一种用于制备大厚度MEMS结构层的浓硼掺杂方法(英文)

在MEMS器件中,浓硼掺杂层通常为器件的结构层.但由于受表面固溶度及浓度梯度影响,该掺杂层(硼原子浓度≥5×1019cm-3)厚度越大所需的扩散时间越长.为了能在同等扩散工艺条件下,制备出更厚的浓硼掺杂层以满足器件要求,提出了多步扩散法.即在保证总的累计扩散时间不变的前提下,将传统的扩散过程分为两个相对短的扩散周期.并且这两个周期连续进行,每个周期各包含一次预扩散和再分布.与传统的两步扩散相比,多步扩散法可为硅基底引入更大量的硼杂质,并且具有一定能力使硼杂质留在一定深度范围内.因此该方法可以获得更大的有效节深.实验中采用该方法成功制备出21μm厚的浓硼掺杂层.然而在文献中提到的采用传统两步法在同样条件下得到的厚度则小于15μm.从而验证了该方法可在同等扩散工艺条件下,可以制备出更厚的浓硼掺杂层.

A Heavily Boron-Doping Method for Fabrication of Thick MEMS Structural Layer

In MEMS devices, heavily boron-doped layers are usually used as structural layers. Due to the influence of solid solubility and concentration gradient in area near surface, the fabrication of a thicker layer（boron concentration≥5 ×10^19 cm-3） needs a longer diffusion duration. In order to fabricate the thicker layer under the same diffusion condition, muhi-step diffusion method is put forth. It divides con- ventional diffusion process into two relatively short periods while maintaining the same cumulative diffu- sion duration. The two periods are performed continuously and each diffusion period includes one pre- deposition and one drive-in. Compared with conventional two-step diffusion method, this multi-step diffu- sion method can bring a larger quantity of boron dopants to silicon substrate and possesses the potential to trap dopants at a certain depth. Thus, it is possible to obtain thicker heavily boron-doped layers. In the experiment, a 21μm thick heavily boron-doped layer was obtained by this method, 6 μm thicker than that obtained in references （less than 15μm） using conventional two-step method under the same diffu- sion condition, which demonstrates that this method can fabricate thicker heavily boron-doped layers un- der the same diffusion condition.