JP4666817B2 - High dielectric etching equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an etching apparatus for processing a high dielectric constant material such as LiNbO ₃ or PZT in plasma.
[0002]
[Prior art]
In this type of conventional etching apparatus, the surface of the substrate electrode is coated with an anodized film of 20 to 30 μm in consideration of corrosion resistance, and the substrate pressing jig or the clamp material is made of alumina. The substrate pressing jig or the back surface of the clamp remains the alumina substrate.
[0003]
Incidentally, the main purpose of the substrate holding mechanism in the conventional etching apparatus is to improve the thermal conductivity. Therefore, unlike a high dielectric constant material, there is no large gap between the surface potential and the back surface potential due to plasma irradiation, and high voltage (electrostatic) breakdown does not occur. Therefore, a substrate electrode structure capable of shape control and uniform etching is used. I wish I had it. In the prior art, it is found that slight undercut occurs when, for example, SiO ₂ is etched using a metal mask. SiO ₂ does not react with active species in plasma having no charge, and etching proceeds by ion bombardment. The mask metal is charged by a charge generated by a slight difference in the amount of ions and electrons reaching the surface, and a potential different from that inside the dielectric is generated. Therefore, it can be interpreted that the trajectory of the incident ions is bent by the action of the electric charges charged on the metal mask on the surface, and as a result, an undercut occurs.
[0004]
In a dielectric having a low dielectric constant, such a slight undercut is generated, and the problem of substrate cracking does not occur. However, it has been confirmed in many experiments that a dielectric material having a high dielectric constant has a large amount of charge and reaches electrostatic breakdown. In the experiment so far, when LiNbO ₃ was etched using Ar + C ₄ F ₈ plasma having a density of 10 ¹¹ cm ⁻³ , the substrate did not crack for 5 minutes, but cracked in 10 minutes.
[0005]
[Problems to be solved by the invention]
The present invention solves the problems associated with the conventional apparatus as described above, and an etching apparatus provided with a substrate holding mechanism capable of maintaining a slight difference between the substrate surface potential and the back surface potential so as not to cause cracking of the substrate. The purpose is to provide.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in an etching apparatus for processing a substrate placed on a substrate electrode by forming a high-density plasma using a microwave or a high frequency by introducing a gas,
A conductive tray including a substrate mounting surface, a substrate pressing jig, and a metal annular foil, and a metal annular foil between the substrate placed on the conductive tray and the substrate pressing jig. Is inserted .
[0007]
The surface accuracy of the substrate mounting surface is preferably mirror-finished to 1 μm or less so that the flatness can be 10 μm or less.
[0009]
Preferably, the plasma is formed by pulse discharge, and a high frequency power source of 10 MHz or more can be used as a high frequency power source for substrate bias.
[0010]
In the etching apparatus according to the present invention configured as described above, in order to minimize the difference between the potential generated on the high dielectric surface and the potential on the back surface when etching the high dielectric substrate, Since the substrate pressing jig or the back surface of the clamp that is in contact is made of a conductor, the high dielectric can be etched to a depth of several microns or more without causing substrate cracking.
[0011]
Further, it is generally known that the use of pulse discharge reduces the surface charging phenomenon, and it is difficult to suppress the charging phenomenon even if a conductor film is used on the substrate pressing jig or the back of the clamp. For the substrate, it is possible to use a method in which plasma is generated in a pulsed manner and charging on the substrate surface is corrected during a pulse pause. In this case, it is desirable that the substrate bias frequency be as high as possible. That is, the charging phenomenon occurs due to a slight difference between positive and negative charged particles. When a bias frequency of 13.56 MHz is used, electrons are incident on the substrate for a few nanoseconds with a phase of (1/2) π, and ions are slow and cannot follow the frequency of 13.56 MHz, so that they steadily reach the substrate surface. To reach. That is, the inflow of electrons occurs in a pulse manner, and the inflow of ions occurs constantly. The electron current and ion current are balanced, and the substrate potential takes a certain value during etching. When the frequency is low, the interval at which electrons are replenished, that is, the interval from (1/2) π to (1/2) π of the next period becomes longer, and the ionic current continues to flow during that interval. In high dielectric etching, it is desirable that this distance be short.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
1 and 2 show a substrate holding mechanism according to an embodiment of the present invention used when etching a high dielectric substrate. 1 and 2, reference numeral 1 denotes a substrate holder on which a metal substrate mounting electrode 2 is attached. The metal substrate placement electrode 2 includes a raised substrate placement region 2a for placing the substrate 3 at the center of the upper surface. The surface of the substrate placement area 2a is mirror finished to 1 μm or less so as to ensure as wide a contact area as possible with the substrate which is an insulator. That is, the surface of the substrate placement region 2a is made to have a smoothness of 1 μm or less and a flatness of 10 μm or less by mirror finishing of 1 μm or less.
