ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 47, no. 5, september 2000 1199

New Seed Geometry for Growth of LowDislocation Synthetic Quartz

Armando H. Shinohara, Member, IEEE, Marcos C. Iano, and Carlos K. Suzuki, Member, IEEE

Abstract—Amethod to grow low dislocation density syn-thetic quartz by using a special cutting seed geometry isreported. With this method, a relatively high dislocationdensity seed material is allowable. For such a purpose, aseed of new geometry was prepared and grown in a stan-dard hydrothermal growth condition, long in Y-directionwith multiple V-shaped notches made on Z-face. The char-acterization study was conducted by X-ray topography.The results showed new growth regions, equal to the

numbers of V-shaped notches made in the seed and usuallynot found in the conventional Y- and Z-bar synthetic quartzcrystals. Each new growth region is composed of two sec-tors of distinct textures. Soon they disappear due to theirhigh growth velocity, and they are replaced by the so-calledZ-region. However, the growth process of these new sectorsgrown perpendicular to the internal faces of the V-shapednotches played an important role in inhibiting the propa-gation of the dislocation originally present in the seed intothe grown Z-region.

I. Introduction

Synthetic quartz growth for resonators is performedby using seed plates of Y-bar or Z-plate extracted from

Z-region with the longest in the Y-direction. The crystalgrown on such seed geometry is suitable for device prepa-ration. The advent of cellular and satellite networks ofhigh frequency, small size, and cost-effective resonator aredriving forces to improve the quality of quartz material interms of crystalline perfection. It is well-known that seedquality is one of the main factors that affects the finalquality of synthetic quartz crystal grown by hydrother-mal technique [1], [2]. Possible defect groups in quartz arepoint, line, plane, and volume defects [3]. In particular,line defects such as dislocations have a good correlationwith the quartz crystal performance [4], [5]. Several linedefects are generated from the surface of the seed crys-tal due to the damaged layers and solid inclusions formedin seed veil. Furthermore, line defects also are generatedfrom the solid inclusions incorporated during the growthprocess and propagate radially from a point and nearlyparallel to the direction of growth. However, these originsof line defects can be controlled with careful seed prepa-ration and doing everything possible to avoid solid inclu-sions in the grown material. For example, lining the auto-

Manuscript received July 6, 1999; accepted March 14, 2000. Theauthors thank FAPESP, Capes, and CNPq for the financial support.A. H. Shinohara is with the Department of Mechanical Engineer-

ing, Center of Technology and Geosciences, Federal University ofPernambuco, Recife-PE, Brazil (e-mail: shinohara@demec.ufpe.br).M. C. Iano and C. K. Suzuki are with the University of Campinas,

School of Mechanical Engineering, Department of Materials Engi-neering, Campinas-SP, Brazil.

clave with noble metals. However, line defects present inthe seed crystal propagate and extend far enough to reachthe crystal surface. Increasing use of photolithography inquartz component manufacture, etch channel and disloca-tion densities, and etch pits formation play a critical role.So far, several investigations have been conducted to im-prove the quality of synthetic quartz crystal [1], [6]–[12].One of the methodologies is the use of high quality natu-ral quartz as a seed crystal. The difficulty of using naturalquartz is that it is becoming very rare and expensive, in-volving a very specialized technique for the inspection ofbig blocks. The technique to prepare Z-cut seeds from the+X region of synthetic quartz has serious limitations interms of the limited size of +X region [7]–[9]. By apply-ing the frame seed method [9], it is possible to get a large+X region, but it is too time consuming. In our previousstudies [13], [14] on synthetic quartz crystals grown on S-,ξ- , and intermediary-bar seeds, several new growth re-gions usually not present in the Y- and Z-bars syntheticquartz crystals have been observed. Even though a highdislocation seed was used, the investigation revealed a po-tentiality to grow a synthetic quartz crystal with a very lowdislocation density. Based on those results, we succeededin growing a synthetic quartz crystal with annihilated dis-location in the large Z-region.

II. Materials and Methods

In the present study, the Z-region of a Z-bar syntheticquartz crystal containing about 100 dislocations/cm2 waschosen to be the seed material. Using a conventional dia-mond saw wheel, multiple V-shaped cuts with a cutting-angle of 90◦ and 2.5 mm in depth were made on one ofthe Z faces as schematically shown in Fig. 1. After theV-shaped cutting process, the seed was polished using sil-icon carbide powders of #320 and #800 mesh and etchedin hydrofluoric acid (40% in solution) for 30 minutes toeliminate the stress introduced by the preparation process.The hydrothermal growth was conducted in an experimen-tal autoclave using the growth conditions listed in Table I.

