Patent Publication Number: US-2023155564-A1

Title: Method for Manufacturing Vibration Element

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-185446, filed Nov. 15, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
       1 . Technical Field 
     The present disclosure relates to a method for manufacturing a vibration element. 
       2 . Related Art 
     JP-A-2007-013382 describes a method for manufacturing a vibration element including a pair of grooved vibrating arms and formed by dry etching. In the manufacturing method described in JP-A-2007-013382, a substrate made of a piezoelectric material is so dry-etched that the width of the grooves is smaller than the width of the space between the pair of vibrating arms to allow the micro-loading effect to make the etched grooves shallower than the etched space between the pair of vibrating arms. The grooves and the outer shape of the vibration element are thus formed all at once. 
     In the vibration element manufacturing method described in JP-A-2007-013382, however, dry etching is performed on both the front and rear surfaces of the substrate, a stepped portion can be undesirably formed at the side surface of each of the vibrating arms due to positional shift between the photoresist film formed at the front surface of the substrate and the photoresist film formed at the rear surface of the substrate. The stepped portion formed at the side surface of each of the vibrating arms causes problems of occurrence of unwanted vibration and damage such as cracking and chipping that originates from the stepped portions and occurs when impact acts on the vibration element. 
     SUMMARY 
     A method for manufacturing a vibration element is a method for manufacturing a vibration element including a first vibrating arm and a second vibrating arm extending along a first direction and arranged side by side along a second direction that intersects with the first direction, the first and second vibrating arms each having a first surface and a second surface being front and rear sides with respect to each other and arranged side by side in a third direction that intersects with the first and second directions, a bottomed first groove that opens to the first surface, a bottomed second groove that opens to the second surface, and a side surface that couples the first surface and the second surface to each other, the method including a preparation step of preparing a quartz crystal substrate having the first surface and the second surface, a first dry etching step of dry-etching the quartz crystal substrate from a first surface side to form the first grooves and outer shapes of the first and second vibrating arms, a second dry etching step of dry-etching the quartz crystal substrate from a second surface side to form the second grooves and the outer shapes of the first and second vibrating arms, and a subsequent wet etching step of wet-etching the side surfaces of the first and second vibrating arms, the first grooves, and the second grooves to form inclining surfaces that couple bottom surfaces to in-groove side surfaces of the first and second grooves, and the first and second grooves satisfy a relationship of D1/D ≥ 0.80, where D represents a depth of each of the first and second grooves, and D 1  represents a result of subtraction of a length of the inclining surfaces in the third direction from the depth in each of the first and second grooves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view showing a vibration element according to a first embodiment. 
         FIG.  2    is a cross-sectional view of the vibration element taken along the line A1-A1 in  FIG.  1   . 
         FIG.  3    shows steps of manufacturing the vibration element according to the first embodiment. 
         FIG.  4    is a cross-sectional view for describing a method for manufacturing the vibration element. 
         FIG.  5    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  6    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  7    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  8    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  9    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  10    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  11    is a cross-sectional view corresponding to the position of a section E 1  in  FIG.  10   . 
         FIG.  12    is a cross-sectional view corresponding to the position of a section E 2  in  FIG.  10   . 
         FIG.  13    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  14    is a graph showing the relationship between a dry ratio and a Q value ratio. 
         FIG.  15    shows graphs illustrating the relationship between the dry ratio and the Q-value ratio in response to changes in an aspect ratio. 
         FIG.  16    shows graphs illustrating the relationship between W / A and Wa / Aa for different etching periods. 
         FIG.  17    shows graphs illustrating the relationship between W / A and Wa / Aa for different reaction gases. 
         FIG.  18    shows a graph illustrating the relationship between Wa /Aa and a CI ratio. 
         FIG.  19    shows steps of manufacturing the vibration element according to a second embodiment. 
         FIG.  20    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  21    is a cross-sectional view for describing the method for manufacturing the vibration element. 
         FIG.  22    is a plan view showing a variation of the vibration element. 
         FIG.  23    is a cross-sectional view of the vibration element taken along the line A2-A2 in  FIG.  22   . 
         FIG.  24    is a plan view showing another variation of the vibration element. 
         FIG.  25    is a cross-sectional view of the vibration element taken along the line A3-A3 in  FIG.  24   . 
         FIG.  26    is a plan view showing another variation of the vibration element. 
         FIG.  27    is a cross-sectional view of the vibration element taken along the line A4-A4 in  FIG.  26   . 
         FIG.  28    is a cross-sectional view of the vibration element taken along the line A5-A5 in  FIG.  26   . 
         FIG.  29    is a plan view showing another variation of the vibration element. 
         FIG.  30    is a cross-sectional view of the vibration element taken along the line A6-A6 in  FIG.  29   . 
         FIG.  31    is a cross-sectional view of the vibration element taken along the line A7-A7 in  FIG.  29   . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       1 . First Embodiment 
     A method for manufacturing a vibration element according to a first embodiment will be described. 
     The configuration of the vibration element 1 will first be described with reference to  FIGS.  1  and  2   , and the method for manufacturing the vibration element 1 will next be described with reference to  FIGS.  3  to  18   . 
     The figures excluding part thereof show axes X, Y, and Z, which are three axes that intersect with one another, for convenience of description. In the present embodiment, the three axes are perpendicular to one another. The direction along the axis X is also called a direction X, the direction along the axis Y is also called a direction Y, and the direction along the axis Z is also called a direction Z. The direction Y corresponds to a first direction, the direction X corresponds to a second direction, and the direction Z corresponds to a third direction. The side facing the arrow attached to each of the axes is also called a positive side, and the side opposite from the positive side is also called a negative side. The positive side of the direction Z is also called an “upper side”, and the negative side of the direction Z is also called a “lower side”. A plan view viewed in the direction Z is also simply called a “plan view”. The axes X, Y, and Z correspond to the crystal axes of quartz crystal, as will be described later. 
     The vibration element  1  is a tuning-fork-type vibration element and includes a vibration substrate  2  and an electrode  3  formed at the front surface of the vibration substrate  2 , as shown in  FIGS.  1  and  2   . 
     The vibration substrate  2  is formed by patterning a Z-cut quartz crystal substrate as a Z-cut quartz crystal plate into a desired shape, spreads in the plane X-Y defined by the axes X and Y, which are the crystal axes of quartz crystal, and has a thickness in the direction Z. The axis X is also called an electrical axis, the axis Y is also called a mechanical axis, and the axis Z is also called an optical axis. 
