gas supply unit for supplying an etching gas to the vacuum chamber, and a pressure control unit for adjusting the pressure in the vacuum chamber The high-frequency power source supplies high-frequency power in the VHF frequency band to the first electrode, and the exhaust system controller adjusts the inside of the vacuum chamber to 50 Pa or more and 150 Pa or less, The gist is that the interelectrode distance between the first electrode and the second electrode is 50 mm or more and 100 mm or less.

  According to a third aspect of the present invention, a substrate is placed on a first electrode provided in a vacuum chamber, and high-frequency power is supplied to the first electrode while supplying an etching gas into the vacuum chamber. To etch the substrate by generating plasma between the first electrode and the second electrode facing the first electrode, the frequency of the first electrode being VHF A high frequency power included in a frequency band is supplied, the inside of the vacuum chamber is adjusted to a pressure of 50 Pa or more and 150 Pa or more, and a distance between the first electrode and the second electrode is 50 mm or more and 100 mm or less. It is a summary.

  According to the first and third aspects of the present invention, when the inside of the vacuum chamber is under a high pressure of 50 Pa or more and 150 Pa or less, it is newly generated in the sheath in the vicinity of the first electrode and contributes to anisotropic etching. The proportion of positive ions is increased. On the other hand, when the plasma is generated under such a high pressure, if the distance between the electrodes is small, the gas stays in the central portion, causing a reduction in the in-plane uniformity of the substrate. Therefore, by setting the inter-electrode distance to 50 mm or more and 100 mm or less, which is larger than the general inter-electrode distance, the retention of gas is suppressed even under high pressure to improve in-plane uniformity, and the decrease in plasma density is also suppressed. can do. Therefore, anisotropic etching can be promoted and the in-plane uniformity of the substrate can be improved.

  According to a second aspect of the present invention, in the etching apparatus according to the first aspect, an electrode position control unit that adjusts the distance between the electrodes by raising and lowering the second electrode is provided, and an inner surface of the vacuum chamber Among them, the gist is that a region where the shortest distance to at least the first electrode is smaller than the inter-electrode distance is covered with an insulator.

  According to the second aspect of the present invention, the first electrode to which the high frequency power is supplied discharges between the vacuum chamber and easily generates plasma. When plasma is generated, the density of plasma generated in the space between the electrodes decreases. In particular, when the distance between the electrodes is set to a large distance such as 50 mm or more and 100 mm or less as described above, the distance between the first electrode and the vacuum chamber becomes smaller than the distance between the electrodes, and discharge easily occurs between them. Therefore, it is possible to suppress the generation of plasma between the first electrode and the vacuum chamber by covering the inner surface of the vacuum chamber with the insulator. Further, when the first electrode is moved up and down, the region where the shortest distance between the first electrode and the vacuum chamber is smaller than the inter-electrode distance is changed each time. For this reason, when raising and lowering the first electrode, it is necessary to cover a wide area with an insulator. However, in order to adjust the distance between the electrodes by raising and lowering the second electrode, the area covered with the insulator is made as small as possible. can do.

  The invention according to claim 4 is the etching method according to claim 3, wherein the etching gas is a mixed gas of fluorine-containing gas and oxygen gas, and the flow rates of the fluorine-containing gas and oxygen gas are as follows: The gist is that they are 50 sccm to 300 sccm and 10 sccm to 300 sccm, respectively.

  According to the invention described in claim 4, since the flow rates of the fluorine-containing gas and the oxygen gas are set in the above ranges, the pressure in the vacuum chamber is increased without lowering the exhaust speed and retaining gas between the electrodes. be able to.

The invention according to claim 5 is the etching method according to claim 3,
The etching gas is a mixed gas of a fluorine-containing gas and a halogenated gas, and the flow rates of the fluorine-containing gas and the halogenated gas are 50 sccm to 300 sccm and 0 sccm to 150 sccm, respectively. .

