Si-TaSi_2共晶自生复合场发射材料的研究
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摘要
Si-TaSi_2共晶自生复合材料作为半导体金属共晶材料(SEM)之一，具有较低的功函数、良好的电传输特性和自生肖特基结等特点。本文采用切克拉斯基法(CZ法)和电子束区熔法(EBFZM)两种定向凝固方法制备该共晶自生复合材料；借助金相技术、电镜技术、图象处理技术等多种分析测试手段，考察了Si-TaSi_2共晶定向凝固组织和及其相应的工艺规范。
本文探讨了CZ法工艺参数对材料凝固组织的影响，确定了制备该复合材料的最佳工艺参数。在晶转12r／min，埚转6r／min，提拉速率12cm／h，埚升速率1.2cm／h工艺条件下，纤维平均间距为9～10μm，平均直径1.79um，平均密度为0.925×10~6rod／cm~2，平均横向面积为8～10μm~2，平均体积分数为2.328％，满足场发射材料的要求。凝固速率在8～20cm／h范围内，随凝固速率R的增加，纤维直径d和纤维间距λ都减小，前者符合线性关系，后者符合λ∝R~(-0.5)关系。随凝固速率的增加TaSi_2纤维体积分数基本不变。
在较好控制固液界面和较低的生长速率定向生长条件下，纤维相TaSi_2生长过程有其独特的规律性，通常可以将其生长过程分为启动、竞争、稳定三个典型阶段。研究纤维相和基体相之间的位相关系发现，纤维相表面光滑，与基体相界面分明，证明两相形成低能界面，其位相关系为[111]_(si)//[0001]_(TaSi_2)，(220)_(si)//(2(?)00)_TaSi_2。考察纤维参数在不同生长阶段的分布规律发现，从顶部到中段纤维密度增大，从中部到根部纤维密度基本不变化。同一晶片上纤维沿径向分布有差异，边缘纤维密度高，中心部位纤维密度低。纤维横向截面形状表现多样。材料的场发射性能良好，其发射开启场强约为4.4V／um，F—N曲线表明该材料的电子发射主要是由隧道效应引起的。
利用EBFZM法，本文研究了区熔工艺和凝固组织之间的关系。结果表明，在区熔速率R=0～0.3mm／min范围内两相很难形成规则共晶，其中基体相定向生长，第二相混乱生长，弥散分布于基体中。区熔速率R=0.6mm／min，Si—TaSi_2共晶体两相形成规则共晶。纤维相生长经历了启动生长、竞争生长、稳定生长过程。比较EBFZM和CZ法生长的共晶体纤维相分布发现，前者纤维相分布更均匀，纤维细且长，但取向性没前者好。
As one of the semiconductor-metal eutectic material (SEM), the rod-like eutectic in-situ composite of Si & TaSi2 has lower work function , excellent electrical transport and the schottky junctions, which was grown-in during the crystal growth step. Therefore, in this paper, two directional solidification methods, Czochralski method and electron-beam floating zone melting method, were used to obtain such material. The directional solidifition microstructures of Si-TaSi2 system was performed using NEOPHOT-1, AMRAY- 100B SEM and JEM-2000CX TEM analysis technique.
The effect of the technique parameters to the microstructure of the eutectic in-situ composite was discussed firstly. On these basis, the. optimum process parameters were founded. With a seed rotation rate of 12rpm, a crucible rotation rate of 6 rpm, a seed puller rate of 12cm/h and a crucible rise rate 1.2cm/h, the average inter-rod spacing was 9-10 um, the average rod diameter was 1.79um, the average rod density was 0.925 X 106 rod/cm2 and the volume fraction was 2.3277%. These parameters all meet the requirement of field emission material. When the solidification rate was changed from 8 to 20 cm/h, with the increase of solidification rate R, the fibre diameter (d) and the inter-rod spacing (A ) both decreased. The former followed linearity rule and the latter followed the rule of λ
εr-0.5 The volume fraction was steadiness when the solidification rate increased. On condition of controlling solid-liquid interface preferably and keeping low directional solidification rate, there were particular phenomena in
TaSi2 fibre development process. Generally, it can be divided into three typical steps. The first was star-up period, the second was competition period, the third was stabilization period. As the relationship of phase interface between Si matrix and TaSi2 fibre was studied, it resulted that the interface between the two phases was evidently. This proved that the low energy inter-face was formed. The rule
of two phase was [111]Si//[0001]TaSi2, (220) Si//(2200)Tasi2. The two coupling phase
was firstly developed in the low-energy surface. In the course of studying the fibre parameter in different development period, it was discovered that the rod density increased from the top to the middle of the boule. But it did nearly not changed from the middle to the bottom. In the same wafer, the fibre parameter was different along the radial. It was high at the edge and low in the center section. The fibre traverse section was multiplicity. The result showed that the composite had excellent field
emission characters. The star-up field intensity was 4.4v/um and the F-Ncurve indicated that the electron emission was leaded by tunnel effect.