     The vibration substrate  2  has the shape of a plate and has a first surface  2 A and a second surface  2 B, which are front and rear sides with respect with each other and arranged side by side in the direction Z. The vibration substrate  2  has a base  21 , and a first vibrating arm  22  and a second vibrating arm  23  extending from the base  21  along the direction Y and arranged side by side along the direction X. 
     The first vibrating arm  22  has a bottomed first groove  221 , which opens to the first surface  2 A, a bottomed second groove  222 , which opens to the second surface  2 B, and a side surface  101 , which couples the first surface  2 A and the second surface  2 B to each other. Similarly, the second vibrating arm  23  has a bottomed first groove  231 , which opens to the first surface  2 A, a bottomed second groove  232 , which opens to the second surface  2 B, and a side surface  103 , which couples the first surface  2 A and the second surface  2 B to each other. The first grooves  221  and  231  and the second grooves  222  and  232  extend along the direction Y, and the inner surface of each of the grooves forms a bottom surface  111 , in-groove side surfaces  112  and  113 , and inclining surfaces  114  and  115 . The in-groove side surfaces  112  and  113  face each other, the in-groove side surface  112 , which faces the negative side of the direction X, is coupled to the bottom surface  111  via the inclining surface  114 , and the in-groove side surface  113 , which faces the positive side of the direction X, is coupled to the bottom surface  111  via the inclining surface  115 . The first vibrating arm  22  and the second vibrating arm  23  thus each have a substantially H-shaped cross-sectional shape. The thus configured vibration element  1  has a reduced thermoelastic loss and excellent vibration characteristics. The bottom surfaces  111  are each a portion at the deepest position in the direction Z separate from the first surface  2 A or the second surface  2 B, and may not necessarily be parallel to the plane X-Y. For example, the first grooves  221  and  231  and the second grooves  222  and  232  may be so shaped that the inclining surfaces  114  and  115  intersect with each other. In this case, the ridge line that couples the inclining surfaces  114  and  115  to each other corresponds to the bottom surface  111 . 
     The electrode  3  includes a signal electrode  31  and a ground electrode  32 . The signal electrode  31  is disposed at the first surface  2 A and the second surface  2 B of the first vibrating arm  22  and the side surface  103  of the second vibrating arm  23 . On the other hand, the ground electrode  32  is disposed at the side surface  101  of the first vibrating arm  22  and the first surface  2 A and the second surface  2 B of the second vibrating arm  23 . When a drive signal is applied to the signal electrode  31  with the ground electrode  32  grounded, the first vibrating arm  22  and the second vibrating arm  23  perform flexural vibration in the direction X, in which the two vibrating arms repeatedly approach each other and separate from each other, as indicated by the arrows in  FIG.  1   . 
     The vibration element  1  has been briefly described above. 
     The method for manufacturing the vibration element  1  will next be described. The method for manufacturing the vibration element  1  includes a preparation step S 1  of preparing a quartz crystal substrate  20 , which is the base material of the vibration substrate  2 , a first protective film formation step S 2  of forming a first protective film  5  at the first surface  2 A of the quartz crystal substrate  20 , a first dry etching step S 3  of dry-etching the quartz crystal substrate  20  from the side facing the first surface  2 A via the first protective film  5 , a second protective film formation step S 4  of forming a second protective film  6  at the second surface  2 B of the quartz crystal substrate  20 , a second dry etching step S 5  of dry-etching the quartz crystal substrate  20  from the side facing the second surface  2 B via the second protective film  6 , a wet etching step S 6  of wet-etching the quartz crystal substrate  20 , and an electrode formation step S 7  of forming the electrode  3  at the front surface of the vibration substrate  2  produced by the steps described above, as shown in  FIG.  3   . 
     The steps described above will be sequentially described below. 
     Preparation Step S1 
     The quartz crystal substrate  20 , which is the base material of the vibration substrate  2 , is prepared, as shown in  FIG.  4   . The quartz crystal substrate  20  has been prepared, for example, by chemical mechanical polishing (CMP) in the form of a substrate having a desired thickness and has a sufficiently smooth first surface  2 A and second surface  2 B. A plurality of vibration elements  1  are formed all at once from the quartz crystal substrate  20 . 
     First Protective Film Formation Step S 2   
     A metal film M 1  is deposited at the first surface  2 A of the quartz crystal substrate  20 , and a metal film M 2  is deposited at the second surface  2 B of the quartz crystal substrate  20 , as shown in  FIG.  5   . Thereafter, a first photoresist film R 1  is deposited on the metal film M 1 , and the deposited first photoresist film R 1  is patterned. Thereafter, the first protective film  5  is deposited at the openings of the first resist film R 1 , and then the first photoresist film R 1  is removed. As a result, the structure shown in  FIG.  6    is achieved. The first protective film  5  is not particularly limited to a specific film and can be any of a variety of metal masks that are resistant to etching, such as a nickel mask. 
     The first protective film  5  has openings  51 ,  52 , and  53  in portions where the quartz crystal substrate  20  should be removed. Out of the openings, the opening  51  coincides with a first groove formation area Q 1 , where the first grooves  221  and  231  are formed. The opening  52  coincides with an inter-arm area Q 4 , which is located between a first vibrating arm formation area Q 2 , where the first vibrating arm  22  is formed, and a second vibrating arm formation area Q 3 , where the second vibrating arm  23  is formed. The opening  53  coincides with an inter-device area Q 5 , which is located between adjacent vibration substrates  2 . That is, the first protective film  5  is formed in the area excluding the first groove formation area Q 1 , the inter-arm area Q 4 , and the inter-device area Q5. 
     First Dry Etching Step S 3   
     The quartz crystal substrate  20  is dry-etched from the side facing the first face  2 A via the first protective film  5  to simultaneously form the first grooves  221  and  231  in the first surface  2 A and the outer shape of the vibration substrate  2 , that is, the outer shapes of the first vibrating arm  22  and the second vibrating arm  23 , as shown in  FIG.  7   . The phrase “simultaneously form” means that two features are formed all at once in a single step. More specifically, the present step is reactive ion etching and is performed by using a reactive ion etching apparatus (RIE apparatus). The reaction gas introduced into the RIE apparatus is not limited to a specific gas and may, for example, be SF 6 , CF 4 , C 2 F 4 , C 2 F 6 , C 3 F 6 , or C 4 F 8 . 
     The present step ends when the first grooves  221  and  231  reach a desired depth. It is known that the “micro-loading effect”, which lowers the etching rate as the pattern density of the first protective film  5  increases, occurs in dry etching. In the present embodiment, comparison between a width W of each of the first grooves  221  and  231 , which is the width in the direction X, and a width A of the inter-arm area Q4, which is the width in the direction X, shows that W &lt; A. Comparison between the width W and a width B of the inter-device area Q5, which is the width in the direction X, shows that W &lt; B. The micro-loading effect therefore causes the etching rate in the first groove formation area Q1 to be lower than that in the inter-arm area Q4 and the inter-device area Q5. Therefore, at the end of the present step, a depth Wa of the first grooves  221  and  231  is smaller than depths Aa and Ba of the outer shape of the vibration substrate  2 . That is, Wa &lt; Aa (Wa / Aa &lt;  1 ) and Wa &lt; Ba (Wa / Ba &lt;  1 ) are satisfied. The depths Aa and Ba are each greater than or equal to half the thickness of the quartz crystal substrate  20 . That is, let Ta be the thickness of the quartz crystal substrate  20 , and Aa ≥ 0.5 Ta and Ba ≥ 0.5 Ta are satisfied. 