  According to the invention described in claim 5, since the flow rates of the fluorine-containing gas and the halogenated gas are in the above ranges, respectively, the pressure in the vacuum chamber is reduced without reducing the exhaust speed and retaining the gas between the electrodes. Can be increased.

1 is a schematic view of an etching apparatus according to the present invention. It is a schematic diagram explaining the process of the etching with respect to a board | substrate, Comprising: (a) shows the effect | action of the positive ion accelerated in the bulk plasma, (b) shows the effect | action of the positive ion accelerated in the sheath. The figure which shows the ion energy distribution of the ion which reaches | attains a board | substrate at the time of supplying the high frequency voltage of a VHF frequency band. It is the scanning electron microscope (SEM) photograph which image | photographed the cross section of the hole obtained in Example 1 which made the distance between electrodes 50 mm, (a) is the hole formed in the center part of a board | substrate, (b) is a board | substrate. The SEM photograph of the hole formed in the edge part. It is the scanning electron microscope (SEM) photograph which image | photographed the cross section of the hole obtained in Example 2 which made distance between electrodes 65mm, (a) is the hole formed in the center part of a board | substrate, (b) is a board | substrate. The SEM photograph of the hole formed in the edge part. It is the scanning electron microscope (SEM) photograph which image | photographed the cross section of the hole obtained in Example 3 which made distance between electrodes 100mm, (a) is the hole formed in the center part of a board | substrate, (b) is a board | substrate. The SEM photograph of the hole formed in the edge part. It is the scanning electron microscope (SEM) photograph which image | photographed the cross section of the hole obtained by the comparative example 1 which made the distance between electrodes 25mm, (a) is the hole formed in the center part of a board | substrate, (b) is a board | substrate. The SEM photograph of the hole formed in the edge part. Schematic of the etching apparatus of a conventional structure.

  Hereinafter, an embodiment in which the etching apparatus and the etching method of the present invention are embodied as a capacitive coupling type etching apparatus and an etching method using the apparatus will be described with reference to FIGS.

  As shown in FIG. 1, the etching apparatus 10 has a covered cylindrical vacuum chamber 11. The vacuum chamber 11 is formed of a conductive material having corrosion resistance such as aluminum and is grounded. An exhaust port 11a for exhausting the fluid in the vacuum chamber 11 is provided at the bottom of the vacuum chamber 11, and an exhaust system 13 having an exhaust pump or the like is connected to the exhaust port 11a. The exhaust system 13 is electrically connected to an exhaust system control unit C2 as a pressure control unit in which a pressure control program is stored. The exhaust system control unit C2 has an exhaust pump drive circuit and the like, and inputs a pressure detection signal obtained by measuring the pressure in the vacuum chamber 11 from a pressure gauge 15 made of a diaphragm gauge or the like. Then, based on the pressure detection signal, the exhaust system 13 is driven in accordance with the pressure control program from the start to the end of each process in the etching apparatus 10 to keep the inside of the vacuum chamber 11 in a predetermined pressure range.

  In addition, a loading / unloading port 11 c for loading and unloading the substrate S into and from the vacuum chamber 11 is formed through the side wall of the vacuum chamber 11. A gate valve V is connected to the loading / unloading port 11c so that the inside of the vacuum chamber 11 can be maintained at a vacuum pressure.

  A grounded upper electrode 12 is disposed in the upper part of the vacuum chamber 11. The upper electrode 12 includes a shower plate 14 having a large number of gas supply holes 14a formed on the lower surface thereof. The gas supply holes 14 a are provided with a substantially uniform density without being biased toward a part of the shower plate 14. Further, the upper electrode 12 includes a buffer chamber 12r whose one surface is surrounded by a shower plate 14, and a gas introduction port 12a as a gas supply portion formed in the upper electrode 12 is communicated with the buffer chamber 12r. ing.

