High Mass Molecular Ion Implantation for Advanced Logic and Memory Devices Manufacturing

Abstract

Semiconductor device manufacturing is facing stringent challenges in advanced COMS process technology nodes. Ion implantation technology has always been a good solution of last resort since it’s got a much wider latitude and stronger flexibility to accommodate new challenges than any other process steps in device fabrication. It is not unusual that people utilize ion implantation not just for doping the silicon substrate, but also for compensating the shortfalls of other process steps. In the past decade, the process window, typically large enough for ion implant engineers to maneuver has gotten narrow, so narrow to a degree so that itself started to create problems which none other process steps can resolve, or compensate. These problems include dopant atoms activation, co-implant species of choice, pre-amorphization implant species of choice, implant damage control, runaway low-energy implant cost. High mass molecular (HMM) ion implantation is investigated in response to all these ion implant related problems. Ion implantation is a process whereby energetic ions impinge on a target, penetrating below the target surface and giving rise to a controlled, predictable, ion distribution. Here we will focus on Si technology; hence the target will be mostly Si. Implanted ions are typically dopants, such as Boron, Phosphorus, Arsenic, Indium and Antimony. Table 1 shows these commonly used dopant elements in the periodic table of the elements. However, the scaling of device features into the sub-100nm regime has added species such as Ge, C, N, and Xe to this list. Implantation energies cover a wide range from 0.2 keV to >3 MeV; doses range from 1 x 1011 cm2 to more than 1 x 1016 cm2; incident angles cover normal incidence (a tilt angle of 0°) to 60°. The industry has been using BF2+, as the molecular form of Boron, to implant in order to attain higher throughput for low-energy applications. This species has the disadvantage of co-implanting fluorine, which retards boron activation and increases contact resistance, both undesirable consequences for doping process (Foad, 2005). HMM implants have recently been introduced as an alternative. As the molecular structure shown in Fig. 1, Octadecaborane (B18H22), which has 18 effective dopant atoms in one molecule, has been proven a viable replacement for boron in poly-doping and BF2 for ultra-shallow junction (USJ) formation. Besides the advantage of higher productivity, HMM implant process advantages have been noticed and explored. Due to its heavy mass, HMM ion implant can eliminate the use of preamorphization implant (PAI). We can use the HMM ions that contains either dopant or coimplant species to replace PAI (Ameen, 2008). Implant damage control is also possible by the use of HMM ion implantation, due to germanium PAI elimination.