CA1128842A - Method of treating a quartz plate - Google Patents
Method of treating a quartz plateInfo
- Publication number
- CA1128842A CA1128842A CA321,713A CA321713A CA1128842A CA 1128842 A CA1128842 A CA 1128842A CA 321713 A CA321713 A CA 321713A CA 1128842 A CA1128842 A CA 1128842A
- Authority
- CA
- Canada
- Prior art keywords
- plate
- quartz plate
- quartz
- etching
- abrasive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
Abstract of the Disclosure Quartz plates are treated to produce a chemically polished quartz crystal surface by lapping the quartz plate with an abrasive and then etching the lapped quartz plate in a fluoride type etchant so that the damage pro-duced by lapping is removed.
Description
This invention relates in general to a method of treating a quartz plate and in particular to such a method that will produce a chemically polished quartz crystal surface.
High precision and high frequency quartz resonators, particularly those for high shock applications, require quartz plates whose surfaces are free of imperfections, such as scratches and pits. The most common method of achieving such surfaces has been mechanical polishing. The difficulty with mechanical polishing, however, has been its inability to produce defect-free surfaces, at the correct frequency, with a high yield. Moreover, as has been known since the last century, even when the polished surfaces appear to be free of defects when examined at high magnification, the surfaces contain hidden defects. These defects can be revealed by etching subsequent to polishing.
The general object of this invention is to provide a method of overcoming the difficulties associated with the mechanical polishing of quartz plates. A further object of the invention is to provide such a method that will produce a polished quartz crystal surface that is free of defects.
A particular object of the invention is to provide a method of polishing quarts chemically. Another object of the invention is to provide a method of making quart~ plates of great strength suitable for high shock resonator applica-tions.
The foregoing objects have now been obtained by a method involving lapping the quartz plate with an abrasive and then etching the quartz plate in a fluoride type etchant at least until the damage produced by lapping is removed.
Etching can be considered as a five step process in which the etchant must diffuse to the surface, be adsorbed, react chemically, and the resulting reaction products must then be desorbed and diffuse away from the surface. The etching rate may be limited by any one of these steps. In chemical polishing, the rate controlling step is generally the diffusion to or from the surface. Diffusion control means that, in particular, the rate at which a reaction takes place at the surface is higher than the rate of ,. ~
88~2 diffusion; that is, the etchant molecules at the surface react at a rate which is faster than the rate at which the concentration at the surface can be replenished by the diffusion of other etchant molecules. A depleted surface layer therefore exists, outside which the etchant concentration is uniform, but inside which the concentration decreases to near zero at the surface~
Under such conditions, the etching is principally determined not by the properties of the surface be~ing etched, but by the diffusion. It is clear that if a surface initially consists of hills and valleys, the probabil-ity of an etchant molecule diffusing to the top of a hill will be muchgreater than the probability of it diffusing to the bottom of a valley. The hills will therefore be etched faster than the valleys, and the surface will become increasingly smooth as the etching progresses.
Eventually, the surface becomes so smooth that the depleted layer can have a uniform thickness. From that point, the surface is etched evenly eve~ywhere, and the surface smoothness no longer improves with further etching.
Chemically polished surfaces are therefore not perfectly flat but are micro-scopically undulating.
Of the known etchants for quartz, particularly desirable are fluor-d ide type etchants such as aqueous solutions of ammonium bifluoride, and of mixtures of hydrogen fluoride and ammonium fluoride.
For a given etchant, the time required to produce a chemically polished surface is primarily a function of the etching bath temperature and of the particle size distribution of the lapping abrasive used for final lapping the quartz plates~ The higher the etching bath temperature, the more rapidly the etching takes place, and the coarser the abrasive, the greater the amount of material which must be removed by etching in order to produce chemically polished surfaces. The details of how the chemical polishing is influenced by the etching bath temperature, abrasive particle size, and other parameters is discussed in "Chemically Polished Quartz" by John R. Vig, John W. LeBus and Raymond L. Filler, published in the Proceedings of the 31st Annual Symposium on Frequency Control, 1-3 June 1977, and in Research and Development Technical Report ECoM-4548, November 1977. For the aluminum oxide abrasives evaluated, the etching should remove from the thickness of the plates an amount which is at least twice the average particle diameter in the final abrasive. For example, if a 3 ~m abrasive is used for final lapping the quartz plates, the chemical polishing process should remove at least 6 um from the plate thicknesses in order to produce surfaces which can be described as chemically polished.
The quality of quartz used is another important consideration.
When chemical polishing is attempted on groups of plates made of several different cultured quartz varieties, it is found that for many of the plates the etching produces large numbers of undesirable etch pits and etch channels.
