The STIC Technology-A Monolithic Approach for Combining Tantalum and Silicon Technologies

Historically, one of the limitations to higher orders of integration in linear integrated circuits has been the need to go off chip for precise passive components. These passive elements are usually precision capacitors and adjustable resistors for accurate circuit characteristics, such as are required in precise frequency shaping circuits. In the Bell System, the usual configuration has been beam-leaded active integrated circuit (IC) chips bonded onto ceramics that contain tantalum thin film resistors. The marriage of these two technologies in a monolithic approach on a silicon substrate is reported here. An overview of the silicon tantalum integrated circuit (STIC) technology is given. Discussion will center around film parameters, component characteristics, and laser trimming capability including optical effects on active silicon. The applications and advantages of this technology will also be described. The STIC technology development program proceeded along several lines; Ta
2
N resistor film characterization and processing on silicon, laser trimming of these resistors, capacitor processing and characterization, and the development of the total process on active silicon. Ta
2
N resistor films with resistivities from 100 to 1000
\Omega
/
\Box$^b$
were processed into resistor patterns on oxidized silicon substrates and on Si
3
N4 capped oxidized silicon substrates. A process has been developed to combine the Ta
2
N resistors onto an active silicon integrated circuit. Accelerated aging test showed the films on SiO2 dieléctrics to be as stable as similar films on ceramic substrates. Resistor films on Si
3
N4 dielectrics behave in an anomalous manner, indicating an interaction between the Ta
2
N and Si
3
N4. The feasibility and compatibility of combining the tantalum thin film and silicon technologies in a monolithic structure has been demonstrated. The STIC technology will permit greater flexibility in circuit design, and additional level in circuit integration, better circuit performance, increased number of circuits processed in a batch mode, and significant economies in production.