     After the present step is completed, the first protective film  5  and the metal film M1 are removed, and the rear surface of the quartz crystal substrate  20  is ready to be processed. 
     Second Protective Film Formation Step S 4   
     The second protective film  6  is deposited on the metal film M2, as shown in  FIG.  8   . The method for depositing the second protective film  6  is the same as the aforementioned method for depositing the first protective film  5 . The second protective film  6  has openings  61 ,  62 , and  63  in portions where the quartz crystal substrate  20  should be removed. Out of the openings, the opening  61  coincides with a second groove formation area Q 6 , where the second grooves  222  and  232  are formed. The opening  62  coincides with the inter-arm area Q4. The opening  63  coincides with the inter-device area Q5. 
     Second Dry Etching Step S5 
     The quartz crystal substrate  20  is dry-etched from the side facing the second face  2 B via the second protective film  6  to simultaneously form the second grooves  222  and  232  in the second surface  2 B and the outer shape of the vibration substrate  2 , that is, the outer shapes of the first vibrating arm  22  and the second vibrating arm  23 , as illustrated in  FIG.  9   . The present step is executed as the first dry etching step S 3  is. 
     The present step ends when the second grooves  222  and  232  reach a desired depth. In the present embodiment, comparison between the width W of the second grooves  222  and  232 , which is the width in the direction X, and the width A of the inter-arm area Q4, which is the width in the direction X, shows that W &lt; A. Comparison between the width W and the width B of the inter-device area Q5, which is the width in the direction X, shows that W &lt; B. The micro-loading effect therefore causes the etching rate in the second groove formation area Q6 to be lower than that in the inter-arm area Q4 and the inter-device area Q5. Therefore, at the end of the present step, the depth Wa of the second grooves  222  and  232  is smaller than the depths Aa and Ba of the outer shape of the vibration substrate  2 . That is, Wa &lt; Aa (Wa / Aa &lt; 1) and Wa &lt; Ba (Wa / Ba &lt; 1) are satisfied. The depths Aa and Ba are each greater than or equal to half the thickness of the quartz crystal substrate  20 . That is, Aa ≥ 0.5 Ta and Ba ≥ 0.5 Ta are satisfied. The inter-arm area Q4 and the inter-device area Q5 therefore pass through the quartz crystal substrate  20 . The inter-arm area Q4 and the inter-device area Q5 passing through the quartz crystal substrate  20  form the first vibrating arm  22  and the second vibrating arm  23 . 
     After the present step is completed, the second protective film  6  and the metal film M2 are removed, as shown in  FIG.  10   . 
     As described above, in the first dry etching step S 3 , the quartz crystal substrate  20  is dry-etched from the side facing the first surface  2 A, and in the second dry etching step S 5 , the quartz crystal substrate  20  is dry-etched from the side facing the second surface  2 B to form the outer shape of the vibration substrate  2 . Therefore, for example, when the positions of the first protective film  5  and the second protective film  6  shift from each other in the plan view viewed in the direction Z due to manufacturing variations, a stepped portion is formed in some cases in each of the side surface  101  of the first vibrating arm  22  and the side surface  103  of the second vibrating arm  23  in an area  105 , where the dry etching in the first dry etching step S 3  and the dry etching in the second dry etching step S 5  are both performed. 
     For example, when the position of the second protective film  6  shifts toward the negative side of the direction X from the position of the first protective film  5 , a stepped portion  107  is formed at the side surface  101  of the first vibrating arm  22  because the outer shape of the vibration substrate  2  formed in the second dry etching step S 5  shifts toward the negative side of the direction X from the outer shape of the vibration substrate  2  formed in the first dry etching step S 3 , as shown in  FIGS.  11  and  12   . Similarly, when the position of the second protective film  6  shifts toward the positive side of the direction X from the position of the first protective film  5 , for example, the stepped portion  107  is formed. The above description has been made with reference to the first vibrating arm  22  by way of example, and the stepped portion  107  is similarly formed at the side surface  103  of the second vibrating arm  23  when position of the second protective film  6  shifts from the position of the first protective film 5. 
     Wet Etching Step S6 
     The wet etching step S 6  is the step of wet-etching the quartz crystal substrate  20  by immersing the quartz crystal substrate  20  in an etchant. The etchant can be hydrofluoric acid or ammonium fluoride. 
     The first vibrating arm  22  and the second vibrating arm  23  are formed as part of the quartz crystal substrate  20  by the first dry etching step S 3  and the second dry etching step S 5 , as described above. That is, the present step is the step of wet-etching the first vibrating arm  22  and the second vibrating arm  23 , and specifically, the step of wet-etching the side surfaces  101  and  103 , the first grooves  221  and  231 , and the second grooves  222  and  232  of the first vibrating arm  22  and the second vibrating arm  23 . In the present step, wet-etching the side surfaces  101  and  103  of the first vibrating arm  22  and the second vibrating arm  23  allows reduction in the size of the stepped portions  107  formed at the side surfaces  101  and  103 . Smaller stepped portions  107  prevent unwanted vibration from occurring when the vibration element  1  is caused to vibrate and the vibration element  1  from being damaged when impact acts thereon. 
     In the present step, wet-etching the first grooves  221  and  231  and the second grooves  222  and  232  causes the inner surfaces of the first grooves  221  and  231  and the second grooves  222  and  232  to form the inclining surfaces  114  and  115  and the bottom surfaces  111 , as shown in  FIG.  13   . 
     Let D 1  be the depth of a groove formed in the first dry etching step S 3  and the second dry etching step S 5 , and D 2  be the depth of a groove formed in the wet etching step S 6 , and the final groove depth D after the wet etching step S 6 , that is, the distance in the direction Z from the first surface  2 A or the second surface  2 B to the bottom surface  111  is D 1  + D2. The depth D 1  is equal to the depth Wa described above. The depth D 1  can be regarded as the distance in the direction Z from one of the boundary between the in-groove side surface  112  and the inclining surface  114  and the boundary between the in-groove side surface  113  and the inclining surface  115 , the boundary farther from the bottom surface  111 , to the first surface  2 A or second surface  2 B. The depth D 2  can be regarded as the distance in the direction Z from the aforementioned boundary farther from the bottom surface  111  to the bottom surface  111 . In the present embodiment, the depth D 1  is the distance in the direction Z from the boundary between the in-groove side surface  112  and the inclining surface  114  to the first surface  2 A or the second surface  2 B, and the depth D 2  is the distance in the direction Z from that boundary to the bottom surface  111 . That is, the depth D 2  is the length of the inclining surface  114  in the direction Z, and depth D 1  is the result of subtraction of the depth D 2  from the depth D. 
