Reducing optoelectric response when functionally tuning thin-film resistors on silicon IC's

Functional laser tuning of monolithic integrated circuits has been used for over twenty years to improve yields and/or device performance. This tuning, or "trimming" is done using Nd:YAG or Nd:YLF laser sources operating at 1.064 microns or 1.047 microns respectively. These conventional wavelengths perform extremely well for passive trimming but can have serious problems when functionally trimming for total device performance. The 1.064 micron or 1.047 micron laser wavelengths or other shorter wavelengths can cause optoelectric responses in semiconductor materials and devices that result in performance drift or complete malfunction of the devices. This paper describes a proprietary, new laser processing technology that dramatically reduces, or virtually eliminates, the laser-induced performance drift or shift of a device during functional trimming. A new laser wavelength is used which is absorbed well by the thin-film resistor materials but is "invisible" to the silicon-based structures. Results are given from actual production devices which were trimmed on an existing laser/tester modified to incorporate the diode pumped laser operating at the new wavelength.