Shallow Junction Formation By Boron Implantation With Energies Between 2 And 5 Kev And Rapid Thermal Annealing

In this article we will show that low-energy implantation is a promising approach for shallow junction formation. The penetration depth of B + ions into silicon is proportional to the square root of the energy, since electronic stopping is the dominant deceleration mechanism. Depths of as-implanted profiles in the range of 75 nm at 1% peak concentration can be obtained. In combination with rapid thermal annealing (RTA), junction depths of 100 nm (1% peak concentration) are achievable without any residual damage in active regions. However, a considerable portion of the low-energy ions is not able to transverse a 5 nm screen oxide and consequently the dose reaching the Si substrate depends significantly on the thickness of the screen oxide. Due to the fact that the peak concentration lies very close to the surface, outdiffusion during annealing requires careful adjustment of the whole process complex. Problems concerning dose control of low-energy implantations by sheet resistance measurements are discussed and compared to dose monitoring by modulated optical reflectance measurements.