A gas supply pipe 18 constituting a gas supply system 17 is connected to the gas inlet 12a. In addition to the gas supply pipe 18, the gas supply system 17 includes a gas supply source 19 that sends out an etching gas, and a mass flow controller 19 m that supplies various gases into the vacuum chamber 11 at a predetermined flow rate. In the case of etching silicon, a mixed gas of fluorine-containing gas and oxygen or a mixed gas of fluorine-containing gas and hydrogen halide gas can be used as an etching gas. As the fluorine-containing gas, for example, sulfur hexafluoride gas (SF ₆ ), fluorocarbon gas (CxHy, x, and y are natural numbers) can be used. As the halogenated gas, bromine hydrogen gas (HBr) or chlorine-based gas can be used. The gas supply source 19 includes a plurality of gas supply sources 19a and 19b for sending out these gases, and includes a gas cylinder filled with each gas, a regulator, and the like. The gases sent from these gas supply sources 19 a and 19 b are mixed in the gas supply pipe 18 and supplied into the vacuum chamber 11.

  The upper electrode 12 has a configuration capable of moving up and down by a predetermined range in a direction parallel to the central axis (X-axis direction in the drawing) of the vacuum chamber 11. In the present embodiment, a cylinder portion 12b formed on the upper surface of the upper electrode 12 and provided so as to be slidable with respect to the fixed gas supply pipe 18, and an elevating mechanism 21 for raising and lowering the upper electrode 12 via the cylinder portion 12b. The position of the upper electrode 12 is adjusted by the electrode position control unit C1 that drives the elevating mechanism 21. The elevating mechanism 21 includes a motor that is a drive source, a motor drive circuit, and a transmission mechanism that converts the rotational force of the motor into a force that slides the cylindrical portion 12b. The motor drive circuit is connected to an electrode position control unit C1 that stores an electrode position adjustment program. The electrode position control unit C1 drives the elevating mechanism 21 according to the electrode position adjustment program, and slides the cylinder part 12b with respect to the gas supply pipe 18.

  A lower electrode 25 is provided below the vacuum chamber 11 so as to face and be parallel to the upper electrode 12. The lower electrode 25 also serves as a stage on which the substrate S is placed. In order to improve anisotropy and an etching rate, the lower electrode 25 is provided with a high frequency power source 26 capable of outputting high frequency power of 60 MHz to 150 MHz included in the VHF frequency band via a matching unit 27, for example. It is connected. The high-frequency power source 26 supplies high-frequency power to the lower electrode 25 and generates an electric field in the plasma generation space PL provided between the upper electrode 12 and turns the etching gas into plasma. The matching unit 27 matches the output impedance of the high frequency power supply 26 with the input impedance of the high frequency power supply 26 including the inside of the vacuum chamber 11.

  Further, the lower electrode 25 connected to the high frequency power source 26 and the grounded bottom wall of the vacuum chamber 11 are insulated by a bottom insulator 30 made of alumina. In the present embodiment, the bottom insulator 30 has a substantially annular shape.

  On the other hand, when a discharge occurs in a region at the end portion of the lower electrode 25 and the upper electrode 12 and outside the substrate S during the etching, the plasma generated in the region hardly contributes to the etching. Therefore, a substantially annular upper insulator 20 is provided on the lower surface of the upper electrode 12 at a position that is an end of the shower plate 14 and does not close the gas supply hole 14a. That is, the upper insulator 20 is provided in a region that does not overlap with the substrate S in a plan view viewed from the upper electrode 12 side. The upper insulator 20 is made of alumina and has a height that does not hinder the flow of gas in the space between the electrodes.

