Boron Deposition Control for p-type Plasma Doping

Plasma doping (PLAD) has long been a mainstay in semiconductor manufacturing, specifically memory devices for poly gate and contact doping applications. PLAD is also an attractive technology for fabricating shallow junctions with low implant energies as well as high aspect ratio structures, which are critical for continued device scaling. Traditionally, PLAD implant process (Process A) using B
₂
H
₆
chemistry results in surface deposition, which can be a challenge for photoresist (PR) removal and to some extent limits the control of the dopant profile in the near surface region. Thus, controlling the deposition during the implant step is of paramount importance for improving the process for current technology nodes and for enabling some of the new aforementioned applications. In this paper we have systematically studied the boron deposition characteristics during the B
₂
H
₆
implant process using several different techniques. Quartz crystal microbalance (QCM) was used extensively to understand the deposition process and good correlation of QCM was observed with other metrologies. Based on the findings in this work, we have developed a new process (Process B) that yields minimal deposition with similar boron dopant profile. The new process provides better tunability of the profile and greatly simplifies the integration scheme by alleviating the clean requirements post implant step. Work is in progress to further optimize the dopant profile using the new process and to evaluate the effect on contact resistance.