JP2010183208A - Wet etching method and method for processing tuning fork type piezoelectric element strip - Google Patents

Abstract

A fine and high aspect ratio structure is processed into a work material with high accuracy by wet etching.
A corrosion resistant film is formed on a surface of a quartz substrate, a photoresist layer is formed on the quartz substrate, and an opening shape of a groove to be processed is patterned, and the exposed corrosion resistant film is removed to remove the exposed quartz substrate. A step of forming a pattern opening 24 exposing the surface, a first wet etching step of wet etching the quartz surface exposed in the pattern opening to form a shallow recess 25, and a Cr protective film on the inner surface of the recess and the pattern opening. 26, and a protective film on the bottom surface of the recess is removed to expose the crystal surface of the bottom surface, and a wet etching is performed on the exposed bottom surface of the recess, and the recess has a desired groove depth. The second etching step is repeatedly performed until it becomes.
[Selection] Figure 1-1

Description

  The present invention relates to a method of wet-etching a material to be processed such as a substrate used for a piezoelectric device, a semiconductor device, and other electronic parts, for example, particularly for processing a structure composed of a concave portion and / or a convex portion of a fine pattern. The present invention relates to a suitable wet etching method.

  Furthermore, the present invention relates to a method of processing a tuning fork type piezoelectric element piece using this wet etching method.

  In general, fine processing in electronic components such as piezoelectric devices and semiconductor devices is performed by an etching technique using a photolithography technique. Etching techniques include wet etching using an etchant and dry etching such as reactive ion etching and sputtering using plasma in a reactive gas. In many piezoelectric devices such as piezoelectric vibrators, wet etching is employed for external processing of a resonator element (see, for example, Patent Documents 1 and 2).

  As described in Patent Document 1, the tuning-fork type crystal vibrating piece illustrated in FIG. 2 is processed by wet etching according to the process shown in FIG. Generally, the tuning fork type crystal vibrating piece 1 has grooves 4 on the upper and lower main surfaces of a pair of vibrating arms 3 extending in parallel from the base 2. First, as shown in FIG. 3A, a corrosion-resistant film 11 having a two-layer structure composed of a Cr film 11a and an Au film 11b is formed on both surfaces of the quartz substrate 10. A photoresist layer 12 is formed on the corrosion-resistant film 11, and the outer shape of the resonator element 1 is patterned to expose the surface of the corrosion-resistant film 11 (FIG. 3B). Next, the exposed portion of the corrosion-resistant film is completely removed by wet etching to expose the surface of the quartz substrate 10 (FIG. 3C). After the remaining photoresist layer 12 is completely removed (FIG. 3D), a new photoresist layer 13 is formed on both surfaces of the quartz substrate 10 (FIG. 3E). The external shape of 1 and the opening shape of the groove 4 are patterned to expose the surface of the quartz crystal substrate 10 and the surface of the corrosion-resistant film 11 corresponding to them (FIG. 3F).

  Next, the exposed surface of the quartz substrate 10 is through-etched with an appropriate etching solution to form the outer shape of the resonator element 1 (FIG. 3G). The exposed corrosion-resistant film 11 is removed by wet etching, and the opening pattern of the groove 4 of the vibrating arm 3 is transferred to expose the crystal surface on the vibrating arm 3 (FIG. 3 (H)). The crystal exposed surface of the vibrating arm 3 is wet-etched to a predetermined depth to process the groove 4 (FIG. 3I). Finally, when the remaining photoresist film 13 and corrosion resistant film 11 are completely removed, a crystal element piece having a desired outer shape and groove shape is formed (FIG. 3J).

  Recently, various electronic components have been miniaturized and fine and high aspect ratio etching has been required. For example, in order to finely process a high aspect ratio etched shape in a nitride semiconductor with high precision, a bias is applied to a nitride semiconductor immersed in an electrolyte solution, which is an aqueous KOH solution, while suppressing ultraviolet irradiation. A wet etching method is known (see, for example, Patent Document 3).

