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.

Nitrogen implantation is used to retard gate oxide growth thereby making it particularly usefulfor dual- VT and System On A chip technologies. This paper discusses the diffusion behavior and the concomitant defect evolution at high doses of implanted nitrogen in silicon. This paper shows that as the nitrogen implant dose is increased, the extent of nitrogen diffusion reduces. This paper also reports based onTEM studies, that upon annealing at 750°C, 5 × 10014 N2+/cm2, 40 keV implant produces Type I extended defects. However, 2 × 1015 N2+/cm2, 40 keV implant, produces a continuous amorphous layer to a depth ofabout 800 to 900 Å from the surface. In addition, upon annealing at 750°C, the 2 × 1015 N2+/cm2, 40 keV implant produces Type V or solid solubility defects in addition to End of Range or Type II defects.

The effect of nitrogen implants on boron transient enhanced diffusion was studied for nitrogen-only, boron-only, and boron plus nitrogen implants. A boron buried layer was used as a detector for interstitial supersaturation in the samples. Boron dose ranged from 1×1014 to 1×1015 cm−2 and N2+ dose from 5×1013 and 5×1014 cm−2. The energies were chosen such that the location of the nitrogen and boron peaks matched. After the implants, RTA and low temperature furnace anneals were carried out. The diffusivity enhancements were extracted from the buried layer profiles by simulation. Nitrogen-only implants were found to cause significant enhanced diffusion on the buried boron layer. For lower doses, the enhancement of the nitrogen implant is about half as that of boron whereas the enhancements are equal at higher doses. Nitrogen coimplant with boron increases the transient enhanced diffusion of boron at low boron doses, which implies that nitrogen does not act as a strong sink for excess interstitials unlike carbon. At high boron doses, nitrogen co-implant does not significantly change boron diffusion. Sheet resistance measurements indicate that low nitrogen doses do not affect the activation of boron whereas high nitrogen doses either reduce the activation of boron or the mobility of the holes.

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.

Nitrogen implantation can be used to control gate oxide thicknesses [1,2]. This study aims at studying the fundamental behavior of nitrogen diffusion in silicon. Nitrogen at sub-amorphizing doses has been implanted as N2+ at 40 keV and 200 keV into Czochralski silicon wafers. Furnace anneals have been performed at a range of temperatures from 650°C through 1050°C. The resulting annealed profiles show anomalous diffusion behavior. For the 40 keV implants, nitrogen diffuses very rapidly and segregates at the silicon/ silicon-oxide interface. Modeling of this behavior is based on the theory that the diffusion is limited by the time to create a mobile nitrogen interstitial.