Evaluation of a copper metallization process and the electrical characteristics of copper-interconnected quarter-micron CMOS

Copper metallization was applied to quarter-micron CMOS circuits using copper chemical vapor deposition (CVD) and chemical mechanical polishing (CMP). Both the metallization process and the electrical characteristics of CMOS devices/circuits were evaluated. Process-induced metal contamination on both sides of the wafer were quantitatively evaluated and reduced to about of 10¹¹ atoms/cm² by using an optimized cleaning sequence. The ability of borophosphosilicate-glass (BPSG) to act as a copper diffusion barrier was discovered and the ability of TiN to do so was also confirmed. Electrical characteristics of n and p MOSFET´s with copper interconnections were stable even after annealing at 550°C. The leakage current of the pn junction, capacitance-voltage characteristics and time-dependent dielectric breakdown characteristics of the MOS diode indicate that the copper metallization process did not deteriorate the pn junction and the gate oxide. Normal operation of a 53-stage quarter-micron CMOS inverter ring oscillator with copper metallization was successfully achieved