JP4423082B2 - Gas nozzle, manufacturing method thereof, and thin film forming apparatus using the same - Google Patents

Description

  The present invention relates to a gas nozzle for injecting a fixed amount of gas, and in particular, in a thin film forming apparatus for injecting a film forming gas and forming a thin film of a semiconductor circuit wiring on a wafer or substrate by a CVD method (chemical vapor deposition method). It is related with the gas nozzle used for.

  Conventionally, for example, in a thin film forming apparatus 30 by a CVD method as shown in FIG. 5, a raw material gas is introduced into a reaction chamber 31 and a CVD reaction energy is applied to form a thin film on a substrate 35. A gas nozzle 34 is used to introduce the raw material gas. This gas nozzle 34 has injection holes for constantly injecting the source gas, and injects the source gas so that the source gas injected from the injection hole becomes uniform in the reaction chamber 31 to form a thin film on the substrate. It is.

  Various types of gas nozzles have been proposed in the past.

For example, in a thin film forming apparatus 30 using, for example, a CVD method used for semiconductor circuit wiring as shown in FIG. For this purpose, the gas nozzle 34 for introducing the raw material gas has a plurality of injection holes, and the gas nozzles are arranged so that the raw material gas injected from the injection holes is uniform in the reaction chamber. The gas nozzle 34 is formed using carbon or ceramics, and the injection hole is processed by cutting. (See Patent Document 1)
In addition, the gas atmosphere in the reaction chamber injected from the gas nozzle of the thin film forming apparatus by the CVD method is sensed by a gas concentration sensor, and the flow rate valve of the gas supply source is controlled based on the measured value, whereby the gas in the reaction chamber is controlled. It has been proposed to make the concentration of the liquid uniform. (See Patent Document 2)
Further, in the puffer-type gas circuit breaker 41 as shown in FIG. 6, a gas nozzle in which a spiral groove 42 is formed on the inner peripheral surface of the nozzle diffusion portion 43 is proposed in order to prevent turbulent flow in the gas injection state. Has been. (See Patent Document 3)
JP 2000-195807 A Japanese Patent Laid-Open No. 9-289170 JP-A-9-92101

  However, in the gas nozzle 34 having a plurality of injection holes as in Patent Document 1, if the injection flow rate of each gas nozzle varies between the nozzles, the concentration distribution of the source gas in the reaction chamber 31 becomes non-uniform, and the substrate 35 Therefore, the uniformity of the thin film produced decreases. Therefore, it is necessary to manage within ± 1% of the specified flow rate of the gas nozzle injection flow. At the same time, the required accuracy for the hole size of the gas nozzle injection hole is high. Dimensional accuracy is required.

  However, even if the dimensional accuracy standards for the spray hole diameter are satisfied, the gas nozzle injection flow may actually vary and may exceed ± 1% of the specified flow rate. It is impossible to manage the flow characteristics. Therefore, as a gas nozzle used in a thin film forming apparatus for forming a semiconductor circuit wiring, it has been requested with priority to control the injection flow rate of the gas nozzle, not the diameter size of the injection hole of the gas nozzle, and to suppress the variation in the injection flow rate. .

In the thin film forming apparatus 30, in the process of growing the thin film on the substrate 35, the thin film grows simultaneously on the inner wall surface of the reaction chamber 31 other than the substrate and the inner and outer wall surfaces of the gas nozzle 34. This thin film differs depending on the type of film (SiO ₂ , Si ₃ O ₄ , Poly-Si, etc.), but when it is deposited to a certain thickness (several tens of μm), cracks are generated due to the internal stress of the film itself, and from the wall surface Peel off. When a large exfoliation material generated by such a phenomenon adheres to the surface of the substrate 35, there is a problem that it becomes a foreign substance (particle) and greatly deteriorates the quality of the thin film.

For example, in a CVD method thin film forming apparatus for forming an insulating oxide film (SiO ₂ ), SiH ₄ gas as a raw material gas is introduced into the reaction chamber 31 through a gas nozzle. When the gas nozzle temperature rises and a highly reactive SiH ₄ gas or the like flows in the gas nozzle whose temperature has risen, the gas temperature rises, causing a thermal decomposition reaction in the gas nozzle, and a reaction side such as polysilicon (Poly-Si). Biology was generated and deposited on the inner wall of the gas nozzle.

