Recrystallization of Implanted LPCVD Amorphous Si Films Using Rapid Thermal Annealing
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RECRYSTALLIZATION OF IMPLANTED LPCVD AMORPHOUS Si FILMS USING RAPID THERMAL ANNEALING R. KWOR*, S.M. TANG*,N.S. ALVI** *Department of Electrical and Computer Engineering, University of Notre Dame, Notre Dame, IN 46556 **Delco Electronics, Kokomo, IN 46902 ABSTRACT The effect of rapid thermal annealing on the crystallization of arsenic and boron implanted amorphous silicon films is studied. Amorphous Si films of 4000 A were qeposited ulipg LPCVD and *planted with arsenic or boron to doses of 5 x 10"', 5 x 10 , and 5 x 1017cm-Ž. These films were then annealed using an Eaton Nova-400 RTA system (with temperature ranging from 900 to 1200 °C and dwell time ranging from 1 to 30 sec). The annealed films were studied using transmission electron microscopy, Hall effect measurement and temperature coefficient of resistance measurement. The optimal annealing conditions for the films were found. INTRODUCTION Significant research effort has been made to precisely control the resistivity of the polysilicon films which are used in bipolar and MOS integrated circuits. Low pressure chemical vapor deposition (LPCVD) is commonly used to prepare amorphous or polysilicon films which are subsequently doped by ion implantation and annealed. Silicon films deposited at temperature above 600 °C are usually polycrystalline, whereas those deposited below that temperature are usually in amorphous form [1]. The characteristics of these films have a strong dependence on the postimplantation anneal process. Furnace annealing has been used to control the grain size in these films and more recently, rapid thermal annealing (RTA) is being investigated as an alternative. Krause et al. [2] used a graphite-heater RTA system to recrystallize arsenic-implanted polysilicon films. They observed that the grain size reached the film thickness of 3500
A within 25 sec. at 1200 °C.
Arai et al.
[3] reported that amorphous
silicon films can be effectively crystallized using a halogen lamp RTA
system. Despite of these efforts, there is still a need for more information on the grain growth in these films. Also needed is a study of dose and dopant dependence of the film resistivity. In this work, a systematic study on crystallization of arsenic and boron implanted, initially amorphous LPCVD silicon films is conducted. An arc-lamp RTA system with a close-loop temperature control is chosen for the study. The dependence of the film characteristics on implantation and RTA process parameters is investigated using transmission electron microscopy (TEM), sheet resistivity and Hall measurements. EXPERIMENTAL PROCEDURE An undoRed amorphous silicon film was deposited onto a silicon dioxide layer (1000 A) which was thermally grown on 5 in., p-type, 14-22 ohm-cm, -oriented silicon wafers. The deposition was done in an LPCVD reactor at 540 °C by pyrolyzing silane under a pressure of 0.33 torr. One group of samples (with amorphous Si film thickness of 40Q A) were iTnlantvd with arsenic at 100 KeV to doses ranging from 5 x 101- t 5 x 10 cm- . The other group (with amorphous S
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