JP6444134B2 - Manufacturing method of tuning fork crystal unit - Google Patents

Description

The present invention relates to an alignment mark shape provided on a quartz wafer in the production of a tuning fork type quartz crystal resonator using a photolithography method.

  Conventionally, tuning fork crystal units have been widely used as reference signal sources in timepieces and devices having timepiece functions. In recent years, with the widespread use of mobile terminals (cell phones and smartphones), customers have been demanding smaller electronic components including tuning fork crystal units. Among them, the tuning fork crystal unit employs a photolithography method that has been used in semiconductors as a manufacturing method corresponding to miniaturization.

  As an example, a manufacturing process of a grooved tuning fork type crystal resonator by photolithography will be described with reference to FIG. First, as a corrosion resistant film forming step, a corrosion resistant film against ammonium fluoride or buffered hydrofluoric acid used for etching the crystal is formed on both the front and back surfaces of the crystal wafer. As the corrosion resistant film, a metal film consisting of two layers of a Cr film and an Au film is generally used, and is formed by vapor deposition or sputtering.

  Next, as a tuning fork patterning process, a photoresist is formed on the corrosion-resistant film formed on both the front and back surfaces of the quartz wafer, and the outer shape of the tuning-fork crystal resonator is exposed, developed, and the previously formed corrosion-resistant film is etched. As a result, the outer shape of the tuning-fork type crystal resonator made of the corrosion-resistant film and the photoresist is obtained on both the front and back surfaces of the crystal wafer.

  Next, as a groove patterning step, the groove shape formed on the branch of the tuning fork type crystal resonator is exposed and developed on the photoresist. The photoresist used at this time may be re-deposited after the photoresist used in the tuning fork patterning step, or may be used without removing the photoresist used in the tuning fork patterning step. In the groove patterning step or the tuning fork patterning step, an alignment mark used for alignment of the crystal wafer on which the outer shape of the tuning fork type crystal resonator is formed and the photomask for electrode film formation is patterned in the electrode patterning step to be performed later.

  Next, as a crystal etching process, the crystal wafer is etched with ammonium fluoride or buffered hydrofluoric acid at room temperature or higher (about 25 to 80 ° C.) for several hours, and a tuning fork type made of crystal, corrosion-resistant film, and photoresist. A groove shape portion made of a crystal resonator outer shape and a crystal and a corrosion-resistant film is obtained. Thereafter, the outer shape of the grooved tuning fork crystal resonator can be formed on the quartz wafer by etching the corrosion-resistant film in the groove-shaped portion and further performing etching with ammonium fluoride or buffered hydrofluoric acid. By this crystal etching process, alignment marks on the crystal wafer used in the subsequent electrode patterning process are formed in the front and back surfaces of the crystal wafer in a form of being dug. In the case where no groove is formed in the tuning fork branch, the groove patterning step can be omitted. Thereafter, all of the corrosion-resistant film and the photoresist used as the corrosion-resistant film are removed.

  Next, as an electrode patterning step, a Cr film and an Au film to be electrode films are formed on an entire surface of the crystal wafer or an arbitrary portion on the crystal wafer by using a mask. In addition to this, combinations of Ti, Pd, Ni, and Au are also widely used as the electrode film, and are appropriately selected. Thereafter, a photoresist used for electrode patterning is formed on a quartz wafer by a spray method or an electrodeposition method, and the electrode shape is exposed using a photomask for electrode formation. Thereafter, development is performed, and an electrode film made of a Cr film or an Au film is etched to obtain a grooved tuning fork type crystal resonator in which the electrode film is formed. In the exposure of the electrode patterning, the alignment mark formed by the tuning fork patterning process or the groove patterning process on the crystal wafer is aligned with the alignment mark provided on the photomask for electrode formation. The electrode forming photomask is exposed with high accuracy with an error of several μm.

  As described above, in the manufacture of a grooved tuning fork type crystal resonator using a photolithographic method, various shapes are formed on a quartz wafer using a photomask, and therefore, high accuracy is achieved between the quartz wafer and the photomask. Need to align. During tuning fork patterning, the pattern used for positioning may not be formed on the wafer surface. Therefore, alignment with the tuning fork shape patterning photomask is performed using the wafer outer shape as a reference, and the tuning fork outer shape and the alignment mark used as a reference. The shape is transferred from a tuning fork shape patterning photomask. In the groove shape patterning, a groove shape pattern or another pattern is superimposed on the basis of the alignment mark formed on the quartz wafer.

