Automotive power electronics products will become a key driver in the semiconductor industry, the automotive power components market prospects

Automotive power electronics are becoming one of the key drivers in the semiconductor industry. These electronics, including power components, are the core components that support the new electric vehicle's cruising range of at least 200 miles.

Although smartphone shipments are much higher than cars (1.4 billion in 2015 [1] and car sales of 88 million [2]), the semiconductor parts of automobiles are much higher. Automotive power ICs are growing steadily, and the industry's compound annual growth rate is expected to reach 8% in 2015-2020 [3]. In particular, battery-powered electric vehicles have become a strong growth driver in the industry. In May 2015, Teardown.com's report on the BMW i3 electric vehicle showed that the vehicle's bill of materials contained more than 100 power-related chips.

Unlike advanced logic transistors that continue to shrink in size under Moore's Law, power component FETs typically use older technology nodes using 200 mm (and smaller) silicon. However, power components have evolved and upgraded over the past few decades. For example, thicker PVD aluminum coatings (3-10 microns) must be deposited on the front side of the power components to achieve heat dissipation and improve electrical performance. If not deposited correctly, the thick aluminum layer is prone to whiskers and misalignment, with catastrophic consequences. Applied Materials' Endura PVD HDR high-speed deposition of aluminum reaction chambers ensures that such defects are minimized and the deposition rate is more than 50% higher than competing technologies.

In addition, thick epitaxial wafers from 5 microns to over 150 microns enable low resistance (Rds), high shutdown resistance (Roff) and faster switching speeds after complex doping.

Compared with traditional epitaxial reaction chambers, Applied Materials' new Centura ProntoTM ATM epi-epitaxial reaction chamber can increase growth rate by more than 30%, reduce chemical consumption by 25%, shorten cleaning time and reduce equipment cost of ownership. The system exhibits excellent in-wafer uniformity and resistivity to meet the demands of advanced power components.

Structural changes in the semiconductor film stack, such as converting the gate structure from a planar (transverse device) to a channel structure (vertical device), enabling insulated gate bipolar transistors (IGBTs) to achieve faster switching at lower loss rates speed. Similarly, the transition from multilayer epitaxy to deep trench fill can significantly improve the performance of super-junction MOSFETs (SJMs).

The etching process requires some improvements and adjustments to accommodate these options, including higher aspect ratio structures. The improved epitaxial silicon film and implant doping profile also enhance product performance.

Power component manufacturers continue to strive for excellence. The publicly available data shows that Hitachi's highly conductive IGBTs use a separate floating P layer to improve gate controllability and turn-on voltage. ABB Semiconductor builds a P-type column implant under the trench gate to create a superjunction effect for faster switching speeds.

By reducing the thickness of the wafer, the stored charge of the high speed switch can be effectively reduced. Fuji Electric recently developed a seventh-generation IGBT with a thinner drift layer, a smaller trench pitch, and a stronger electric field termination layer.

However, experts have realized that the performance of silicon-based devices is approaching the limit. Power components are limited by the silicon material itself, and each performance improvement can only bring a little improvement.

Wide bandgap power components

The power IC industry is looking for new wide bandgap (WBG) materials to take semiconductor performance to a whole new level. Silicon carbide (SiC) and gallium nitride (GaN) are currently the preferred materials, both of which have certain advantages and disadvantages. As semiconductor composites, they have a larger forbidden band width and breakdown field strength, and the resulting power components have unmatched performance of silicon materials. They are widely believed to lead the next generation of power components and revolutionize the semiconductor era. Figure 1 shows the general voltage range for SiC and GaN applications in the end market.

Figure 1: Wide bandgap power components enhance the performance of electric vehicles and other systems, but material cost is a challenge

(Source: YoleDéveloppement and Applied Materials)

The change is accompanied by new challenges, and the wide bandgap power IC industry is no exception. Cost is currently the biggest obstacle, including production difficulties caused by wafer warpage and high defect rates associated with substrate and epitaxial processing. According to market research firm YoleDéveloppement (Lyon, France), the cost of current 6-inch SiC substrates plus epitaxial wafers has reached the level of thousands of dollars, and this cost may rise rapidly as control of device defects becomes more stringent.

The subsequent processing process is also facing many challenges. For example, annealing is required at a high temperature close to 2000 ° C, and the annealing reactor commonly used for silicon materials is far from this temperature. In addition, the implantation process of SiC is also quite complicated.

In view of the broad application prospects of wide bandgap power components, many companies, groups and university research centers are working to solve various obstacles. In fact, both SiC and GaN products are currently in use, albeit in a limited number. However, the advantages of wide bandgap products – including power savings, simplified circuitry, and reduced module size – are difficult to convert into a rich return on investment before the cost is significantly reduced.

For example, a typical automotive inverter box may contain more than 40 power transistors and diodes. The use of SiC simplifies the circuit, reduces parts and reduces module size by up to 80%. New semiconductor materials require breakthroughs in device size, material cost, and energy savings to add significant value to silicon power components (see Table 1).

* Corresponding to the value of the heterostructure

Table 1: GaN and SiC exhibit excellent band gap and breakdown field strength compared to current silicon power components

(Source: F. Iacopi et al., May 2015, MRS BulleTIn; Stanford University, Dr. Jim Plummer)

Fortunately, other steps in the semiconductor process, such as CVD, PVD, etch, and CMP, are relatively easy for wide bandgap power components because the general process is very similar to silicon. Although the processing technology and hardware need to be slightly adjusted, the prior art can be applied to the production of wide band gap products.

Power components based on GaN have great potential in consumer, communications, and automotive applications, but GaN also has shortcomings, including wafer cost and process integration. Due to the size limitation of GaN production, only 2 inch GaN wafers are produced on the market. The mainstream of GaN-based devices is based on Si. However, the lattice mismatch between GaN and Si requires a buffer layer, such as AIN/AIGaN. Due to current architecture limitations, GaN devices are normally open, which creates reliability issues and affects market acceptance. GaN devices need to be improved to overcome this shortcoming. Therefore, although the performance advantages of the wide bandgap device are unquestionable, whether the device can solve the cost problem, mass production is still a question mark.

At Applied Materials' recent power component seminar, Stanford University professor Jim Plummer suggested that to make these new products successful in the market, it is worthwhile to find a new field where silicon materials cannot compete. Plummer believes this will increase production and help reduce wafer costs.