Semiconductor Manufacturing

Laser pulses can vary over a very wide range of duration (milliseconds to femtoseconds) and fluxes, and can be precisely controlled. This makes pulsed laser ablation very valuable for both research and industrial applications.

Laser Ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave (CW) laser if the laser intensity is high enough. The depth over which the laser energy is absorbed, and thus the amount of material removed by a single laser pulse, depends on the material’s optical properties and the laser wavelength.

Laser pulses can vary over a very wide range of duration (milliseconds to femtoseconds) and fluxes, and can be precisely controlled. This makes laser ablation very valuable for both research and industrial applications.

The 193 nm solid-sampling-system GeoLasPro is a self-contained laser ablation system for sample introduction in high-resolution LA-ICP MS (laser ablation inductively-coupled plasma mass spectrometry). GeoLasPro integrates the COMPexPro 193 nm ablation laser including beam homogenizing and shaping optics, a sample chamber, and unmatched microscopic sample observation capability. 193 nm sampling speed can be varied in a wide range from 1 Hz up to 100 Hz.

GeoLasPro includes several innovative features that enhance the performance of the overall LA-ICP-MS system. For example, the new sample observation microscope is made perfectly co-linear with the laser beam delivery optics through the use of an all-mirror microscope objective, which is free of chromatic aberration. This objective is also able to operate at higher laser power without the risk of coating damage that can occur when using lens-based objectives. These beam delivery optics can achieve a homogenized spot with a diameter as small as five (5) microns, which is ideal for sampling small fluid inclusions. The optics also include interchangeable circular and square beam shaping masks providing high sampling flexibility.

GeoLasPro is designed for geological and nuclear physics research and for quality control of materials and pharmaceutical samples. Examples include analysis of fluid inclusions in minerals, age determination of samples by isotope ratio analysis and analyzing high purity semiconductor materials.

Advantages of Laser Ablation

• The 193 nm wavelength couples readily with difficult materials like highly transparent quartz for near matrix-independent ablation.
• The air-cooled excimer laser has exceptional stability, within 2%.

The dramatic miniaturization of electrical and opto-electrical circuits and the growing need of high precision measurements of the shape of surfaces in industry are the driving force of the laser-based inspection market.

The laser is perfectly suited for high precision inspection, because of its high resolution and the various wavelengths available that can be selected according to the material under investigation.

What is Laser Inspection?
Laser inspection can be divided into two segments. One is the quality control of microscopically generated features and the determination of contamination in the semiconductor field. Microscopic laser inspection uses scattering, absorption and ultrasonic techniques to determine and locate a defect or a contamination of sizes in the range of the wavelength used. The Verdi series of CW solid-state lasers in the green and the Sapphire™ family in the blue cover scattering and absorption techniques, whereas the Vitesse family of femtosecond lasers serve ultrasonic applications.

Laser Inspection Equipment
The other segment in laser inspection is the determination of the quality of the macroscopic shape and its deviation to a reference. For this purpose, interferometry, shearography and holography using visible and deep UV wavelengths are widely used methods that achieve accuracy on the order of the wavelength employed. Coherent offers solutions to this ever-expanding marketplace with laser inspection equipment including the Verdi series (green - 532 nm), Sapphire (blue - 488 nm) and the Azure (deep UV - 266 nm). All of these lasers have the unique PermAlign™ technique for superior stability and lifetime. For the blue spectrum, Coherent offers the revolutionary Sapphire family at 460 and 488 nm.

DPSS, ion and optically pumped semiconductor lasers enable front-end semiconductor manufacturing.

In front-end semiconductor manufacturing, lasers are mainly used in two applications: in lithography tools and in inspection. There are many different inspection steps in a modern semiconductor fab and Coherent lasers are used in most of them: mask inspection, bare and patterned wafer inspection. Coherent has many years of experience building lasers for these very demanding applications, which require ultra-high precision and no unscheduled down time.

Illuminating the semiconductor roadmap.

Laser technology’s role in semiconductor and microelectronics fabrication is growing exponentially as manufacturers seek to produce smaller, more powerful, reliable devices. More integrated components per area of silicon and reduced circuit geometries are the overriding benefits as lasers enable a complete range of semiconductor fabrication processes. As lasers trend towards shorter (UV) wavelengths, higher power and high reliability, they are expanding the bounds of semiconductor manufacturing.

Applications Knowledge
Unparalleled Technology Depth

• Reticle - Laser-direct writing, inspection, repair
• Wafer - Inspection (bare and patterned), dicing, marking, scribing
• Metrology - Thin-film diagnostics, optics inspection
• Device - Test & measurement, marking, trimming and memory repair
• Printed Circuit Boards (PCBs) - Laser-direct imaging, inspection, via drilling

Coherent has the technology experience and diversity in all leading laser disciplines used in semiconductor and microelectronics manufacturing.

• Solid-state lasers, CW and pulsed (visible and UV)
• Ion lasers
• CO₂ lasers
• Semiconductor diode lasers (IR, visible, violet)
• Measurement Instruments

Pulsed laser deposition (PLD) is a laser-based technique used to grow high-quality thin films of complex materials on substrates like Silicon wafers. The material to be deposited (target) is vaporized by short and intense laser pulses and forms a plasma plume. Then, the vaporized target material from the plasma bombards the substrate and – under the right conditions – creates a thin homogenous layer on this substrate. For each laser shot, a layer of only a few nanometers of material is ablated to form the plasma plume in a process that typically last a few tens of picoseconds. To enable this process, nanosecond pulses with energies of tens to hundreds of mJ are necessary and UV wavelengths are usually preferred. These requirements match very well the performances of excimer lasers.

The first laser deposition experiments took place in the mid to late 1960s, but PLD gained tremendous interest after T. Venketesan in 1987 first applied this method to create high temperature superconductive (HTSC) films. Since then, many hundreds of lasers have been sold to drive research, process development and small-scale production of thin film devices, such as superconductive magnetic sensors (SQUIDs), thin film ferroelectrics and “high k” gate resistors, semiconductor alloys, carbon nano-tubes, and more.

High pulse energy lasers provide several benefits. First, they extend the range of usable target materials. Second, they enable to ablate a larger area of the sample with the desired fluence. This increases the deposition rate and reduces the plume angle, resulting in higher deposition efficiency. Third, higher pulse energy lasers provide a larger process window, allowing a more consistent process.

Coherent’s COMPex and LEAP laser series are designed for demanding high-pulse energy applications and are highly effective tools for pulsed laser deposition. They deliver the beam stability and energy stability performance required to achieve superior results in sophisticated thin film deposition experiments.