Brian W. Baird

Generation of programmable temporal pulse shape and applications in micromachining

In this paper we presented a pulse shaping technique on regular solid-state lasers and the application in semiconductor micromachining. With a conventional Q-switched laser, all of the parameters can be adjusted over only limited ranges, especially the pulse width and pulse shape. However, some laser link processes using traditional laser pulses with pulse widths of a few nanoseconds to a few tens of nanoseconds tend to over-crater in thicker overlying passivation layers and thereby cause IC reliability problems. Use of a laser pulse with a special shape and a fast leading edge, such as tailored pulse, is one technique for controlling link processing. The pulse shaping technique is based on light-loop controlled optical modulation to shape conventional Q-switched solid-state lasers. One advantage of the pulse shaping technique is to provide a tailored pulse shape that can be programmed to have more than one amplitude value. Moreover, it has the capability of providing programmable tailored pulse shapes with discrete amplitude and time duration components. In addition, it provides fast rising and fall time of each pulse at fairly high repetition rate at 355nm with good beam quality. The regular-to-shaped efficiency is up to 50%. We conclude with a discussion of current results for laser processing of semiconductor memory link structures using programmable temporal pulse shapes. The processing experiments showed promising results with shaped pulse.

Advances in laser processing of microelectronics

We report on recent advances in laser processing of solar cells, flexible printed circuit boards, integrated circuit packages, and semiconductor memory in the nanosecond pulsewidth regime. These process advances are enabled by innovations in lasers and continue to drive requirements for emerging pulsed solid state and fiber lasers. Demand for increased throughput is projected to push the pulse repetition frequency for pulsed solid state sources utilized in many of these applications past 100 KHz. Ongoing device miniaturization continues to enable new applications for visible and ultraviolet pulsed laser processes, particularly for semiconductor devices. This paper summarizes the current status of these select laser processes, the laser sources that power them, and the outlook for future innovations in the field.

Tandem photonic amplifier employing a pulsed master oscillator fiber power amplifier with programmable temporal pulse shape capability

We report on recent advances in the development of a 1064 nm pulsed master oscillator fiber power amplifier (MOFPA) with integrated modulators enabling programmable temporal pulse shapes and its employment in a tandem photonic amplifier. The MOFPA amplifier chain is seeded by a laser diode operated in the CW regime, yielding very stable spectral characteristics that are independent of the pulse repetition rate and pulse shape. The use of 3 GHz integrated LiNbO3 electro-optic modulators in conjunction with high speed digital electronics results in an excellent pulse shaping capability, a fine pulse amplitude stability and high repetition rate operation (100 kHz-1MHz) with fast rise times (<1ns). Energy per pulse of 8-10 μJ with good beam quality characteristics are obtained using advanced large mode area (LMA) fiber designs in the final power amplifier stage. The output is linearly polarized with a spectral bandwidth of < 0.1 nm. When employed in a tandem amplifier configuration, in which the MOFPA output is input to a single-stage, single-pass Nd:YVO4 amplifier pumped by a single 30 W fiber-coupled 808 nm diode, a 600 mW average power at 100 KHz signal input from the MOFPA was amplified to 6 W with faithful amplification of the input temporal pulse profile while achieving excellent beam quality (M2<1.1) and pulse amplitude stability (< ±3%, 3σ). A model of tandem amplifier performance shows good agreement with experimental results and indicates prospective performance of advanced tandem photonic amplifier configurations.

Picosecond laser micromachining of advanced semiconductor logic devices

Advanced semiconductor logic devices are increasingly complex, typically composed of multiple layers of dielectric, metal, and semiconductor materials. Laser micromachining is employed on these devices to form cut-outs, microvias, and perform partial material removal, including scribing and dicing operations. The recent development of high average power (> 10 W), < 20 ps, 1064 nm diode-pumped mode-locked solid state lasers, operating at pulse repetition frequencies > 100 KHz, enables an attractive short pulsewidth laser process alternative to existing nanosecond process technologies, particularly for laser micromachining of complex alloy structures. Emerging 45 and 65 nm node logic devices may contain greater than eight metal layers, typically aluminum and copper. They may also contain advanced low K layers which have proven difficult to process using conventional mechanical techniques, such as dicing saws. Efficient operation at 355 nm was readily achieved using extracavity conversion by employing non-critically phasematched LBO for SHG and critically phase-matched LBO for THG. Over 3 W at 355 nm at 100 KHz was achieved with an input of 8.5 W at 1064 nm. Preliminary micromachining results on advanced logic devices containing multiple low k and Cu layers at harmonic wavelengths (532 nm and 355 nm) yielded micromachining rates of > 300 mm/s with good workpiece quality.

355 nm Tailored Pulse Tandem Amplifier

We report on a 355 nm tailored pulse tandem amplifier. 1064 nm tailored pulse fiber laser output was amplified in a diode-pumped Nd:vanadate amplifier and then frequency converted to produce 0.6 W at 100 KHz.

Ultraviolet laser repair of advanced semiconductor memory devices

Summary form only given. Fabrication of semiconductor memory devices, including dynamic random access memory (DRAM) and static random access memory (SRAM), relies upon laser repair. Laser repair of memory involves the single pulse severing of fuses to enable decoders to address redundant memory cells, thereby improving the wafer-level yield of useful die. The development of next generation memory devices, such as 1 gigabyte (GB) DRAM will utilize fuse sizes of less than 500 nm on link pitches of 1500 nm and smaller and utilize Cu and Al fuses. Current laser memory repair systems employ Q-switched diode-pumped Nd:YLF and Nd:YVO/sub 4/ lasers operating at 1.047 /spl mu/m and 1.343 /spl mu/m, respectively. Systems operating in the infrared are expected to encounter difficulty in repairing devices at this scale due to wavelength-induced spot size limitations. To overcome these difficulties, we have recently demonstrated the extension of laser memory repair to the ultraviolet region and at link severing rates as high as 20,000 Hz.

High Excited Ion Density Effects on the Effective Fluorescence Lifetime in Q-Switched Solid State Lasers

A new expression for the pulse energy dependence at high excited ion densities is presented along with experimental measurements of fluorescence lifetimes in diode-pumped Nd:YLF.