This is particularly true for plates made of relatively low Q, fast grown materials. When plates made of natural quartz or swept (i.e., "electrolyzed") cultured quartz are used, the incidence of etch pits and etch channels is far fewer. Of the cultured quartz varieties, the one variety which has been vacuum swept in accordance with the method described in U.S. Patent No.
3,932,777 issued January 13, 1976 to James Claude King for "Vacuum Electrolysis ; of Quartz," has the lowest incidence o etch channelsO
~-~ AT-cut plano-plano natural quartz plates are final lapped with a 3 micrometer aluminum oxide abrasive and then etched in a saturated solution of ammonium bifluoride at an etch bath temperature of 75C. Chemically polished surfaces are produced in less than 30 minutes.
The chemical polishing process can remove large amounts of material from lapped plates while simultaneously producing an improved surface finish, without producing shifts in the angles of cuto The process will also produce plates of great strength, which is particularly important for high shock applications.
The particular apparatus used to carry out the etching method is not critical. One particular apparatus that can be conveniently used includes a 1000 ml glass outer beaker containing water and a floating 400 ml Teflo ~
beaker, which in turn contains the saturated ammonium bifluoride solution. A
temperature controlled stirring hot plate with a thermistor sensor can be 38g~;2 used to control the temperature of the water surrounding the Teflon~beaker.
The temperature of the ammonium bifluoride solution can thus be controlled to about + 105C. A thick Teflon disc with a diameter slightly larger than the outer beaker is used as a cover to minimize evaporation from the beakers.
The weight of this disc also serves to push the inner beaker down to assure that the fluid level in the inner beaker is always about 3 cm below the water level in the outer beaker. A hole through the center of the disc permits the agitation of crystals during etching.
The quartz plates are loosely held in a Teflon~jig which is designed to assure that only point contacts exist between the jig and the plates. The plates are agitated slowly in both directions by means of a constant speed electric motor. The motor is set to rotate the etching jig through an angle of approximately 360 before reversing direction. The rate of agitation is about 5 cycles per minute.
A convenient etching procedure involves first the preparation of a saturated solution of ammonium bifluoride in a Teflon container. The ammonium bifluoride (NH4F~HF) flakes are mixed with distilled water, and the solution heated to the desired tempera-ture. The amount of NH4FHF used is such that after the solution reaches the equilibrium temperature, some undis-solved flakes remain in the bottom of the container throughout the etchingprocess. (The solubility of NH4F-HF in water increases from 61 gms per 100 ml of solution at 60 C to 86 gms per 100 ml at 100 C.) The solution prepara-tion and the etching are performed under a vented hood to prevent inhalation of the vapors from the etching bath. Then, the plates are cleaned thoroughly.
To assure that the surfaces are etched evenly, it is particularly important to remove all contaminants such as waxes and greases, which may be impervious to the etchant. Any number of cleaning techniques may be used, as long as contaminants that are impervious to the etchant are removed. One method which has consistently produced good results involves the immersion of the blanks in ethyl alcohol in a Petri dish the bottom of which is lined with open cell urethane foam, and then scrubbing both sides of each blank with a -foam swab. The crystal plates are then placed into the slots in the etching ~1%~3842 fixture and agitated ultrasonically in a detergent solution, then rinsed thoroughly in distilled water. A second satisfactory cleaning technique involves plasma cleaning in an oxygen plasma followed by a thorough rinse in distilled water.
From the final rinse the plates are transferred, while wet, into the etching bath, and are shaken vigorously to make sure that there are no trapped air bubbles in the etching fixture. During etching, the plates are agitated in both directions to assure even etching of both sides.
After the plates reach the desired frequency, the etching fixture is removed rapidly from the etch bath and is immersed immediately into a container of hot water, given a thorough rinse under running hot water, then agitated ultrasonically in hot water, then given another rinse in running distilled water, then dried by spin drying. A thorough rinse is important in order to remove all residues of the etchant.
The plates are usually etched to the desired frequency by first measuring the etch rates as a function of temperature, selecting a suitable temperature between 20C and 90C, calculating the etching time required to reach the desired frequency, and etching the plates for a time slightly less than the time calculated. The reason for etching for less than the time calculated is that experience has shown that there are slight variations from plate to plate in the rates at which quartz plates etch at a gi~en temperature.
In practice, therefore, in order to etch a group of quartz plates to a narrow range about a target frequency, an iterative procedure is often necessaryO
That is, the plates are etched for a time slightly less than the time calcula-ted, then the plates are rinsed, dried and the frequencies are measured.
Those plates whose frequency is within the target range are removed from the etching fixture, a new etching time is calculated for the remaining plates, the plates are etched again, rinsed, dried, measured, and the process is repeated until all the plates in the group have been etched to the proper frequency range.