  Moreover, when the frequency of the high frequency power supplied from the high frequency power supply 26 is included in the ultra-short frequency band, the surface of the inner peripheral surface 11b of the vacuum chamber 11 and the lower electrode 25 are easily inductively coupled via plasma. Particularly, in the region where the distance from the lower electrode 25 on the inner peripheral surface 11 b of the vacuum chamber 11 is equal to or less than the interelectrode distance L, which is the relative distance between the upper electrode 12 and the lower electrode 25, Discharge tends to occur. When plasma is generated by generating discharge in such a region, high-frequency power is lost by that amount, and the high-frequency power consumed for generating plasma that contributes to etching is reduced. As a result, the plasma density is lowered, and the etching anisotropy and the etching rate are lowered.

  For this reason, the vacuum insulator 11 is provided with a side insulator 32 that covers a region that easily discharges between the inner peripheral surface 11 b and the edge of the lower electrode 25. The side insulator 32 is provided so as to cover the inner peripheral surface 11b of the vacuum chamber 11 at least from the upper end position of the movable range of the shower plate 14 of the upper electrode 12 to the exhaust port 11a.

  The side insulator 32 includes a first side insulator 33 made of alumina and a second side insulator 34 made of quartz. The first side insulator 33 is provided in a range from the upper end position of the movable range of the shower plate 14 to a position below the lower electrode 25. In addition, a through hole 32a that connects the inside of the vacuum chamber 11 and the loading / unloading port 11c is formed at a position where the first side insulator 33 overlaps the loading / unloading port 11c. The second side insulator 34 is located below the first side insulator 33 and is provided on the exhaust port 11a side.

  A lower insulator 31 made of quartz is provided on the outer periphery of the lower electrode 25. The lower insulator 31 is provided so as to cover the entire outer peripheral surface of the lower electrode 25, and includes a substrate accommodating portion 31 a for accommodating the substrate S on the upper portion thereof.

  Next, the operation of the present embodiment will be described in accordance with the etching processing procedure.

  First, the electrode position control unit C1 adjusts the position of the upper electrode 12 by driving the elevating mechanism 21 according to the electrode position control program, so that the inter-electrode distance L is in the range of 50 mm to 100 mm. At this time, the position of the shower plate 14 of the upper electrode 12 is the same position as the upper end position of the side insulator 32 or a position lower than that.

  Then, the gate valve V is opened, and the substrate S placed on the tray or the like is loaded from the loading / unloading port 11c. The substrate S is placed on the lower electrode 25 and inside the substrate accommodating portion 31 a of the lower insulator 31. When the substrate S is placed on the lower electrode 25, the gate valve V is closed, and the exhaust system controller C2 drives the exhaust system 13 to depressurize the vacuum chamber 11 according to the exhaust control program.

Also, for example, SF ₆ gas and O ₂ gas are sent from the gas supply system 17 while being adjusted to a predetermined flow rate by the mass flow controller 19m, and are supplied into the vacuum chamber 11 as a mixed gas. The exhaust system controller C2 adjusts the pressure in the vacuum chamber 11 so that the pressure in the vacuum chamber 11 is as high as 50 Pa or more and 150 Pa or less. At this time, the flow rate of the fluorine-containing gas such as SF ₆ gas is preferably 50 sccm or more and 300 sccm or less, and the flow rate of O ₂ gas is preferably 10 sccm or more and 300 sccm or less. When the mixed gas is composed of a fluorine-containing gas such as SF ₆ and a halogenated gas such as HBr, the flow rate of the fluorine-containing gas is preferably 50 sccm or more and 300 sccm or less, and the flow rate of the halogenated gas is more than 0 sccm and 150 sccm or less. Is preferred. The high frequency power supply 26 applies a high frequency voltage in a VHF frequency band of 60 MHz to 150 MHz to the lower electrode 25.

  The reason why the pressure in the vacuum chamber 11 is adjusted to the above range is as follows. That is, in the plasma generation space PL between the upper electrode 12 and the lower electrode 25, a sheath (dark part) positioned on the side of each electrode 12, 25 and bulk plasma sandwiched between the sheaths are formed. The positive ions that enter the substrate S without colliding with other particles include the following. That is, the electric field is accelerated by the bulk plasma, the energy obtained by the acceleration is maintained as it is, and the first positive ions incident on the substrate S and the neutrons are generated in the sheath formed in the vicinity of the lower electrode 25. The second positive ions are newly generated by exchanging electrons with the positive ions and accelerated in the sheath.