       FIG.  14    is a graph showing the result of a simulation of the relationship between a dry ratio D1/D and a Q value ratio. The dry ratio D1/D is the ratio of the depth D 1  of the groove formed by the dry etching to the final depth D of the groove. The Q value ratio is a normalized Q value of the vibration element  1 , provided that the Q value of the vibration element  1  manufactured under the condition that the dry ratio D1/D is  0 , that is, the Q value achieved when the first grooves  221  and  231  and the second grooves  222  and  232  are formed only by the wet etching is regarded as 100%. The Q value of the vibration element  1  changes in accordance with a change in the dry ratio D1/D, as shown in  FIG.  14   . Specifically, as the dry ratio D1/D increases, the Q value also increases, and when the dry ratio D1/D falls within a range D1/D ≥ 0.80, the Q value is substantially constant. The substantially constant Q value is comparable to the Q value achieved when the dry ratio D1/D is 1.00, that is, the Q value achieved when an ideally shaped first vibration arm  22  and second vibration arm  23  with no stepped portion  107  are formed by the dry etching alone. Forming the first grooves  221  and  231  and the second grooves  222  and  232  in such a way that the dry ratio D1/D ≥ 0.80 is satisfied as described above can greatly improve the Q value as compared with the case where the grooves are formed by the dry etching alone. 
       FIG.  15    shows graphs illustrating the results of the simulation of the relationship between the dry ratio D1/D and the Q-value ratio in response to changes in an aspect ratio D/W, which is the ratio of the groove depth D to the groove width W. Even when the aspect ratio D/W changes, causing the dry ratio D1/D to fall withing the range D1/D ≥ 0.80 can greatly improve the Q value, as shown in  FIG.  15   . Furthermore, forming the first grooves  221  and  231  and the second grooves  222  and  232  in such a way that the dry ratio D1/D falls within a range D1/D ≥ 0.85 can achieve a better Q value. 
     In the wet etching step S 6 , the amount by which the side surfaces  101  and  103  are etched is preferably greater than or equal to 0.01 µm. The thus set etching amount reduces the size of the stepped portions  107 , preventing unwanted vibration from occurring when the vibration element  1  is caused to vibrate and the vibration element  1  from being damaged when impact acts thereon. The amount by which the side surfaces  101  and  103  are etched is the amount of displacement, before and after the wet etching step S 6 , of the side surfaces  101  and  103  in the direction X, which is the direction perpendicular to the side surfaces  101  and  103 . 
     In addition, in the present step, the amount by which the side surfaces  101  and  103  are etched is preferably smaller than or equal to 1 µm. When the amount by which the side surfaces  101  and  103  are etched exceeds 1 µm, each portion of the vibration substrate  2  excluding the stepped portions  107 , for example, the first surface  2 A, the second surface  2 B, the first grooves  221  and  231 , and the second grooves  222  and  232  are wet-etched, so that the outer shape of the vibration element  1  undesirably has dimensions different from desired values. The vibration element  1  can therefore undesirably vibrate at a frequency far off a desired frequency. Maintaining the amount by which the side surfaces  101  and  103  are etched smaller than or equal to  1  µm allows suppression of deviation from the desired frequency. 
     Furthermore, in the present step, the amount by which the side surfaces  101  and  103  are etched is preferably smaller than or equal to 0.5 µm. When the amount by which the side surfaces  101  and  103  are etched exceeds 0.5 µm, the corners of the vibrating arms  22  and  23 , where the first surface  2 A and the second surface  2 B are coupled to the side surfaces  101  and  103 , and other portions are wet-etched, resulting in a complicated shape of the vibration element  1  that differs from a desired shape. Unwanted vibration may therefore occur when the vibration element  1  is caused to vibrate, resulting in deterioration of the vibration characteristics, such as the Q value. Maintaining the amount by which the side surfaces  101  and  103  are etched smaller than or equal to 0.5 µm allows suppression of occurrence of undesired vibration. 
     A plurality of vibration substrates  2  are collectively formed from the quartz crystal substrate  20  by executing steps S 1  to S 6  described above. 
     Electrode Formation Step S7 
     A metal film is deposited at the front surface of the vibration substrate  2 , and the metal film is patterned to form the electrode 3. 
     The vibration element  1  is thus manufactured. 
     As described above, the dry etching allows processing without being affected by the crystal planes of the quartz crystal, thus achieving excellent dimensional accuracy. Forming the first grooves  221  and  231 , the second grooves  222  and  232 , and the outer shape of the vibration substrate  2  all at once allows reduction in the number of steps of manufacturing the vibration element  1  and the cost of the vibration element  1 . Furthermore, positional shift of the first grooves  221  and  231  and the second grooves  222  and  232  from the outer shape is prevented, whereby the accuracy of formation of the vibration substrate  2  increases. 
     The wet etching allows reduction in the size of the stepped portions  107  formed at the side surface  101  of the first vibrating arm  22  and the side surface  103  of the second vibrating arm  23  when the quartz crystal substrate  20  is dry-etched from both the sides facing the first surface  2 A and the second surface  2 B. The smaller stepped portions  107  can suppress unwanted vibration that occurs when the vibration element  1  is caused to vibrate and damage made to the vibration element  1  when impact acts thereon. 
     The method for manufacturing the vibration element  1  has been described above. 
     The conditions under which the micro-loading effect more reliably manifests itself will next be described with reference to  FIGS.  16  and  17   . 
       FIG.  16    shows the relationship between W / A and Wa / Aa for different etching periods. As can be seen from  FIG.  16   , the micro-loading effect notably manifests itself at each point of time in the region where W / A ≤ 40% is satisfied. 
     The micro-loading effect manifests itself in a variety of manners in accordance with the type of reaction gas used in the dry etching.  FIG.  17    shows the relationship between W / A and Wa / Aa in a case where three typical reaction gases different from one another are used. 
     For example, when a fluorine-based gas having a large carbon content, such as C 2 F 4 , C 2 F 6 , C 3 F 6 , and C 4 F 8 , is used as the reaction gas, a thick sidewall protective film is produced, and the slope of the graph representing the relationship decreases, as in the case of a gas type G3. Wa / Aa therefore tends to increase with the width A being smaller than the width W, whereby the size of the vibration element  1  can be reduced. For example, to design the frequency and the CI value of the vibration element  1 , a width W greater than or equal to a certain value and a depth Wa close to the depth Aa are required in some cases. In the design process, the width A needs to be a small value to reduce the size of the vibration element  1 , and at least one of C 2 F 4 , C 2 F 6 , C 3 F 6 , and C 4 F 8  is particularly effective in this case. 
     On the other hand, when a fluorine-based gas containing little or no carbon, such as SF 6  and CF 4 , is used alone or in combination with a fluorine-based gas having a large carbon content, a thin sidewall protective film is produced, and the slope of the graph increases, as in the case of a gas type G1. The width A can therefore be greater than the width W with the depth Wa maintained greater than the depth Aa. For example, when it is desired to achieve a narrow first vibrating arm  22  and second vibrating arm  23  but a large width A while achieving a large depth Wa, at least one of SF 6  and CF 4  is particularly effective. 
     Let x be W / A and y be Wa / Aa, and the gas type G 1  is expressed by Expression (1) below, a gas type G 2  is expressed by Expression (2) below, and the gas type G 3  is expressed by Expression (3) below. 
     
