Flat Shoulder Congruent Lithium Niobate Crystals Grown by the Czochralski Method

doi:10.15541/jim20230067

Abstract

Abstract:

The shoulder of the crystals grown by the Czochralski method is generally inclined, leading to poor quality and difficult processing, which then result in low utilization rate of the grown crystal. Take congruent lithium niobate (CLN) crystal as an example, this study used numerical simulation and experimental method to investigate the thermal field and growth process of flat shoulder crystal growth by the Czochralski method which can well acceptedly overcome the above problems. The result shows that the shape of the solid-liquid interface should be convex toward melt at the stage of shouldering. Temperature gradient near solid-liquid interface can be reduced by lowering the after-heater position (10 mm) to avoid the formation of polycrystalline. Control of the shouldering speed is the main way while control heating power is the accurate way to ensure the trend of shouldering. Accelerating the speed at the initial stage of shouldering (ϕ≤30 mm) and slowdown the speed at the middle and later stage of shouldering (ϕ≥35 mm) can shorten the period of shouldering and avoid defect inclusion. The pulling rate (0-1.5 mm/h) can be changed rapidly (1.5-2 h) without affecting the trend and quality of shouldering by adjusting power with a small amplitude (Δt=10 min, ∆v= 0.2 mm/h). By using these adjusting ways to thermal field and growth process, a series of 3-inch (1 inch=25.4 mm) flat shoulder CLN crystals with good optical homogeneity have been successfully grown.

Key words: lithium niobate crystal, thermal field design, flat shoulder crystal, Czochralski method, crystal growth

CLC Number:

O782

QIN Juan, LIANG Dandan, SUN Jun, YANG Jinfeng, HAO Yongxin, LI Qinglian, ZHANG Ling, XU Jingjun. Flat Shoulder Congruent Lithium Niobate Crystals Grown by the Czochralski Method[J]. Journal of Inorganic Materials, 2023, 38(8): 978-986.

Figures/Tables 9

Fig. 1 Schematic diagram of crystal growth system

Fig. 2 Photos of series flat shoulder CLN crystals grown by different methods (a) Non-optimized thermal field and growth process, as CLN-N1; (b) Optimized thermal field, as CLN-N2; (c-g) optimized thermal field and growth process, as CLN-Y1, CLN-Y2, CLN-Y3, Fe:CLN-Y4 and Er:CLN-Y5, respectively

Table 1 Growth parameters of flat shoulder CLN

Crystal	CLN-N1	CLN-N2	CLN-Y1	CLN-Y2	CLN-Y3	Fe:CLN-Y4	Er:CLN-Y5
Distance between after-heater and crucible/mm	20	20	10	10	10	10	10
Time of shouldering/min	-	200	720	540	320	310	370
Rotation rate/(r·min^-1)	6	6	7	7	7	7	7
Range of reducing pulling rate/(mm·h^-1)	1.5-0	1.5-0	1.5-0	1.5-0	1.5-0	1.5-0	1.5-0
Decrement of pulling rate each step/(mm·h^-1)	0.5	0.3	0.3	0.2	0.2	0.2	0.2
Interval of reducing pulling rate/min	20	20	15	10	10	10	10
Range of lifting pulling rate/(mm·h^-1)	0-1.5	0-1.5	0-1.5	0-1.5	0-1.5	0-1.5	0-1.5
Increment of pulling rate each step/(mm·h^-1)	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Interval of lifting pulling rate/min	20	20	13	15	13	15	10

Fig. 3 Interface shape (a) and temperature gradient (b) of inclined shoulder and flat shoulder Colorful figures are available on website

Fig. 4 Flat shoulder morphologies of CLN crystals (a) Before optimized the thermal field; (b) After optimized the thermal field

Fig. 5 Crystal weight change of shouldering

Fig. 6 Photos of CLN crystal flat shoulder (a) Before optimized the speed of shouldering; (b-f) After optimized the speed of shouldering

