Power Electronics

One development requiring higher performing power electronics is the growing adoption of electric vehicles (EVs) and expectations of longer driving ranges and faster charging times. Another trend calling for more advanced power electronics is the shift towards renewable energy sources which rely on efficient power conversion and reduced power losses. Additionally, further advancements in consumer electronics and telecom demand power electronics that can manage higher power densities and faster switching speeds while providing better thermal management.

Silicon-based power electronics are able to serve a portion of the applications described above, but they are mostly suitable for applications such as home appliances, power tools, and less demanding data center functions—for these types of applications, lower to mid-range switching frequencies are suitable, and cost often takes precedence over performance or form factor. But beyond mid-range switching frequencies, silicon-based power electronics fall short due to the inherent bandgap of silicon. Hence, semiconductors with wider bandgaps than silicon are necessary because they can provide higher power, switching frequency, operating temperature, switching voltages and better efficiency. Two materials in particular with wide bandgaps have already proven their worth for power electronics: silicon carbide (SiC) and gallium nitride (GaN). The bandgaps of SiC and GaN are over two and three times greater in electron volts (eV) than silicon's.

SiC-based power electronics are ideal for high-power/high-switching frequency applications. For instance, the potential for EVs with SiC-based power electronics includes longer driving ranges, faster charging times, and lighter vehicle weight. Also, more compact and more efficient energy storage systems may be possible with SiC. While GaN is limited to medium-power applications, it offers the highest operating frequency among these technologies. As such, GaN-based power electronics opens up many new possibilities in consumer electronics and telecom, such as ubiquitous use of wireless charging and faster communication speeds.

It is also important to recognize that all of these technologies overlap in roughly the mid-power/mid-frequency space, creating a "competing zone" amongst them. In this arena, silicon may be preferred when cost is the primary concern. But when higher performance, better efficiency, or smaller-sized products are desired, SiC or GaN should be considered.

Manufacturing of traditional silicon-based power electronics is well known and established, but SiC- and GaN-based power electronics presents new and more difficult challenges.

SiC as a raw material is much more costly than silicon is, and finished devices are about three times more expensive. SiC wafers are more brittle, thinner and smaller than silicon wafers are, so handling SiC wafers during the manufacturing process is more delicate, complex, and expensive.

GaN wafers are even more brittle, thinner and smaller than SiC wafers, so handling GaN wafers is even more complicated and costly than handling SiC wafers. Interestingly, however, GaN-based products can be cheaper than those made of silicon for equivalent power conversion specifications—this is due to GaN's higher efficiency, lower operating costs and smaller footprint.

While SiC and GaN wafer fabs share many steps used in silicon wafer manufacturing, there are some notable differences. For example, SiC and GaN wafer ingot slicing is typically performed by lasers instead of mechanical diamond saws to improve wafer yields and lower costs by reducing material waste and scrap. Also, an existing silicon wafer processing line cannot be used as is on SiC or GaN wafers—one reason is that wafer handling equipment developed for silicon my not be appropriate for SiC or GaN wafers.

The good news is that MKS has decades of experience with silicon wafer processing from the front-end to back-end and can work with you to develop and build the best solution for your SiC or GaN needs.

As a leader in silicon wafer processing from the front-end to back-end for decades, MKS has a deep understanding of the challenges faced in designing and manufacturing power electronics. We've turned this knowledge into unique product features that provide an advantage when used for SiC- and GaN-based power electronics. Some of these features are described here.

SiC and GaN Processing Applications:

• Ingot slicing
• Scribing
• Grooving
• Dicing
• Marking

Lasers are superior to traditional mechanical methods such as blades and drills in applications including ingot slicing, scribing, grooving, dicing and marking. For example, the time-consuming process of slicing a SiC ingot with a mechanical diamond saw can waste up to 75% of the material. Moreover, as SiC is a significantly harder material than silicon is, a blade will wear faster, leading to increased replacement costs and more frequent downtime. By comparison, laser ingot slicing for SiC and GaN results in minimal material loss, and there is no tool wear. And by employing the appropriate laser and slicing methodology, laser ingot slicing can be considerably faster than mechanical slicing.

MKS' lasers are very high-precision devices, so they can cut and drill accurately and repeatably on the order of microns with ease, which may not be the case with mechanical tools. SiC and GaN wafers are already more brittle than silicon and must be handled more delicately, and as SiC and GaN devices become more complex, they might be even more difficult to produce solely through mechanical means. In addition to the high precision, lasers also offer more flexible patterns for cutting and drilling, which further enables more complex designs and higher performing devices to be made.

Another important advantage that lasers present over traditional processes is the quality of their results. With slicing, scribing, grooving and dicing, lasers produce fewer burrs and less damage to the surrounding areas than mechanical cuts do. This results in higher manufacturing yields, as less of the material is wasted. Additionally, laser operations result in fewer latent defects and cracks compared to mechanical operations, which can lead to better quality and reliability of the product in the field, as not all of these types of issues are discovered before products leave the factory. And like laser ingot slicing, laser scribing, grooving, dicing and marking are contact-free operations, so there is no tool wear, and the replacement downtime is exceedingly infrequent compared to mechanical methods.

Taken all together, SiC and GaN processing with lasers will enable the production of devices that are mainstream enough to complement and compete with silicon-based electronics.