       
         
           
             y 
               
               
             = 
               
               
             − 
             4.53 
               
               
             × 
               
               
             
               
                 10 
               
               
                 − 
                 6 
               
             
             
               x 
               4 
             
             + 
             3.99 
               
               
             × 
               
               
             
               
                 10 
               
               
                 − 
                 4 
               
             
             
               x 
               3 
             
             − 
             1.29 
               
               
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                 10 
               
               
                 − 
                 3 
               
             
             
               x 
               2 
             
             + 
             1.83 
               
               
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                 10 
               
               
                 − 
                 1 
               
             
             x 
               
           
         
       
     
     
       
         
           
             
               
                 y 
                   
                   
                 = 
                   
                   
                 − 
                 5.59 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     8 
                   
                 
                 
                   x 
                   4 
                 
                 + 
                 1.48 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     5 
                   
                 
                 
                   x 
                   3 
                 
                 − 
               
             
             
               
                 1.43 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     3 
                   
                 
                 
                   x 
                   2 
                 
                 + 
                 6.09 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     2 
                   
                 
                 
                   x 
                   ′ 
                 
                   
               
             
           
         
       
     
     
       
         
           
             
               
                 y 
                   
                   
                 = 
                   
                   
                 − 
                 6.90 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     10 
                   
                 
                 
                   x 
                   4 
                 
                 + 
                 5.47 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     7 
                   
                 
                 
                   x 
                   3 
                 
                 − 
               
             
             
               
                 1.59 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     4 
                   
                 
                 
                   x 
                   2 
                 
                 + 
                 2.03 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     2 
                   
                 
                 x 
                   
               
             
           
         
       
     
     When y is in a region P between the graphs expressed by Expressions (1) and (3) , as shown in  FIG.  17   , that is, when y satisfies Expressions (4) and (5) below, the micro-loading effect more reliably manifests itself with a typical reaction gas. Therefore, the vibration element  1  can be readily manufactured, and the manufacturing cost thereof can be reduced. 
     