The plates are then inspected under a microscope for uniformity of etch, and for defects such as scratch marks, etch pits and etch channels.
389L~
The inspection of etched plates is performed under a microscope at about 40 X magnification, with the light incidence perpendicular to the axis of the microscope, and with using a black background. First, the plate is inspected for surface irregularities such as scratch marks, pits and twinned areas by tilting the plate so as to reflect light into the micro-scope. The crystal plate is then inspected for etch channels by holding it so that the light incidence is in the plane of the plate (i.e., edge illumin-ation). The etch channels are most visible when the edge illumination is incident along a direction perpendicular to the direction of the channels.
For example, in many types of cultured quartæ, the etch channels tend to be along directions near the Z directionO These channels are most easily visible therefore with the light incident from the X direction. To help make the etch channels more visible without rotating the crystals, it is helpful to use for the edge illumination two lights incident at a right angle to each ; other, or a ring light. The etch channels appear as small, bright streaks which extend through the plate from one side to the other. The thicker the plate, the longer the streaks, and the deeper the plate has been etched, the brighter the streaks. To facilitate inspection for etch channels, it is desirable to etch the plates until a minimum of 16 ~m is removed from the plate thicknesses.
In the method of the invention, the etching is believed to be diffusion controlled. That is, for a lapped initial surface, the surface becomes increasingly smooth as the etching progresses. The rougher the initial surface, the rougher the final equilibrium surface, where the depleted surface layer of etching solution has uniform thickness everywhere, and the hills therefore, are no longer etched faster than the valleys. A smooth, undisturbed initial surface remains smooth ever after a large amount of material is removed by the etching. No signs of preferential etching along the different crystallographic axes appear on blanks which have been suitably polished mechanically prior to etching.
Many abrasives are suitable for use in the method of the invention including aluminum oxide, silicon carbide, diamond, cerium oxide, and ~884~2 zirconium oxide. Abrasives having different particle siæe distributions and/or shapes, produce different equilibrium surface topographies upon chemical polishing. The more uniformly disturbed the surface is prior to etching, the smoother will be the chemically polished surface. Accordingly, one should lap the plates with progressively finer abrasives prior to etch-ing. The final abrasive should be as fine as possible. It is highly desir-able to have the average particle size in the final abrasive 5 micrometers or less.
The temperature at which the etching is performed can vary from about 20 C to about 90 C. The higher the temperature, the faster the etch rate. A convenient etching temperature has been found to be 75C.
During etching, proper agitation, preferably in both directions, is important to assure that the crystals are etched uniformly on both sides.
Agitation also serves to minimize temperature gradients in the etch bath, which in turn minimizes plate to plate etch r~te variations.
After lapped plates are polished chemically, the surfaces are microscopically undulating, i.e9, the topographies consist of hills and valleys. In some high frequency applications, the undulations can scatter the acoustic waves and thereby degrade the resonators' Q. The undulations, however, can be removed by polishing the plates chemomechanically; that is, by combined chemical and mechanical action, for example, with cerium oxide and water, or with a colloidal silica polishing agent such as Syton~as manu-factured by Monsanto Company or Ludox as manufactured by DuPont Company.
The chemomechanical polishing can produce a smooth, undamaged surface which remains smooth upon further etching.
Example 2 AT-cut plano-plano quartz plates are final lapped with 1 um aluminum oxide abrasive to a frequency of 18.0 MHz. The plates are then etched in a saturated solution of ammonium bifluoride at 75C, to a frequency of 25.0 MHz. The surfaces at this point are microscopically undulating, with a surface roughness of about 0.12 ,um. The plates without etch channels are selected, and are polished chemomechanically with Ludox~until the ~ ~rq ~ f k 38~Z
undulations are removedO At the completion of chemomechanical polishing, the frequencies are about 26.0 MHz. The plates are then etched again in the saturated solution of ammonium bifluoride, at 75C, until a frequency of 50.3 MHz is reached. The surfaces have remained smoothO The fundamental mode 50 MHz resonators which are fabricated of these plates show no Q degra-dation.
Example 3 Resonators are prepared using chemically polished plates. All of the resonators are fundamental mode, in the range of 18 MHz to 22 MHæ. The plates are plano-plano, AT-cut, 6.4 mm diameter, and are made of vacuum swept cultured quartz. The depths of etch range from ~ f=-2-f ff to ~ f=22f ff where ~ f is the change in frequency in kHz, and f and ff are the initial and final frequencies, respectively, in MH . The surfaces prior to etching are final lapped with a 1 micrometer aluminum oxide abrasive. Subsequent to etching, the plates are free of etch channels. In the case of the highest Q resonators, the motional capacitances range from 12 fF to 13.5 fF, the resistances range from 3 ohms to 5 ohms, and the Q's range from 140,000 to 210,000 with no apparent Q degradation with depth of etching.