  At this time, due to the influence of reaction byproducts accumulated on the inner wall surface of the injection hole, the hole diameter of the injection hole gradually decreases and the injection flow rate of the gas nozzle also decreases simultaneously, but when the hole diameter dimension of the injection hole is not the same, There is a difference in the amount of deposits accumulated in the injection holes of the gas nozzle, and as a result, there is a problem that variations in the injection flow rate of the gas nozzle occur when the film formation is repeated.

In order to remove deposits deposited on the inner wall surface of the reaction chamber and the inner and outer wall surfaces of the gas nozzle, dry cleaning using NF ₃ gas or the like was regularly performed. However, glass and quartz with insufficient corrosion resistance were used. In the case of metal members such as stainless steel, there has been a problem that the surface properties are changed by etching with fluorine or chlorine cleaning gas.

  Moreover, in the method of detecting the gas atmosphere state in the reaction chamber injected from the gas nozzle of the thin film forming apparatus as in Patent Document 2 with a gas concentration sensor and controlling the flow rate valve of the gas supply source based on the measured value, There is a problem that it is difficult to maintain the sensitivity of the gas concentration sensor within ± 1% because the thin film forming gas is not equalized in a good opportunity because feedback control of the measured value occurs and there is a time difference in the control from the measurement.

  In order to supply the source gas with high precision onto the substrate, the supply source usually controls the amount of gas supplied onto the wafer using a mass flow controller (MFC) or the like. At this time, if there is a variation in the injection flow rate of the gas nozzle that is the gas outlet member, the variation in the amount of the raw material gas to be injected becomes large, and as a result, the uniform level of the thin film produced on the substrate has been reduced.

  On the other hand, in the puffer-type gas circuit breaker 41 shown in Patent Document 3, the spiral groove 42 is formed on the inner peripheral surface of the nozzle diffusing portion 43. However, the hole diameter is reduced to the slot portion 44 that is a substantial injection hole. Was not formed with the spiral groove 42, and the groove size of the spiral groove was large, which was different from the purpose of suppressing the variation in the injection flow rate of the gas nozzle within ± 1%.

  An object of the present invention is to provide a gas nozzle in which variation in injection flow rate is stable within ± 1%, and to obtain a uniform thin film with a thin film forming apparatus by eliminating variation in the injection flow rate of the gas nozzle. It is intended.

  Another object of the present invention is to provide a gas nozzle that prevents adhesion of particles during film formation on a semiconductor circuit wiring, has high film quality, and has a long exchange life.

In view of the above problems, a gas nozzle for injecting a gas used for film formation in the interior of the thin film forming apparatus, a supply hole of the tubular guiding the gas, and the injection hole which is connected to the feed hole provided, the injection hole has a plurality of fine grooves inclined toward the gas injection direction on the inner wall surface of that, in which the inner wall surface of at least the injection holes and a gas nozzle which is formed of ceramics.

  The fine groove is preferably a gas nozzle formed so that the groove width is 0.1 to 2 μm and the groove depth is 0.1 to 2 μm.

  The surface roughness of the inner wall surface of the injection hole is preferably a gas nozzle in the range of Ra 0.02 to 0.15 (μm).

  It is preferable that the injection hole has a cylindrical shape, the diameter of the injection hole is in a range of 0.02 to 1.0 mm, and the length of the injection hole is longer than the diameter of the injection hole.

  The fine groove is preferably a gas nozzle formed on the inner wall surface of the injection hole so as to have an inclination of 45 ° or less with respect to the gas injection direction.

  Preferably, the fine groove is a gas nozzle formed in a spiral shape on the inner wall surface of the injection hole.

  It is preferable to use a gas nozzle in which the fine groove is formed in a cross-hatched shape on the inner wall surface of the injection hole.

Further, the inner wall surface of at least the injection hole of the nozzle shall be the gas nozzle which is formed of ceramics.

  Moreover, it is preferable to form the fine groove | channel provided in the said gas nozzle by the wire grinding | polishing process using a diamond abrasive grain.

  Further, the present invention provides a thin film forming apparatus that has a reaction chamber for forming a thin film, introduces a film forming gas into the reaction chamber using the gas nozzle, and generates a thin film on a substrate by a CVD method. .

  A thin film forming apparatus having a structure in which the gas nozzle is detachable is preferable.