The characterization study was made/conducted by anX-ray double-crystal topography of nonparallel (+,−) set-ting [15] using the Laue case (transmission geometry) andCuKα radiation monochromated by a highly asymmetricSi(111) monochromator with asymmetric factor 1/b = 20.X-ray radiation was generated in a sealed-off fine-focusX-ray tube of 1.5 kW coupled to the DMax-2200 systemequipment by Rigaku International Corp. Sample align-

0885–3010/$10.00 c© 2000 IEEE

1200 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 47, no. 5, september 2000

Fig. 1. Schematic diagram of a seed with V-shaped notches and cut-ting of 90◦ made on Z-face.

TABLE ISynthetic Quartz Crystal Growth Condition.

Growth rate 0.68 mm/dGrowth temperature 356◦CPressure 1300 kgf/cm2

Solution 3.8% NaOHGrowth period 39 dAutoclave dimension φ200 mm× 3.5 m

ment for X-ray topographic imaging was conducted witha Kohzu Seiki precision goniometer model KTG-11P. Thissetting is slightly dispersive, but it helps to obtain a verysharp X-ray topographic image with high sensitivity withrespect to the lattice distortions. Samples for X-ray topo-graphic imaging were cut perpendicularly to the Y-axis,and the thickness was adjusted to have µt between 3.0 to3.5 (where µ and t are linear absorption coefficient andthe sample thickness, respectively) to give a better con-trast due the intermediary image formation of dynamicaland kinematical diffraction effects.

III. Results and Discussion

Fig. 2 shows an X-ray topographic image of syntheticquartz crystal grown on a seed with two V-shaped notchesand two oblique faces relative to the Z face. Each newregion grown from the V-shaped cut is composed of twosectors with distinct textures, which are separated by theplane of fluid inclusion. They are indicated in Fig. 2 topand bottom. In regard to the new growth sectors, for con-venience called R1, R2, VR11, VR12, VR21, and VR22 sec-tors, as schematically shown in Fig. 2(bottom), they grewperpendicular to the growing surface and met one to an-other at the plane of fluid inclusion, forming a square-like shape. The texture of growth sectors is dependent on

Fig. 2. (top) X-ray topographic image of Y-cut sample from a syn-thetic quartz crystal with V-shaped notches obtained using asymmet-ric diffraction planes {2020}. (bottom) Schematic diagram of Y-cutsample with several new growth sectors in Z-direction.

the growth direction. So, the textures of sectors VR12 andVR22 are similar to the sector R1. However, the texturesof sectors VR11 and VR21 are similar to the sector R2.In order to have a general view of the effect of growthsurface orientation on the texture, Fig. 3 shows the X-raytopographic image of a synthetic quartz crystal grown ona cylindrical seed. Although the cylindrical seed has allthe growing surfaces parallel to the Y-axis, only eight newgrowth regions have been observed. However, six of themare replaced by the typical growth regions found in a stan-dard synthetic quartz crystal. Even though the growth ofsynthetic quartz crystals from V-shaped cut and cylindri-cal seeds had been conducted in the different run, the tex-ture of growth sector appeared quite similar, for example,VR12 sector is similar to CR12 sector so is VR11 and CR41.

The region grown from the V-shaped notch is composedof a plane of fluid inclusion with two phases (gas andliquid) formed along the internal vertex of the V-shapednotch. The formation mechanism of fluid inclusion is not

shinohara et al.: new seed geometry and synthetic quartz 1201

Fig. 3. X-ray topographic image of Y-cut sample of a synthetic quartz crystal grown from cylindrical seed. This image was obtained usingasymmetric diffraction planes {2020}. Six new growth sectors appear at the first stage of growth, and they soon are replaced by the Z-regions.