  In addition, in the wet etching of a metal material, the etching proceeds isotropically from the opening of the resist pattern to just below the resist, so that a problem of side etching occurs. In order to solve this problem, after forming the hot melt resist pattern on the metal material, the first etching is performed, and after the side etching is slightly advanced, the pattern is heated and softened to flow, and the shallow side of the etching side surface A wet etching method is known in which the second etching is performed so as to prevent the side etching from progressing and form an etching shape with a high aspect ratio (see, for example, Patent Document 4).

  On the other hand, various methods for processing fine and high aspect ratio structures using dry etching have been developed. For example, in the anisotropic etching method of silicon called the Bosch method, an etching process for introducing an etching gas such as a fluorine-based gas and a polymerization for introducing a deposition gas are alternately repeated to excite these gases. Plasma is generated to perform edge processing perpendicular to the silicon wafer at a high aspect (see, for example, Patent Document 5). Further, there has been proposed an ultra-fine processing method for performing ultra-fine processing on an insulating substrate such as glass, quartz, or diamond by combining electron beam lithography and fast atom beam irradiation (see, for example, Patent Document 6). ).

JP 2004-200915 A JP 2004-260593 A JP 2006-80274 A JP 2004-214523 A JP 7-503815 A JP-A-10-274700

  Single crystal materials such as quartz and single crystal silicon have crystal anisotropy that the etching rate of wet etching differs depending on the crystal direction. In the case of quartz, the etching rate is large in the Z-axis (optical axis) direction, but small in the X-axis (electric axis) direction, and smaller in the Y-axis (mechanical axis) direction. Therefore, when wet etching is performed on a quartz material such as a groove or hole having a high aspect ratio, it is preferable to orient the Z axis of the quartz in the normal direction of the processed surface. Also in this case, the side etching in the X axis direction and the Y axis direction increases as the etching depth increases.

The inventor of the present application simulated the effect of side etching on the processed shape of a groove when a high aspect ratio groove having a fine width and a large depth was wet etched on a quartz crystal substrate. FIG. 4A shows a case where a mask 16 is arranged on the surface of a crystal substrate 15 made of a so-called crystal Z plate cut out with the Z-axis of the crystal aligned with the principal surface normal direction, and the groove 17 is processed by wet etching. Show. The pattern opening width w ₀ of the mask 16 was set to 3 μm. As shown in FIG. 4A, in the state where the groove 17 is processed to a depth d = 45 μm, the maximum groove width w in the vicinity of the opening is substantially equal to the pattern opening width w ₀ of the mask 16. When the groove 17 was further deeply processed, as shown in FIG. 4B, clear side etching was recognized in the ± X-axis direction of the quartz at a depth d = 60 μm. When the depth d of the groove 17 is 90 μm, as shown in FIG. 4C, side etching in the ± X axis direction further proceeds, and the maximum groove width w in the vicinity of the opening of the groove 17 is increased to about 20 μm.

  As with other piezoelectric devices, semiconductor devices, and other electronic components, tuning fork crystal units are required to be further downsized. As a result, the width of the vibrating arm is further reduced, and the groove formed in the vibrating arm needs to be processed to be narrower. However, as the groove width becomes narrower and the aspect ratio becomes higher, the effect of side etching on the shape and dimensions of the groove becomes larger, and high-precision microfabrication becomes more difficult.

  Further, the wet etching method described in Patent Document 4 allows the resist pattern on the metal material to soften and flow by heating so as to cover the etching side surface by slightly causing side etching in the first etching. Since this method is premised on isotropic etching of a metal material, it is not suitable for wet etching of a workpiece having crystal anisotropy such as crystal. Moreover, since the opening width of the etching shape to be obtained is defined by side etching, it is difficult to control with high accuracy.

  In general, dry etching can easily process a concave portion or a convex portion such as a fine, high aspect ratio groove or hole as compared with wet etching. However, dry etching of an insulating material such as quartz or glass is not practical because the etching rate is considerably lower than that of wet etching and the processed surface tends to be rough. In particular, the Bosch method has a problem that the side wall of the processed groove has a stepped shape. Moreover, dry etching requires expensive equipment such as an airtight reaction chamber and a plasma generator, which requires a great deal of cost. Furthermore, when a fluorine-based gas is used as a reaction gas, there is a risk of polluting the environment.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object thereof is various work materials such as a piezoelectric material such as quartz, an insulating material such as glass, and a substrate made of a semiconductor material. To provide a method capable of forming a structure having recesses and / or protrusions having fine dimensions and shapes and a high aspect ratio with high accuracy without causing side etching. is there.