  On the other hand, in an exposure machine having an automatic alignment function that performs tuning fork, groove, and electrode patterning, a photomask used for each patterning and a crystal wafer are positioned on a crystal wafer by an image processing apparatus built in the exposure machine. The alignment mark for positioning is recognized, the center of gravity position or reference point of the recognized alignment mark is calculated, and the center of gravity position or reference point is similarly calculated for the alignment mark provided in the photomask to be overlaid, Exposure is performed by accurately aligning the alignment mark coordinates on the quartz wafer and the photomask.

  In general, an image processing apparatus used in an exposure machine having an automatic alignment function employs a method for obtaining a figure centroid from a line-symmetrical or rotationally symmetric figure in the vertical and horizontal directions. The reason why a line-symmetrical or rotationally symmetric figure is recommended is that a vertical line is provided on each of two parallel sides facing up, down, left, and right, and the intersection of the perpendiculars is obtained as the figure centroid. This is because it is difficult to be affected by straightness and parallelism deviation.

JP 2009-194696 A

  Regarding the formation of alignment marks used in the electrode formation of a tuning fork type crystal resonator, Patent Document 1 has been proposed, and a polygonal shape (particularly a triangle) having sides parallel to the X axis, which is the crystal axis of the crystal, has been proposed. .

  In general, a quartz wafer having an XY plane is used for a tuning fork type crystal resonator. In addition, the alignment marks on the quartz wafer used in the electrode patterning process formed in the tuning fork patterning process or the groove patterning process according to the process shown in FIG.

  Furthermore, in an exposure machine having an automatic alignment function, when the image processing apparatus recognizes an alignment mark, a vertically / left / right rotationally symmetric figure is recommended. It is not a shape. The center of gravity of a triangle is obtained from the intersection of two bisectors that form a narrow angle, but if one of the sides collapses, that is, the straight line of the side that is the cause of foreign matter, scratches, etc. during exposure In a situation where the performance is impaired, it is difficult to uniquely set the center of gravity of the triangle due to an error in linear interpolation of a certain side.

  Next, the case where the quadrangle, the round shape, and the hexagon shown in FIGS.

  FIG. 2 shows a change in the shape of the square alignment mark on the crystal surface when the resist pattern and the crystal surface are etched with buffered hydrofluoric acid when the alignment mark has a quadrangular shape. FIG. 2B shows a state in which the quartz etching is performed for about 30 minutes, but no change from the shape of the rectangular resist pattern 1 shown in FIG. On the other hand, FIG. 2 (c) shows the crystal surface etched with buffered hydrofluoric acid for about 240 minutes. However, due to the crystal anisotropy of the quartz crystal, the alignment from the rectangular shape of FIGS. 2 (a) and 2 (b) occurs. It can be seen that the shape of the mark 2 is greatly broken.

  FIG. 3 shows a change in the shape of the circular alignment mark on the crystal surface when the resist pattern and the crystal surface are etched with buffered hydrofluoric acid when the alignment mark has a circular shape. FIG. 3B shows a state in which the crystal surface etching is performed for about 30 minutes, but no change from the shape of the round resist pattern shown in FIG. On the other hand, FIG. 3 (c) shows the crystal surface etched with buffered hydrofluoric acid for about 240 minutes, but the crystal anisotropy of the crystal causes the round shape of FIGS. 3 (a) and 3 (b). It can be seen that the shape is greatly collapsed.

  FIG. 4 shows the shape change of the hexagonal alignment mark on the crystal surface when the resist pattern and the crystal surface are etched with buffered hydrofluoric acid when the alignment mark is hexagonal. FIG. 4B shows a state in which the crystal surface etching is performed for about 30 minutes, but no variation from the shape of the hexagonal resist pattern shown in FIG. On the other hand, FIG. 4 (c) shows the crystal surface etched with buffered hydrofluoric acid for about 240 minutes. However, due to the crystal anisotropy of the crystal, the hexagonal shape of FIG. 4 (a) and FIG. It can be seen that the shape is greatly collapsed.

  FIG. 6 is a schematic diagram in which the square-shaped resist pattern 1 shown in FIG. 2A and the square-shaped alignment mark 2 shown in FIG. The square alignment mark 1 based on the resist pattern of FIG. 2A is an ideal square alignment mark, but the square alignment mark 2 when the crystal etching of about 240 minutes in FIG. Compared with the square alignment mark 1 by the pattern, the etching amount ΔX1 in the −X direction is etched larger than the etching amount ΔX2 in the + X direction after the crystal etching due to the crystal anisotropy of the crystal.

