JP2015192102A - Reactive ion etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactive ion etching device that is able to inhibit a significant decrease in etching rate even if power supplied to a stage is small, while inhibiting radiation of vacuum ultraviolet light with respect to an object to be processed.SOLUTION: A reactive ion etching device comprises: a vacuum processing chamber 1a; a stage 2 provided in the vacuum processing chamber and holding an object W to be processed; gas introduction means 4 for introducing etching gas into the vacuum processing chamber; plasma generating means 5, E2 for generating, in the vacuum processing chamber, plasma for ionizing the etching gas; and a power source E1 for supplying bias power to the stage. A shield plate 6 having an outside shape equal to or larger than the outside shape of the stage in the vacuum processing chamber and having a plurality of through holes 61 is arranged opposite to the stage. A space above the shield plate within the vacuum processing chamber is used as a plasma generation space SP. The proportion of the total of the areas of the through-holes in an underside 60 of the shield plate facing the plasma generation space from the stage side, to the area of the surface projected on the shield plate of the stage, is set within 10 to 80%.

Description

  The present invention relates to a reactive ion etching apparatus, and more particularly to an apparatus suitable for etching a gallium nitride film.

  Since the gallium nitride film has a large band gap, it is used as a power device material, for example. In the power device manufacturing process, the gallium nitride film is etched using, for example, a reactive ion etching apparatus. As a reactive ion etching apparatus, a stage provided in a vacuum processing chamber for holding an object to be processed, a gas introduction means for introducing an etching gas into the vacuum processing chamber, and a plasma for ionizing the etching gas are generated in the vacuum processing chamber. It is known to have a plasma generating means to be applied and a power source for supplying bias power to the stage. Here, since the gallium nitride film is easily damaged by the plasma, the bias power is generally set to be small (for example, 5 W or less). However, when the vacuum ultraviolet light from the plasma is irradiated to the gallium nitride film, the nitridation is performed. It is known that gallium films are damaged.

  For example, Patent Document 1 discloses a microwave plasma etching apparatus that includes a shielding plate that is disposed to face a stage in a vacuum processing chamber, so that irradiation of vacuum ultraviolet light onto a processing target can be suppressed. In this case, the shielding plate is made of a material that does not transmit vacuum ultraviolet light, and a plurality of through holes extending obliquely from the stage side so that the plasma generation space above the shielding plate is not visible from the stage side are formed. Therefore, the processing object is not irradiated with the vacuum ultraviolet light from.

  Therefore, it is conceivable to apply the shielding plate to a reactive ion etching apparatus to etch the gallium nitride film, but it has been found that the etching rate of the gallium nitride film is significantly reduced. This is because the shielding plate is formed so that the through hole of the shielding plate does not face the plasma generation space from the stage side, so that almost no ions are supplied to the gallium nitride film through the through hole and applied to the gallium nitride film. This is thought to be because the self-bias voltage applied is significantly reduced.

JP 2006-12962 A

  In view of the above points, the present invention provides a reactive ion etching apparatus capable of suppressing a significant decrease in the etching rate even when the input power to the stage is small while suppressing the irradiation of the vacuum ultraviolet light onto the object to be processed. The task is to do.

  In order to solve the above problems, a vacuum processing chamber, a stage provided in the vacuum processing chamber for holding a processing object, a gas introduction means for introducing an etching gas into the vacuum processing chamber, and a plasma for ionizing the etching gas are provided. The reactive ion etching apparatus of the present invention comprising plasma generating means for generating in a vacuum processing chamber and a power source for supplying bias power to the stage has an outer shape equal to or greater than the outer shape of the stage in the vacuum processing chamber, and has a plurality of transparent materials. The shield plate with holes is placed facing the stage, the direction from the stage toward the shield plate is the top, the space above the shield plate in the vacuum processing chamber is the plasma generation space, and the area of the projection surface onto the shield plate of the stage The ratio of the sum of the areas of the through holes on the lower surface of the shielding plate facing the plasma generation space from the stage side is set within a range of 10 to 80%. And wherein the door.