Fig. 7 Change of pulling rate (a) and diameter (b) during lifting

Fig. 8 Conoscopic interference pattern of crystal (a) Part of shoulder; (b) Part of cylindrical crystal

References 39

[1]	MIN N B. The Physical Basis of Crystal Growth. Nanjing: Nanjing University Press, 2019: 7- 11.
[2]	YANG L, ZUO R, SU W J, et al. Study on numerical simulation of thermal stress at different stages in Kyropoulos sapphire crystal growth. Materials Reports, 2012, 26(11): 134.
[3]	MÜLLER G. Experimental analysis and modeling of melt growth processes. Journal of Crystal Growth, 2002, 237-239(3): 1628. DOI URL
[4]	ZHANG H, JIANG T Y, CHEN X J. Blossom of boule shoulder in growing Nd:YAG crystals. Journal of Synthetic Crystals, 1991, Z1: 265.
[5]	ZHOU Y D, ZANG J C, LIU G Q. Growth technique of Pb₂MoO₅ single crystal and analysing the causes of crystal cracks. Journal of Beijing University of Technology, 1983, 9(1): 35.
[6]	JIN J R, XU R Y, ZHU Q B, et al. Growth of high quality lithium niobate crystal. Journal of Synthetic Crystals, 1981, 1: 11.
[7]	YAN T. Growth, Structure and Properties of High Quality LiNbO₃ and LiTaO₃ Crystals. Jinan: Doctoral Dissertation of Shandong University, 2008.
[8]	STELIAN C, SEN G, DUFFAR T. Comparison of thermal stress computations in Czochralski and Kyropoulos growth of sapphire crystals. Journal of Crystal Growth, 2018, 499: 77. DOI URL
[9]	CHEN C H, CHEN J C, CHIUE Y S, et al. Thermal and stress distributions in larger sapphire crystals during the cooling process in a Kyropoulos furnace. Journal of Crystal Growth, 2014, 385: 55. DOI URL
[10]	YAO T, ZUO H B, HAN J C, et al. The simulation of the stress distribution in sapphire crystal growth progress. Journal Harbin University Science & Technology, 2006, 11(5): 100.
[11]	LIU J H, QIAO M Y. Theoretical analysis of the cracking of crystal grown by Czochralski method. Journal of Crystal Growth, 1984, 4: 281.
[12]	CHEN Y. Application of flat crystal formation in Germanium mono-crystal growing. Yunnan Metallurgy, 2002, 31(6): 36.
[13]	BUDENKOVA O, VASILIEV M, YUFEREV V, et al. Effect of internal radiation on the solid-liquid interface shape in low and high thermal gradient Czochralski oxide growth. Journal of Crystal Growth, 2007, 303(1): 156. DOI URL
[14]	BERMÚDEZ V, BUDENKOVA O N, YUFEREV V S, et al. Effect of the shouldering angle on the shape of the solid-liquid interface and temperature fields in sillenite-type crystals growth. Journal of Crystal Growth, 2005, 279(1/2): 82. DOI URL
[15]	GROUP of 104. Growth of <104> orientated lithium niobate crystals. Journal of Inorganic Materials, 1977, 02: 9.
[16]	GALAZKA Z. Radial temperature distribution in LiNbO₃ crystals pulled by the Czochralski technique. Journal of Crystal Growth, 1997, 178(3): 345. DOI URL
[17]	XU Y Q, LI X C, SUN N F, et al. The study of ϕ100 mm sulfur doped InP single crystal growth. Semiconductor Technology, 2004, 29 (3): 31.
[18]	LI Y R, HUANG Q F, LI X L, et al. Study on the progress of seeding and shoulder controlling on HP-LEC InP single crystal growth. Semiconductor Technology, 2013, 38(11): 840.
[19]	ROJO J C, DIÉGUEZ E, DERBY J J. A heat shield to control thermal gradients, melt convection, and interface shape during shouldering in Czochralski oxide growth. Journal of Crystal Growth, 1999, 200(1/2): 329. DOI URL
[20]	SONG W. Numerical Simulation Analysis of Czochralski Growth Processes for Langasite Crystal. Jinan: Master Dissertation of Shandong University, 2009.
[21]	ZHANG Z J. Growth of flat shoulder germanium single crystal using large size ratio of crystal to crucible. Journal of Yunnan University, 2002, 24(1A): 78.
[22]	QIN J, SUN J, HAO Y X, et al. Effect of exposed crucible wall on the Czochralski growth of an LN crystal. CrystEngComm, 2023, 25: 450. DOI URL
[23]	SHANG J F, SUN J, ZHANG Y J, et al. A method to measure electro-optic coefficients of crystals by combining conoscopic interference and near optical axis electro-optic modulation. Journal of Synthetic Crystals, 2015, 44(11): 2925.
[24]	WU B C. Improvement of optical homogeneity of LN crystal by heat treating. Chinese Journal of Lasers, 1978, 5(1): 40.
[25]	TAKAGI K, FUKAZAWA T, ISHII M. Inversion of the direction of the solid-liquid interface on the Czochralski growth of GGG crystals. Journal of Crystal Growth, 1976, 32(1): 89. DOI URL
[26]	WANG S. Hot Zone Design and Thermal Stress Analysis during Growth of Bulk Crystals. Hubei: Doctoral dissertation of Huazhong University of Science and Technology, 2016.
[27]	STOCKMEIER L, LEHMANN L, MILLER A, et al. Dislocation formation in heavily as-doped Czochralski grown silicon. Crystal Research & Technology, 2017, 52(8): 1600373.
[28]	BRICE J C. The cracking of Czochralski-grown crystals. Journal of Crystal Growth, 1977, 42: 427. DOI URL
[29]	LIU J H, QIAO M Y, LI J L. Growth of LN crystal. Journal of Changchun University of Science and Technology, 1987, 3: 73.
[30]	WANG S, FANG H. Dependence of thermal stress evolution on power allocation during Kyropoulos sapphire cooling process. Applied T1ermal Engineering, 2016, 95: 150.
[31]	MIL'VIDSKII M G, BOCHKAREV E P. Creation of defects during the growth of semiconductor single crystals and films. Journal of Crystal Growth, 1978, 44(1): 61. DOI URL
[32]	TSUKADA T, KAKINOKI K, HOZAWA M, et al. Numerical and experimental studies on crack formation in LiNbO₃ single crystal. Journal of Crystal Growth, 1997, 180(3/4): 543. DOI URL
[33]	ZHANG X Y, GUAN X J, PAN Z B, et al. Simulation on effect of heat shield position on the V/G and point defect and thermal stress of Czochralski silicon. Journal of Synthetic Crystals, 2014, 43(4): 771.
[34]	GUAN X J, ZHANG X Y, PAN Z B, et al. Simulation on effect of heat shield position on the melt and solid liquid interface Cz silicon. Journal of Synthetic Crystals, 2015, 44(2): 329.
[35]	CHEN Q H. On the crystal diameter change during the shouldering process in the Czochralski. Journal of Synthetic Crystals, 1984, 4: 345.
[36]	LIANG D D. Study on the Flat Shoulder Growth of Lithium Niobate Crystal. Tianjin: Master Dissertation of Nankai University, 2017.
[37]	YU G J, ZONG Y M, ZHANG Z H, et al. Bubbles distribution in sapphire crystal grown by Kyropoulos method. Journal of Synthetic Crystals, 2014, 43(6): 1332.
[38]	LI S H, PAN X H, LIU Y, et al. Interactions between bubble and interface during KTa_1-_xNb_xO₃ crystal growth. Journal of Inorganic Materials, 2017, 32(11): 1223. DOI URL
[39]	MUKAIYAMA Y, SUEOKA K, MAEDA S, et al. Numerical analysis of effect of thermal stress depending on pulling rate on behavior of intrinsic point defects in large-diameter Si crystal grown by Czochralski method. Journal of Crystal Growth, 2020, 531: 125334.