Grain growth in boron doped LPCVD polysilicon films
- PDF / 1,981,499 Bytes
- 5 Pages / 593.28 x 841.68 pts Page_size
- 63 Downloads / 210 Views
T.T. Sheng AT& T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (Received 5 July 1989; accepted 9 October 1989)
Dopant induced grain growth in LPCVD polysilicon films has been investigated using BBr3 as the diffusion source at 900 and 950 °C. TEM and sheet resistance measurements indicate rapid growth under such doping conditions. Results are compared with the grain growth observed during (a) PBr3 doping of similar films, and (b) during anneals in ambients containing 1% oxygen in nitrogen, similar to that used during BBr3 or PBr3 doping. The results clearly demonstrate the rapid grain growth induced by both types of dopants, although phosphorus is more effective in inducing this grain growth.
I. INTRODUCTION
The use of LPCVD polycrystalline silicon films has been widely accepted by the semiconductor industry in the last decade mainly because of the ease with which it has lent itself to high volume wafer fabrication.1 It is now most commonly used as gate electrode material in MOS devices, as a conductor in multilevel metallization, and as a contact material for shallow junction devices.2 The structure of polysilicon has been studied in some detail,1'2 and it can be briefly outlined as follows: LPCVD polysilicon is amorphous when deposited below 575 °C and polycrystalline with columnar grains at deposition temperatures —630 °C. At deposition temperatures above 650 °C a multigrain structure similar in nature to metals develops with a higher deposition temperature leading to a larger grain size. The actual temperature of transition from amorphous to crystalline deposition depends on variables such as the total pressure within the LPCVD reactor, the deposition rate, the hydrogen partial pressure, and the influence of dopants and impurities. On annealing the polysilicon films, recrystallization and grain growth is observed in both the amorphous and the columnar structures. Recrystallization and growth are significantly influenced by the presence of dopants and impurities.2 The final average grain diameter depends on the anneal temperature, time, and the dopant concentration. In undoped polysilicon deposited around 630 °C, the fine grained columnar structure seen after deposition remains fairly stable up to at least 1000 °C. Above 1200 °C, coarse large grains of nearly uniform size form by primary recrystallization.3 At 1350 °C, secondary recrystallization occurs wherein some grains grow at the expense of others, leading to a distribution of grain sizes. In contrast, heavily doped films show significant grain growth at 900-950 °C. It has been observed that amorphous and columnar polysilicon films attain a grain size ranging from 0.5 to 1.0 jim during a phosphorus 360
http://journals.cambridge.org
J. Mater. Res., Vol. 5, No. 2, Feb 1990
Downloaded: 25 Mar 2015
diffusion at 950 °C.2 Films heavily doped with phosphorus, using ion implantation, yielded similar results on annealing between 900 °C and 1000 °C for 20 min.4 Arsenic shows a similar influence, but the grain growth enhancement decreases
Data Loading...