  As shown in FIG. 2, the substrate S to be processed has a mask S2 having an opening OP on, for example, a silicon substrate S1. The hole H is formed by etching the silicon substrate S1 through the opening OP. The positive ions that contribute to the straightness of the side surface of the hole H are positive ions that are mainly accelerated immediately above the opening OP. The positive ions include the first positive ions and the second positive ions described above.

  Further, as shown in FIG. 2A, the first positive ions located directly above the opening OP include the first positive ions flying in the normal direction of the surface of the silicon substrate S1, and the normal direction. There are first positive ions that fly in different directions. Since the first positive ions are accelerated by the bulk plasma and have a long flight distance, the first positive ions flying in the normal direction enter the silicon substrate S1 through the opening OP as indicated by an arrow in the center in the figure. The bottom of the formed hole H is reached. The first positive ions flying in a direction different from the normal direction deviate from the opening OP before reaching the substrate S as shown by the left and right arrows in the figure, and do not reach the silicon substrate S1. Or, the collision with the side surface of the hole H increases.

  On the other hand, as indicated by the arrows in FIG. 2B, the second positive ions flying in the normal direction of the surface of the silicon substrate S1 and the normal direction are also the second positive ions. There are second positive ions that fly in different directions, but the second positive ions are accelerated in the sheath and therefore have a relatively short flight distance. For this reason, as indicated by the arrows at the left end and the right end, even when accelerated in a direction different from the normal direction, the probability of reaching the bottom surface of the hole H is higher than that of the first positive ions.

  Therefore, in order to improve the anisotropy of the etching shape, it is preferable to increase the ratio occupied by the second positive ions among the positive ions generated in the plasma generation space PL. It is known that the factor that determines the ratio of the second positive ions is the pressure in the vacuum chamber 11 in addition to the frequency band of the high-frequency power supplied to the lower electrode 25.

  As shown in the ion energy distribution of FIG. 3, the peak derived from the first positive ion is a bimodal peak BP which is a pair of peaks P1 and P2. Further, the peak derived from the second positive ion is a low energy peak P3 appearing in an energy region lower than the bimodal peak BP. That is, the first positive ion has a higher ion energy (eV) than the second positive ion. FIG. 3 shows the energy distribution obtained when the high frequency power is in the frequency band of 150 MHz, and a plurality of low energy peaks P3 appear. In order to increase the ratio of the second positive ions, the inside of the vacuum chamber 11 may be set to a pressure that increases the strength (or half-value width) of the low energy peak P3. Moreover, in order to obtain a favorable etching rate, it is preferable in practical use that the first positive ions having high ion energy are also present.

  From the ion energy distribution of FIG. 3, when the pressure is less than 50 Pa, the low energy peak P3 attributed to the second positive ion is not detected. When the pressure exceeds 150 Pa, not only the low energy peak P3 but also bimodal. It can be seen that no peak BP is detected.

  On the other hand, both the low energy peak P3 and the bimodal peak BP are not observed in both the case where the pressure is 50 Pa or more and 150 Pa or less and the frequency band of the high frequency power is less than 60 MHz and more than 150 MHz. (Not shown).

  Therefore, when the frequency of the high frequency power is adjusted to 60 MHz or more and 150 MHz or less and the pressure is adjusted to 50 Pa or more and 150 Pa or less, the ratio of the second positive ions can be increased. Thus, the gas can be exhausted without being retained between the electrodes.

