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Three techniques based on transmission electron microscope (TEM) have been successfully applied to measure strain/stress in the channel area of PMOS semiconductor devices with embedded SiGe in the source/drain areas: convergent beam electron diffraction (CBED), nano beam diffraction (NBD) and dark-filed holography (DFH). Consistent channel strain measurements from the three techniques on the same TEM sample (eSiGe PMOS with 17%Ge) were obtained. Reliable strain/stress measurement results in the channel area have been achieved with very good agreement with computer-aided design (TCAD) calculations.
Convergent electron beam diffraction (CBED) has been successfully applied to measure strain/stress in the channel area in PMOS semiconductor device with embedded SiGe (eSiGe) for 65nm technology. Reliable results of strain/stress measurements in the channel area have been achieved by good fitting of experimental CBED patterns with theoretical calculations. Stress measurements from CBED are in good agreement with simulations. A compressive stress as high as 823.9 MPa was measured in the <110> direction in the channel area of a PMOS device with eSiGe with 15% Ge and a thickness of 80nm. Stress measurements from CBED also confirm that the depth of the eSiGe and defects such as dislocation loops within the eSiGe relax strain/stress within the film and reduce strain/stress in the channel area.
Nitrogen diffusion and defect structure were investigated after medium to high dose nitrogen implantation and anneal. 11 keV N2+ was implanted into silicon at doses ranging from 2×1014 to 2×1015 cm−2. The samples were annealed with an RTA system from 750°C to 900°C in a nitrogen atmosphere or at 1000°C in an oxidizing ambient. Nitrogen profiles were obtained by SIMS, and cross-section TEM was done on selected samples. TOF-SIMS was carried out in the oxidized samples. For lower doses, most of the nitrogen diffuses out of silicon into the silicon/oxide interface as expected. For the highest dose, a significant portion of the nitrogen still remains in silicon even after the highest thermal budget. This is attributed to the finite capacity of the silicon/oxide interface to trap nitrogen. When the interface gets saturated by nitrogen atoms, nitrogen in silicon can not escape into the interface. Implant doses above 7×1014 create continuous amorphous layers from the surface. For the 2×1015 case, there is residual amorphous silicon at the surface even after a 750°C 2 min anneal. After the 900°C 2 min anneal, the silicon fully recrystallizes leaving behind stacking faults at the surface and residual end of range damage.
A highly selective nitride etch was developed for gate stack spacer process in advanced memory programs. Based on methyl fluoride chemistry with better than 8:1 selectivity of nitride:oxide, this process exhibits minimal erosion to the underlying RTO thermal oxide for consistent diffusion ion-implant control. As the groundrule changed to 0.175um and below, a two-step etch scheme was employed to maintain the profile control in high-aspect-ratio structures. The stability and repeatability of the process is demonstrated in the SPC chart of the post etch FTA site measurement.
The dose loss and transient enhanced diffusion of indium in silicon were studied as a function of dose. Indium was implanted into silicon through a 90 A oxide at 50 keV for doses ranging from 3x 1012 to 2x14 cm−2. These conditions provide peak concentrations that approximately range from 1x1018-1x1020 cm−3. After an RTA anneal at 1000°C for 5s, indium exhibits substantial motion at both the tail and peak regions for high doses. The enhanced diffusion is mostly over within 5s. There was not any observable enhanced diffusion in the tail region at the lowest dose although there was significant movement at the peak region. The dose loss correlates very well with the enhancement in the diffusivity. TEM images show that the amorphization dose lies between 3x1013 and 8x1013 cm−2. In spite of the amorphization, diffusion enhancement in the tail region still keeps increasing with dose, which is contrary to a model of “+1” interstitials and complete removal of interstitials in the regrown layer. The 550°C lh anneals show that the dose loss can partially be attributed to the sweeping of the dopant by the growing a/c interface. Previously, the solubility of indium has been estimated to be around 1–2×1018 cm−3. At high doses, significant movement is observed at the peak of the indium profile although the peak concentration exceeds the solubility level by at least an order of magnitude. This shows that indium is not precipitating into an immobile phase like antimony or boron.
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