  And at least the surface of the gas nozzle exposed to the film forming gas is formed of any one of aluminum oxide (alumina), silicon carbide, silicon nitride, yttria, yttrium aluminum garnet (YAG), and aluminum nitride (aluminum nitride). It is preferable to use a thin film forming apparatus using the gas nozzle.

  According to the gas nozzle of the present invention, by forming a plurality of fine grooves inclined toward the gas injection direction on the inner wall surface of the injection hole, the gas passing through the injection hole is more uniform than the injection hole due to the rectifying effect of the fine groove. Can be injected.

  The groove width of the fine groove is in the range of 0.1 to 2 μm, the groove depth is in the range of 0.1 to 2 μm, and the surface roughness of the inner wall surface of the injection hole is Ra 0.02 to 0.15 (μm). By setting the range, it is possible to enhance the above-described rectifying effect while maintaining the hole diameter accuracy of the injection holes.

  Further, the fine groove has an inclination of 45 ° or less with respect to the gas injection direction on the inner wall surface of the injection hole. It is possible to prevent the turbulent flow of the generated gas jet and improve the straightness.

  When the thin film deposited on the inner and outer wall surfaces of the injection hole peels off due to the internal stress of the film itself, the unevenness due to the fine groove becomes the crease of the peeling, so that the peeled material peels off in a miniaturized state, resulting in large peeling. The generation of things is reduced. As a result, foreign matter (particles) adhering to the substrate surface becomes fine, and the film formation yield is improved.

  Further, since the injection hole has a cylindrical shape, it is possible to manufacture the injection hole with high processing accuracy and at low cost.

  Furthermore, the gas nozzle is made of any one of aluminum oxide (alumina), silicon carbide, silicon nitride, yttria, yttrium aluminum garnet (YAG), and aluminum nitride (aluminum nitride), resulting in high accuracy and long life. A gas nozzle can be provided.

  And even if the gas nozzle is replaced with a new product, the flow rate characteristics do not change, so the thin film that can be formed on the substrate surface also has uniform characteristics, and the yield of film formation is improved.

  Embodiments of the present invention will be described below.

  FIG. 1 shows a central cross-sectional view of the gas nozzle of the present invention, (b) is an enlarged schematic view of the gas nozzle tip of (a), and FIG. 2 shows a fine groove pattern of the gas nozzle of the present invention. It is a schematic diagram shown.

  A gas nozzle 1 according to the present invention includes a tubular supply hole 5 for guiding gas and an injection hole 2 connected to the supply hole 5. The gas nozzle 1 injects gas from the injection hole 2, and gas is applied to the inner wall surface 3 of the injection hole 2. A plurality of fine grooves 4 inclined toward the injection direction are formed. The gas flowing through the injection hole 2 plays a role of a rectifying effect of preventing gas turbulence in the injection hole by flowing along the fine groove 4 inclined toward the gas injection direction, and the injection flow rate of the gas nozzle is stabilized. .

  In order to stabilize the injection flow rate of the gas nozzle, it is important that the shape of the fine groove 4 is controlled so as not to affect the variation in the injection flow rate. For this reason, the groove width of the fine groove 4 is preferably in the range of 0.1 to 2 μm, and the groove depth is preferably in the range of 0.1 to 2 μm. When the concave width of the fine groove 4 is smaller than 0.1 μm or the depth of the concave groove is smaller than 0.1 μm, the gas flowing through the injection hole 2 hardly flows along the fine groove 4, so that the rectifying effect is obtained. I can't expect it. Further, when the concave width of the fine groove 4 is larger than 2 μm or the depth of the concave groove is larger than 2 μm, the effect of preventing gas turbulence in the injection hole is sufficient, but the fine groove 4 Since it is difficult to manage each dimension, the dimensional accuracy of the injection hole 2 varies as a result, and the injection flow rate cannot be controlled.

  Similarly, in order to stabilize the dimensional accuracy of the injection hole 2, the surface roughness of the inner wall surface 3 of the injection hole 2 is also important, and the inner wall surface 3 other than the fine grooves preferably has a smooth surface. Therefore, when the surface roughness of the inner wall surface of the injection hole is quantified including the fine groove, it is preferably in the range of Ra 0.02 to 0.15 (μm).

  It is preferable that the injection hole 2 has a cylindrical shape because the dimensional accuracy control of the injection hole 2 can be simplified and the surface of the inner wall surface 3 can be stably and smoothly finished.

