Laser systems and methods using triangular-shaped tailored laser pulses for selected target classes

#This disclosure relates to laser processing systems. In particular, this disclosure relates to laser systems and methods for severing electrically conductive links and/or micromachining semiconductor devices with laser pulses having shaped temporal profiles.

#Laser processing systems employed for processing dynamic random access memory (DRAM) and other semiconductor devices commonly use a Q-switched diode pumped solid state laser. When processing memory devices, for example, a single laser pulse is commonly employed to sever an electrically conductive link structure. In other industrial applications, laser scribing is used to remove metal and dielectric semiconductor materials from a semiconductor device wafer prior to dicing. Lasers may also be used, for example, to trim resistance values of discrete and embedded components.

#Some laser processing systems use different operating modes to perform different functions. For example, the ESI Model 9830 available from Electro Scientific Industries, Inc. of Portland, Oreg., the assignee of the present patent application, uses a diode pumped Q-switched neodymium-doped yttrium vandate (Nd:YVO4) laser operating at a pulse repetition frequency of approximately 50 kHz for laser processing of semiconductor memory and related devices. This laser system provides a pulsed laser output for processing link structures and a continuous wave (CW) laser output for scanning beam-to-work targets. As another example, the ESI Model 9835, also available from Electro Scientific Industries, Inc., uses a diode pumped Q-switched, frequency-tripled Nd:YVO4 laser for laser processing semiconductor memory and related devices. This laser system uses a first pulsed laser output at a PRF of approximately 50 kHz for processing link structures and a second pulsed laser output at a PRF of approximately 90 kHz for scanning beam-to-work targets. In some systems, higher PRFs (e.g., approximately 100 kHz) are also possible. Generally, the pulse widths of laser pulses generated by such laser systems are functionally dependent on the PRF selected and are not independently adjustable based on differences between target structures or other process variables.

#FIGS. 1A and 1B are example temporal pulse shapes of laser pulses generated by typical solid state lasers.

#FIGS. 2A, 2B, 2C, and 2D are cross-sectional block diagrams of a semiconductor device that includes passivated electrically conductive link structures.

#FIG. 3 is an electron micrograph showing unpassivated link structures having an area where adjacent links have melted together during laser processing using a Gaussian-shaped pulse.

#This disclosure describes processing unpassivated electrically conductive link structures and other structures on semiconductor devices using laser pulses with triangular-shaped temporal pulse profiles (e.g., power vs. time). As discussed in detail below, a “triangular-shaped” temporal pulse profile includes a profile having equal rise and fall times (e.g., symmetrical triangle shape), as well as sawtooth-shaped temporal pulse profiles where the rise time does not equal the fall time (e.g., an asymmetrical triangle shape). Thus, for an asymmetrical (sawtooth) triangular-shaped temporal pulse profile, the pulse's maximum peak power is located somewhere other than at the center (in time) of the pulse.

#In certain embodiments, laser pulses having triangular-shaped temporal pulse profiles may be generated using, for example, the lasers and systems described in U.S. Pat. No. 7,348,516, which is assigned to the assignee of the present patent application, and which is hereby incorporated herein in its entirety. Other example laser system embodiments for generating tailored laser pulses with triangular-shaped temporal pulse profiles are described below.

#In certain embodiments, families or classes of temporal pulse profiles may be defined for different types of target structures. For symmetrical triangle shapes, families of pulse shapes can be generated by maintaining a constant pulse duration (e.g., temporal width) while increasing or decreasing the maximum peak value. Additional families for the symmetrical triangle shape may be created, for example, by using different pulse durations while maintaining, increasing, or decreasing the maximum peak value. For asymmetrical triangle shapes, families of pulse shapes may be generated by changing pulse durations and/or maximum peak values. Additional families for the asymmetrical triangle shape may be created by, for example, moving the time of the maximum peak value and/or changing the rise and/or fall times.