  On the other hand, in the Y direction, ΔY1 and ΔY2 are substantially equal between the square alignment mark 1 before crystal etching and the square alignment mark 2 after crystal etching. However, since the anisotropic shape 3 that is greatly beaten in the + Y direction side appears, in the image processing apparatus that recognizes the alignment mark, the anisotropic shape 3 becomes noise when performing shape recognition. The square shape cannot be recognized correctly. Further, since the size of the anisotropic shape 3 increases in proportion to the etching time, ΔY1> ΔY2 when the time for etching the crystal becomes long, and the same shape appears in the transition of the crystal etching time. However, even with a pattern recognition method in which the image processing apparatus learns an arbitrary shape in advance, it is difficult to recognize the correct shape of the alignment mark.

  Therefore, in the superposition of FIG. 2A and FIG. 2C shown in FIG. 6, the shape of the square alignment mark is greatly different before and after the crystal etching, so that a center-of-gravity position deviation ΔXo occurs in the X direction. Furthermore, the center-of-gravity position shift in the Y direction may also occur due to fluctuations in the crystal etching time.

  The magnitude of ΔXo varies depending on the length of the set quartz etching time. Therefore, if the crystal etching time is set uniquely, ΔXo is given as a correction value to the image processing unit during exposure for performing alignment mark recognition by the image processing apparatus, so that the overlay accuracy between the crystal wafer and the photomask is increased. Can be improved. However, the crystal etching time is a parameter that determines the frequency, which is an important characteristic of the tuning fork type crystal resonator. For this reason, for example, at the development stage, there is a problem that it is difficult to perform desired characteristic evaluation due to a drop in overlay accuracy caused by fluctuations in crystal etching time and ΔXo during prototype evaluation.

  It is an object of the present invention to provide a method for manufacturing a tuning fork type crystal resonator capable of suppressing a decrease in pattern overlay accuracy due to a variation in the shape of an alignment mark in crystal etching.

  As a means for solving the above-mentioned problems, a so-called Z-plate quartz wafer composed of an XY plane used for a tuning fork type quartz crystal resonator maintains the vertical and horizontal symmetry before and after the quartz etching, and the shape fluctuation is changed with respect to the etching time fluctuation. Select fewer alignment mark shapes. The present invention is a quadrilateral having vertices on the X and Y axes, and is a parallelogram having an angle between two sides extending from the Y axis vertices to the X axis of 60 ± 10 ° (* FIG. 7). Is a schematic diagram in which 5a and 5c are overlapped) A so-called rhombus shape is used as an alignment mark.

  FIG. 5 shows how the diamond-shaped alignment mark changes in shape as the crystal etching progresses, as in FIGS. FIG. 5B shows the case where the crystal etching is performed for about 30 minutes with respect to the resist pattern 3 in FIG. 5A, and FIG. 5C shows the case where the crystal etching is performed for about 240 minutes. When FIG. 5A, FIG. 5B, and FIG. 5C are compared, there is no change in shape due to the variation in the crystal etching time as shown in FIGS. FIG. 7 is a schematic diagram in which the rhombus-shaped resist pattern 3 shown in FIG. 5A and the rhombus-shaped alignment mark 5 shown in FIG. As shown in FIG. 7, the diamond-shaped alignment mark 5 in FIG. 5C is slightly larger than the diamond-shaped resist pattern 4 in FIG. 5A, but ΔD1 = ΔD2 = ΔD3. = It was confirmed that the relationship of ΔD4 was maintained. Therefore, the rhombus shape shown in FIG. 5 (c) does not lose the vertical and horizontal symmetry, and the four sides are along the crystal orientation of the crystal. However, since the influence is stronger than the pattern defect, four sides with high linearity are obtained, and there are also deviations in the angles formed by the two sides of the four angles (two narrow angles and two obtuse angles). Since it is not seen, it can be determined that the shape satisfies the condition as an alignment mark.

  In the production of a tuning fork type crystal resonator using a photolithographic method, when an alignment mark is formed on a Z-plate crystal wafer with ammonium fluoride or buffered hydrofluoric acid, the two alignment marks intersecting the crystal Y axis. By making a parallelogram, so-called rhombus shape, in which the angle formed is 60 ± 10 ° and the angle formed by two sides intersecting on the crystal X axis is 120 ± 10 °, etching time is also measured before and after crystal etching. Regardless of the length, the rhombus shape will not be deformed. By forming rhombus-shaped alignment marks on the quartz wafer, the alignment mark recognition degree in the image processing device due to deformation due to the size of the quartz etching time of the alignment mark, and the resulting deterioration in overlay accuracy in the exposure machine are suppressed. Therefore, it is possible to provide a method for manufacturing a tuning fork type crystal resonator having good electrical characteristics by suppressing variation in shape during mass production.

