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New High-Productivity EPI Chamber for Thick Silicon Epitaxy

Carlos Caballero

Semiconductor technology is undergoing a sea change as proliferating mobile technologies and the growing Internet of Things broaden the use of semiconductors in more products across more market segments than ever before. Among many design and manufacturing changes, these forces are stimulating the fabrication of devices in which performance is enhanced by using much thicker films than are typically associated with semiconductors. Applications calling for thick epitaxial silicon (Si) can now benefit from a versatile new single-wafer chamber specifically designed for that purpose. A new Centura Epi chamber has a >6μm/min. growth rate that enables more than 100μm of silicon epitaxy in a single pass through exceptional chemical efficiency, delivering both high productivity and lower cost of ownership.

Today’s semiconductor industry may be more dynamic than ever before. While leading-edge chip designers explore the far frontier of scaling below 10nm, a growing variety of devices are being fabricated using films that are thousands of times thicker. Thick, doped epitaxial Si forms electrical isolation for higher-voltage, faster-switching power semiconductors, such as insulated-gate bipolar transistors (IGBTs), used in appliances, stereos, trains, etc. It also improves device performance and lowers manufacturing costs of price-sensitive sensors and actuators by incorporating microelectromechanical systems (MEMS) in power-efficient, "smart" applications.

Commercially viable manufacturing of power devices and advanced MEMS requires epitaxial Si 30–150μm thick to be grown on systems that deliver high productivity at the lowest possible cost of ownership. Many of these devices can be cost-effectively manufactured on 200mm systems and are rejuvenating the market for this equipment. Applied Materials actively supports the expansion of 200mm technologies and has enhanced the capabilities of several of its 150mm and 200mm systems—including its widely used 200mm Applied Centura Epi chamber—to meet evolving industry requirements.

A pioneer in epitaxy and the market leader in epitaxial deposition equipment, Applied Materials has leveraged its long-established expertise in materials engineering to redesign the 200mm Centura Epi chamber specifically for superior quality thick Si (20–100μm) without compromising its already excellent results for thinner layers (<20μm). The new 200mm Applied Centura Epi chamber features process kit modifications that combine to enable (1) growth of up to 100μm of Si in a single pass; (2) shorter clean time compared to that of a standard chamber; (3) multi-wafer processing between cleans (for <20um); and (4) significantly lower consumable costs.

Once an epitaxy tool is fully depreciated, running cost has a major direct impact on profitability, so tight control of consumable costs is critical to overall profitability.

Upgrading the Chamber

Power devices and MEMS require extremely uniform epitaxial Si and resistivity of less than 2%. To meet these demands, key hardware and software components of the standard 150mm and 200mm Centura Epi chambers were upgraded for the new Epi chambers.

Motorized Susceptor Lift: The Applied Centura Epi system can accommodate up to three of the newly-designed chambers. In each chamber, a wafer rests in a pocket on a susceptor that rotates while precursor gas is injected into the chamber and the epitaxial process takes place. Exact positioning of the wafer is essential for optimizing within-wafer uniformity of the epitaxial layer and wafer-to-wafer repeatability of the process. Therefore, in the new chambers, the conventional pneumatic susceptor lift has been replaced with a motorized lift whose speed can be much more carefully controlled to avoid wafer movement within the susceptor pocket (see figure 1). A new susceptor-leveling mechanism complements the motorized lift to enhance positioning repeatability (see figure 2).

Reliable centering of wafers also minimizes bridging, i.e., the tendency of wafers to stick to the susceptor. This effect can occur when the susceptor surface is exposed between the edge of the wafer and the pocket sidewall, allowing epitaxial growth to spread over this area.

Chamber: Several design changes to other components improve laminar gas flow to facilitate higher growth rates, improve uniformity of film growth and resistivity, and reduce unintentional coating of chamber components, including the upper and lower dome. Reduced coating is particularly important in ensuring good temperature uniformity and stable film growth across the entire wafer.

Closed-loop dome temperature control: This new software feature has the dual benefit of improving on-wafer performance and boosting system productivity. Maintaining a stable process environment temperature (see figure 3) is important for promoting the desired single-crystal growth. Closed-loop temperature control also helps minimize coating of the dome.

Minimal coating has implications for both film quality and system productivity. Producing thicker films requires longer process times, increasing the possibility that coatings or byproducts will build up on chamber surfaces. The thicker the deposits, the greater the risk that the material will flake off and fall onto the wafer, creating yield-limiting defects.

From a productivity standpoint, a thin coating can be removed speedily and with only a small volume of hydrochloric acid (HCL). This contributes to lowering the cost of consumables, and lessens the system’s potential environmental hazards. For thinner epitaxy (≤20μm), negligible dome coating allows throughput of three wafers between chamber cleans rather than only one, as is typically the case.

Improving Performance

As summarized in table 1, the modifications described earlier enable Applied’s new epi chamber to satisfy all key market requirements by mitigating the major challenges posed by thick epitaxy. It achieves an unmatched growth rate of high-quality Si, formed with excellent thickness and doping uniformity and negligible defectivity. In addition, it ensures repeatable wafer placement and eliminates bridging, which are both essential for high-yield volume manufacturing. Moreover, this industry-leading performance is delivered at a lower cost of operation than competing alternatives offer.

Figure 4 illustrates the higher growth rate produced by the new, smaller Centura Epi chamber and more efficient chemistry, while figure 5 shows the uniformity of thickness and resistivity achieved. The new chamber offers the versatility of equally good results for both thick and thin epitaxy (see figure 6). Resistivity targets are reached rapidly and remain stable throughout the entire growth process (see figures 7–8).

Summary

With the introduction of the new Centura Epi chamber, Applied Materials has significantly upgraded its workhorse 150mm and 200mm Centura Epi chambers to meet the industry need for cost-effective production of thick Si in power-device and MEMS applications. In a 500-wafer marathon, the redesigned chamber demonstrated a >6μm/min growth rate in producing 100μm-thick blanket silicon— triple that of batch technology. In addition, its chamber design and shorter process times promote optimum efficiency and productivity of the TCS precursor, a cleaner chamber, and lower consumption of HCL used in removing dome coating. These economies offer the competitive benefits of a lower cost of consumables relative to batch systems, as well as higher throughput.

For additional information, contact carlos_caballero@amat.com