  Furthermore, the object of the present invention is to provide a method for processing a tuning fork type piezoelectric element piece having a fine groove on a narrow vibrating arm with high precision by utilizing this wet etching method in response to a demand for miniaturization. There is to do.

  According to the present invention, in order to achieve the above object, a step of forming a corrosion-resistant film on the surface of the work material, and forming and patterning a photoresist layer on the corrosion-resistant film, and removing the exposed corrosion-resistant film. A pattern opening for exposing the surface of the work material, and a first wet etching process for wet etching the surface of the work material exposed in the pattern opening to form a recess in the work material. And a second wet etching step of covering at least the inner surface of the recess and the inner surface of the pattern opening with a protective film, removing the protective film on the bottom surface of the concave portion to expose the bottom surface, and wet etching the bottom surface of the exposed concave portion. A wet etching method is provided.

  In this way, the wet etching of the material to be processed is divided into a plurality of times, and the etching depth of one time is made smaller than the desired final depth, thereby suppressing the influence of side etching in the first wet etching step, and In the second wet etching process, by performing wet etching while leaving the protective film on the side surface of the recess, the etching depth is further increased while maintaining the width dimension of the recess processed earlier and suppressing the influence of side etching. Can be processed. Therefore, it is possible to form a structure composed of a concave portion and / or a convex portion having a fine size and shape and a high aspect ratio in the work material. In addition, since expensive equipment such as the dry etching method is not required, the processing cost can be suppressed, and no harmful reactive gas is used, so that the influence of environmental pollution is very small.

  In one embodiment, the second etching process is repeated until the recess reaches a desired depth, thereby enabling fine processing with a higher aspect ratio.

  In another embodiment, a high aspect ratio through hole can be formed by wet etching by repeating the second etching step until the recess penetrates the workpiece.

  In some embodiments, when the material to be processed is a quartz crystal Z plate, the etching rate is high in the depth direction, so that processing with a high aspect ratio is easy.

  According to another aspect of the present invention, a step of forming a corrosion resistant film on the surface of the piezoelectric substrate, a first photoresist layer is formed on the corrosion resistant film, and an outer shape of the tuning fork type piezoelectric element piece is patterned, Removing the exposed corrosion-resistant film to expose the surface of the piezoelectric substrate; removing the remaining first photoresist layer; forming and patterning a second photoresist layer on the surface of the piezoelectric substrate; Forming a photoresist film having a shape corresponding to the groove of the vibrating arm of the piezoelectric element piece on the corrosion-resistant film, and wet-etching the surface of the piezoelectric substrate exposed from the corrosion-resistant film to form the outer shape of the piezoelectric element piece And removing the portion of the corrosion-resistant film exposed from the photoresist film, forming an opening corresponding to the groove of the vibrating arm in the corrosion-resistant film, and wet etching the surface of the piezoelectric substrate exposed in the opening to resonate the vibrating arm Shaped groove The step of forming the groove of the vibrating arm comprises wet etching the surface of the piezoelectric substrate exposed in the opening of the corrosion-resistant film to form a recess that is shallower than the desired depth of the groove of the vibrating arm. A first wet etching step, covering at least the inner surface of the recess and the inner surface of the opening of the corrosion-resistant film with a protective film, removing the protective film on the bottom surface of the recess to expose the bottom surface, and exposing the bottom surface of the exposed recess to the wet A method for processing a tuning-fork type piezoelectric element piece comprising a second wet etching step for etching is provided.

  Accordingly, in response to the downsizing of the tuning fork type piezoelectric vibrating piece, a fine and high aspect ratio groove can be processed with high accuracy in the vibrating arm.

  In one embodiment, the groove of the vibrating arm can be processed to a higher aspect ratio by repeating the second etching process until the recess reaches a desired depth of the groove of the vibrating arm.

