VCSELs, mini/microLEDs, power and RF devices point to another boom for this technology.
Several equipment makers are developing or ramping up new metalorganic chemical vapor deposition (MOCVD) systems in the market, hoping to capture the next wave of growth applications in the arena.
Competition is fierce among the various MOCVD equipment suppliers in the market, namely Aixtron, AMEC and Veeco. In addition, MOCVD equipment suppliers are looking for renewed growth in 2020, but business conditions remain cloudy.
MOCVD is one of the key systems used to manufacture lasers, LEDs, optoelectronic components, power/RF devices and solar cells. The technology has been in the market for several years. Basically, an MOCVD system deposits thin single crystal layers on the surface of a device. MOCVD is generally used to deposit III-V compound semiconductor materials, such as indium phosphide (InP), gallium arsenide (GaAs) and gallium nitride (GaN), on devices.
The biggest market for MOCVD has been LEDs, but that segment has been in a slump. So vendors are focusing their efforts on other markets. “For example, you have the VCSEL boom for facial ID,” said Ronald Arif, senior manager of product marketing at Veeco. “Right now, we are looking at potentially another big boom. This is mainly for miniLEDs and microLEDs.”
Targeted for next-generation displays, both microLEDs and miniLEDs are smaller versions of today’s light-emitting diodes (LEDs). All LEDs convert electrical energy into light. Meanwhile, vertical-cavity surface-emitting lasers (VCSELs) enables the facial recognition features in smartphones. Facial recognition detects the owner of a phone and unlocks it. In addition, MOCVD is also enabling GaN-based RF and power semiconductor devices.
Despite a myriad of growth drivers, the MOCVD equipment market is a mixed picture. After experiencing a slowdown in 2019, MOCVD vendors are looking for a rebound in 2020, although the recovery may take time. In total, the MOCVD equipment market is expected to reach $445 million in 2020, down from $465 million in 2019, according to Bob Johnson, an analyst at Gartner.
Sluggish business conditions and other factors are impacting the MOCVD market. The fastest growing segments for MOCVD are power electronics, VCSELs and related products. “I estimate that this may be a $200 million to $250 million marketplace,” said Patrick Ho, an analyst with Stifel Nicolaus. “It’s hard to say how much it grows, because the industry is still working through some excess inventory in this market.”
What is MOCVD?
MOCVD was originally invented by North American Aviation (Rockwell) in 1968. The early MOCVD tools were built in-house, and were used to grow III-V materials on substrates.
The first commercial MOCVD systems appeared in the 1980s. MOCVD has evolved and became one of several deposition technologies in the market. Deposition is a process that deposits a blanket of materials or films on a surface.
There are several deposition tool types in the market, and each one is targeted for different applications. For years, chipmakers have used chemical vapor deposition (CVD) to produce logic and memory devices in a fab. “In CVD, gaseous precursor chemicals flow into a process chamber that contains the silicon wafer. These precursors react on the wafer surface, forming the desired film along with byproducts that are removed from the chamber,” said Dennis Hausmann, technical director in the deposition group at Lam Research, in a blog.
Physical vapor deposition (PVD) is another tool type that forms thin films on surfaces. Atomic layer deposition (ALD) is a different technology, where materials are deposited one layer at a time.
MOCVD is different and perhaps not as well-known or understood as the other deposition types like CVD. CVD makes use of a reactor with a gas source. The same reactor can be used for MOCVD, but MOCVD utilizes a metalorganic source.
In simple terms, wafers are loaded into an MOCVD system and pure gases are injected into a reactor. The gas flow consists of chemical precursors, which decompose in the reactor. The reaction enables the growth of crystalline layers on a device. Some refer to this process as epitaxy, which is the deposition of thin layers on a substrate.
MOCVD is used for III-V materials. “If you look at the main material systems grown by MOCVD, they belong to two classes of materials. One is the gallium-nitride based. That’s gallium nitride on sapphire, gallium nitride on silicon carbide, and gallium nitride on silicon for power electronics,” Veeco’s Arif explained.
The second class falls under the arsenic phosphide group, which includes GaAs and InP. “This is for VCSELs and edge-emitting lasers. Mini and microLEDs are a combination of both. Red is arsenic phosphide. Blue green is gallium nitride,” Arif said.
Each MOCVD vendor has a different way to enable the growth process in a system. For example, Aixtron’s MOCVD tools use a horizontal laminar gas flow.
Veeco’s MOCVD systems use a different technology called TurboDisc. In the system, wafers are rotating at high speeds. TurboDisc combines laminar vertical gas injection and a high-speed rotating disc in a vacuum environment, enabling epitaxial growth with good uniformities.
Veeco’s latest system, called the Lumina MOCVD platform, includes two models. Applications include edge-emitting lasers, mini/microLEDs and VCSELs. The tools are capable of depositing arsenic phosphide epitaxial layers on wafers up to 150mm.
Veeco’s system is capable of handling several different apps on the same platform. Rival Aixtron is working on a similar system.