       
         
           
             
               
                 y 
                   
                   
                 ≧ 
                   
                 − 
                 4.53 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     6 
                   
                 
                 
                   x 
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                 + 
                 3.99 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     4 
                   
                 
                 
                   x 
                   3 
                 
                 − 
               
             
             
               
                 1.29 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     3 
                   
                 
                 
                   x 
                   2 
                 
                 + 
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                 × 
                   
                   
                 
                   10 
                   
                     − 
                     1 
                   
                 
                 x 
                   
               
             
           
         
       
     
     
       
         
           
             
               
                 y 
                   
                   
                 ≦ 
                   
                   
                   
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                   10 
                   
                     − 
                     10 
                   
                 
                 
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                     − 
                     7 
                   
                 
                 
                   x 
                   3 
                 
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                 1.59 
                   
                   
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                   10 
                   
                     − 
                     4 
                   
                 
                 
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                   2 
                 
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                 2.03 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     2 
                   
                 
                 x 
                   
               
             
           
         
       
     
     When y does not satisfy Expression (4), the change in the depth Wa is greater than the change in the width W, so that the depth Wa may undesirably vary. The variation can be suppressed by y that satisfies Expression (4). When y does not satisfy Expression (5), it is difficult to increase y in regions where x is large, and the depth Wa decreases. To increase the depth Wa, a condition closer to W = A needs to be achieved, which tends to cause geometrical constraints. The geometrical constraints can be suppressed by y that satisfies Expression (5). 
     For example, when the width W and the depth Wa are fixed, selecting the gas type G 2  allows reduction in the width A as compared with the width A achieved when the gas type G 1  is selected and therefore allows reduction in the size of the vibration element  1 . Selecting the gas type G 3  allows further reduction in the width A as compared with the width A achieved when the gas type G 2  is selected and therefore allows further reduction in the size of the vibration element  1 . As described above, from the viewpoint of size reduction, it is preferable that y is in the region P, and it is more preferable that y is in a region PP between the graphs expressed by Expressions (2) and (3). That is, it is preferable that y satisfies Expression (6) below and Expression (5) described above. 
     
       
         
           
             
               
                 y 
                   
                   
                 ≧ 
                   
                   
                 − 
                 5.59 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     8 
                   
                 
                 
                   x 
                   4 
                 
                 + 
                 1.48 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     5 
                   
                 
                 
                   x 
                   3 
                 
                 − 
               
             
             
               
                 1.43 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     3 
                   
                 
                 
                   x 
                   2 
                 
                 + 
                 6.09 
                   
                   
                 × 
                   
                   
                 
                   10 
                   
                     − 
                     2 
                   
                 
                 x 
                   
               
             
           
         
       
     