[0013]
The surface of the peripheral portion 2b of the substrate mounting electrode 2 surrounding the side surface of the substrate holder 1, the side surface of the substrate mounting electrode 2 and the substrate mounting region 2a is covered with a dielectric material layer 4 such as alumina.
[0014]
Reference numeral 5 denotes a clamp member for the substrate holding mechanism, which can move up and down in a direction perpendicular to the surface of the substrate mounting electrode 2. The clamp member 5 is made of a dielectric material such as alumina, and a conductor film 6 is formed on the back surface thereof by an electroless plating method, a vapor deposition method, a sputtering method, or the like.
[0015]
By the way, if the clamp member 5 is made of metal, it is not necessary to form the conductor film 6 on the back surface thereof, but the surface of the clamp member 5 is also sputtered by plasma irradiation during the operation of the apparatus. 6 material may adhere to the surface of the high dielectric material being processed and cause metal contamination. Accordingly, when a metal is used as the material of the clamp member 5, the etching rate of the metal is high, and thus there is a problem of durability as well as contamination.
[0016]
On the other hand, a high dielectric material such as alumina is generally a metal oxide and has a lower etching rate than a metal. Accordingly, alumina having a high etching resistance is most suitable as a material for the clamp member 5. However, quartz can be used when chlorine-based gas is used.
[0017]
Instead of forming a conductor film on the back surface of the clamp member 5 by vapor deposition, sputtering, electroless plating, or the like, a thin metal foil may be bonded. The material of the conductor film or the metal foil 6 is preferably Ni or the like having corrosion resistance, but Cu or Al can also be used.
[0018]
The mask pattern on the substrate 3 is preferably made of metal, and is preferably connected to the peripheral portion in contact with the conductor film 6 on the back surface of the clamp member 5 at any position on the substrate.
[0019]
The operation of the illustrated apparatus configured as described above will be described.
A substrate in a loading chamber (not shown) is transferred by a transfer robot (not shown) onto the substrate mounting region 2 a of the mirror-finished substrate mounting electrode 2, and the substrate 3 is transferred by the base clamp member 5. 2 in close contact with the substrate mounting region 2a. Helium was introduced up to 15 Torr on the back side of the substrate 3 by a helium cooling mechanism (not shown). The temperature of the substrate mounting electrode 2 was set to −10 ° C. by a cooling mechanism using a refrigerant (not shown).
[0020]
Next, a mixed gas of Ar and C ₄ F ₈ is introduced into a vacuum chamber (not shown) at 100 sccm, and a high frequency power of 13.56 MHz is supplied to a plasma forming dielectric coil (not shown) at 1400 W. Etching was performed by applying 350 W of high frequency power of 13.56 MHz to the placement electrode 2. As a result, the substrate cracking occurred within 10 minutes when the conventional substrate holding mechanism was used, but no cracking occurred and etching for 30 minutes was possible.
[0021]
3 and 4 show an embodiment of the present invention when a tray is used as the substrate holding mechanism. 3 and 4, reference numeral 11 denotes a substrate holder, on which a metal tray 12 constituting a substrate mounting electrode is attached. The surface of the metal tray 12 is mirror-finished with an accuracy of 1 μm or less. In the illustrated example, the metal tray 12 has a thickness of 2 mm, and an annular edge 12 a having a width of 10 mm and a thickness of 1 mm is formed on the peripheral edge. The inner region of the annular edge 12a is made of Cu having a thickness of 0.1 mm or less having an outer diameter substantially equal to the inner diameter of the annular edge 12a and an inner diameter 4 mm smaller than the outer diameter of the dielectric substrate 13 to be processed. When the dielectric substrate 13 to be processed is received, the inner peripheral edge of the annular foil 14 overlaps with the outer peripheral edge of the 2 mm substrate 13. Reference numeral 15 denotes an annular substrate retainer jig for the substrate 13, and this annular substrate retainer jig 15 is made of Al ₂ O ₃ , has a thickness of 1.5 mm, and fits inside the annular edge portion 12 a of the metal tray 12. The inner diameter is 6 mm smaller than the outer diameter of the dielectric substrate 13 to be processed, and the press margin for the outer peripheral edge of the substrate 13 is 3 mm. The annular substrate pressing jig 15 includes a step portion 15a on the lower side of the inner peripheral edge portion thereof, and the step portion 15a has a radial depth of 3.5 mm. Reference numeral 16 denotes a clamp member configured to press the annular substrate pressing jig 15 from the upper surface during operation.