  In another embodiment, when the piezoelectric substrate is a quartz crystal Z plate, the etching rate is high in the depth direction, so that a groove with a high aspect ratio can be easily processed.

Sectional drawing which consists of (A)-(F) figure which shows the Example of the wet etching method of this invention to process order. Sectional drawing which consists of (G)-(J) figure which shows the process following FIG. 1-1 in order of a process. FIG. 3 is a schematic perspective view showing a known general tuning fork type crystal vibrating piece with its electrode film omitted. Sectional drawing which consists of (A)-(J) figure which shows the conventional wet etching method which processes the external shape of the tuning fork type | mold crystal vibrating piece in the II-II line | wire of FIG. FIGS. 4A to 4C are cross-sectional views showing changes in the shape of fine grooves wet-etched in a quartz substrate.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIGS. 1-1 and 1-2 show a process of forming a narrow and high aspect ratio groove on a quartz substrate by applying the wet etching method of the present invention. In this embodiment, the quartz substrate that is the material to be processed is a quartz plate called a quartz Z plate. In addition, the crystal Z plate includes not only a crystal whose Z axis completely coincides with the main surface normal direction but also a crystal Z plate cut out from the main surface normal direction with a certain range of cut angles.

  First, as shown in FIG. 1-1A, a corrosion-resistant film 21 is formed on the surface of the crystal substrate 20. The corrosion-resistant film 21 has a two-layer structure in which a Cr film 21a as an underlayer having excellent adhesion to quartz and an Au film 21b having excellent corrosion resistance against a crystal etching solution are laminated by sputtering or vapor deposition, respectively. Is done. Other corrosion resistant metal materials having good adhesion to quartz include Ni, Al, Ti, etc., and these can be used in combination with an Au film. A photoresist layer 22 is formed on the corrosion-resistant film 21 by spin coating or the like (FIG. 1-1 (B)).

  As shown in FIG. 1C, the corrosion-resistant film 21 is patterned using a photomask 23 having a groove pattern to be processed to expose the surface of the corrosion-resistant film 21. The exposed portion of the corrosion-resistant film 21 is completely removed by wet etching using an appropriate etching solution to expose the surface of the quartz substrate 20 (FIG. 1-1 (D)). As a result, the pattern opening 24 corresponding to the pattern of the groove to be processed is transferred to the laminate of the corrosion-resistant film 21 and the photoresist layer 22.

  Next, as a first wet etching step, as shown in FIG. 1-1 (E), the surface of the quartz substrate 20 exposed in the pattern opening 24 is wet etched using an appropriate etching solution such as hydrofluoric acid, A shallow recess 25 is formed. The etching depth of the recess 25 is set smaller than the desired depth of the groove to be processed. This first wet etching step is preferably stopped to the extent that side etching to the side of the recess 25 does not substantially proceed. The photoresist layer 22 remaining on the corrosion-resistant film 21 is preferably left as it is in order to avoid the possibility that wet etching of the recess 25 damages the corrosion-resistant film 21. Of course, it is also possible to perform the first wet etching process after removing the photoresist layer 22.

  Next, a second wet etching process is further performed in which the recess 25 of the quartz substrate 20 is further wet etched. Cr is formed by sputtering, and the inner surfaces of the recesses 25 and the pattern openings 24 and the upper surface of the photoresist layer 22 are covered with a protective film 26 as shown in FIG. As the material for the protective film, in addition to Cr, it is possible to use Ni, Ti or the like that has good adhesion to the crystal and has corrosion resistance to the crystal etchant. The protective film 26 may be formed at least on the inner surface of the recess 25 and the pattern opening 24.

Next, an ion beam of Ar ⁺ or the like is irradiated perpendicularly to the surface of the quartz substrate 20 to leave the protective film 26a on the side surface of the concave portion 25 and the inner surface of the pattern opening 24, and from the bottom surface of the concave portion 25 and the upper surface of the photoresist layer 22 26 is removed, and the crystal surface is exposed on the bottom surface of the recess 25 (FIG. 1-1G). At this time, it is also possible to irradiate the ion beam using a mask or the like so as to selectively remove only the protective film 26 on the bottom surface of the recess 25. As another method for removing the protective film 26, for example, a sandblast method can be used.

