Effect of nitride sidewall spacer process on boron dose loss in ultrashallow junction formation

Abstract

Articles you may be interested inInteractions of B dopant atoms and Si interstitials with SiO 2 films during annealing for ultra-shallow junction formation J. Appl. Phys. 97, 073520 (2005); 10.1063/1.1884246 Secondary ion mass spectrometry characterization of source/drain junctions for strained silicon channel metal-oxide-semiconductor field-effect transistors A nitride spacer with an underlying deposited tetraethoxysilane oxide, that behaves as a convenient etch stop layer, is a popular choice for sidewall spacer in modern complementary metal-oxidesemiconductor process flows. In this work we have investigated the effect of the silicon nitride spacer process on the boron profile in silicon and the related dose loss of B from the Si into the silicon dioxide. This is reflected as a dramatic decrease in the junction depth. We find that the silicon nitride influences the concentration of hydrogen in the silicon dioxide during the final source/drain anneal. The presence of H enhances the diffusivity of B in the silicon dioxide and thereby results in a significant dose loss from the Si into the silicon dioxide. In this work we have shown this dose loss can be lowered by altering the silicon nitride stoichiometry.

Fundamental characterization of the effect of nitride sidewall spacer process on boron dose loss in ultra-shallow junction formation

“…BTBAS nitride that results in the highest retained B dose in Si and therefore the least B dose loss from Si into oxide shows the lowest H peak concentration, whereas RTCVD nitride which shows the least retained B dose in Si shows the highest H peak concentration in TEOS after the final anneal. These observations correlate well with the dose loss model proposed by us before [2]. Based on our observations, BTBAS seems to be a less effective barrier to H out-diffusion from the TEOS into the ambient through the nitride compared to DCS or RTCVD nitride.…”

“…Primarily, we model the diffusion of H through various spacer layers (oxide 1/nitride/oxide 2) and its effect on B diffusion in Si and oxide. As has been suggested in literature [2] and also in this work, deposited oxides contain large amount of H. This H is highly volatile and out-diffuses readily. A nitride on top of oxide acts as a barrier to the out-diffusing H. Due to the differences in composition, different nitrides lead to different concentrations in the oxide (oxide 1) after final source/drain anneal.…”

“…The H concentration in the TEOS after annealing is much higher (2.6E21 atoms/cm 3 ) if the nitride is present during annealing as compared to the H concentration in the TEOS after annealing without nitride (1.9E21 atoms/cm 3 ). This suggests that it is the high H concentration during anneal in the presence of BTBAS nitride that causes enhanced B diffusion [2].…”

“…However, with transient enhanced diffusion (TED) being less pronounced for low implant energies and sharper anneal temperature profiles, surface reactions and related processes are starting to dominate the formation of ultra-shallow junctions [1]. Recent work by Kohli et al has emphasized the importance of interactions of dopants with silicon nitride spacer layers on ultra-shallow junction formation [2]. They investigated the influence of silicon nitride spacer (from now on we will refer to silicon nitride as nitride and silicon dioxide as oxide) with an underlying deposited tetraethoxysilane (TEOS) oxide on B dose loss from the Si into the oxide.…”

“…However, the presence of nitride acts as a diffusion barrier for the out-diffusing H, resulting in high concentration of retained H in the TEOS even after annealing. The presence of this high level of retained H causes an enhancement of B diffusivity in the oxide [2][3][4][5][6] and thereby enhances the amount of B dose loss into the oxide from the Si. Lesser retained dose leads to shallower profile because of Fermi level effects, coupled diffusion effects and also due to the fact that shift of the profile downwards (due to lesser concentration/dose) moves the point where concentration of B drops to a certain value towards the surface (to the left).…”