  Moreover, since the rectification | straightening effect of the microgroove 4 mentioned above can be acquired when the hole diameter of the injection hole 2 is the range of 0.02-1.0 mm, it is preferable. If the hole diameter of the injection hole 2 is smaller than 0.02 mm, it is difficult to process the injection hole 2, resulting in manufacturing variations. If the hole diameter of the injection hole 2 is larger than 1.0 mm, the central part of the injection hole 2 is produced. This is because the flow rate of the gas flowing through the flow increases, and the influence of the rectifying effect of the fine grooves 4 becomes smaller than the overall flow rate.

  At the same time, it is important that the hole diameter of the injection hole 2 is uniform in the injection hole in order to suppress variations in the injection flow rate, and the hole length of the injection hole 2 should be longer than the hole diameter of the injection hole 2. Thus, the rectifying effect acting along the inner wall surface 3 of the injection hole 2 can be enhanced, which is preferable. That is, the hole length of the injection hole 2 is preferably in the range of 1 to 20 as compared with the hole diameter of the injection hole 2.

  The fine grooves 4 are preferably formed on the inner wall surface 3 of the injection hole 2 with an inclination of 45 ° or less, more preferably 15 ° or less with respect to the gas injection direction. When the inclination of the fine groove 4 is larger than 45 °, the fine groove 4 is provided so as to cross the gas flowing through the injection hole 2, so that the gas flow is inhibited and the gas injection resistance in the injection hole is reduced. growing. For this reason, the hole diameter of the injection hole 3 and the value of the injection flow rate have the following relationship.

Q = (π / 4) d ² · u
Q: Flow rate, d: Hole diameter, u: Average flow rate In other words, if the hole diameter and the average flow rate are the same, the flow rate of the injected jet is the same. However, in reality, even when the hole diameter of the injection hole 2 is the same, the value of the injection flow rate does not become the same. This is because the average flow velocity changes, and a frictional force acts between the gas and the inner wall surface 3 of the injection hole 2 to make a difference between them, so that it is considered that a difference in the injection flow rate occurs even if the hole diameter is the same. Therefore, when the fine groove 4 is formed on the inner wall surface 3 of the injection hole 2 so that the frictional force between the gas and the inner wall surface 3 of the injection hole 2 is reduced and uniform, the value of the injection flow rate varies. Therefore, it is possible to obtain a gas nozzle having a small injection flow characteristic as intended.

  The rectifying effect is increased by forming a plurality of the fine grooves 4, and in particular, by forming a spiral on the inner wall surface 3 of the injection hole 2, the gas flows along the spiral fine grooves 4. There is no turbulence.

  Actually, when the fine groove 4 inclined at an inclination of 45 ° or less in the gas injection direction is formed on the inner surface of the injection hole 2 in a spiral shape, the spiral fine groove 4 crosses. The wall 3 may be formed in a cross-hatched shape. The fine grooves 4 in which the cross hatches are formed have the same effect of preventing gas turbulence as that of the spiral shape, and at the same time, foreign matter (particles) attached to the inner wall surface 3 of the injection hole 2 divided into the cross hatch shape is peeled off. In this case, the unevenness of the fine groove 4 becomes a peeling crease, so that the peeled material is peeled off in a miniaturized state, and the generation of large peeled material (particles) can be reduced. In order to enhance this effect, the interval between the fine grooves 4 is preferably 3 μm or less.

  In addition, about this fine groove | channel 4, after cleaving a gas nozzle so that the inner wall surface 3 of the injection hole 2 can be observed from the front, SEM (scanning electron microscope Hitachi, Ltd .: S-800) is used, and the inner wall surface is 2500 times. By observing the surface state of 3, a plurality of fine grooves 4 can be confirmed. The concave groove width of the fine groove, the inclination angle of the fine groove, and the groove interval can be measured using this observation result.

  Further, the depth of the concave groove of the fine groove 4 is determined by dividing the gas nozzle so that the inner wall surface 3 of the injection hole 2 can be measured, and expanding the inner wall surface 3 with a surface roughness meter (Kosaka Laboratory: SE-30). It can be measured from the surface state measurement chart.

