Effects of Double-Implant on the Epitaxial Growth of Amorphous Silicon
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EFFECTS OF DOUBLE-IMPLANT ON THE EPITAXIAL GROWTH OF AMORPHOUS SILICON
L.J. CHEN, AND C.W. NIE!! Department of Materials Science and Engineering, Tsing Hua University, Hsinchu, Taiwan, ROC.
National
ABSTRACT Investigation has been made on the effects of double implant of BF2+-As+, BF 2 +-P+, B+-As+ and B+-P+ on the For specimens thermal annealing behaviors of silicon. with As+ or P+ as the major dopants, the annealing behaviors were similar to those singly implanted with As+ For samples with BF2+ or B+ as the major or P+. impurities, drastic changes in annealing characteristics were found in comparison with BF2+ or B+ single implant specimens. High density twins, including primary twins on all four f1111 planes and twelve types of secondary twins were observed in BF2+-As+ and BF2+-P+ double implant samples.
I.
INTRODUCTION
The annealing behaviors of ion-implanted silicon have been extensively The collision of studied for its wide applications in solid state devices. energetic ions can cause considerable damage to the crystalline substrate. Continuous amorphous layer may be formed for implantation above a critical dose. To reduce the disorder, samples must be annealed either thermally or by high intensity energy beam. During annealing, the amorphous layer It has been well known that the regrows epitaxially on substrate silicon. impurity has strong influence on the regrowth behaviors of amorphous silicon (1,2]. Arsenic, boron and phosphorus, having an impurity concentration near On the other 0.5 at%, can increase the growth rate by factors of 6-25. hand, carbon, oxygen and nitrogen at the level of about 0.5 at% strongly retard the growth rate. For amorphous layer double implanted with equal amount of As and B or P and B, to concentrations of about 0.5 at%, the The dominant defects growth rate was decreased 2-3 order of magnitude [3]. and their density were also dependent on the type and amount of impurities. 14 For (111) oriented silicon wafers, implanted either by 5x10 As+, 15 15 1 5 2 16 Au, 5x10 Ar, 3x10 Pb or Bx10 Si/cm, post annealing defects ix10 16 2 were dominated by twins [4,5]. While implanted by 1x10 B+ or P+/cm , dislocation lines were the major defects [6). For (100) substrates 15 14 15 15 0 or Ne, 7x10 Kr, 2x10 Ar, 5x10 implanted with either 8x10 1 5 2 5x10 N/cm , the dominate defects after thermal annealing were twins [7,8], 16 2 whereas implanted by B+, P+ or As+ to about ixl0 /cm , the dominant defects The general trend for twin formation was were dislocation lines and loops. above a critical dose (Dc), twin will be formed on both (111) and (100) specimens. Dc for (100) substrate was higher than that for (111) substrate and was different for each implant species [8]. Atomic size difference between impurity and host atoms leads to the generation of misfit dislocations. The atomic radius of Si is 1.17 A, if it was doped with B or P, having an atomic radius of 0.88 A and 1.10 AO, If the silicon substrate respectively, misfit dislocation will be formed. was doped with both P and Ge (atomic radius 1
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