well understood yet, but the experiments showed that sizeof such plane depended on the depth and cutting-angleof the V-shaped notch made on the Z face. For example,the V-shaped notch with cutting angle of 90◦ and 2.5 mmand 5 mm in depth, the size of the plane of fluid inclusionappeared to be 5 mm and 9.5 mm, respectively. However,for cutting angles of 25◦, 45◦, and 60◦ and constant depthof 2.5 mm, almost a linear correlation was found, but theresults showed an inverse relationship between the cuttingangle and the size of plane of fluid inclusion, as shownin Fig. 4. This effect can be explained by the fact thatthe growth velocity in the Y-direction is practically neg-ligible in the usual hydrothermal growth condition. For asmaller cutting angle, the internal surface of the V-shapedcut becomes close to the Y planes {1010}. So, the growthvelocity appeared to be relatively slow, increasing the heal-ing time and, as a consequence, forming a larger plane offluid inclusion. Furthermore, after a complete trapping ofthe fluid inclusion in the synthetic quartz, a new and nar-row growth region was generated and propagated from theedge of each fluid inclusion. As can be observed, the lengthof the tail-like regions appeared to be independent of thedepth and cutting angle parameters. Moreover, such re-gions disappeared after a certain growth period.

Line defects present in seed are the main sources ofline defects found in the grown Z-region. They propagatethrough the flat growth surface and extend in a rectilinear

Fig. 4. A correlation between length of fluid inclusion plane andcutting angles of V-shaped notches with 2.5 mm depth in hydrother-mally grown synthetic quartz crystal.

manner almost parallel to the Z-axis direction, as shownin the X-ray topographic image (Fig. 3). However, the Z-region grown from V-shaped notches is almost free of dis-location. Furthermore, as the growth sector occurs per-pendicular to a growth face in the hydrothermal method,na asymmetric (oblique) surface made on Z-face {0001}

1202 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 47, no. 5, september 2000

close to the edge of the seed induced the appearance ofnew growth sectors with high growth velocity and tex-tures similar as also was observed in a our previous study[14], [16]. As observed in the present X-ray topographic im-age, this kind of oblique surface is believed to have inducedan abrupt change in the propagation direction of disloca-tion that is almost perpendicular to the growth surface.In this sense, the V-shaped notch with two asymmetricsurfaces made 90◦ one to another played a very importantrole in trapping the dislocations into these newly grownsectors.

IV. Conclusions

The following conclusions can be obtained from thepresent study.

Most dislocations are generated from the seed. Eventhough the mechanism of origin and propagation of dislo-cations in synthetic quartz is quite complex, Z-region witha very low dislocation density can be obtained with theV-shaped notch method because the growth on Z-surfaceseeds with such special cutting resulted in annihilation ofdislocations with the appearance of new and complex re-gions. Fluid inclusion and defect trail are created at eachnotch by a mechanism not yet understood, and the depthand cutting angle of V-shaped notch influenced the result-ing fluid inclusion in terms of length and size. A system-atic investigation on the V-shaped notch parameters suchas cutting angle, depth, and superficial finishing can beuseful for a better control of propagation of dislocation insynthetic quartz crystal grown from a low quality seed.

Acknowledgments

We would like to thank Mr. Y. Mikawa, Dr. Y. Banno,and Mr. M. Hatanaka of Fine Crystal Co., Ltd. for theirassistance in growing the synthetic quartz crystal and con-tinuous encouragements, and Professor J. S. Rohatgi ofUFPE – Federal University at Pernambuco for the criticalreading of this manuscript.

References

[1] R. L. Barns, P. E. Freeland, E. D. Kolb, R. Laudise, and J. R.Patel, “Dislocation-free and low-dislocation quartz prepared byhydrothermal crystallization,” J. Crystal Growth, vol. 43, pp.676–686, 1978.

[2] S. Taki, “Improvement of growth process and characterizationof quartz crystals,” Prog. Crystal Growth Charact., vol. 23, pp.313–339, 1991.

[3] W. Hanson, “Transmission X-ray topography of single crystalusing white beam synchrotron radiation,” in Proc. IEEE Int.Freq. Contr. Symp., 1987, p. 228.

[4] J. Asahara, K. Takazawa, E. Yazaki, J. Okuda, and N. Asanuma,“Defects in synthetic quartz crystals and their influence on theelectrical characteristics of quartz crystal resonators,” in Proc.28th Annu. Symp. Freq. Contr., 1974, pp. 211–215.

[5] J. C. Brice, “Crystals for quartz resonators,” Rev. Modern Phys.,vol. 57, pp. 105–146, 1985.

[6] A. F. Armington and J. F. Balascio, “The growth of high purity,low dislocation quartz,” in Proc. 38th Annu. Freq. Contr. Symp.,1984, pp. 3–7.