Such a gas nozzle 1 has at least the inner wall surface 3 of the injection hole 2 having a high Young's modulus and a low thermal expansion coefficient, particularly preferably a Young's modulus of 200 GPa or more and a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. By using the following ceramics, the dimensional accuracy of the injection hole 2 can be maintained high. When ceramics having an average crystal grain size of 3 μm or less is used, the inner surface of the injection hole 2 can be finished smoothly.

  As a manufacturing method of the fine groove 4 of the present invention, after the injection hole 2 is processed by a processing method such as cutting, pressing, etching, or laser processing, the inner wall surface of the injection hole is formed using a wire to which diamond abrasive grains are attached. 3 is preferably polished and finished. It is important to use diamond grains having a grain size of 2 μm or less.

  As an example of a method of processing the injection hole 2 in FIG. 3 and forming the fine groove 4 in the inner wall surface 3 of the injection hole 2, a method by wire polishing will be described. FIG. 3 is a schematic diagram showing a central sectional view of the gas nozzle 1 during wire polishing for easy understanding of the processing state. The wire 22 is inserted into the injection hole 2 and diamond abrasive grains 21 are pasted into the wire 22. It is made to adhere.

  First, the wire 22 is inserted into the injection hole 2 having a rough hole surface (surface before processing). A polishing paste mixed with diamond abrasive grains 21 having an average particle size of 2 μm or less is applied to the wire 22, and the wire 22 is reciprocated in the gas injection direction of the injection hole 2. At the same time, the gas nozzle 1 is rotated to perform polishing. At this time, in order to expand the hole diameter dimension of the injection hole 2, the insertion portion of the wire 22 has a gentle taper shape (not shown), and after the rough hole surface is expanded by the taper portion of the wire 22, the wire 22 By controlling the wire diameter size of the straight portion, the particle size of the diamond abrasive grains 21 to be used, and the speed and timing of the processing movement of the wire 22 and the gas nozzle 1, the hole diameter of the injection hole 2 to be polished is It can be accurately finished to a dimension of ± 0.005 mm or less with respect to the reference hole dimension.

  Next, a thin film forming apparatus using the gas nozzle of the present invention will be described with reference to FIG.

The thin film forming apparatus 10 has a reaction chamber 11 for forming a thin film, introduces a film forming gas into the reaction chamber using the gas nozzle 14 of the present invention, and generates a thin film on the substrate 15 by plasma CVD. A thin film forming apparatus.

A substrate 15 such as a wafer is placed on a wafer holder such as an electrostatic chuck 16 having internal electrodes. The internal electrode is connected to a bias power source 17 outside the apparatus. On the upper part of the substrate 15, the source gas supplied from the gas nozzle 14 is turned into plasma at a high frequency from the coil 18 outside the upper cover 13, and a thin film is deposited on the substrate. When forming a SiO ₂ insulating thin film on the substrate or a SiO ₂ coating film on the inner surface of the reaction chamber, source gases such as SiH ₄ (silane) gas, Ar gas, and O ₂ gas are supplied to remove unnecessary deposits. When cleaning, a cleaning gas such as NF ₃ (nitrogen trifluoride) gas or C ₃ F ₈ (octafluoropropane) gas is used. In FIG. 4, only three gas nozzles 14 are shown, but a larger number of gas nozzles are used to generate stable plasma on the substrate and form a uniform thin film.

  The gas nozzle is fixed to the inner surfaces of the upper cover 13 and the lower cover 12 of the thin film forming apparatus 10 by a mechanical fastening method such as screws, and can be removed and replaced. The raw material gas for forming the thin film passes through the gas nozzle 14 from the atmosphere side of the apparatus and is led into the reaction chamber.

  As a material of the gas nozzle 14 used in the thin film forming apparatus 10 of the present invention, aluminum oxide (alumina) is used for at least the surface of the gas nozzle 14 exposed to the film forming gas. More preferably, it is made of silicon carbide, silicon nitride, yttria, yttrium aluminum garnet (YAG), or aluminum nitride (aluminum nitride).

  Examples of the present invention will be described below.

  A gas nozzle was manufactured by the wire polishing method described in FIG.

  Prepare a rough hole of the gas nozzle injection hole using 99.5% alumina with an average particle diameter of 2 μm, apply diamond abrasive grains with an average particle diameter of 1 μm to a tungsten wire (wire diameter φ0.398 mm), The fine grooves were subjected to wire polishing so that the groove width was 1.0 μm, the groove width was 0.5 μm, and the diameter of the injection hole was φ0.4 ± 0.0004 mm.