Laser Advantages:

• High precision
• Flexible and complex patterns
• Fewer burrs
• Less surrounding damage
• Fewer latent defects and cracks
• Contact-free operation

Wafer positioning performance for processes including lithography, inspection and dicing can be very challenging, often with sub-micron and even nanometer scale accuracy and repeatability required. Moreover, this very precise level of operation must be delivered quickly, with speeds up to 1 meter/sec, to maximize throughput.

To address the wafer positioning demands of the semiconductor manufacturing industry, MKS developed the Newport DynamYX® series positioner, a high-throughput, high-accuracy solution based on air bearing and linear motor technology. With over 20 years of field-proven success in more than 1,000 systems installed worldwide, DynamYX provides the highest level of commercially available positioning performance. Additionally, MKS offers the Newport HybrYX® series positioner, a hybrid air and mechanical bearings system with linear motors, that also delivers high throughput and accuracy.

All DynamYX and HybrYX systems are custom-designed, so the techniques and solutions developed for silicon processing can be adapted and applied to SiC and GaN processing.

Below is a selection guide for the various applications and our recommended motion platforms. Please keep in mind that this is only a guide, and we’d love to discuss your application and requirements in detail with you so we can help provide the best solution for you. For wafer inspection, our DynamYX systems are the best-in-class, and HybrYX is also a good value. The IDL and XM Series linear stages can also be used depending on your requirements. For lithography, reticle inspection and repair, and mask writing, DynamYX is also the best. For wafer dicing, HybrYX is ideal because of its outstanding price-to-performance value, but you can also consider the DynamYX and the IDL stages.

There are many factors to consider when selecting optics for power electronics applications. Here are the criteria to start with.

First is the wavelength required. For the laser, it’s likely going to be 355 nanometers UV, and sometimes 532 nanometers green or 1064 nanometers IR. There are broadband and laser line optics available, but when you know specifically which wavelength you’ll have, we recommend using laser line optics when possible because they’re optimized for a specific wavelength and will perform better than a broadband optic.

The next thing to consider is an optic’s LIDT, or how much laser power or energy the optic can withstand before it gets damaged, and if that will work in your system. You’ll want to use not only substrates that are known for high laser damage thresholds but also coatings that are properly tested for high damage thresholds as well.

You should then look at how well it reflects light if it’s a mirror, or how well it transmits light if it’s a lens. And for other types of optics like a beamsplitter or waveplate, you’ll want to evaluate how well light passes through them as well. The less light you lose as a result of the optic itself, the easier it will be for you to manage the light throughout the rest of your system, and the better your results will be.

Lastly, optics are available in all different sizes and shapes depending on your requirements.

High-energy laser mirrors optimized for 355, 532 and 1064 nm offer very high reflectivity and damage thresholds.

High-energy lenses optimized for 355, 532 and 1064 nm offer very high transmission and damage thresholds.

Highest laser damage resistance and lowest reflection loss.

Even with the advantages that lasers have over traditional tools, laser systems can still degrade over time. Some causes of degradation include thermal effects on a laser system's internal components, vibrations or shock, and debris near the processing site. These issues could affect laser performance in a number of ways. First, output power may be reduced, causing the laser to be less efficient. Another problem that may be caused is a change in the focus or other profile of the beam, which may lead to a cut or drill to be off target, too deep, low quality or possibly damaging to another part of the material.

Therefore, to ensure the highest quality of manufacturing SiC and GaN wafers and to minimize the possibility of production down-time, it is crucial to monitor the laser beam frequently with appropriate instruments—like Ophir® power sensors, power meters and beam profilers—that can characterize the laser while handling its maximum output power level.

• SP932U Beam Profiling Camera: high resolution, real-time viewing and measuring of laser structure with highest accuracy in the industry.

	SP932U
Spectral Range	190-1100 nm (Optimized for NIR & Nd:YAG)
Damage Threshold	50 W/cm2 1 J/cm2, <100 ns pulse width
Beam Sizes	34.5 µm – 5.3 mm
Pixels	2048 x 1536 Effective Pixels 3.45 µm Pixel Size
PC Interface	USB 3.0
Other Features	BeamGage® software included UltraCal™ correction algorithm Measures cross-sectional intensity 72 dB true dynamic resolution 24 Hz frame rate in 12-bit mode A variety of attenuators available

MKS offers a comprehensive portfolio of Ophir^® laser thermal power sensors, several of which can measure the optical output power of short- and ultrashort-pulsed lasers such as IceFyre, Talon, Talon Ace and Quasar. These sensors have a very high damage threshold to withstand the high optical peak power delivered by each pulse. Ophir sensors and meters meet the ISO/IEC 17025 standard for calibrated devices.

• Laser Thermal Power Thermal Sensors: very high damage thresholds for hundreds of watts power measurement.

	F150(200)A-CM-16	30(150)A-SV-17	F80(120)A-CM-17
Spectral Range	0.248-9.4 µm	0.19-11 µm	0.248-9.4 µm
Power Range	300 mW - 200 W	100 mW - 150 W	100 mW - 120 W
Energy Range	50 mJ – 200 J	50 mJ – 300 J	50 mJ – 200 J
Max Avg Power Density	35 kW/cm2	60 kW/cm2	35 kW/cm2
Max Energy Density (2 msec)	45 J/cm2	50 J/cm2	45 J/cm2
Aperture	Ø16 mm	Ø17 mm	Ø17.5 mm
Response Time	3 sec	1.7 sec	2 sec
Other Features	Not water-cooled