The formation mechanism of non-recessed Au–free Ohmic contacts on the AlGaN/GaN heterostructures is investigated for various Ti/Al atomic ratios (Al–rich versus Ti–rich) and annealing temperatures ranging from 500 to 950 °C. It is shown that Ti/Al atomic ratio is the key parameter defining the optimum annealing temperature for Ohmic contact formation. Ti–rich contacts processed at high temperature result in low contact resistance ∼0.7 Ω mm, better to those obtained at low temperature or with Al–rich metal stacks. The variation of the contact resistance with Ti/Al atomic ratio and annealing temperature is correlated with the intermetallic phase changes and interfacial reaction. Depending on the Ti/Al atomic ratio, two distinct mechanisms can be distinguished. For a small quantity of Ti (e.g., Al–rich contacts), Ohmic contact formation is done through a weak interfacial reaction which is nonexistent at high temperature due to the degradation of the metal morphology. However, for a quantity of Ti higher than 25 at. % (e.g., Ti–rich contacts), the agglomeration is delayed by 200 °C as compared to Al–rich contacts, and optimal contacts are formed at high temperature through a strong interfacial reaction.
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Abstract-In this paper, the mechanism of plasma-charging damage (PCD) of metal-insulator-metal (MIM) capacitors as well as possible protection schemes are discussed. A range of test structures with different antennas simulating interconnect layout variations have been used to investigate the mechanism of PCD of MIM capacitors. Based on the experimental results, two models are presented, describing the relation between the damage and the ratio of the area of the exposed antennas connected to the MIM capacitors plates. New design rules are proposed in order to predict and automatically flag possible PCD sites. Furthermore, layout solutions to reduce PCD are suggested.
Index Terms-Antenna ratio (AR), metal-insulator-metal (MIM), plasma-charging damage (PCD).
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