The method of the invention may allow manufacturers to stock lapped plates at only a few frequencies at each commonly used angle of cut and then etch the plates to the required frequencies as the need arises~ The method may also permit the manufacturing of miniature contoured high frequency resonators, since such small diamter resonators can now be contoured at con-ventional frequencies and then etched up to high frequencies. If a masking material which is resistant to the etch solution can be found, the method may also permit the fabrication of high frequency resonators and filters with the inverted mess structure.
In addition to the AT-cut, the etching technique described has also been shown to be capable of chemically polishing BT-cut quartz plates, and ST-cut quartz plates which are frequently used in surface acoustic wave devices.
z We wish it to be understood that we do not desire to be limited to the exact details as described, for obvious modifications will occur to a person skilled in the artO
High precision and high frequency quartz resonators, particularly those for high shock applications, require quartz plates whose surfaces are free of imperfections, such as scratches and pits. The most common method of achieving such surfaces has been mechanical polishing. The difficulty with mechanical polishing, however, has been its inability to produce defect-free surfaces, at the correct frequency, with a high yield. Moreover, as has been known since the last century, even when the polished surfaces appear to be free of defects when examined at high magnification, the surfaces contain hidden defects. These defects can be revealed by etching subsequent to polishing.
The general object of this invention is to provide a method of overcoming the difficulties associated with the mechanical polishing of quartz plates. A further object of the invention is to provide such a method that will produce a polished quartz crystal surface that is free of defects.
A particular object of the invention is to provide a method of polishing quarts chemically. Another object of the invention is to provide a method of making quart~ plates of great strength suitable for high shock resonator applica-tions.
The foregoing objects have now been obtained by a method involving lapping the quartz plate with an abrasive and then etching the quartz plate in a fluoride type etchant at least until the damage produced by lapping is removed.
Etching can be considered as a five step process in which the etchant must diffuse to the surface, be adsorbed, react chemically, and the resulting reaction products must then be desorbed and diffuse away from the surface. The etching rate may be limited by any one of these steps. In chemical polishing, the rate controlling step is generally the diffusion to or from the surface. Diffusion control means that, in particular, the rate at which a reaction takes place at the surface is higher than the rate of ,. ~
88~2 diffusion; that is, the etchant molecules at the surface react at a rate which is faster than the rate at which the concentration at the surface can be replenished by the diffusion of other etchant molecules. A depleted surface layer therefore exists, outside which the etchant concentration is uniform, but inside which the concentration decreases to near zero at the surface~
Under such conditions, the etching is principally determined not by the properties of the surface be~ing etched, but by the diffusion. It is clear that if a surface initially consists of hills and valleys, the probabil-ity of an etchant molecule diffusing to the top of a hill will be muchgreater than the probability of it diffusing to the bottom of a valley. The hills will therefore be etched faster than the valleys, and the surface will become increasingly smooth as the etching progresses.
Eventually, the surface becomes so smooth that the depleted layer can have a uniform thickness. From that point, the surface is etched evenly eve~ywhere, and the surface smoothness no longer improves with further etching.
Chemically polished surfaces are therefore not perfectly flat but are micro-scopically undulating.
Of the known etchants for quartz, particularly desirable are fluor-d ide type etchants such as aqueous solutions of ammonium bifluoride, and of mixtures of hydrogen fluoride and ammonium fluoride.
For a given etchant, the time required to produce a chemically polished surface is primarily a function of the etching bath temperature and of the particle size distribution of the lapping abrasive used for final lapping the quartz plates~ The higher the etching bath temperature, the more rapidly the etching takes place, and the coarser the abrasive, the greater the amount of material which must be removed by etching in order to produce chemically polished surfaces. The details of how the chemical polishing is influenced by the etching bath temperature, abrasive particle size, and other parameters is discussed in "Chemically Polished Quartz" by John R. Vig, John W. LeBus and Raymond L. Filler, published in the Proceedings of the 31st Annual Symposium on Frequency Control, 1-3 June 1977, and in Research and Development Technical Report ECoM-4548, November 1977. For the aluminum oxide abrasives evaluated, the etching should remove from the thickness of the plates an amount which is at least twice the average particle diameter in the final abrasive. For example, if a 3 ~m abrasive is used for final lapping the quartz plates, the chemical polishing process should remove at least 6 um from the plate thicknesses in order to produce surfaces which can be described as chemically polished.
The quality of quartz used is another important consideration.