  On the other hand, when etching is performed under such a relatively high pressure, the interelectrode distance L is preferably 50 mm or more and 100 mm or less as described above. When the distance L between the electrodes is less than 50 mm under high pressure, the gas flow conductance decreases, so that the gas stays in the central portion of the plasma generation space PL, and the pressure gradient between the central portion and the surroundings is large. Become. Since the ratio of the second positive ions changes according to the pressure condition as described above, when the pressure gradient in the plasma generation space PL increases, the ratio of the second positive ions in the central portion and the second in the vicinity thereof. The difference in the proportion of positive ions increases. As a result, the difference in the ratio of the second positive ions contributing to anisotropy increases, resulting in a decrease in the uniformity of the etching shape obtained at the substrate center and the substrate edge, and a decrease in the in-plane uniformity of the etching rate. To do.

  In addition, when the distance L between the electrodes is in the range of 50 mm or more and 100 mm or less, the difference in the ratio of the second positive ions is reduced and the plasma density is increased, so that in-plane uniformity is good and the etching rate is maximum. There exists a distance L between the electrodes. When the distance L between the electrodes is made longer than that distance and approaches 100 mm, the plasma density between the electrodes gradually decreases, so that the etching rate gradually decreases. If the distance L between the electrodes is more than 100 mm, the plasma density is lowered by the amount of expansion of the plasma generation space PL, and the etching rate is greatly lowered as a whole.

  On the other hand, by setting the interelectrode distance L within the above range, the gas can be prevented from staying in the central portion and the pressure gradient can be reduced. For this reason, the difference between the ratio of the second positive ions in the central part of the substrate and the ratio of the second positive ions in the edge part of the substrate is small, so the difference between the etching rate at the center and the etching rate at the edge part. The in-plane uniformity represented by the following formula is within 5%, and the uniformity of the etching shape can also be improved.

  When a high frequency voltage is applied to the lower electrode 25 with the interelectrode distance L in the above range, active species such as positive ions in the plasma are drawn into the substrate S. In addition, a product such as silicon fluoride or silicon oxide is generated by the reaction between the active species and silicon atoms, and is deposited on the side wall of the hole H extending in the thickness direction of the substrate S. And the etching of a side wall can be suppressed and anisotropic etching can be promoted.

Below, the Example according to this embodiment and the comparative example with respect to an Example are shown.
[Example 1]
Etching was performed using the etching apparatus 100 of the above embodiment under the following conditions.

Substrate: Silicon substrate, thickness 750 μm, 8 inches, opening diameter 50 μm
Gas composition and flow rate: SF ₆ (flow rate 75 sccm), O ₂ (flow rate 75 sccm), HBr (flow rate 15 sccm)
High frequency power: 60 MHz
Power supplied from high frequency power supply for bias: 1200W
Pressure: 50Pa
Processing time: 600 seconds Distance between electrodes: 50mm
As shown in the SEM photograph of FIG. 4, the holes obtained by carrying out the etching under these conditions had high rectilinearity on the side wall at both the substrate center and the substrate edge. Further, the etching rate Rcnt at the center of the substrate when etching is performed, the etching rate Redg at the substrate edge portion, and in-plane uniformity are shown below.

Etching rate Rcnt at the center of the substrate: 10.6 μm / min
Etching rate Redg of substrate edge part: 11.4 μm / min
In-plane uniformity: {(Redg-Rcnt) / (Redg + Rcnt)}. 100% = 3.6%
[Example 2]
Etching was performed by changing the interelectrode distance L of Example 1 to 65 mm. The conditions are the same as in Example 1 except for the distance between the electrodes. As shown in the SEM photograph of FIG. 5, holes with high straightness of the sidewalls were obtained at both the substrate center and the substrate edge. Each etching rate and in-plane uniformity are shown below.