     The effect of improvement of the CI value of the vibration element  1  provided when the first grooves  221  and  231  and the second grooves  222  and  232  are formed will next be described with reference to  FIG.  18   . 
       FIG.  18    shows the relationship between Wa /Aa and a CI ratio. The CI ratio is a normalized CI value of the vibration element  1 , provided that the CI value of the vibration element  1  manufactured under the condition that none of the first grooves  221  and  231  and the second grooves  222  and  232  is formed is regarded as 1.0. It is preferable that Wa / Aa ≥ 0.2 is satisfied, as shown in  FIG.  18   . Note that Wa / Aa &lt; 1 is satisfied in the present embodiment, in which the micro-loading effect is used. The condition described above allows reduction in the CI value to at least 30% of the CI value achieved when none of the first grooves  221  and  231  and the second grooves  222  and  232  is formed. A vibration element  1  having excellent vibration characteristics can therefore be manufactured. It is further preferable that Wa / Aa ≥ 0.4 is satisfied, in which case, the CI value can be reduced to at least 10% of the CI value achieved when none of the first grooves  221  and  231  and the second grooves  222  and  232  is formed. 
     The conditions under which the micro-loading effect more reliably manifests itself in the method for manufacturing the vibration element  1  have been described above. 
     As described above, the method for manufacturing the vibration element  1  is a method for manufacturing a vibration element that includes the first vibrating arm  22  and the second vibrating arm  23 , which extend along the direction Y, which is the first direction, and are arranged side by side along the direction X, which is the second direction and intersects with the direction Y, the first vibrating arm  22  and the second vibrating arm  23  each having the first surface  2 A and the second surface  2 B, which are front and rear sides with respect with each other and are arranged side by side in the direction Z, which is the third direction and intersects with the directions X and Y, the first vibrating arm  22  and the second vibrating arm  23  further having the bottomed first grooves  221  and  231 , which open to the first surface  2 A, the bottomed second grooves  222  and  232 , which open to the second surface  2 B, and the side surfaces  101  and  103 , which couple the first surface  2 A and the second surface  2 B to each other, the method including the preparation step S 1  of preparing the quartz crystal substrate  20  having the first surface  2 A and the second surface  2 B, the first dry etching step S 3  of dry-etching the quartz crystal substrate  20  from the side facing the first surface  2 A to form the first grooves  221  and  231  and the outer shapes of the first vibrating arm  22  and the second vibrating arm  23 , the second dry etching step S 5  of dry-etching the quartz crystal substrate  20  from the side facing the second surface  2 B to form the second grooves  222  and  232  and the outer shapes of the first vibrating arm  22  and the second vibrating arm  23 , and the subsequent wet etching step S 6  of wet-etching the side surfaces  101  and  103  of the first vibrating arm  22  and the second vibrating arm  23 , the first grooves  221  and  231 , and the second grooves  222  and  232  to form the inclining surfaces  114  and  115 , which couple the bottom surfaces  111  of the first grooves  221  and  231  and the second grooves  222  and  232  to the in-groove side surfaces  112  and  113 , and the first grooves  221  and  231  and the second grooves  222  and  232  satisfy D1/D ≥ 0.80, where D represents the depth of the first grooves  221  and  231  and the second grooves  222  and  232 , and D 1  represents the result of subtraction of the length of the inclining surface  114  in the direction Z from the depth. 
     According to the manufacturing method described above, the size of the stepped portions  107  formed at the side surfaces  101  and  103  of the first vibrating arm  22  and the second vibrating arm  23  can be reduced. The stepped portions  107  having the reduced size can suppress unwanted vibration that occurs when the vibration element  1  is caused to vibrate and damage made to the vibration element  1  when impact acts thereon. Furthermore, the dry ratio D1/D satisfies D1/D ≥ 0.80, whereby the Q value can be improved, as described above. 
     In the method for manufacturing the vibration element  1 , it is preferable that the first grooves  221  and  231  and the second grooves  222  and  232  are formed under the condition that the dry ratio D1/D satisfies D1/D ≥ 0.85, as described above. The Q value can thus be improved. 
     In the method for manufacturing the vibration element  1 , it is preferable that the amount by which the side surfaces  101  and  103  are etched in the wet etching step S 6  is greater than or equal to 0.01 µm, as described above. The thus set etching amount reduces the size of the stepped portions  107 , preventing unwanted vibration from occurring when the vibration element  1  is caused to vibrate and the vibration element  1  from being damaged when impact acts thereon. 
     In the method for manufacturing the vibration element  1 , it is preferable that the amount by which the side surfaces  101  and  103  are etched in the wet etching step S 6  is smaller than or equal to 1 µm, as described above. Deviation from the desired frequency that occurs when the vibration element  1  is caused to vibrate can thus be suppressed. 
     In the method for manufacturing the vibration element  1 , it is preferable that the amount by which the side surfaces  101  and  103  are etched in the wet etching step S 6  is smaller than or equal to 0.5 µm, as described above. Unwanted vibration that occurs when the vibration element  1  is caused to vibrate can thus be suppressed. 
     In the method for manufacturing the vibration element  1 , it is preferable that Wa / Aa &lt;  1  is satisfied in at least one of the first dry etching step S 3  and the second dry etching step S 5 , as described above, where Wa represents the depth of the first grooves  221  and  231  formed in the first dry etching step S 3  and the depth of the second grooves  222  and  232  formed in the second dry etching step S 5 , and Aa represents the depth of the outer shapes of the first vibrating arm  22  and the second vibrating arm  23  formed in the first dry etching step S 3  and the depth of the outer shapes of the first vibrating arm  22  and the second vibrating arm  23  formed in the second dry etching step S5. The first grooves  221  and  231 , the second grooves  222  and  232 , and the outer shape of the vibration substrate  2  can thus be formed all at once. The number of steps of manufacturing the vibration element  1  and the cost of the vibration element  1  can therefore be reduced. Furthermore, positional shift of the first grooves  221  and  231  and the second grooves  222  and  232  from the outer shape is prevented, whereby the accuracy of formation of the vibration substrate  2  increases. 
     2. Second Embodiment 
     The method for manufacturing the vibration element  1  according to a second embodiment will be described with reference to  FIGS.  19  to  21   . The same components as those in the first embodiment have the same reference characters, and no redundant description of the same components will be made. 
     The second embodiment is the same as the first embodiment except that a third protective film formation step S10 is provided between the second dry etching step S 5  and the wet etching step S 6 , that third protective films  109  are formed at the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20  in the third protective film formation step S10, and that the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20  is masked by the third protective film  109  in the wet etching process S6. 
     The method for manufacturing the vibration element  1  according to the second embodiment includes the preparation step S 1  of preparing the quartz crystal substrate  20 , which is the base material of the vibration substrate  2 , the first protective film formation step S 2  of forming the first protective film  5  at the first surface  2 A of the quartz crystal  20 , the first dry etching step S 3  of dry-etching the quartz crystal substrate  20  from the side facing the first surface  2 A via the first protective film  5 , the second protective film formation step S 4  of forming the second protective film  6  at the second surface  2 B of the quartz crystal substrate  20 , the second dry etching step S 5  of dry-etching the quartz crystal substrate  20  from the side facing the second surface  2 B via the second protective film  6 , the third protective film formation step S10 of forming the third protective films  109  at the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20 , the wet etching step S 6  of wet-etching the quartz crystal substrate  20 , and the electrode formation step S 7  of forming the electrode  3  at the front surface of the vibration substrate  2  produced by the steps described above, as shown in  FIG.  19   . 
     The preparation step S 1  to the second dry etching step S 5  are the same as those in the first embodiment and will therefore not be described, and the third protective film formation step S10 and the following steps will be described. The second protective film  6  and the metal film M 2  are removed from the quartz crystal substrate  20  after the completion of the second dry etching step S 5 , as in the first embodiment. 
     Third Protective Film Formation Step S10 
