MICRO: Brave New Materials

Tests demonstrate that an aerosol cleaning technology using argon and nitrogen is compatible with copper and low-k processes and effective at removing associated particle defects. or several years, the semiconductor industry has been using cryokinetic cleaning with a solid aerosol derived from argon and nitrogen to remove particle defects from the wafer surface during aluminum metallization and interconnect processing. The cryokinetic cleaning technology is a completely dry, gas-phase, nonreactive process that does not damage sensitive films and has a minimal environmental impact. In contrast, traditional particle removal methods involve potentially damaging megasonic energy and reactive liquid chemicals that can change film properties and require extensive waste treatment. IC manufacturers have found the argon/nitrogen aerosol process easy to implement in the production line. The process has been implemented in copper/low-k dielectric processing on 200- and 300-mm production lines. After describing the cryokinetic aerosol process and briefly discussing its successful use with aluminum/TEOS and high-density plasma deposition processes, this article focuses on the suitability of the cleaning technique in copper and low-k applications. Various tests have demonstrated that the technique is highly efficient at removing defects that remain after copper chemical-mechanical polishing (CMP) without affecting the properties of low-k dielectric materials. Introduced by FSI International (Chaska, MN) in 1996, the cryokinetic process uses an aerosol formed from a cryogenically cooled mixture of argon and nitrogen. A 3:1 mixture of these gases first flows into a coil immersed in a dewar of liquid nitrogen, where it is cooled and partially liquified at a temperature of ~100 K and a pressure of ~75 psia. This mixture of gas and liquid then flows through a vacuum-jacketed line into the cleaning system's single-wafer chamber. The aerosol is formed when the mixture is dispensed from several small holes in the wall of a tube extending across the wafer