  According to the present invention, a plurality of through holes are formed in the shielding plate so as to face the plasma generation space from the stage side, and the total area of the portions of the respective through holes on the lower surface of the shielding plate facing the plasma generation space is determined as follows. By setting within a range of 10 to 80% with respect to the area of the projection surface on the shielding plate, ions can be efficiently supplied to the object to be processed through each through hole. For this reason, even if the bias power is small, the self-bias voltage applied to the object to be processed does not decrease, and a significant decrease in the etching rate can be suppressed. In addition to this, vacuum ultraviolet light from the plasma can be efficiently shielded at portions other than the through holes of the shielding plate. Therefore, it is possible to obtain a reactive ion etching apparatus capable of suppressing a significant decrease in the etching rate even if the input power to the stage is small while suppressing the irradiation of the vacuum ultraviolet light to the processing object. In addition, when the through holes are opened so as to extend obliquely with respect to the lower surface of the shielding plate, “the portion of each through hole on the lower surface of the shielding plate facing the plasma generation space from the stage side” means each through hole on the lower surface of the shielding plate. When projected on the upper surface of the shielding plate, it means a portion overlapping with each through hole on the upper surface of the shielding plate.

  In the present invention, each of the through holes can be opened on a concentric circle centered on the center of the shielding plate so as to have the same circumferential length. In the present invention, each of the through holes can be circular or rectangular in plan view.

  In this invention, it is preferable to set the distance from the said shielding board to a process target object in the range of 30 mm-100 mm. If it is shorter than 30 mm, the difference between the etching rate of the processing object located immediately below the through hole of the shielding plate and the etching rate of the processing object located directly below the portion excluding the through hole of the shielding plate becomes large. There is a problem that the in-plane uniformity is worsened. On the other hand, when the length is longer than 100 mm, there is a problem that plasma leaks to the stage side of the shielding plate, and the irradiation of the vacuum ultraviolet light onto the object to be processed cannot be effectively suppressed.

The figure which shows typically the reactive ion etching apparatus of embodiment of this invention. (A)-(c) is a top view which shows the example of a shielding board, respectively. The graph which shows the experimental result which confirms the effect of this invention. The graph which shows the experimental result which confirms the effect of this invention. The graph which shows the experimental result which confirms the effect of this invention.

  A reactive ion etching apparatus (hereinafter referred to as “etching apparatus”) according to an embodiment of the present invention will be described below with reference to the drawings. Referring to FIG. 1, EM is an etching apparatus, and the etching apparatus EM includes a vacuum chamber 1 that defines a vacuum processing chamber. The upper opening of the vacuum chamber 1 is closed with a top plate 11 formed of a dielectric material such as quartz. A flange 1a is provided on the upper side wall of the vacuum chamber 1, and a gap between the flange 1a and the top plate 11 is sealed by an O-ring 12 fitted in a groove 1b formed on the upper surface of the flange.

  A substrate stage 2 is provided at the bottom of the vacuum chamber 1 via an insulator I so that the processing object W can be positioned and held by a known electrostatic chuck (not shown) with its processing surface facing upward. It has become. The substrate stage 2 is connected to the output from the high-frequency power source E1 through the lower opening of the vacuum chamber 1 so that a bias potential can be applied to the processing object W. Note that a heating medium flow path (not shown) is formed in the substrate stage 2, and the processing object W can be heated to a predetermined temperature by flowing a temperature controlled temperature medium through the heating medium flow path.

  An exhaust pipe 3 leading to vacuum exhaust means such as a vacuum pump (not shown) is connected to the bottom of the vacuum chamber 1 so that the inside of the vacuum chamber 1 can be evacuated. Further, a gas pipe 4 communicating with a gas source is connected to the side wall of the vacuum chamber 1 via a flow rate control means (mass flow controller) (not shown) so that an etching gas can be introduced into the vacuum chamber 1 at a predetermined flow rate. ing.