  Then, by controlling the speed of the wire reciprocating motion and the rotational motion of the gas nozzle, samples having different inclination angles with respect to the gas injection direction of the injection holes and the groove intervals of the fine grooves as shown in Table 1 were produced.

  Moreover, the gas nozzle which does not attach a fine groove | channel to an injection hole was produced as a comparative example.

Since the difference in the injection flow rate of these gas nozzles was measured, the other shapes and dimensions were the same. Then, nitrogen (N ₂ ) gas is used as the gas for measuring the injection flow rate, and the reference value of the injection flow rate at an injection pressure of 0.4 MPa is 3.0 l / min (liter / min). As a result of examining the variation in the flow rate, in the example of the present invention, the variation in the injection flow rate was 2% or less (± 1%).

The center sectional drawing of the gas nozzle which concerns on this invention is shown, (b) is the schematic diagram which expanded the gas nozzle front-end | tip part of (a). It is a figure which shows the fine groove pattern of the gas nozzle which concerns on this invention. It is a schematic diagram which shows an example of the processing method of the fine groove | channel of the gas nozzle which concerns on this invention. It is an apparatus block diagram of the thin film forming apparatus of this invention. It is an apparatus block diagram of the conventional thin film forming apparatus. It is the schematic diagram which showed the front-end | tip part of the puffer type gas circuit breaker with the center sectional drawing as a conventional gas nozzle.

Explanation of symbols

1: Gas nozzle 2: Injection hole 3: Inner wall surface 4: Fine groove 5: Supply hole 6: Fixed part 10: Thin film forming apparatus 11: Reaction chamber 12: Lower cover 13: Upper cover 14: Gas nozzle 15: Substrate 16: Electrostatic Chuck 17: Power supply 21: Diamond abrasive grain 22: Wire G: Gas

Claims (12)

A gas nozzle for injecting a gas used for film formation in the interior of the thin film forming apparatus, comprising: a supply hole of the tubular guiding the gas, and the injection hole which is connected to the supply hole, the injection holes, As a A gas nozzle comprising a plurality of fine grooves inclined toward the gas injection direction on an inner wall surface, wherein at least the inner wall surface of the injection hole is formed of ceramics . 2. The gas nozzle according to claim 1, wherein the fine groove has a groove width of 0.1 to 2 [mu] m and a groove groove depth of 0.1 to 2 [mu] m. The gas nozzle according to claim 1 or 2, wherein the surface roughness of the inner wall surface of the injection hole is in the range of Ra 0.02 to 0.15 (µm). The said injection hole is a cylindrical shape, the hole diameter of an injection hole exists in the range of 0.02-1.0 mm, and the hole length of an injection hole is longer than the hole diameter of an injection hole, It is characterized by the above-mentioned. The gas nozzle in any one of -3. The fine grooves, a gas nozzle according to any one of claims 1 to 4, characterized in that provided at less than 45 ° slope on the inner wall surface with respect to the gas injection direction of the injection hole. The fine grooves, a gas nozzle according to any one of claims 1 to 5, characterized in that provided in a spiral shape on the inner wall surface of the injection hole. The gas nozzle according to claim 1 , wherein the fine groove is provided in a cross-hatched shape on an inner wall surface of the injection hole. The gas nozzle according to any one of claims 1 to 7, wherein the injection hole has the plurality of fine grooves on an inner wall surface from a joint portion with the supply hole to a tip portion. A method for producing a gas nozzle, wherein the fine groove provided in the gas nozzle according to any one of claims 1 to 8 is formed by wire polishing using diamond abrasive grains. A reaction chamber for forming a thin film is formed, a film forming gas is introduced into the reaction chamber using the gas nozzle according to any one of claims 1 to 8 , and the thin film is formed on the substrate by chemical vapor deposition. Thin film forming apparatus that produces The thin film forming apparatus according to claim 10 , wherein the gas nozzle is detachable.
A gas nozzle in which at least the surface exposed to the film forming gas of the gas nozzle is formed of any one of aluminum oxide (alumina), silicon carbide, silicon nitride, yttria, yttrium aluminum garnet (YAG), and aluminum nitride (aluminum nitride). The thin film forming apparatus according to claim 10 or 11, wherein:

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