Etching rate Rcnt at the center of the substrate: 10.7 μm / min
Etching rate Redg at substrate edge: 10.8 μm / min
In-plane uniformity: 0.5%
[Example 3]
Etching was performed by changing the distance L between the electrodes in Example 1 to 100 mm. The conditions are the same as in Example 1 except for the distance between the electrodes. As shown in the SEM photograph of FIG. 6, holes with high straightness of the sidewalls were obtained at both the substrate center and the substrate edge. Each etching rate and in-plane uniformity are shown below.

Etching rate Rcnt at the center of the substrate: 6.9 μm / min
Etching rate Redg of substrate edge portion: 7.28 μm / min
In-plane uniformity: 2.7%
The in-plane uniformity is good within 5%, but it is a large value as compared with the case where the inter-electrode distance L is 65 mm, and it can be seen that it is slightly lowered. In addition, the etching rate is smaller than when the distance L between the electrodes is 65 mm.
[Comparative Example 1]
Etching was performed by changing the inter-electrode distance L of Example 1 to 25 mm, which is less than the preferred range of the inter-electrode distance L. The conditions are the same as in Example 1 except for the distance between the electrodes. As shown in the SEM photograph of FIG. 7A, it can be seen that the side surface of the hole is etched at the center of the substrate, and isotropic etching has progressed. As shown in FIG. 7B, a hole having a shape in which the straightness of the side wall was maintained was obtained at the substrate edge portion. That is, the uniformity of the etching shape obtained at the central portion of the substrate and the etching shape obtained at the edge portion of the substrate was lowered. Each etching rate and in-plane uniformity are shown below. The in-plane uniformity of the etching rate was over 5%, which was greatly reduced as compared with each example.

Etching rate Rcnt at the center of the substrate: 6.4 μm / min
Etching rate Redg at substrate edge: 8.2 μm / min
In-plane uniformity: 12.3%
In addition, since the in-plane uniformity and the etching rate are slightly reduced from 65 mm to 100 mm, the inter-electrode distance L is more than 100 mm. It is clear that the etching rate decreases.

  According to the above embodiment, the following effects can be obtained.

  (1) In the above embodiment, a high frequency voltage in the VHF frequency band is supplied from the high frequency power supply 26 to the lower electrode 25, and the inside of the vacuum chamber 11 is maintained at 50 Pa to 150 Pa by the exhaust system 13. Etching is performed by setting the distance L between the electrodes to 50 mm to 100 mm. That is, by setting the pressure range, the ratio of the second positive ions newly generated in the sheath can be increased without annihilating the first positive ions. In addition, by setting the interelectrode distance L to 50 mm or more and 100 mm or less, which is larger than the general interelectrode distance, while suppressing gas retention even under high pressure, the in-plane uniformity of the etching rate and the etching shape is improved. Further, a decrease in plasma density due to an increase in the interelectrode distance L can be suppressed.

  (2) In the above embodiment, the side insulator 32 covers the region of the inner surface of the vacuum chamber 11 where at least the shortest distance to the lower electrode 25 is smaller than the inter-electrode distance L. That is, as described above, when the interelectrode distance L is set to a large distance such as 50 mm or more and 100 mm or less, the distance between the lower electrode 25 and the vacuum chamber 11 becomes smaller than the interelectrode distance L, and electric discharge is likely to occur between them. Become. Therefore, by covering the inner surface of the vacuum chamber 11 with the side insulator 32, it is possible to suppress the generation of plasma between the lower electrode 25 and the vacuum chamber 11. Further, if the lower electrode 25 can be moved up and down, the region covered by the insulator must be enlarged according to the range in which the lower electrode 25 is moved up and down. For this reason, the area | region covered with an insulator can be made as small as possible by raising / lowering the upper electrode 12. FIG.

  (3) In the above embodiment, the etching gas is a mixed gas of fluorine-containing gas and oxygen gas, and the flow rates of the fluorine-containing gas and oxygen gas are 50 sccm to 300 sccm and 10 sccm to 300 sccm, respectively. For this reason, the pressure in the vacuum chamber 11 can be increased without reducing the exhaust speed and retaining the gas flow between the electrodes.