  A loop antenna coil 5 having a plurality of stages (two stages in the present embodiment) is provided outside the top plate 11, and an output from a high frequency power source E2 is connected to the antenna coil 5 to generate a high frequency for plasma generation. Power can be turned on. The antenna coil 5 and the high-frequency power source E2 constitute “plasma generating means” of the present invention, and can generate plasma in a space SP (hereinafter referred to as “plasma generating space”) above a shielding plate 6 described later.

  Here, when the processing object W is irradiated with the vacuum ultraviolet light from the plasma, the processing object W is damaged. In order to suppress such irradiation of vacuum ultraviolet light, the etching apparatus EM has the shielding plate 6 having an outer shape equal to or greater than the outer shape of the stage 2 disposed opposite to the stage 2. The shielding plate 6 is supported on an upper portion of a support portion 7 that stands on the bottom of the vacuum chamber 1 outside the stage 2. As the material of the shielding plate 6 and the support portion 7, a material that shields vacuum ultraviolet light, such as quartz, alumina, aluminum, and titanium, can be used. Further, as the shielding plate 6, a material obtained by covering the surface of a metal base material such as aluminum or titanium with an alumina film can be used.

  Referring also to FIG. 2A, the shielding plate 6 has a plurality of circular through holes 61 that are circular in plan view. These through holes 61 are formed so as to face the plasma generation space SP from the stage 2, that is, to extend in a direction orthogonal to the lower surface of the shielding plate 60. The ratio (hereinafter referred to as “aperture ratio”) of the total area of the portions of the through holes 61 on the lower surface 60 of the shielding plate facing the plasma generation space SP from the stage 2 side with respect to the area of the projection surface onto the shielding plate 6 of the stage 2 It is set within a range of 10 to 80%, preferably within a range of 20 to 50%. When the aperture ratio is less than 10%, there is a problem that the plasma leaking to the stage side of the shielding plate 6 is reduced and the etching process becomes difficult. In view of production efficiency (productivity), it is preferable to set the aperture ratio to 20% or more. On the other hand, when the aperture ratio is higher than 80%, there is a problem that the irradiation of the processing object W with vacuum ultraviolet light cannot be effectively suppressed. Since the PL shift amount, which will be described later, which is an index of damage to the processing object W is preferably a value close to 1.0, it is preferable to set the aperture ratio to 50% or less. The diameter of the through hole 61 can be set within a range of 3 to 40 mm. Moreover, the thickness of the shielding board 6 can be suitably set within the range of 2-15 mm according to the material, for example. The distance from the shielding plate 6 to the processing object W is preferably set within a range of 30 mm to 100 mm. If shorter than 30 mm, the difference between the etching rate of the processing object W located immediately below the through hole 61 of the shielding plate 6 and the etching rate of the processing object W located directly below the portion excluding the through hole 61 of the shielding plate 6. There is a problem that the in-plane uniformity of the etching rate is deteriorated. On the other hand, when it is longer than 100 mm, there is a problem that plasma leaks to the stage side of the shielding plate 6 and the irradiation of the vacuum ultraviolet light to the processing object W cannot be effectively suppressed.

  An electrode 7 is disposed along the top plate 11 between the top plate 11 and the antenna coil 5. An output from the high-frequency power source E2 is connected to the electrode 7 via a variable capacitor (for example, 100 pF to 200 pF) 8. When a voltage is applied to the electrode 7 in a state where plasma is generated in the vacuum chamber 1, The ions are attracted to the lower surface 11a of the top plate 11 facing 7 so that reaction by-products attached to the lower surface 11a can be removed.

  Although not particularly shown, the etching apparatus EM has known control means including a microcomputer, a sequencer, etc., and the control means operates the power supplies E1, E2, the mass flow controller, the vacuum exhaust means, and the like. It is supposed to manage and manage. Hereinafter, an etching method in which the processing object W is a sapphire substrate on which a gallium nitride film is formed and the gallium nitride film is etched using the etching apparatus EM will be described.