As shown in FIG. 1-1 (H), the quartz surface exposed on the bottom surface of the recess 25 is similarly wet etched using an appropriate etching solution, and the recess 25 somewhat deeper than the recess 25 formed by the first wet etching process. ₁ is formed. Etching amount of the second wet etching process also, it is preferable to stop to the extent that side etching to the side of the recess 25 ₁ is not substantially proceed. Thus, it is possible to form the concave portion 25 ₁ of the vertical sides a width corresponding to the size of the pattern opening 24. In fact, the side face of the recess 25 _1, in particular on the side facing the + X-axis direction of the quartz crystal axis, its crystals surface is affected somewhat, there is a possibility that appears somewhat inclined surface. However, a substantially vertical side surface can be obtained by reducing the etching amount in the second wet etching step.

Next, the second wet etching process described above is repeated. Similarly by sputtering Cr, as shown in FIG. 1-2 (I), covering the inner surface as well as the upper surface of the photoresist layer 22 of the recesses 25 ₁ and the pattern opening 24 in the protective film 27. The protective film 27 may be coated after the protective film 26a left in the previous step is removed, or may be coated on the protective film 27 while leaving it. The protective film 26a can be removed with an appropriate etching solution.

Then, leaving the protective film 27a in the recess 25 ₁ side and the pattern opening 24 inner surface, and removing the protective film 27 from the recess 25 _first bottom surface and the photoresist layer 22 the top surface by the ion beam, exposing the crystal face in the recess bottom surface (FIG. 1-2 (J)). Crystal plane exposed in the recess 25 ₁ bottom wet etching with a suitable etchant, further formed somewhat deeper recess 25 ₂ than the recess 25 _1. Again, it is preferable that the side etching of the lateral recesses 25 ₂ stops wet etching to an extent that does not substantially proceed.

In this embodiment, as shown in FIG. 1-2 (L), the second wet etching process is repeated n times (n ≧ 3) until the depth of the recess 25 _n reaches the desired groove depth. The last second wet etching process recess 25 _n sides and pattern the protective film 28 left in the opening 24 inner surface completely removed with a suitable etchant (FIG. 1-2 (M)). Finally, the photoresist layer 22 and the corrosion resistant film 21 remaining on the surface of the quartz substrate 20 are completely removed. As a result, a groove 29 having a desired fine width and a high aspect ratio is formed in the quartz substrate 20.

  The number of executions n of the second wet etching step and the etching amount per time are determined in consideration of the depth and aspect ratio of the groove 29 to be processed. In the above embodiment, the second wet etching process is performed many times. However, if the desired groove depth is small, one second wet etching process may be sufficient.

  As described above, an inclined surface due to the influence of the crystal plane of quartz may appear on the side surface of the concave portion being processed. This can be solved by adjusting the etching amount in one second wet etching step to suppress the progress of side etching, and the groove 29 having a substantially vertical side surface is obtained.

  The wet etching method of the present invention can be applied to the step of forming a groove in the vibrating arm in the processing of the tuning-fork type crystal element piece described above with reference to FIG. This will be described with reference to FIG. The steps up to FIG. 3H for forming the outer shape of the resonator element on the quartz substrate 10 and patterning the corrosion-resistant film 11 on the surface of the vibrating arm into the shape of the groove opening are the same as those in the prior art.

  Next, in FIG. 3I, a first wet etching process is performed in which the crystal exposed surface of the vibrating arm 3 is wet etched to form a recess shallower than the desired depth of the groove 4. Next, in the second wet etching step, the inner surface of the opening patterned on the inner surface of the recess and the corrosion-resistant film 11 is formed by sputtering with Cr and covered with a protective film, and the protective film on the bottom surface of the concave is removed. Then, the crystal surface of the bottom surface is exposed, and the exposed crystal surface is wet-etched. This second wet etching process is repeated until the necessary groove 4 depth is obtained. Thus, the groove 4 having a fine width and a high aspect ratio can be formed with high accuracy in the vibrating arm of the tuning-fork type crystal element piece.