  In addition, you may change the said embodiment as follows.

  In the above embodiment, the gas supply source 19 sends out two types of gas, but may send out three or more types of gas.

  In the above embodiment, the upper electrode 12 is movable and the lower electrode 25 is fixed. However, the lower electrode 25 may be movable and the upper electrode 12 may be fixed. In this case, the side insulator 32 covers the side surface of the vacuum chamber 11 up to the range reaching the lower end of the movable range of the lower electrode 25 in the axial direction.

  In the above embodiment, the etching apparatus 10 includes a mechanism that can adjust the inter-electrode distance L. However, the mechanism may be omitted, and the inter-electrode distance L may be fixed to a fixed distance.

  In the above embodiment, the upper insulator 20, the bottom insulator 30, and the first side insulator 33 are made of alumina, and the lower insulator 31 and the second side insulator 34 are made of quartz. As another configuration, the upper insulator 20, the bottom insulator 30, the first side insulator, the lower insulator 31, and the second side insulator 34 may be formed from the same insulating material. Further, the upper insulator 20, the bottom insulator 30, and the first side insulator 33 may be formed of quartz, and the lower insulator 31 and the second side insulator 34 may be formed of alumina. Moreover, you may change the combination of the member which consists of the same insulating material.

  C2: Exhaust system control unit as a pressure control unit, C1 ... Electrode position control unit, PL ... Plasma generation space, S ... Substrate 10, 100 ... Etching apparatus, 11 ... Vacuum chamber, 12 ... Upper part as second electrode Electrode, 12a: Gas inlet as gas supply unit, 21: Elevating mechanism, 25: Lower electrode as first electrode, 26: High frequency power source, L: Distance between electrodes, 32: Side insulator.

Claims (5)

A vacuum chamber containing the substrate;
A first electrode on which the substrate is placed;
A second electrode facing the first electrode via a plasma generation space;
A high frequency power source connected to the first electrode;
A gas supply unit for supplying an etching gas to the vacuum chamber;
An etching apparatus comprising a pressure control unit that adjusts the pressure in the vacuum chamber,
The high frequency power supply supplies high frequency power in a VHF frequency band to the first electrode,
The pressure control unit adjusts the inside of the vacuum chamber to 50 Pa or more and 150 Pa or less,
An etching apparatus, wherein an inter-electrode distance between the first electrode and the second electrode is 50 mm or more and 100 mm or less. While comprising an electrode position controller that adjusts the distance between the electrodes by raising and lowering the second electrode,
2. The etching apparatus according to claim 1, wherein an area of the inner surface of the vacuum chamber that is at least the shortest distance to the first electrode is smaller than the distance between the electrodes is covered with an insulator. A substrate is placed on a first electrode provided in a vacuum chamber, and high-frequency power is supplied to the first electrode while supplying an etching gas into the vacuum chamber, whereby the first electrode and the first electrode An etching method for etching the substrate by generating plasma between a first electrode and a second electrode facing the first electrode,
Supplying the first electrode with high-frequency power having a frequency included in a VHF frequency band;
The inside of the vacuum chamber is adjusted to a pressure of 50 Pa or more and 150 Pa or more,
An etching method, wherein an interelectrode distance between the first electrode and the second electrode is 50 mm or more and 100 mm or less. The etching gas is a mixed gas of fluorine-containing gas and oxygen gas,
The etching method according to claim 3, wherein flow rates of the fluorine-containing gas and the oxygen gas are 50 sccm to 300 sccm and 10 sccm to 300 sccm, respectively. The etching gas is a mixed gas of a fluorine-containing gas and a halogenated gas,
The etching method according to claim 3, wherein the flow rates of the fluorine-containing gas and the halogenated gas are 50 sccm or more and 300 sccm or less and more than 0 sccm and 150 sccm or less, respectively.