When chemical polishing is attempted on groups of plates made of several different cultured quartz varieties, it is found that for many of the plates the etching produces large numbers of undesirable etch pits and etch channels.
This is particularly true for plates made of relatively low Q, fast grown materials. When plates made of natural quartz or swept (i.e., "electrolyzed") cultured quartz are used, the incidence of etch pits and etch channels is far fewer. Of the cultured quartz varieties, the one variety which has been vacuum swept in accordance with the method described in U.S. Patent No.
3,932,777 issued January 13, 1976 to James Claude King for "Vacuum Electrolysis ; of Quartz," has the lowest incidence o etch channelsO
~-~ AT-cut plano-plano natural quartz plates are final lapped with a 3 micrometer aluminum oxide abrasive and then etched in a saturated solution of ammonium bifluoride at an etch bath temperature of 75C. Chemically polished surfaces are produced in less than 30 minutes.
The chemical polishing process can remove large amounts of material from lapped plates while simultaneously producing an improved surface finish, without producing shifts in the angles of cuto The process will also produce plates of great strength, which is particularly important for high shock applications.
The particular apparatus used to carry out the etching method is not critical. One particular apparatus that can be conveniently used includes a 1000 ml glass outer beaker containing water and a floating 400 ml Teflo ~
beaker, which in turn contains the saturated ammonium bifluoride solution. A
temperature controlled stirring hot plate with a thermistor sensor can be 38g~;2 used to control the temperature of the water surrounding the Teflon~beaker.
The temperature of the ammonium bifluoride solution can thus be controlled to about + 105C. A thick Teflon disc with a diameter slightly larger than the outer beaker is used as a cover to minimize evaporation from the beakers.
The weight of this disc also serves to push the inner beaker down to assure that the fluid level in the inner beaker is always about 3 cm below the water level in the outer beaker. A hole through the center of the disc permits the agitation of crystals during etching.
The quartz plates are loosely held in a Teflon~jig which is designed to assure that only point contacts exist between the jig and the plates. The plates are agitated slowly in both directions by means of a constant speed electric motor. The motor is set to rotate the etching jig through an angle of approximately 360 before reversing direction. The rate of agitation is about 5 cycles per minute.
A convenient etching procedure involves first the preparation of a saturated solution of ammonium bifluoride in a Teflon container. The ammonium bifluoride (NH4F~HF) flakes are mixed with distilled water, and the solution heated to the desired tempera-ture. The amount of NH4FHF used is such that after the solution reaches the equilibrium temperature, some undis-solved flakes remain in the bottom of the container throughout the etchingprocess. (The solubility of NH4F-HF in water increases from 61 gms per 100 ml of solution at 60 C to 86 gms per 100 ml at 100 C.) The solution prepara-tion and the etching are performed under a vented hood to prevent inhalation of the vapors from the etching bath. Then, the plates are cleaned thoroughly.
To assure that the surfaces are etched evenly, it is particularly important to remove all contaminants such as waxes and greases, which may be impervious to the etchant. Any number of cleaning techniques may be used, as long as contaminants that are impervious to the etchant are removed. One method which has consistently produced good results involves the immersion of the blanks in ethyl alcohol in a Petri dish the bottom of which is lined with open cell urethane foam, and then scrubbing both sides of each blank with a -foam swab. The crystal plates are then placed into the slots in the etching ~1%~3842 fixture and agitated ultrasonically in a detergent solution, then rinsed thoroughly in distilled water. A second satisfactory cleaning technique involves plasma cleaning in an oxygen plasma followed by a thorough rinse in distilled water.
From the final rinse the plates are transferred, while wet, into the etching bath, and are shaken vigorously to make sure that there are no trapped air bubbles in the etching fixture. During etching, the plates are agitated in both directions to assure even etching of both sides.
After the plates reach the desired frequency, the etching fixture is removed rapidly from the etch bath and is immersed immediately into a container of hot water, given a thorough rinse under running hot water, then agitated ultrasonically in hot water, then given another rinse in running distilled water, then dried by spin drying. A thorough rinse is important in order to remove all residues of the etchant.
The plates are usually etched to the desired frequency by first measuring the etch rates as a function of temperature, selecting a suitable temperature between 20C and 90C, calculating the etching time required to reach the desired frequency, and etching the plates for a time slightly less than the time calculated. The reason for etching for less than the time calculated is that experience has shown that there are slight variations from plate to plate in the rates at which quartz plates etch at a gi~en temperature.
In practice, therefore, in order to etch a group of quartz plates to a narrow range about a target frequency, an iterative procedure is often necessaryO
That is, the plates are etched for a time slightly less than the time calcula-ted, then the plates are rinsed, dried and the frequencies are measured.