Big to tiny LEDs
All of this has a long history that dates back to 1962, when GE developed the first visible-spectrum LED using an early epitaxial process. Later, MOCVD was used to make LEDs.
An LED is a PN diode, which converts electrical energy into light. LEDs comes in different configurations, such as monochrome and multi-color. An RGB (red, green, blue) LED is one popular type. LEDs are used for backlights in LCD displays, billboards, consumer electronic products and solid-state lighting.
LEDs are made in LED fabs. The process starts with a sapphire or silicon carbide (SiC) substrate. GaN is deposited on the substrate using MOCVD. Then, the structure undergoes a series of patterning, deposition and etch steps.
The big boom for LEDs occurred in the 2000s, when the solid-state-lighting market took off. LED bulbs are attractive because they consume less energy than traditional incandescent bulbs.
But during that period, a number of LED companies from China entered the market, and subsequently built up too much fab capacity. By 2010, the LED market fell into an oversupply mode and LED prices plummeted.
At the time, the Chinese government handed out subsidies to LED makers in China to buy MOCVD tools. LED suppliers bought too many tools, causing an oversupply of systems in the market, as well.
Today, the situation is nearly the same in China. “Massive subsidies in China have led to an excessive LED capacity build-up. The MOCVD market is now in a situation of significant overcapacity for GaN LED production,” said Amandine Pizzagalli, an analyst at Yole Développement.
In China, the commodity LED business is dominated by one MOCVD vendor. “The commodity blue LED market has been cornered by the Chinese, namely AMEC, and that is not likely to change over the foreseeable future,” Stifel Nicolaus’ Ho said.
Still, there are some new and potentially large opportunities for MOCVD beyond LEDs. Dozens of companies are working on two related technologies called microLEDs and miniLEDs. Apple, Facebook, Samsung and TSMC are just a few of the companies developing microLEDs.
A miniLED is a smaller version of a traditional LED and ranges in size from 100μm and above. Like LEDs, miniLEDs are targeted for backlights in displays.
Still in R&D, microLEDs are microscopic versions of an LED. One microLED measures less than 100μm, which can be 1/100 the size of a conventional LED.
MicroLEDs are self-emissive and don’t require a backlight. In theory, a display using microLEDs provides more color and higher brightness with lower power than today’s displays.
MicroLEDs are targeted for two main display types. “In the development area of microLEDs, we see good progress being made in the industry towards the commercialization of microLED displays — either very large displays or very small displays for wearables,” said Bernd Schulte, president of Aixtron, in a recent conference call.
But microLEDs face several challenges. For example, one HDTV requires 6 million individual microLEDs. So in a fab, 6 million microLEDs must be manufactured and then transferred onto a backplane in the TV. Making microdisplays using microLEDs is also daunting.
There are various ways to make microLEDs. In one flow, the first step is to make an assortment of microLEDs on a substrate. For this, a GaN or other materials are deposited on the substrate using MOCVD.
This is a challenging process. “Defectivity and wavelength uniformity are among the challenges,” Veeco’s Arif said.
Another challenge for MOCVD is to generate high-quality epitaxial growth across a large wafer population with tight uniformities. High epitaxy yields are required to reduce the possibility of dead pixels in the display.
“At the microLED device level, the epitaxy process step must be very well controlled to make sure there are not yield-limiting particles, pits, and scratches,” said Steve Hiebert, senior director of marketing at KLA. “Inline inspection and metrology are critical during epi to enable subsequent high yield and uniformity. Following epi, at the microLED chip formation, controlling patterning defects is essential for high yield. A major challenge is the small size and complex structure of microLED chips. For microLEDs, these dimensions are one to two orders of magnitude smaller than traditional LEDs, which drives higher-sensitivity patterned wafer inspections capable of detecting smaller, sub-micron scale defects.”
Following the MOCVD step, meanwhile, the resulting structure is a substrate with a multitude of microLEDs. Then, the individual microLEDs are diced, tested and then transferred to a backplane using mass-transfer techniques. There are several ways to transfer microLEDs to a backplane, all of which are challenging.
All steps require various process control measures. “It’s critical to have effective inspection and metrology at various steps in the process to ensure high yields,” said Subodh Kulkarni, president and CEO of CyberOptics. “The six key steps include incoming quality inspection of the flexible circuits, solder paste inspection, automated optical inspection at the pre- and post-reflow stages, coordinate measurements post-placement of the LED die, and final test.”
All told, microLEDs aren’t ready for prime time just yet. The industry still requires more innovations.
3D sensing takes off
Vertical cavity surface emitting lasers (VCSELs) are also hot technologies. A VCSEL is a semiconductor-based laser diode that emits an optical beam vertically from its top surface, according to Finisar.
VCSELs are multi-layer structures. An active region is sandwiched between two distributed Bragg reflector (DBR) mirrors. A typical VCSEL consists of 60 to 70 layers. The total structure thickness is about 10um.
Figure 1. Typical VCSEL Cross Section Source: II-VI Inc.