     The third protective films  109  are formed at the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20 , as shown in  FIG.  20   . The third protective films  109  are each, for example, a metal film formed by sequentially depositing chromium and gold from the side facing the quartz crystal substrate  20 . The third protective films  109  can be formed by depositing the metal films at the surfaces of the quartz crystal substrate  20 , for example, by using sputtering or chemical vapor deposition (CVD) and patterning the metal films by using photolithography and etching techniques. 
     Wet Etching Step S 6   
     In the present step, the quartz crystal substrate  20  is wet-etched by immersing the quartz crystal substrate  20  in an etchant. 
     In the second embodiment, prior to the present step, the third protective films  109  are formed at the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20  in the third protective film formation step S10. Therefore, in the present step, the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20  are masked by the third protective films  109 . In other words, the first surface  2 A and the second surface  2 B of the first vibrating arm  22  and the second vibrating arm  23  are masked by the third protective films  109 . That is, the first surface  2 A and the second surface  2 B of the first vibrating arm  22  and the second vibrating arm  23  are not wet-etched in the present step. The masking third protective films  109  prevents the dimensions and shape of the vibration element  1  from being different from the desired dimensions and shape. Deviation from the desired frequency and occurrence of unwanted vibration of the vibration element  1  can thus be suppressed. 
     Since no third protective film  109  is formed at the side surface  101  of the first vibrating arm  22  and the side surface  103  of the second vibrating arm  23 , the size of the stepped portions  107  formed at the side surfaces  101  and  103  can be reduced, as in the first embodiment. 
     After the present step is completed, the third protective films  109  are removed, as shown in  FIG.  21   . A plurality of vibration substrates  2  are thus collectively formed from the quartz crystal substrate  20 . 
     Electrode Formation Step S 7   
     The present step is executed in the same manner as in the first embodiment. A metal film is deposited at the front surface of the vibration substrate  2 , and the metal film is patterned to form the electrode 3. 
     The vibration element  1  is thus manufactured. 
     The present embodiment can provide the following effect in addition to the effects provided by the first embodiment. 
     In the wet etching step S 6 , the first surface  2 A and the second surface  2 B of the quartz crystal substrate  20  are masked by the third protective films  109 , which prevent the dimensions and shape of the vibration device  1  from being different from the desired dimensions and shape. Deviation from the desired frequency and occurrence of unwanted vibration of the vibration element  1  can thus be suppressed. 
     The vibration element manufacturing method according to the present disclosure has been described above based on the first and second embodiments. 
     The present disclosure is, however, not limited thereto, and the configuration of each portion can be replaced with any configuration having the same function. Furthermore, any other constituent element may be added to any of the embodiments of the present disclosure. Moreover, the embodiments may be combined as appropriate with each other. 
     For example, in the embodiments described above, Wa / Aa &lt;  1  is satisfied in each of the first dry etching step S 3  and the second dry etching step S 5 , but not necessarily, and Wa / Aa &lt;  1  only needs to be satisfied in at least one of the steps. 
     The vibration element manufactured by the vibration element manufacturing method according to the present disclosure is not limited to a specific device and may, for example, be a vibration element  1 A shown in  FIGS.  22  and  23   . In the vibration device  1 A, a pair of first grooves  221  are formed side by side in the direction X at the first surface  2 A of the first vibrating arm  22 , and a pair of second grooves  222  are formed side by side in the direction X at the second surface  2 B of the first vibrating arm  22 . Similarly, a pair of first grooves  231  are formed side by side in the direction X at the first surface  2 A of the second vibrating arm  23 , and a pair of second grooves  232  are formed side by side in the direction X at the second surface  2 B of the second vibrating arm  23 . In the configuration described above, the width W of each of the grooves tends to decrease because a plurality of grooves are arranged in one direction. It is therefore preferable to use at least one of SF 6  and CF 4  as the reaction gas in the first dry etching step S 3  and the second dry etching step S5. The depth of each of the grooves can therefore be a deep groove, whereby the CI value can be lowered. 
     The vibration device may instead be a double-tuning-fork-type vibration device  7  shown in  FIGS.  24  and  25   . Note that no electrode is shown in  FIGS.  24  and  25   . The double-tuning-fork-type vibration element  7  includes a pair of bases  711  and  712 , and a first vibrating arm  72  and a second vibrating arm  73 , which link the bases  711  and  712  to each other. The first vibrating arm  72  and the second vibrating arm  73  have bottomed first grooves  721  and  731 , which open to a first surface  7 A, and bottomed second grooves  722  and  732 , which open to a second surface  7 B. 
     The vibration element may still instead, for example, be a gyro vibration element  8  shown in  FIGS.  26  to  28   . No electrode is shown in  FIGS.  26  to  28   . The gyro vibration element  8  includes a base  81 , a pair of detection vibration arms  82  and  83 , which extend from the base  81  toward opposite sides of the direction Y, a pair of linkage arms  84  and  85 , which extend from the base  81  toward opposite sides of the direction X, drive vibration arms  86  and  87 , which extend from the tip of the linkage arm  84  toward opposite sides of the direction Y, and drive vibration arms  88  and  89 , which extend from the tip of the linkage arm  85  toward opposite sides of the direction Y. When an angular velocity ωz around the axis Z acts on the thus configured gyro vibration element  8  with the drive vibration arms  86 ,  87 ,  88 , and  89  undergoing flexural vibration in the direction labeled with an arrows SD in  FIG.  26   , the Coriolis force newly excites flexural vibration of the detection vibration arms  82  and  83  in the direction labeled with an arrows SS, and the angular velocity ωz is detected based on the electric charges outputted from the detection vibration arms  82  and  83  due to the flexural vibration. 
     The detection vibration arms  82  and  83  have bottomed first grooves  821  and  831 , which open to a first surface  8 A, and bottomed second grooves  822  and  832 , which open to a second surface  8 B. The driving vibrating arms  86 ,  87 ,  88 , and  89  have bottomed first grooves  861 ,  871 ,  881 , and  891 , which open to the first surface  8 A, and bottomed second grooves  862 ,  872 ,  882 , and  892 , which open to the second surface  8 B. In the thus configured gyro vibration element  8 , for example, pairs of vibrating arms adjacent to each other in the direction X, such as the detection vibration arm  82  and the drive vibration arm  86 , the detection vibration arm  82  and the drive vibration arm  88 , the detection vibration arm  83  and the drive vibration arm  87 , and the detection vibration arm  83  and the drive vibration arm  89 , can be regarded as the first and second vibrating arms. 
     In the case of the gyro vibration element  8 , the inter-arm areas Q 4  each need to have a large size for a structural reason. In such a case, the depth Wa may decrease in the region between the graphs expressed by Expressions (2) and (3) described above, undesirably resulting a decrease in sensitivity. It is therefore preferable to use the region between the graphs expressed by Expressions (1) and (2) described above. 
     The vibration element may still instead, for example, be a gyro vibration element  9  shown in  FIGS.  29  to  31   . The gyro vibration element  9  has a base  91 , a pair of drive vibration arms  92  and  93 , which extend from the base  91  toward the positive side of the direction Y and arranged side by side in the direction X, and a pair of detection vibration arms  94  and  95 , which extend from the base  91  toward the negative side of the direction Y and arranged side by side in the direction X. When an angular velocity ωy around the axis Y acts on the thus configured gyro vibration element  9  with the drive vibration arms  92  and  93  undergoing flexural vibration in the direction labeled with the arrows SD in  FIG.  29   , the Coriolis force newly excites flexural vibration of the detection vibration arms  94  and  95  in the direction labeled with the arrows SS, and the angular velocity ωy is detected based on the electric charges outputted from the detection vibration arms  94  and  95  due to the flexural vibration. 
     The drive vibration arms  92  and  93  have bottomed first grooves  921  and  931 , which open to a first surface  9 A, and bottomed second grooves  922  and  932 , which open to a second surface  9 B. The detection vibration arms  94  and  95  have bottomed first grooves  941  and  951 , which open to the first surface  9 A, and bottomed second grooves  942  and  952 , which open to the second surface  9 B. In the thus configured gyro vibration element  9 , the drive vibration arms  92  and  93  or the detection vibration arms  94  and  95  form the first and second vibrating arms.