Those plates whose frequency is within the target range are removed from the etching fixture, a new etching time is calculated for the remaining plates, the plates are etched again, rinsed, dried, measured, and the process is repeated until all the plates in the group have been etched to the proper frequency range.
The plates are then inspected under a microscope for uniformity of etch, and for defects such as scratch marks, etch pits and etch channels.
389L~
The inspection of etched plates is performed under a microscope at about 40 X magnification, with the light incidence perpendicular to the axis of the microscope, and with using a black background. First, the plate is inspected for surface irregularities such as scratch marks, pits and twinned areas by tilting the plate so as to reflect light into the micro-scope. The crystal plate is then inspected for etch channels by holding it so that the light incidence is in the plane of the plate (i.e., edge illumin-ation). The etch channels are most visible when the edge illumination is incident along a direction perpendicular to the direction of the channels.
For example, in many types of cultured quartæ, the etch channels tend to be along directions near the Z directionO These channels are most easily visible therefore with the light incident from the X direction. To help make the etch channels more visible without rotating the crystals, it is helpful to use for the edge illumination two lights incident at a right angle to each ; other, or a ring light. The etch channels appear as small, bright streaks which extend through the plate from one side to the other. The thicker the plate, the longer the streaks, and the deeper the plate has been etched, the brighter the streaks. To facilitate inspection for etch channels, it is desirable to etch the plates until a minimum of 16 ~m is removed from the plate thicknesses.
In the method of the invention, the etching is believed to be diffusion controlled. That is, for a lapped initial surface, the surface becomes increasingly smooth as the etching progresses. The rougher the initial surface, the rougher the final equilibrium surface, where the depleted surface layer of etching solution has uniform thickness everywhere, and the hills therefore, are no longer etched faster than the valleys. A smooth, undisturbed initial surface remains smooth ever after a large amount of material is removed by the etching. No signs of preferential etching along the different crystallographic axes appear on blanks which have been suitably polished mechanically prior to etching.
Many abrasives are suitable for use in the method of the invention including aluminum oxide, silicon carbide, diamond, cerium oxide, and ~884~2 zirconium oxide. Abrasives having different particle siæe distributions and/or shapes, produce different equilibrium surface topographies upon chemical polishing. The more uniformly disturbed the surface is prior to etching, the smoother will be the chemically polished surface. Accordingly, one should lap the plates with progressively finer abrasives prior to etch-ing. The final abrasive should be as fine as possible. It is highly desir-able to have the average particle size in the final abrasive 5 micrometers or less.
The temperature at which the etching is performed can vary from about 20 C to about 90 C. The higher the temperature, the faster the etch rate. A convenient etching temperature has been found to be 75C.
During etching, proper agitation, preferably in both directions, is important to assure that the crystals are etched uniformly on both sides.
Agitation also serves to minimize temperature gradients in the etch bath, which in turn minimizes plate to plate etch r~te variations.
After lapped plates are polished chemically, the surfaces are microscopically undulating, i.e9, the topographies consist of hills and valleys. In some high frequency applications, the undulations can scatter the acoustic waves and thereby degrade the resonators' Q. The undulations, however, can be removed by polishing the plates chemomechanically; that is, by combined chemical and mechanical action, for example, with cerium oxide and water, or with a colloidal silica polishing agent such as Syton~as manu-factured by Monsanto Company or Ludox as manufactured by DuPont Company.
The chemomechanical polishing can produce a smooth, undamaged surface which remains smooth upon further etching.
Example 2 AT-cut plano-plano quartz plates are final lapped with 1 um aluminum oxide abrasive to a frequency of 18.0 MHz. The plates are then etched in a saturated solution of ammonium bifluoride at 75C, to a frequency of 25.0 MHz. The surfaces at this point are microscopically undulating, with a surface roughness of about 0.12 ,um. The plates without etch channels are selected, and are polished chemomechanically with Ludox~until the ~ ~rq ~ f k 38~Z
undulations are removedO At the completion of chemomechanical polishing, the frequencies are about 26.0 MHz. The plates are then etched again in the saturated solution of ammonium bifluoride, at 75C, until a frequency of 50.3 MHz is reached. The surfaces have remained smoothO The fundamental mode 50 MHz resonators which are fabricated of these plates show no Q degra-dation.
Example 3 Resonators are prepared using chemically polished plates. All of the resonators are fundamental mode, in the range of 18 MHz to 22 MHæ. The plates are plano-plano, AT-cut, 6.4 mm diameter, and are made of vacuum swept cultured quartz. The depths of etch range from ~ f=-2-f ff to ~ f=22f ff where ~ f is the change in frequency in kHz, and f and ff are the initial and final frequencies, respectively, in MH . The surfaces prior to etching are final lapped with a 1 micrometer aluminum oxide abrasive. Subsequent to etching, the plates are free of etch channels. In the case of the highest Q resonators, the motional capacitances range from 12 fF to 13.5 fF, the resistances range from 3 ohms to 5 ohms, and the Q's range from 140,000 to 210,000 with no apparent Q degradation with depth of etching.