“You have the DBR, which is the bottom mirror, the active region that emits light, and the top mirror,” Veeco’s Arif explained. “The active region emits light. It gets bounced off by the top and bottom layers many times. Every time it passes the active layer, it gets amplified. At some point, the amplification is so high that it overcomes the reflectivity of the mirror and a laser beam shoots out.”
GaAs is the broad class of materials used for VCSELs. “Within a typical commercial VCSEL structure, one utilizes a combination of materials such as GaAs, indium-gallium-arsenide (InGaAs), gallium-arsenide-phosphide (GaAsP), and aluminum-gallium-arsenide (AlGaAs),” Arif said. “The VCSEL active region is what we call a multi-quantum well structure. This is made up of an InGaAs quantum well sandwiched by a GaAs, AlGaAs, or GaAsP quantum barrier.”
The multi-layer structure is developed using MOCVD. CD control and uniformity are critical. Another issue is cost. “Our customers will get more and more pressure to reduce cost on these high-end devices such as VCSELs,” Aixtron’s Schulte said.
Commercialized by Honeywell in 1996, VCSELs were used in computer mice and other PC peripherals. Then, in 2004, Finisar bought Honeywell’s VCSEL division and expanded the technology into the networking field. For some time, VCSELs have been used as light sources in fiber-to-copper interfaces for carrier-grade data networking equipment.
VSCELs began to take off in 2017, when Apple incorporated this component in the iPhone X. It paved the way towards what many call 3D sensing.
Apple’s phone consists of three sensor modules (dot, illuminator and proximity) using VCSELs. First, a dot projector produces more than 30,000 dots of infrared light on the object, according to LEDinside. Light is reflected back from the object to create a 3D landscape. The data is passed to the chips to identify a face for authentication, which will unlock the phone, according to LEDinside.
Other smartphone OEMs are developing phones with 3D sensing features. In addition, VCSELs are moving into other applications. “VCSEL’s future applications can be applied to automotive, industrial, gaming and military,” said Barry Lin, CTO of Wavetek, a III-V foundry vendor that is part of UMC’s New Business group. “In addition, a new format of micro-VCSEL is in progress for imaging and display applications.”
Lin listed a number of emerging applications for VCSELs. Among them:
Going with GaN
GaN is another big market for MOCVD. GaN is a binary III-V material that has 10 times the breakdown field strength when compared to silicon, and double the number of electrons.
For years, GaN has been used for the production of LEDs, power semiconductors and RF devices. “GaN can be used in electronics or photonics,” Lin said. “Due to its high bandgap, the breakdown field can be very high. Another characteristic is its high mobility. As a result, GaN conversion efficiency in power management can be very high. The RF application band can also be very high.”
Each product type uses a different process. In one GaN-based power semiconductor flow, a thin layer of aluminum nitride (AlN) is deposited on a substrate. Using MOCVD, a GaN layer is grown on the AlN layer. A source, gate and drain are formed on the GaN layer.
“For MOCVD, the general challenge in GaN is not that different from arsenic phosphide. On the performance side, things such as uniformity, materials quality, defectivity, interface sharpness, and background dopant concentration are critical,” Veeco’s Arif said.
The RF version of GaN is taking off in base stations for wireless networks. In base stations, RF GaN is targeted for power amplifiers. But GaN-based power amps face some competition from an incumbent technology. Traditionally, base stations have used RF power amps based on laterally-diffused metal-oxide semiconductor (LDMOS) devices.
“GaN on silicon carbide semiconductors are releasing engineers and designers from the restraints of silicon with unprecedented power and efficiency. GaN improves system performance across multiple applications by utilizing smaller, lighter equipment that has high power density and the ability to operate at high frequencies. With the explosive growth of the 5G revolution, which is driven by exponential rise in data rate and bandwidth requirements, GaN on silicon carbide is the optimal material to support this technology,” said Gerhard Wolf, vice president and general manager of RF products at Wolfspeed, A Cree Company.
In addition, GaN is also used for power semicoductors. GaN-based power semiconductors compete against IGBTs, power MOSFETs and SiC power devices. GaN is often compared to SiC. Both are wide-bandgap materials, meaning they are more efficient than silicon-based devices like IGBTs and power MOSFETs.
“In many ways, GaN has even greater potential than SiC. It is ideally suited for addressing high-volume applications in rapid charging solutions because of its superior performance at high frequencies. Furthermore, it has the potential for integration into silicon-based technologies,” said David Haynes, managing director of strategic marketing at Lam Research.
“However, from a technical perspective, GaN remains less mature than SiC. If one considers GaN-on-silicon HEMT (high electron mobility transistor) technologies, yield remains a concern because of the quality of GaN MOCVD growth on silicon,” Haynes said. “There are also challenges associated with device performance and reliability. These later factors are highly tied to the HEMT fabrication process.”
Conclusion
Clearly, MOCVD is a critical technology, which in many respects has flown under the radar. For years, it was mainly associated with LEDs. Now, the deposition technology is paving the way for some new and emerging apps.
Like most equipment markets, MOCVD vendors face a challenging business environment in 2020. And to be sure, Aixtron, AMEC, Veeco and perhaps others will battle each other for the new and emerging apps. The competition has just begun.
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