Shallow buried SiNx layers

Abstract

High dose nitrogen implantations have been performed at an energy of 30 keV. After high temperature annealing, 1200°C, a buried layer composed mostly of silicon nitride is formed leaving an overlayer with a high fraction of crystalline silicon. The lattice constant of the overlayer and the region below the SiN x are reduced in 0.13% and 0.089%, respectively. The substitutional N seems to be responsible for this reduction. © 2000 American Institute of Physics. ͓S0021-8979͑00͒00211-5͔Separation by implantation of oxygen is a well established technology for a variety of applications such as ultralow scale integration, high voltage devices, and micromachining of sensors and actuators. Nitrogen implantation has also been proposed to synthesize silicon-on-insulator ͑SOI͒ layers because of the better stability, the lower doses required, and the excellent barrier against impurity diffusion of the Si 3 N 4 compared to SiO 2 . [1][2][3][4] More recently the use of SOI layers as compliant substrates has been reported. [5][6][7][8] For these applications, O ϩ ions, for instance, 6 are implanted in silicon wafers. After implantation a high temperature annealing leads to the growth of a SiO 2 buried layer and a good crystalline quality Si overlayer. If the buried layer is close enough to the surface, it might be possible to grow thicker layers without degradation because most of the stress is expected to be absorbed on the thin substrate. 9,10 In this communication we report the formation of a shallow buried SiN x layer by low energy N ϩ ion implantation and subsequent annealing.N type float zone ͑FZ͒ ͗100͘ silicon wafers were used in these experiments. These wafers have a resistivity over 50 ⍀ cm and oxygen content below 0.3 ppm. Implantations were carried out in a modified Varian Extrion ion implanter. Different doses of 14 N ϩ , 1ϫ10 16 , 1ϫ10 17 , and 6.7 ϫ10 17 cm Ϫ2 , well over the critical amorphization dose for these ions in silicon ͑of about 10 15 cm Ϫ2 ), at an energy of 30 keV were implanted. The sample holder used for the implantations was maintained at room temperature by means of a closed cycle circuit, and the slight increase of the sample temperature only allowed some relaxation of the amorphous network. The highest dose was chosen to obtain a concentration of nitrogen in about 0.1 m similar to the bulk silicon concentration. Afterwards the samples were annealed in nitrogen gas. Two of the samples of each dose were rapid thermal annealed ͑RTA͒ for 1 min at 600 and 1200°C and a third one furnace annealed for 15 min at 1200°C.Fourier transform infrared ͑FTIR͒ spectroscopy, spectroscopic ellipsometry, x-ray diffraction ͑XRD͒, and spreading resistance techniques were used for characterization.IR measurements in transmission mode, shown in Figs. 1͑a͒ and 1͑b͒, were performed in Bruker equipment to identify the chemical bonds present in the samples. An unimplanted silicon wafer has been used as reference and no baseline correction has been done. The antireflecting behavior of the implanted layer leads to an overesti...