The method of the invention may allow manufacturers to stock lapped plates at only a few frequencies at each commonly used angle of cut and then etch the plates to the required frequencies as the need arises~ The method may also permit the manufacturing of miniature contoured high frequency resonators, since such small diamter resonators can now be contoured at con-ventional frequencies and then etched up to high frequencies. If a masking material which is resistant to the etch solution can be found, the method may also permit the fabrication of high frequency resonators and filters with the inverted mess structure.
In addition to the AT-cut, the etching technique described has also been shown to be capable of chemically polishing BT-cut quartz plates, and ST-cut quartz plates which are frequently used in surface acoustic wave devices.
z We wish it to be understood that we do not desire to be limited to the exact details as described, for obvious modifications will occur to a person skilled in the artO
Claims (23)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of treating a quartz plate selected from the group consis-ting of an AT-cut quartz plate, a BT-cut quartz plate and an ST-cut quartz plate to produce a chemically polished quartz crystal surface of great strength that is free from etch channels comprising lapping the quartz plate with an abrasive, etching the lapped quartz plate in a fluoride type etchant an amount that removes from the plate a thickness that is at least twice the average particle diameter in the final lapping abrasive, identifying a defective quartz plate that contains etch channels by edge illumination along the X
direction of the plate, and selecting that plate that is free from etch channels for high shock resonator applications.
direction of the plate, and selecting that plate that is free from etch channels for high shock resonator applications.
2. Method according to claim 1 wherein the fluoride type etchant is selected from the group consisting of an aqueous solution of ammonium bifluor-ide, and mixtures of aqueous solutions of hydrogen fluoride and ammonium fluoride.
3. Method according to claim 2 wherein the fluoride type etchant is an aqueous solution of ammonium bifluoride.
4. Method according to claim 2 wherein the fluoride type etchant is a mixture of aqueous solutions of hydrogen fluoride and ammonium fluoride.
5. Method according to claim 1 wherein the lapped quartz plate is etched in the fluoride type etchant at about 20°C to about 90°C.
6. Method according to claim 1 wherein the abrasive is selected from the group consisting of aluminum oxide, silicon carbide, diamond, cerium oxide, and zirconium oxide.
7. Method according to claim 6 wherein the abrasive is aluminum oxide.
8. Method according to claim 6 wherein the abrasive is silicon carbide.
9. Method according to claim 1 wherein the quartz plate is agitated during etching.
10. Method according to claim 1 wherein the quartz plate is cleaned prior to etching until all contaminants which are impervious to the etchant are removed.
11. Method according to claim 1 wherein the quartz plate is thoroughly rinsed after etching to remove all residues of the etchant.
12. Method of treating an AT-cut plano-plano natural quartz plate to produce a chemically polished quartz crystal surface of great strength that is free from etch channels comprising final lapping the quartz plate with 3 micron aluminum oxide abrasive, etching the lapped plate in a saturated aqueous solution of ammonium bifluoride at an etching bath temperature of about 75°C
for about 30 minutes, identifying a defective quartz plate that contains etch channels by edge illumination along the X direction of the plate, and select-ing that plate that is free from etch channels for high shock resonator appli-cations.
for about 30 minutes, identifying a defective quartz plate that contains etch channels by edge illumination along the X direction of the plate, and select-ing that plate that is free from etch channels for high shock resonator appli-cations.
13. Method according to claim 12 wherein the quartz plate is agitated during etching.
14. Method according to claim 12 wherein the quartz plate is cleaned prior to etching until all contaminants which are impervious to the etchant are removed.
15. Method according to claim 12 wherein the quartz plate is thorough-ly rinsed after etching to remove all residues of the etchant.
16. Method according to claim 1 wherein the quartz plate is final lapped with a 1 micrometer aluminum oxide abrasive, and wherein the final lapped quartz plate is etched to a range from .DELTA.f=2f0ff to .DELTA.f=22f0ff where .DELTA.f is the change in frequency in kHz and f0 and ff are the initial and final frequencies, respectively, in MHz.
17. Method according to claim 1 wherein the quartz plate is made of a material selected from the group consisting of natural quartz and swept cultured quartz.
