Search

The concept of fully encapsulated, semi-insulating silicon (SI-Si) Cz-SOI substrates for silicon microwave devices is presented. Results show that, using gold as a compensating impurity, a silicon resistivity of 180 kOcm can be achieved. Sufficiently high resistivity substrates for microwave applications are obtained by depositing gold on silicon and annealing for one hour at 1000C. Silicon oxide and silicon nitride are considered as diffusion barriers for use in the new technology. At 1000C the diffusivity of gold in PECVD silicon nitride is found to be ~ 3.7x10-13cm2s-1, whilst for silicon oxide it is less than 6x10-14cm2s-1. These results imply that silicon nitride would be ineffective as a diffusion barrier in the SI-Si technology but that a silicon oxide BOX 600nm thick might allow devices to be processed with a thermal budget of up to 15 hours at 1000C without impurity contamination.

A modified dislocation unlocking technique is used to measure dislocation locking due to nitrogen implanted into Czochralski silicon. The results show that near-surface dislocations can be locked by implanted nitrogen. The magnitude of the locking measured suggests that nitrogen transport proceeds by a dissociative mechanism, where transport occurs by the splitting of immobile dimers into fast monomers, rather than movement of nitrogen dimers. In other experiments, nitrogen-doped float-zone silicon is investigated using the standard dislocation unlocking technique. The results give an activation energy for effective nitrogen diffusion in silicon of 3.24{plus minus}0.25eV at 500 to 750{degree sign}C. Using the assumption that the dislocation locking strength per nitrogen atom is the same as that of oxygen, a value of 200,000cm2s-1 can be inferred for the effective diffusivity pre-factor. If analysed using the dissociative model, an activation energy of 1.1 to 1.4eV is found for nitrogen monomer diffusion, with a diffusivity pre-factor of 30cm2s-1.

A novel dislocation locking technique is used to study the behaviour of nitrogen in float-zone silicon (FZ-Si). Specimens containing well-defined arrays of dislocation half-loops are subjected to isothermal anneals of controlled duration, during which nitrogen diffuses to the dislocations. The stress required to bring about dislocation motion is then measured. From measuring this unlocking stress as a function of annealing time and temperature it is possible to deduce information on nitrogen transport and nitrogen-dislocation interactions. In this paper, the results obtained by using the dislocation locking technique are reviewed. Furthermore, deep-level transient spectroscopy (DLTS) and high-resolution DLTS (HR- DLTS) are applied to nitrogen-doped silicon. A deep-level with an emission enthalpy of approximately 0.50eV and a concentration of order 1011cm-3 was found in n-type nitrogen- doped FZ-Si and n-type nitrogen-doped neutron transmutation doped FZ-Si. No additional deep-levels with a concentration of greater than 6 x 1010cm-3 were found in either material. No deep-levels were found in p-type nitrogen-doped Czochralski silicon (Cz-Si), for which the detection limit was approximately 1012cm-3.