The connection of microstructure and floating zone melting process was studied . The result indicated that the two phases in eutectic had difficulty in growing regularly on condition that the floating zone melting rate was in the scope of 0~0.3mm/min. The matrix phase was directional grown and the other phase was grown with no order. It was dispersed in the matrix phase . At the rate of 0.6mm/min, the two phases of Si-TaSi2 system was grown eutectic regularly. The fibre phase was developed in star-up process, competition process and stabilization process. Compared with the fibre distribution by CZ method and EBFZM method, it was discovered that the former was uniformity and slim, the latter was better for alignment.
本文探讨了CZ法工艺参数对材料凝固组织的影响，确定了制备该复合材料的最佳工艺参数。在晶转12r／min，埚转6r／min，提拉速率12cm／h，埚升速率1.2cm／h工艺条件下，纤维平均间距为9～10μm，平均直径1.79um，平均密度为0.925×10~6rod／cm~2，平均横向面积为8～10μm~2，平均体积分数为2.328％，满足场发射材料的要求。凝固速率在8～20cm／h范围内，随凝固速率R的增加，纤维直径d和纤维间距λ都减小，前者符合线性关系，后者符合λ∝R~(-0.5)关系。随凝固速率的增加TaSi_2纤维体积分数基本不变。
在较好控制固液界面和较低的生长速率定向生长条件下，纤维相TaSi_2生长过程有其独特的规律性，通常可以将其生长过程分为启动、竞争、稳定三个典型阶段。研究纤维相和基体相之间的位相关系发现，纤维相表面光滑，与基体相界面分明，证明两相形成低能界面，其位相关系为[111]_(si)//[0001]_(TaSi_2)，(220)_(si)//(2(?)00)_TaSi_2。考察纤维参数在不同生长阶段的分布规律发现，从顶部到中段纤维密度增大，从中部到根部纤维密度基本不变化。同一晶片上纤维沿径向分布有差异，边缘纤维密度高，中心部位纤维密度低。纤维横向截面形状表现多样。材料的场发射性能良好，其发射开启场强约为4.4V／um，F—N曲线表明该材料的电子发射主要是由隧道效应引起的。
利用EBFZM法，本文研究了区熔工艺和凝固组织之间的关系。结果表明，在区熔速率R=0～0.3mm／min范围内两相很难形成规则共晶，其中基体相定向生长，第二相混乱生长，弥散分布于基体中。区熔速率R=0.6mm／min，Si—TaSi_2共晶体两相形成规则共晶。纤维相生长经历了启动生长、竞争生长、稳定生长过程。比较EBFZM和CZ法生长的共晶体纤维相分布发现，前者纤维相分布更均匀，纤维细且长，但取向性没前者好。
As one of the semiconductor-metal eutectic material (SEM), the rod-like eutectic in-situ composite of Si & TaSi2 has lower work function , excellent electrical transport and the schottky junctions, which was grown-in during the crystal growth step. Therefore, in this paper, two directional solidification methods, Czochralski method and electron-beam floating zone melting method, were used to obtain such material. The directional solidifition microstructures of Si-TaSi2 system was performed using NEOPHOT-1, AMRAY- 100B SEM and JEM-2000CX TEM analysis technique.
The effect of the technique parameters to the microstructure of the eutectic in-situ composite was discussed firstly. On these basis, the. optimum process parameters were founded. With a seed rotation rate of 12rpm, a crucible rotation rate of 6 rpm, a seed puller rate of 12cm/h and a crucible rise rate 1.2cm/h, the average inter-rod spacing was 9-10 um, the average rod diameter was 1.79um, the average rod density was 0.925 X 106 rod/cm2 and the volume fraction was 2.3277%. These parameters all meet the requirement of field emission material. When the solidification rate was changed from 8 to 20 cm/h, with the increase of solidification rate R, the fibre diameter (d) and the inter-rod spacing (A ) both decreased. The former followed linearity rule and the latter followed the rule of λ
εr-0.5 The volume fraction was steadiness when the solidification rate increased. On condition of controlling solid-liquid interface preferably and keeping low directional solidification rate, there were particular phenomena in
TaSi2 fibre development process. Generally, it can be divided into three typical steps. The first was star-up period, the second was competition period, the third was stabilization period. As the relationship of phase interface between Si matrix and TaSi2 fibre was studied, it resulted that the interface between the two phases was evidently. This proved that the low energy inter-face was formed. The rule
of two phase was [111]Si//[0001]TaSi2, (220) Si//(2200)Tasi2. The two coupling phase
was firstly developed in the low-energy surface. In the course of studying the fibre parameter in different development period, it was discovered that the rod density increased from the top to the middle of the boule. But it did nearly not changed from the middle to the bottom. In the same wafer, the fibre parameter was different along the radial. It was high at the edge and low in the center section. The fibre traverse section was multiplicity. The result showed that the composite had excellent field
emission characters. The star-up field intensity was 4.4v/um and the F-Ncurve indicated that the electron emission was leaded by tunnel effect.
The connection of microstructure and floating zone melting process was studied . The result indicated that the two phases in eutectic had difficulty in growing regularly on condition that the floating zone melting rate was in the scope of 0~0.3mm/min. The matrix phase was directional grown and the other phase was grown with no order. It was dispersed in the matrix phase . At the rate of 0.6mm/min, the two phases of Si-TaSi2 system was grown eutectic regularly. The fibre phase was developed in star-up process, competition process and stabilization process. Compared with the fibre distribution by CZ method and EBFZM method, it was discovered that the former was uniformity and slim, the latter was better for alignment.
引文
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2. Ishikawa Junzo, et al..Jpn. J. Appl.. phys., 1993, 32 (3A):342～345
3. Cade N A, Howell D F, et al ,Clean and metal coated silicon field emission cathode. Technical digest 5th Int.Vacuum Microelectronics ,Vienna, Austria, 1992,29～30
4. Djubua B Ch ,Ilyin V N, et al.Platinum alloyed with a metal of the II-nd group of the periodic system-an effective source of electron emission. Technical Digest 4th Int. Vacuum Microelectronics, Nagahama, Japan, 1991, 162～163
5. Silzars A. Information Display, 1993, 9, (6): 22
6. Mousa M S, et al. Hydrogen and acetylene adsorption on microfabricated field emitter. Abstract 39th Int. Field Emission Symposium, Hilifax, Canada, 1992, 88
7. Ishizawa Y, et al. Stable field emisson and surface evlution of surface—processed NbC <110> tips,同[6], 50
8. B.M. Ditchek J. Hefter, Micro. Si—TaSi_2 eutec, Journal of crystal Growth, 1990, 401～402
9. B.G. Yacobi等 Chara. of multiple. composite. Appl. Phys. Lett..50(16). 20. April, 1987, 55～57
10．胡汉起．金属凝固学原理．机械工业出版社．2000．北京。
11. R.W. Kraft, D.L. Albright, Trans. Met, Soc. AIME. 1961, 221,95.
12．W. Kurz,P. R. Sahm 定向凝固共晶材料，李新立译，冶金工业出版社，北京。
13．平井寿敏，田原龙夫，上野英俊等，日本金属学会志，64(6)(2000)474～480．
14．周尧和，胡壮麒，介万奇，凝固技术原理．国防工业出版社．北京．1997
15. J.S. Langer, Mod. Phys. Rev., 52 (1980)1.
16. H. Fredriksson, S. E. Wetterfall, The Metallurgy of Cast Iron (edited by B. Lux, I. Minkoff and F. Mollard) p. 277 Georgi Pub. Co., St. Saphorin (1975)
17. G. Lesoult, M. Turpin, The Metallurgy of Cast Iron (edited by B. Lux, I. Minkoff and F. Mollard) p.255, Georgi Pub. Co., St. Saphorin (1975)
18. T. Sato and Y. Sayama, J. Cryst. Growth, 22(1974) 259
19. D.J. Fisher and W. Kurz., Acta Metal., 28(1980)777～794
20. P. Magnin and W. Kurz. Acta metall., 35(5) (1987) 1119～1128.
21. G.E. Nash, J. Cryst. Growth, 38 (1977) 155～180.
22. L. Pandey and P. Ramachandrarao, Acta metal., E5 (10)(1987)2549～2556
23. JUNMIN LIU and YAOHE ZHOU. Acta metal. Mater., 38(9)(1990) 1625～1630
24．胡汉起，金属凝固原理，机械工业出版社，北京，1991，p．172～174
25. P.R. Sahm: Schweitzer Archiv, 36(1970)165～178
26. B. Cantor, in "Interphase interfaces", ed. G. A. Chadwick, Academic Press, 1983.
27．M．麦克莱恩 著，陈石卿 译，定向凝固高温合金，航空工业出版社．北京．1989，p63．
28. K.A. Jackson and Hunt: Trans. Metal. Soc. AIME, 1966, 236, 1129.
29. D.D.DOUBLE: Mater.Sci. Eng. 1973, 11,325.
30. B.M. Ditchek J. Hefter, Micro. Si-TaSi_2 eutec, Journal of crystal Growth, 1990, 401～402
31. B.G. Yacobi等 Chara. of multiple. composite. Appl. Phys. Lett. 50(16). 20. April, 1987, 55～57
32．于金江，西北工业大学博士学位论文，2001．2
33．孙恒慧，包宗明主编，半导体物理实验。北京，高等教育出版社(1995)。
34．王季陶，刘明登主编，半导体材料。北京，高等教育出版社(1990)。
35. W.R. Runyan. Semiconductor measurements and instruments, New York McGraw-Hill (1975).
36．冶金工业部科技情报产品标准研究所编。半导体材料和高纯金属分析。北京，中国工业出版社 (1971)。
37．刘文明主编，半导体物理学。长春，吉林人民出版社。
38．SEMI标准年鉴。北京，中国标准出版社。
39．理学电机株式会社分析中心编集。浙江大学分析测试中心组织编译。X射线衍射手册。
40．徐亚伯编著，表面分析导论。杭州，浙江大学出版社。
41．闵乃本，晶体生长的物理基础，上海科学技术出版社，1982
42．程心一，计算流体力学—偏微分方程的解法，科学出版社，1984
43．张丽波等，CZ法生长Nd：YAG晶体的数值解析，沈阳工业学院学报，2001，9 p53～57。
44. P. Hartman, W.G. Perdok, Acta Cryst., 8(1955)49～52.
45. P. Hartman, J, Crystal Growth ,49(14)(1980)157～163.
46. A. Calverkey, B. Sc., M. Davis, J. of Scientific Instruments, 34(1957)142.
47. V.G. Glebovsky, V. V. Lomeyko and V. N. Semenov, Journal of the Less Common Metals, 117(1986)385
48. J.D. Verhoeven and R. H. Homer, Met. Trans, (1970)3437
49. K.G. Davis and P. Fryzuk, Growth of off-eutectic composites by zone melting, CANADIAN METALLURGICAL QUARTERLY, 10 (4)(1971) 273～275
50．陈昌明，周万城，张军，张立同，用电子束区熔法制备LaB_6-ZrB_2共晶自生复合材料，西北工业大学学报，14(4)(1996)647
51．藤敏之，特种加工，东京株式会社，养生堂发行，1983，p．40
52. J. Bohm, Fundamentals of the floating zone technique, Handbook of Crystal Growth Bulk Crystal Growth Basic Techniques, edited by D. T. J. Harle, Bristal, 1993 D. Fort: J. Cryst. Grow., 94(1981), p85.
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54. International Contrefer Diffraction Data in Coopration with the American Society for testing and Materials. National Association of Corrosion Engineers American Ceramic,1989,sets 21 to 22 p.3, sets 6 to 10 p.438
55．程国华，赵经晨等，金属学报，1995，Vol．31，No．1
56. B. Cantor, in "Interphase interfaces" , ed. G. A. Chadwick, Academic Press, 1983.
2. Ishikawa Junzo, et al..Jpn. J. Appl.. phys., 1993, 32 (3A):342～345
3. Cade N A, Howell D F, et al ,Clean and metal coated silicon field emission cathode. Technical digest 5th Int.Vacuum Microelectronics ,Vienna, Austria, 1992,29～30
4. Djubua B Ch ,Ilyin V N, et al.Platinum alloyed with a metal of the II-nd group of the periodic system-an effective source of electron emission. Technical Digest 4th Int. Vacuum Microelectronics, Nagahama, Japan, 1991, 162～163
5. Silzars A. Information Display, 1993, 9, (6): 22
6. Mousa M S, et al. Hydrogen and acetylene adsorption on microfabricated field emitter. Abstract 39th Int. Field Emission Symposium, Hilifax, Canada, 1992, 88
7. Ishizawa Y, et al. Stable field emisson and surface evlution of surface—processed NbC <110> tips,同[6], 50
8. B.M. Ditchek J. Hefter, Micro. Si—TaSi_2 eutec, Journal of crystal Growth, 1990, 401～402
9. B.G. Yacobi等 Chara. of multiple. composite. Appl. Phys. Lett..50(16). 20. April, 1987, 55～57
10．胡汉起．金属凝固学原理．机械工业出版社．2000．北京。
11. R.W. Kraft, D.L. Albright, Trans. Met, Soc. AIME. 1961, 221,95.
12．W. Kurz,P. R. Sahm 定向凝固共晶材料，李新立译，冶金工业出版社，北京。
13．平井寿敏，田原龙夫，上野英俊等，日本金属学会志，64(6)(2000)474～480．
14．周尧和，胡壮麒，介万奇，凝固技术原理．国防工业出版社．北京．1997
15. J.S. Langer, Mod. Phys. Rev., 52 (1980)1.
16. H. Fredriksson, S. E. Wetterfall, The Metallurgy of Cast Iron (edited by B. Lux, I. Minkoff and F. Mollard) p. 277 Georgi Pub. Co., St. Saphorin (1975)
17. G. Lesoult, M. Turpin, The Metallurgy of Cast Iron (edited by B. Lux, I. Minkoff and F. Mollard) p.255, Georgi Pub. Co., St. Saphorin (1975)
18. T. Sato and Y. Sayama, J. Cryst. Growth, 22(1974) 259
19. D.J. Fisher and W. Kurz., Acta Metal., 28(1980)777～794
20. P. Magnin and W. Kurz. Acta metall., 35(5) (1987) 1119～1128.
21. G.E. Nash, J. Cryst. Growth, 38 (1977) 155～180.
22. L. Pandey and P. Ramachandrarao, Acta metal., E5 (10)(1987)2549～2556
23. JUNMIN LIU and YAOHE ZHOU. Acta metal. Mater., 38(9)(1990) 1625～1630
24．胡汉起，金属凝固原理，机械工业出版社，北京，1991，p．172～174
25. P.R. Sahm: Schweitzer Archiv, 36(1970)165～178
26. B. Cantor, in "Interphase interfaces", ed. G. A. Chadwick, Academic Press, 1983.
27．M．麦克莱恩 著，陈石卿 译，定向凝固高温合金，航空工业出版社．北京．1989，p63．
28. K.A. Jackson and Hunt: Trans. Metal. Soc. AIME, 1966, 236, 1129.
29. D.D.DOUBLE: Mater.Sci. Eng. 1973, 11,325.
30. B.M. Ditchek J. Hefter, Micro. Si-TaSi_2 eutec, Journal of crystal Growth, 1990, 401～402
31. B.G. Yacobi等 Chara. of multiple. composite. Appl. Phys. Lett. 50(16). 20. April, 1987, 55～57
32．于金江，西北工业大学博士学位论文，2001．2
33．孙恒慧，包宗明主编，半导体物理实验。北京，高等教育出版社(1995)。
34．王季陶，刘明登主编，半导体材料。北京，高等教育出版社(1990)。
35. W.R. Runyan. Semiconductor measurements and instruments, New York McGraw-Hill (1975).
36．冶金工业部科技情报产品标准研究所编。半导体材料和高纯金属分析。北京，中国工业出版社 (1971)。
37．刘文明主编，半导体物理学。长春，吉林人民出版社。
38．SEMI标准年鉴。北京，中国标准出版社。
39．理学电机株式会社分析中心编集。浙江大学分析测试中心组织编译。X射线衍射手册。
40．徐亚伯编著，表面分析导论。杭州，浙江大学出版社。
41．闵乃本，晶体生长的物理基础，上海科学技术出版社，1982
42．程心一，计算流体力学—偏微分方程的解法，科学出版社，1984
43．张丽波等，CZ法生长Nd：YAG晶体的数值解析，沈阳工业学院学报，2001，9 p53～57。
44. P. Hartman, W.G. Perdok, Acta Cryst., 8(1955)49～52.
45. P. Hartman, J, Crystal Growth ,49(14)(1980)157～163.
46. A. Calverkey, B. Sc., M. Davis, J. of Scientific Instruments, 34(1957)142.
47. V.G. Glebovsky, V. V. Lomeyko and V. N. Semenov, Journal of the Less Common Metals, 117(1986)385
48. J.D. Verhoeven and R. H. Homer, Met. Trans, (1970)3437
49. K.G. Davis and P. Fryzuk, Growth of off-eutectic composites by zone melting, CANADIAN METALLURGICAL QUARTERLY, 10 (4)(1971) 273～275
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