18. Method according to claim 1 wherein the quartz plate is AT-cut.
19. Method according to claim 1 wherein the quartz plate is BT-cut.
20. Method according to claim 1 wherein the quartz plate is ST-cut.
21. Method of treating an AT-cut plano-plano natural quartz plate to produce a chemically polished quartz crystal surface of great strength that is free from etch channels, said method consisting of the steps of (a) final lapping the quartz plate with a 1 micron aluminum oxide abrasive, (b) thoroughly cleaning the plate, (c) etching the plate in a saturated aqueous solution of ammonium bifluoride while agitating the plate in both directions to assure even etching on both sides, (d) etching the plate until an amount of material is removed from the plate such that the thickness of the plate is reduced by an amount which is equal to at least twice the average particle size in the final lapping abrasive, (e) removing the plate from the etching solution after the desired frequency is reached and thoroughly rinsing the plate to remove all residues of the etchant, and (f) identifying a defective quartz plate that contains etch channels by edge illumination along the X direction of the plate, and selecting that plate that is free from etch channels for high shock resonator applications.
22. Method according to claim 1 wherein the quartz plate is polished chemomechanically after etching and the quartz plate then etched again in a fluoride type etchant.
23. Method of treating a quartz plate to produce a chemically polished quartz crystal surface of great strength that is free from etch channels, comprising lapping the quartz plate with an abrasive, etching the lapped quartz plate in a fluoride type etchant an amount such that a minimum of 16 micro-meters is removed from the plate thickness, identifying a defective quartz plate that contains etch channels by edge illumination along the X direction of the plate, and selecting that plate that is free from etch channels for high shock resonator applications.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US91911378A | 1978-06-26 | 1978-06-26 | |
| US919,113 | 1986-10-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128842A true CA1128842A (en) | 1982-08-03 |
Family
ID=25441529
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA321,713A Expired CA1128842A (en) | 1978-06-26 | 1979-02-09 | Method of treating a quartz plate |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1128842A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112743446A (en) * | 2020-12-29 | 2021-05-04 | 北京无线电计量测试研究所 | Shape modification method for quartz crystal square piece |
| CN117921451A (en) * | 2024-03-25 | 2024-04-26 | 宁波云德半导体材料有限公司 | Quartz ring and processing technology thereof |
-
1979
- 1979-02-09 CA CA321,713A patent/CA1128842A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112743446A (en) * | 2020-12-29 | 2021-05-04 | 北京无线电计量测试研究所 | Shape modification method for quartz crystal square piece |
| CN112743446B (en) * | 2020-12-29 | 2022-05-20 | 北京无线电计量测试研究所 | Shape modification method for quartz crystal square plate |
| CN117921451A (en) * | 2024-03-25 | 2024-04-26 | 宁波云德半导体材料有限公司 | Quartz ring and processing technology thereof |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4267013A (en) | Method for dry-etching aluminum and aluminum alloys | |
| US4274907A (en) | Method of chemically polishing a doubly rotated quartz plate | |
| KR19980703246A (en) | Single-etch Stop Process for Fabrication of Silicon Insulator Wafers | |
| US4244775A (en) | Process for the chemical etch polishing of semiconductors | |
| KR100979691B1 (en) | Process for producing polished glass substrate | |
| US5472370A (en) | Method of planarizing polycrystalline diamonds, planarized polycrystalline diamonds and products made therefrom | |
| JP2000507304A (en) | Composition for cleaning and etching electronic displays and substrates | |
| CN106826408A (en) | A kind of lbo crystal polishing method based on crystal oxidant | |
| Vondeling | Fluoride-based etchants for quartz | |
| TW483079B (en) | Method for the detection of processing-induced defects in a silicon wafer | |
| US6984334B2 (en) | Method of manufacturing optical element | |
| US2461840A (en) | Method of forming low-reflecting surfaces on optical elements | |
| CA1128842A (en) | Method of treating a quartz plate | |
| US5968849A (en) | Method for pre-shaping a semiconductor substrate for polishing and structure | |
| TW583149B (en) | Quartz article having sand blast-treated surface and method for cleaning the same | |
| JP2001098298A (en) | Cleaning liquid for aluminosilicate glass base or ceramic glass base and method for cleaning thereof | |
| JP3686910B2 (en) | Etching method of silicon wafer | |
| CA1168134A (en) | Method of chemically polishing both sides of an sc- cut quartz crystal plate | |
| US3860467A (en) | Method of etching a surface of a substrate comprising LITAO{HD 3 {B and chemically similar materials | |
| Davisson | Surface finishing of alkali halides | |
| JP2001046991A (en) | Method for washing glass substrate | |
| JPH0795541B2 (en) | Processing method | |
| Wegner et al. | Chemical etching of dislocations in forsterite | |
| Zhao et al. | Diamond film polishing with argon and oxygen ion beams | |
| JP2002329690A (en) | Semiconductor wafer manufacturing method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |