Moriz Jelinek

A Novel Method for Simultaneous on Wafer Level Monitoring of Ion Implantation Energy and Dose

Semiconductor technology needs the control of processes on wafer level. For ion implanation control there are two well established methods, namely the photothermal response techniques on as-implanted product or monitor wafers and the determination of resistivity via sheet resistance measurement on as-implanted and annealed wafers. In fact, both methods are sensitive to implant dose but rather insensitive to implant energy. In particular the established methods are not capable to distinguish between effects of dose and energy. Especially in a high energy regime above 1 MeV it is of high interest to verify the implant energy on wafer level. This is in principle achievable by spreading resistance profiling (SRP) or secondary ion mass spectroscopy (SIMS) with the disadvantage of long feedback times, expensive processing and limited ability of resolution. It was shown that the wide frequency sweep used in the photothermal heterodyne equipment TWIN can be sensitive to the depth of damage profiles. In this study we present a developed energy and dose sensitive method based on a specially designed tool TWIN-SC4 produced by PVA Metrology&Plasma Solutions GmbH. Making use of the unique ability to vary the modulation frequency of the excitation laser enables inspection of different regions of the respective implant damage profiles. Consequently, we propose a method, combining measurements with two modulation frequencies and being sensitive to energy and dose which requires only a single as-implanted wafer.

The Efficiency of Hydrogen-Doping as a Function of Implantation Temperature

– For a conventional proton implantation doping process applied to crystalline silicon comprising proton implantation and subsequent furnace annealing the effect of the substrate temperature set during implantation is examined for temperatures between 50 °C and 200 °C. The formation efficiency of the hydrogen related donors in the maximum of the related doping profiles is shown to linearly increase with the implantation temperature. Regarding the dose rate, a reverted effect is found. The appearing effects are explained by considering the evolution of the initial implantation damage towards a vacancy related precursor species of the hydrogen related donor. Additional information about the implantation temperature dependent defect distribution is gained from Fourier-DLTS results.

Metastable Defects in Proton Implanted and Annealed Silicon

Two metastable defects with energy levels at Ec-0.28eV and Ec-0.37eV, which previously have been reported in proton implanted- and in proton implanted and annealed crystalline silicon are discussed. Recent results on the peculiar behavior of these defects upon periodical application of two different bias conditions during DLTS measurement are reviewed. Two specifically designed DLTS measurement sequences are proposed in order to further reveal the defects transformation rates and respective activation energies.

H + implantation profile formation in m:Cz and Fz silicon

Implanting hydrogen ions (H+) into silicon creates defects that can act as donors. The microscopic structure of these defects is not entirely clear. There is a difference in the resulting doping profiles if the silicon is produced by the float zone (Fz) process or the magnetic Czochralski (m:Cz) process. Silicon produced by the m:Cz process has higher concentrations of oxygen and carbon than silicon produced by the Fz process. The presence of the oxygen and carbon affects the formation of defects and thereby the doping profile. We implanted high resistivity p-type m:Cz and Fz wafers with protons. Due to the n-type doping from the H+ implantation, a pn-junction was generated in the sample. Simulations indicate that the H+ implantation depth is 148 μm. Spreading Resistance Profiling (SRP) measurements of as-implanted and not annealed samples show a donor peak at 148 μm in the Fz samples but the peak is at about 160 μm depth in m:Cz samples. After a low temperature anneal of the m:Cz samples at temperatures between 150 and 250 °C for at least 30 minutes, the expected end of range (EOR) donor peak (at about 148 μm) appears. For higher annealing temperatures, the hydrogen related donor complexes (HTDs) become activated and the EOR peak becomes dominant in the implantation profile. In an SRP study we show the evolution of the doping profile of hydrogen implanted m:Cz and Fz wafers as a function of the annealing temperature. To monitor the depth of the formed pn-junction and the effective local diffusion length in the proton radiation damaged region, Electron Beam Induced Current (EBIC) measurements were performed.

MeV-proton channeling in crystalline silicon

Hydrogen implantation has become an important application in the fabrication of power semiconductor devices. With the product requirement of a well-defined implantation profile, adequate control of the incident beam angle is necessary in order to avoid channeling effects. With respect to the different scan systems of commercial implanters and the crystal alignment of the bulk material the implant tilt and twist angles have to be adapted. We used commercially available <;100>-oriented silicon wafers to examine planar channeling along a {110}-plane for proton energies in the range of 0.5-2.5 MeV. The critical angle as a function of proton energy is determined from photothermal response measurements (TWIN).

Multiple Proton Implantations into Silicon: A Combined EBIC and SRP Study

Protons with energies of 1 MeV and 2.5 MeV were implanted into a p-doped silicon wafer and then the wafer was annealed at 350 °C for one hour. This resulted in two n-doped layers in the otherwise p-doped sample. The carrier concentration was measured using spreading resistance profiling while the positions of the four pn-junctions were measured using electron beam induced current measurements. The carrier concentration is not limited by the available hydrogen but by the concentration of suitable radiation induced defects.