  First, in a state where the vacuum evacuation unit is operated and the vacuum chamber 1 is evacuated to a desired degree of vacuum, the processing object W is transferred using the transfer robot (not shown) and placed on the substrate stage 2. Then, a chlorine-containing gas is introduced into the vacuum chamber 1 from the gas pipe 4 at a flow rate of 20 to 50 sccm, and in this state, for example, high frequency power of 13.56 MHz is input to the antenna coil 5 from 100 W to 500 W from the high frequency power source E2. As a result, plasma P is generated in the vacuum chamber 1. In addition, 1 to 5 W of high frequency power of 400 kHz, for example, is input to the stage 2. Here, as shown in FIG. 2A, the shielding plate 6 in which a plurality of through holes 61 having a diameter of 30 mm (aperture ratio 50%) is formed is disposed opposite to the stage 2, so that the plasma P passes through the through holes 61. Leak moderately to the stage 2 side. For this reason, chlorine ions are drawn into the processing object W and the gallium nitride film is etched.

  As described above, since the processing object W faces the plasma P through the through hole 61 of the shielding plate 6, the plasma can be appropriately leaked to the stage 2 side of the shielding plate 6 through the through hole 61. it can. For this reason, even if the bias potential applied to the processing object W is low (for example, 2 W), chlorine ions can be efficiently drawn into the processing object W. Further, the vacuum ultraviolet light from the plasma P can be shielded by the portions other than the through holes 61 of the shielding plate 6. Therefore, it is possible to obtain a reactive ion etching apparatus that can surely etch the gallium nitride film while suppressing the irradiation of the processing object W with vacuum ultraviolet light.

  As mentioned above, although embodiment of this invention was described, this invention is not limited above. In the above-described embodiment, the shielding plate 6 having the through hole 60 having a circular shape in plan view has been described as an example. However, the shape of the through hole is not limited thereto, and for example, the shielding plate 6a illustrated in FIG. In this way, a through hole 61a having a rectangular shape in plan view may be opened. In this case, the plurality of through holes 61a can be opened by patterning the shielding plate 6a in a lattice shape. Further, like the shielding plate 6b shown in FIG. 2 (c), each of the through holes 61b (the through holes 61c and 61d) has the same circumferential length on a concentric circle centered on the center of the shielding plate 6b. It may be established as follows. In this case, the through holes 61b, 61c, 61d may be opened at equal intervals in the radial direction. In this case, the shielding plate 6b is partitioned by a circular base portion 63a, a plurality of (eight in the present embodiment) main branch portions 63b extending in the radial direction from the base portion 63a, and main branch portions 63b adjacent to each other. It can be configured by an arc-shaped follower 63c that divides the space into a plurality of through holes.

  Moreover, although the said embodiment demonstrated the case where the through-hole extended in the orthogonal direction with respect to the shielding board surface was demonstrated, you may open the through-hole extended diagonally with respect to the shielding board surface. In this case, the portion of each through-hole in the lower surface of the shielding plate facing the plasma generation space from the stage side is mutually overlapped with each through-hole in the upper surface of the shielding plate when each through-hole in the lower surface of the shielding plate is projected onto the upper surface of the shielding plate. The part to do. In the above conventional example, there is no such part.

  In the above embodiment, the shielding plate 6 is supported by the support portion 7, but the shielding plate 6 may be fixed to the side wall of the vacuum chamber 1. Further, the method for generating plasma is not limited to the method of applying high-frequency power to the antenna coil, and other known methods can be used.

