Development and characterization of an ultrathin rapid thermal silicon nitride for IC sensor applications

Considerable attention has been focused on the development of ultrathin insulators for use in the IC industry. In particular, solid-state sensors require physically durable and electrically suitable materials. One possible choice is silicon nitride: an excellent diffusion barrier, physically rugged, and a suitable insulator. For most thin film applications, CVD silicon nitride is the preferred material; however, it is difficult to deposit ultrathin layers (<50A). Thus, RIP thermal nitridation of silicon was investigated as an alternative to CVD silicon nitride for IC sensor applications. Ultrathin silicon nitride films have been thermally grown in ammonia and nitrogen ambients by rapid thermal processing. The effects of several variables on the growth of thermal nitride and its material properties were evaluated electrically (1-V behavior) and physically (etch resistance to HF). Some conditions gave the expected results: longer nitridation times and higher nitridation temperatures (generally) improved nitride properties. Other variables gave mixed results, improving physical resistance at the expense of electrical properties (annealing, two-step nitridation, in situ gaseous cleaning} or vice-versa (extended purges, low-pressure nitridation). By varying these process parameters, a film with an etch rate of 2.64 Atmin and a second film with a field strength of 8.16 MV/cm (to pass 1 uA through a 104 ul'f12 structure} were achieved. However, the single film with the best overall physical and electrical properties had an etch rate of 3.66 Atmin in 5:1 BHF, required a field of MV/cm, and maintained a current density of 0.12 mA/cm2 at -1 V

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