[7] A. Zarka, L. Lin, and M. Buison, “Influence de la LocalisationSectorielle du Germme sur la Qualite Crystalline de Quartz deSynthese,” J. Crystal Growth, vol. 54, p. 398, 1981.

[8] A. Zarka, L. Lin, and M. Buison, “Influence du Germe surla Densite de Dislocations Produites lors de la Croissance deQuartz de Synthese,” J. Crystal Growth, vol. 57, p. 466, 1982.

[9] Y. Mikawa, M. Hatanaka, and Y. Banno, “New technique todecrease dislocations in synthetic quartz crystal,” in Proc. 1999Joint Meeting of EFTF-IEEE IFCS, pp. 773–776, 1999.

[10] S. Ishigami, M. Sato, F. Uchiyama, K. Agatsuma, and K.Tsukamoto, “Growth of high quality quartz crystal and its appli-cation to temperature sensors,” in Proc. IEEE Int. Freq. Contr.Symp., 1994, pp. 99–106.

[11] J. F. Balascio and T. Lind, “The growth of piezoelectric alphaquartz crystals,” Curr. Opinion Solid State Mater. Sci., vol. 2,pp. 588–592, Oct. 1997.

[12] C. K. Suzuki, M. S. Tanaka, and A. H. Shinohara, “Growthand characterization of optical grade synthetic quartz,” in Proc.IEEE Int. Freq. Contr. Symp., 1996, pp. 78–83.

[13] A. H. Shinohara, “Influence of aluminium impurity in the syn-thetic quartz technology,” master thesis, School of MechanicalEngineering, University of Campinas, 1990.

[14] A. H. Shinohara and C. K. Suzuki, “Study of S- and ξ-barssynthetic quartz by X-ray topography,” in Proc. IEEE Int. Freq.Contr. Symp., 1996, pp. 71–77.

[15] K. Kohra, H. Hashizume, and J. Yoshimura, “X-ray diffractiontopography utilizing double-crystal arrangement of (+,+) ornon-parallel (+,−) setting,” Jpn. J. Appl. Phys., vol. 9, pp.1029–1038, 1970.

[16] F. Iwasaki, A. H. Shinohara, H. Iwasaki, and C. K. Suzuki,“Effect of impurity segregation on crystal morphology of Y-barsynthetic quartz,” Jpn. J. Appl. Phys., vol. 29, pp. 1139–1142,June 1990.

Armando Hideki Shinohara (M’96) wasborn in Brazil in 1962. He earned a bachelordegree in mechanical engineering from Camp-inas University, Campinas, Sao Paulo State,Brazil, in 1986, and a doctorate degree inengineering from Tohoku University, Sendai,Miyagi Prefecture, Japan, in 1994. After that,he spent 1 1/2 years, 1994 to 1995, at KimuraMetamelt Project, Japan Science Corporationas visiting scientist working on the structureof molten silicon by EXAFS. From 1995 to1998, he became an associate researcher at

the Department of Material Engineering, Campinas University andworked in the characterization of natural and synthetic quartz crys-tals, silica glass, and diamond crystals by X-diffraction and scat-tering techniques. His present position is associate professor at theDepartment of Mechanical Engineering, The Federal University atPernambuco, Brazil, since 1998.

His main research field of interest is R&D in the growth of syn-thetic quartz of high crystalline perfection from low-grad natural andsynthetic quartz crystals.

Marcos Chogi Iano was born in Flora RicaCity, Brazil, March 20, 1971. He earned aB.Sc. degree in mechanical engineering fromthe Technological Faculty of Sorocaba, SaoPaulo, Brazil. He is a postgraduate studentat the Department of Materials Engineering,Faculty of Mechanical Engineering, State Uni-versity of Campinas, Brazil.

shinohara et al.: new seed geometry and synthetic quartz 1203

Carlos Kenichi Suzuki (M’96) was bornin Sao Paulo City, Brazil, June 19, 1945. Heearned a B.Sc. degree in physics from the SaoPaulo University and a Ph.D. degree in ap-plied physics engineering from the Universityof Tokyo. He is involved in the technology ofseed for synthetic quartz and the X-ray imag-ing by diffraction topography.

He is a professor of materials engineer-ing and Head of the Laboratory of IntegratedQuartz cycle of the State University of Camp-inas, Brazil. He is a member of the IEEE, the

Japanese Society of Synchrotron Radiation Research, and the Brazil-ian Ceramic Society. He received a special award of the BrazilianCeramic Society as the best technical contribution of the year.