Manufacturing flow of tuning fork crystal units The figure explaining the shape change of a square alignment mark The figure explaining the shape change of a round alignment mark The figure explaining the shape change of the hexagonal alignment mark The figure explaining the shape change of the rhombus-shaped alignment mark in this invention Schematic diagram explaining the change in square shape Schematic diagram explaining the change of the rhombus shape in the present invention

  In FIG. 1, an embodiment of the present invention will be described according to a process of forming a grooved tuning fork type crystal resonator using photolithography. In the present invention, the alignment mark formed on the quartz wafer in the tuning fork patterning step or the groove shape patterning step shown in FIG. 1 is not on the generally recommended square, round or cross shape, but on the crystal Y axis. The angle formed by two intersecting sides is 60 ± 10 °, and the angle formed by the two sides intersecting on the crystal X axis is 120 ± 10 °, which is a so-called rhombus shape.

  First, as a corrosion resistant film forming step, a corrosion resistant film against ammonium fluoride or buffered hydrofluoric acid used for etching the crystal is formed on both the front and back surfaces of the crystal wafer. As the corrosion resistant film, a metal film consisting of two layers of a Cr film and an Au film is generally used, and is formed by vapor deposition or sputtering.

  Next, as a tuning fork patterning step, a photoresist is formed on the corrosion-resistant film, exposed using an exposure machine using a photomask in which the outer shape of the tuning fork crystal unit is formed, and then developed and previously formed. By etching the Cr film and Au film which are corrosion resistant films, the outer shape of the tuning fork type crystal resonator made of the corrosion resistant film and the photoresist is obtained on both the front and back surfaces of the quartz wafer. The photomask is made of quartz glass or soda glass, and a tuning fork shape, a groove shape, and an electrode shape, which are patterns to be transferred onto a quartz wafer, are accurately formed on the surface of the photomask by a chromium oxide film.

  On the quartz wafer before the exposure process of the tuning fork patterning process, an alignment mark serving as a reference for positioning the quartz wafer and the photomask in normal exposure is not formed. For this reason, the crystal wafer and the photomask are aligned based on the outer shape of the wafer, and the pattern on the photomask is transferred onto the crystal wafer. On the photomask, in addition to the external shape of the tuning-fork crystal unit, alignment marks that serve as a reference for overlaying the photomask and crystal wafer to be used in the next groove patterning process, and other various patterns as required Are simultaneously transferred.

  At that time, alignment marks for positioning the quartz wafer and the photomask are simultaneously formed in the subsequent electrode patterning step. In the alignment mark shape formed here, the angle formed by two sides intersecting on the crystal Y axis according to the present invention is 60 ± 10 °, and the angle formed by the two sides intersecting on the crystal X axis is 120 ± 10 °. It is a parallelogram, so-called rhombus shape.

  Next, as a groove patterning step, the groove shape is exposed and developed on the branches of the grooved tuning fork type crystal resonator. Similar to the photomask used for tuning fork patterning, the photomask used for exposure in the groove patterning process is not limited to the groove shape, and various patterns are formed as necessary. A parallelogram shape, so-called rhombus-shaped alignment, in which the angle formed by two sides intersecting on the crystal Y axis according to the present invention is 60 ± 10 ° and the angle formed by the two sides intersecting on the crystal X axis is 120 ± 10 °. The mark can be formed not in the tuning fork patterning process but in the groove patterning process. This is a design requirement because the electrode shape formed in the electrode patterning step should be positioned with respect to the outer shape of the tuning fork type quartz crystal resonator or the groove shape. In the case where no groove is formed in the tuning fork branch, the groove patterning step can be omitted.

  Next, as a crystal etching process, the crystal wafer is etched with ammonium fluoride or buffered hydrofluoric acid at room temperature or higher (about 25 to 80 ° C.) for several hours to form a tuning fork type crystal resonator made of a corrosion-resistant film and a photoresist. Etch the exposed quartz part other than the shape and the groove shape made of the corrosion-resistant film. Thereafter, the corrosion-resistant film in the groove-shaped portion is etched, and further, etching with ammonium fluoride or buffered hydrofluoric acid is performed, whereby the outer shape of the grooved tuning-fork type crystal resonator can be formed on the crystal wafer. By this crystal etching process, alignment marks used in the electrode patterning process are formed on the front and back surfaces of the crystal wafer in a form in which the crystal surface is dug. Thereafter, the Cr film, Au film, and photoresist used as the corrosion-resistant film are all peeled off, and a Cr film and an Au film to be electrode films are formed. In addition to this, a combination of Ti, Pd or Ni, Au is generally used as the electrode film, and is appropriately selected.