  Next, in order to confirm the above effect, the following experiment was performed using the etching apparatus EM. In this experiment, it is assumed that a gallium nitride film is formed as a processing object W on a sapphire substrate with a thickness of about 30 nm by sputtering, and this gallium nitride film is etched. Etching conditions are as follows. That is, the shielding plate 6 is made of alumina having a plurality of apertures of φ30 mm with an aperture ratio of 50%, the distance between the shielding plate 6 and the object to be processed W is set to 60 mm, and the flow rate of the chlorine-containing gas is set. 30 sccm (the pressure in the vacuum chamber 1 at this time is about 0.5 Pa), and the input power to the stage 2 is set to 400 kHz and 2 W, and the input power to the antenna coil 5 is set to 13.56 MHz and 150 W. did. As a result of measuring the band edge strength and in-band strength of the gallium nitride film before and after etching, the band edge strength before etching (initial) was 43 (au) and the in-band strength was 3797 (au). On the other hand, the band edge strength after etching was 41 (au) and the in-band strength was 3765 (au). From this, the ratio of in-band strength to in-band strength before and after etching (in-band strength / band-end strength) was found to change 1.08 times from 88.3 before etching to 91.8 after etching. Confirmed to do. Hereinafter, the change in the ratio before and after etching (in-band intensity / band edge intensity) is referred to as “PL shift amount” and is used as an index of damage. The etching rate in this experiment was 8 nm / min.

  Further, etching is performed in the same manner as described above except that the aperture ratio of the through holes 61 is changed to 10%, 20%, 40%, 70%, 80%, 90%, 100% (no shielding plate). FIG. 3 shows the result of obtaining the PL shift amount. The etching rates when the aperture ratio is 10%, 20%, 80%, and 100% were also measured, and the measurement results are shown in FIG. From the results shown in FIG. 3 and FIG. 4, it was found that the gallium nitride film can be etched while suppressing the PL shift amount if the aperture ratio of the through holes 61 is set in the range of 10% to 80%. Furthermore, it was found that if the aperture ratio is set within a range of 20 to 50%, the production efficiency can be increased and the PL shift amount can be further suppressed.

  Moreover, except that the material of the shielding plate 6 is changed to quartz and aluminum, etching is performed in the same manner as described above (opening ratio 50%), and the result of obtaining the PL shift amount is shown in FIG. According to this, the material of the shielding plate 6 is preferably alumina. However, since it is difficult to form a through-hole in an alumina shielding plate, it is preferable to form an alumina film on at least the plasma side surface of a metallic shielding plate such as aluminum or titanium. As a forming method, a thermal spraying method can be used.

  EM ... Reactive ion etching apparatus, W ... Substrate (object to be processed), 1a ... Vacuum processing chamber, 2 ... Stage, 4 ... Gas pipe (gas introducing means), 5 ... Antenna coil (plasma generating means), E1 ... Power supply , E2 ... high frequency power source (plasma generating means), 6 ... shielding plate, 60 ... bottom surface of shielding plate, 61 ... through hole.

Claims (4)

A vacuum processing chamber, a stage provided in the vacuum processing chamber for holding an object to be processed, a gas introducing means for introducing an etching gas into the vacuum processing chamber, and plasma generation for generating plasma for ionizing the etching gas in the vacuum processing chamber In a reactive ion etching apparatus comprising means and a power source for supplying bias power to the stage,
A shielding plate having an outer shape equal to or larger than the outer shape of the stage in the vacuum processing chamber is arranged opposite to the stage, and the direction from the stage toward the shielding plate is upward, and the shielding plate in the vacuum processing chamber is The upper space is the plasma generation space,
The ratio of the total area of the portions of the through holes on the lower surface of the shielding plate facing the plasma generation space from the stage side to the area of the projection surface on the shielding plate of the stage is set within a range of 10 to 80%. Reactive ion etching equipment.   2. The reactive ion etching apparatus according to claim 1, wherein each of the through holes is provided on a concentric circle centered on the center of the shielding plate so that the circumferential lengths are equal.   The reactive ion etching apparatus according to claim 1, wherein each of the through holes is circular or rectangular in a plan view.   The reactive ion etching apparatus according to claim 1, wherein a distance from the shielding plate to the object to be processed is set in a range of 30 mm to 100 mm.

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