Improving the Yield and Turn-Around Time of Focused Ion Beam Microsurgery of Integrated Circuits by LCVD Method

Tungsten conductor lines deposited by focused ion beam (FIB) from W(CO)₆ precursor gas quite often have too high a resistivity (typically 100-200 mu Omega cm) in practical integrated circuit edit work. Even if the high resistivity of the deposited conductor line can be tolerated the FIB deposition process of conductor lines with length over 100 mum can take several hours. This can cause serious problems in analogue or mixed signal type integrated circuit (IC) microsurgery often encountered in RF-band circuits. We present a method for the reduction of the FIB deposited tungsten conductor line resistance by subsequent laser chemical vapor deposition (LCVD) of copper from an organometal Cu(hfac)tmvs precursor. In this way, the resistance of the FIB deposited tungsten line can be reduced by order of magnitude from its original value by subsequent LCVD process. LCVD takes place selectively only on the FIB deposited tungsten line with high spatial resolution. As another practical application LCVD can be used to fabricate charge dissipation routes before FIB operations and thus protect transistors from charged ion beam induced discharge damages. Furthermore, the feasibility of the FIB/LCVD process in circuit edit work is discussed in this paper. Examples of both technologies used successfully in a combined way and the developed process flow for the circuit edit are presented. We applied the combined method to over different 200 circuit edit cases manufactured by various semiconductor processes. We found that the developed combined method could be used in about 20%-30% of the circuit edit cases to either improve the yield in circuit edit or speed up the total turnaround time.