  Next, as an electrode patterning step, an electrode pattern is formed on the grooved tuning fork type crystal resonator. When forming electrode patterning, a photoresist is deposited on the entire surface of the quartz wafer by spraying or electrodeposition, and the electrode shape is exposed on the quartz wafer using a photomask, followed by development, etching of the Cr film and Au film. Further, the grooved tuning fork type crystal resonator in which the electrode film is formed can be obtained by further peeling the photoresist. Not only the electrode shape of the crystal resonator but also various patterns as necessary are formed on the photomask used for the electrode patterning exposure and formed on the crystal wafer. During electrode patterning, when the diamond-shaped alignment mark formed on the quartz wafer in the tuning fork patterning process or groove patterning process is exposed with an exposure machine equipped with an automatic alignment mechanism, the exposure machine operates in the following procedure. To do.

  The description will be made on the assumption that the proximity type exposure apparatus is used. The exposure machine is mounted on the exposure stage after simple alignment based on the outer shape of the wafer. Thereafter, an electrode-forming photomask is superimposed on the quartz wafer, and a rhombus alignment mark formed on the quartz wafer is detected through the alignment mark of the electrode-forming photomask. Since the rhombus alignment mark does not show the shape variation due to the individual difference of the target quartz wafer or the quartz etching time difference between lots, the center of gravity of the alignment mark or the arbitrary point coordinates can be recognized with high accuracy. The exposure machine searches the alignment mark formed on the electrode forming photomask, and alignment is performed by superimposing the center of gravity of the alignment mark of the crystal wafer-like diamond alignment mark and the alignment mark of the electrode forming photomask or an arbitrary point. The shape of the alignment mark provided on the electrode-forming photomask is formed with accuracy guaranteed by the photomask manufacturer and is not exposed to processes such as crystal etching. A round shape or a cross shape is also possible, and the shape can be arbitrarily selected.

DESCRIPTION OF SYMBOLS 1 Square-shaped resist pattern 2 Square-shaped alignment mark 3 Anisotropic shape of square-shaped alignment mark 4 Rhombus-shaped resist pattern 5 Rhombus-shaped alignment mark

Claims (2)

Forming a first metal film as an underlayer on both front and back surfaces of a quartz wafer made of a Z plate, and forming a second metal film thereon;
Applying a photoresist by spin coating or spray coating on both sides of the quartz wafer; and
Exposing the contour shape of a tuning-fork type crystal resonator on the quartz wafer coated with the photoresist;
By developing the quartz wafer, a contour shape of a tuning fork type quartz crystal resonator made of photoresist is obtained on the quartz wafer, and then the tuning metal fork is formed by the photoresist and the second metal film by etching the second metal film. Forming a contour shape of the quartz crystal unit,
Exposing and developing a groove shape formed in a vibrating arm portion of a tuning fork type crystal resonator in a photoresist on the crystal wafer;
By immersing the quartz wafer in an ammonium fluoride solution or a buffered hydrofluoric acid solution, the first metal film and the quartz are etched along the contour shape of the tuning fork type quartz vibrator, and the tuning fork type quartz vibrator is formed on the quartz wafer. Next, the second metal film corresponding to the groove formed on the vibrating arm portion is etched, the first metal film is further etched, and the groove portion of the vibrating arm portion is again etched with ammonium fluoride or buffered hydrofluoric acid solution. Etching the exposed quartz substrate;
The photoresist layer, the second metal film layer, and the first metal film layer remaining on the quartz wafer are sequentially removed by etching, and a third metal film serving as an electrode film is further applied to the front and back surfaces and side portions of the quartz wafer. Forming a film, and further forming a fourth metal film on the third metal film;
A step of depositing a photoresist for forming an electrode shape on the quartz wafer by a dipping method or a spray coating method;
Transferring the electrode shape to the quartz wafer by an exposure machine;
In a method of manufacturing a tuning fork type crystal resonator using a photolithography method having
An alignment mark is formed by etching on the surface of the quartz wafer,
In the step of exposing the electrode shape of the crystal wafer, the shape of the alignment mark to be aligned with the photomask for electrode formation formed on the crystal wafer is a quadrilateral having apexes in the Y-axis direction and the X-axis direction of the crystal wafer, A method for manufacturing a tuning fork type crystal resonator, characterized in that an angle formed by two sides extending in two directions from two vertices on the Y axis is 60 ± 10 °.   The method of manufacturing a tuning fork type crystal resonator according to claim 1, wherein the alignment mark is formed in the step of forming a contour shape of the tuning fork type crystal resonator.