  In the above embodiment, the case where the bottomed groove of the substrate is processed has been described. However, the wet etching method of the present invention can be similarly applied to the case where the through groove is processed. The present invention is applicable not only to the processing of recesses such as grooves and holes, but also to wet etching of fine and high aspect ratio convex portions or fine structures including concave and convex portions. Can do.

  The present invention is not limited to the above embodiments, and can be implemented with various modifications or changes within the technical scope thereof. For example, as long as wet etching is possible as the material to be processed, the present invention is isotropic with respect to wet etching, such as piezoelectric materials other than quartz, insulating materials such as glass, and semiconductor materials such as single crystal silicon. It can be applied to various materials used for various electronic parts including those. Further, the material to be processed may have various forms other than the substrate. Further, in the above embodiment, the corrosion-resistant film on the surface of the quartz substrate is formed with a metal film having a two-layer structure. However, if the metal material has adhesion to the piezoelectric substrate and etching resistance, it is formed with a single-layer metal film. You can also

DESCRIPTION OF SYMBOLS 1 ... Quartz vibrating piece, 2 ... Base, 3 ... Vibrating arm, 4 ... Groove 10, 15 ... Quartz substrate, 11, 21 ... Corrosion-resistant film, 11a, 21a ... Cr film, 11b, 21b ... Au film, 12, 13 , 22 ... Photoresist layer, 16, 23 ... Mask, 17, 29 ... Groove, 20 ... Quartz substrate, 24 ... Pattern opening, 25 ... Recess, 26, 26a, 27, 27a, 28 ... Protective film.

Claims (7)

Forming a corrosion-resistant film on the surface of the work material;
Forming and patterning a photoresist layer on the corrosion-resistant film, removing the exposed corrosion-resistant film, and forming a pattern opening that exposes a surface of the workpiece; and
A first wet etching step of wet-etching the surface of the work material exposed in the pattern opening to form a recess in the work material;
Second wet etching that covers at least the inner surface of the recess and the inner surface of the pattern opening with a protective film, removes the protective film on the bottom surface of the recess to expose the bottom surface, and wet-etches the exposed bottom surface of the recess A wet etching method comprising the steps of:   The wet etching method according to claim 1, wherein the second etching step is repeated until the concave portion has a desired depth.   The wet etching method according to claim 1, wherein the second etching step is repeated until the concave portion penetrates the workpiece.   4. The wet etching method according to claim 1, wherein the material to be processed is a quartz crystal Z plate. Forming a corrosion-resistant film on the surface of the piezoelectric substrate;
Forming a first photoresist layer on the corrosion-resistant film and patterning an outer shape of a tuning fork type piezoelectric element piece, removing the exposed corrosion-resistant film, and exposing the surface of the piezoelectric substrate;
The remaining first photoresist layer is removed, a second photoresist layer is formed on the surface of the piezoelectric substrate and patterned to form a photoresist film having a shape corresponding to the groove of the vibrating arm of the piezoelectric element piece Forming on the corrosion-resistant film,
Forming the outer shape of the piezoelectric element piece by wet etching the surface of the piezoelectric substrate exposed from the corrosion-resistant film;
The portion of the corrosion-resistant film exposed from the photoresist film is removed, an opening corresponding to the groove of the vibrating arm is formed in the corrosion-resistant film, and the surface of the piezoelectric substrate exposed in the opening is wet-etched Forming a groove of the vibrating arm,
The step of forming the groove of the vibrating arm includes a first wet etching step of wet-etching the exposed surface of the piezoelectric substrate to form a recess shallower than a desired depth of the groove of the vibrating arm, and at least the recess A second wet etching that covers the inner surface of the recess and the inner surface of the opening of the corrosion-resistant film with a protective film, removes the protective film on the bottom surface of the recess to expose the bottom surface, and wet-etches the exposed bottom surface of the recess A tuning fork type piezoelectric element piece processing method comprising the steps of:   6. The tuning-fork type piezoelectric element piece processing method according to claim 5, wherein the second etching step is repeated until the concave portion reaches a desired depth of the groove of the vibrating arm.   7. The method for processing a tuning-fork type piezoelectric element piece according to claim 5, wherein the piezoelectric substrate is a crystal Z plate.

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