[0022]
Although not shown, a substrate cooling mechanism capable of gas cooling the substrate 13 is incorporated in the substrate holder 11. The substrate 13 is transported while being placed on the tray 12.
[0023]
In FIG. 3 and FIG. 4, Cu foil is used as the annular foil 14, but other metal foil may naturally be used. Moreover, the dimension of each part in FIG. 3 is for illustration only, and is not limited to this dimension.
[0024]
5 and 6 show a modification of the embodiment of the present invention. In this case, a metal tray 21 having a substrate mounting portion having a convex structure is used, and the surface of the substrate mounting area 21a of the metal tray 21 is flat with a smoothness of 1 μm or less by a mirror finish of 1 μm or less. The degree is set to 10 μm or less. Reference numeral 22 denotes a substrate pressing jig made of a dielectric material such as alumina, and a metal film 23 is formed on the rear surface thereof by a method such as vapor deposition, sputtering, or electroless plating. Similar to the structure shown in FIGS. 1 and 2, by making the substrate mounting portion a convex structure, there is an advantage that it is easier to obtain surface accuracy than the concave structure as shown in FIGS. 3 and 4. Further, as in the case of FIGS. 3 and 4, although not shown, a mechanism capable of directly cooling the gas of the substrate 23 is provided.
[0025]
By using the tray shown in FIGS. 3, 4, 5, and 6, in the unlikely event that it breaks, there is a high possibility that the next substrate can be used without debris remaining in the vacuum chamber. That is, in the system shown in FIGS. 1 and 2, if the substrate is broken, the vacuum must be broken and the fragments must be taken out. Although this operation usually takes 2 to 3 hours, the tray system shown in FIGS. 3, 4, 5, and 6 may save time even if it breaks.
[0026]
Next, an example of etching using pulse discharge will be described.
Pulse discharge was performed by a 100 kHz pulse modulation method using a 13.56 MHz high frequency power source. When the duty ratio was changed from 100% (discharge stop time 0) at 20% intervals, the substrate was not cracked at 60% or less, and etching could be performed for 30 minutes. However, since the etch rate was reduced, it was not possible to process to the desired depth. From this, it is not possible to obtain a condition in which substrate cracking does not occur until processing to a desired depth, but it is considered that the condition can be obtained by examining in more detail.
[0027]
【The invention's effect】
As described above, according to the present invention, the substrate mounting portion is mirror-finished to increase the contact area between the substrate and the mounting portion, and a metal film (foil) is provided on the back surface of the substrate pressing jig or the clamp. Since the potential difference generated between the front surface and the back surface of the high dielectric material during plasma irradiation (etching) is made small, it is several microns to 10 microns or more without causing substrate cracking due to voltage breakdown. There is an effect that high dielectric processing becomes possible.
[0028]
For substrates for which it is difficult to suppress the charging phenomenon even if a conductor film (foil) is used on the back surface of the substrate pressing jig or clamp, plasma is generated in a pulsed manner, and charging on the substrate surface is corrected during the pulse pause. By using the method, the possibility of being applicable to a wider range of high dielectric materials is obtained. This is significant in the sense that it will give a bright outlook for device processing in the field of optical communications, and its application is expected.
[Brief description of the drawings]
FIG. 1 is a schematic exploded view showing a main part of a substrate holding mechanism according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a substrate holding state by the substrate holding mechanism shown in FIG. 1;
FIG. 3 is a schematic exploded view showing a main part of a substrate holding mechanism according to another embodiment of the present invention.
4 is a schematic view showing a substrate holding state by the substrate holding mechanism shown in FIG. 3;
5 is a schematic exploded view showing a modification of the substrate holding mechanism shown in FIG.
6 is a schematic view showing a substrate holding state by the substrate holding mechanism shown in FIG.
[Explanation of symbols]
1: substrate holder 2: metal substrate placement electrode 2a: substrate placement region 3: substrate 4: dielectric material layer 5: clamp member 6: conductor film 11: substrate holder 12: metal tray 12a: annular edge Unit 13: Dielectric substrate 14 to be processed: Ring foil 15: Ring substrate holding jig 15a: Step portion 16: Clamp member 21: Metal tray 21a: Substrate placement region 22: Substrate holding jig 23: Substrate

Claims (1)

In an etching apparatus for processing a substrate placed on a substrate electrode by forming a high-density plasma using a microwave or high frequency by introducing a gas,
A conductive tray including a substrate mounting surface, a substrate pressing jig, and a metal annular foil, and a metal annular foil between the substrate placed on the conductive tray and the substrate pressing jig. Is an etching apparatus.

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