EMCORE corporation: The science of epitaxy

EMCORE Corporation: The Science of Epitaxy EMCORE Corporation is a US based company that has focused on the development of a unique approach to Metal-Organic Chemical Vapor Deposition (MOCVD). With a foundation from long experience at Bell Laboratories at Murray Hill, New Jersey, EMCORE has created a distinctive and successful company. Having sold approximately 100 units around the world it has established a unique company as a major contender for industry leadership in advanced materials. Its devotion to technological improvements and customer support has led EMCORE to be called "the miniature Applied Materials" in Japan. E

M C O R E was founded on the basic premise that materials growth technology for device applications required a fundamental commitment to materials science, process engineering and equipment development. This commitment is expressed in the diagram in Figure 1, where the foundations of materials science, equipment development and process engineering provide the underpinning for device development and production. With the experience of 20 years of working with both Bell Labs demands and Western Electric m a n u f a c t u r i n g r e q u i r e ments, E M C O R E selected a systems approach to its business, not only equipment development but also the application of its TurboDisc technology to customer needs. Over the years it has earned a reputation, not only as the most innovative MOCVD equipment vendor, but also as the most flexible and supportive company in the field. Sales have grown continually over the last eight years to total more than $60, 000, 000, with most sales being to Fortune 500 corporations in all three major market areas. With a solid base of technical talent that comprises more than 50% of 60 Device Production / .......

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employees, E M C O R E provides a comprehensive support program to its customers in Asia, Europe, and, of course, in the US.

TurboDisc Deposition Technology

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Figure 1: E M C O R E commitment.

Although the characteristics of a rotating disc in a viscous fluid had been studied for many years, EMCORE was the first to appreciate the potential of this simple concept for materials deposition systems. The rotating disc transfers momentum from the disc to the adjacent boundary layer of the gas and thus creates a

significant pumping action within the reaction chamber. With the aid of substantial theoretical modelling of the rotating disc, E M C O R E designed its reaction chamber to correspond to theory and demonstrated the validity of the concept. In particular, the computer model allows one to select operating parameters; such as pressure, gas flow, temperature, reactant distributions in EMCORE's FlowFlange, etc., to achieve optimum uniformity and to pick broad process windows. Figure 2 shows the c o m p u t e r generated plots of flow streamlines and temperature gradients in an E M C O R E reaction chamber. One

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sees clearly the dramatic effect of the rotation on the fluid flow characteristics. The rapid flow over the disc creates a uniform temperature over the surface of the disc that is critical to achieving composition and doping uniformity in InGaAs, InGaAsP, InGaA1P, as well as other ternary and quaternary materials. The sharp temperature gradients are also important. Steep gradients reduce prenucleation and increase thermophoretic forces that contribute to the low particulate contamination observed in TurboDisc systems. Also, the gaseous reactants do not pyrolyze until they are close to the wafer surface, where they diffuse rapidly at the low pressure. Combined with the precise control of the reactant distribution achievable with the E M C O R E FlowFlange, deposition efficiency can be as high at 50% compared to 10% for horizontal and barrel designs or 25% for other vertical but slow rotation systems. Finally, the control of recirculation and the low pressure allow for atomically abrupt composition changes in multi-layer growths with minimal auto doping effects. Uniform selective epitaxy is also easily achieved at low pressure. The major advantage of flow modelling is the ability to understand and use the scaling parameters for the construction of larger equipment. The TurboDisc system is unique in its ability to transfer growth conditions for small scale systems of less than 75 mm diameter to 400 mm discs with no loss of uniformity or other material characteristics. Similarly, the modelling capability is convenient for the construction of initial growth conditions when new materials are used or

new requirements are necessary for a device structure. Using its in-house modelling capability, E M C O R E has assisted customers to achieve better than 1% uniformity in processes involving new materials and conditions that initially resulted in 25% uniformity using previous conditions. The fundamental basis for the flow characteristics and behavior of the TurboDisc allows E M C O R E to use the slogan "Research to Production - One Technology" and is representative of the development of the science of epitaxy, rather than the historic 'black magic' conditions previously attributed to MOCVD system behaviour.

System Design Stainless steel construction has been a hallmark of the E M C O R E TurboDisc system that has resulted in a robust and safe alternative to quartz chambers. The applications of ultra high vacuum techniques for system construction and the introduction of a clean and safe vacuum load lock for wafer handling has brought silicon industry standards to the III-V world (see Figure 3). In addition to the reduced handling contamination, the stainless steel construction coupled with the flow

patterns in the systems allows for the easy replacement of parts with no degradation of the system performance characteristics. The elimination of the quartz chambers also allowed E M C O R E to easily scale systems to handle multiple wafers from 50 mm to 200 mm in diameter. Cassette wafer handling allows a full shift of wafers to be loaded into the turbo molecular pumped load lock where oxygen and water vapor content can be reduced below 100 parts per billion. This reduced level of contamination allows for excellent process reproducibility from run to run; in particular for high performance devices that are sensitive to oxygen and water vapor contamination. With reduced chemical consumption and uniform flow in the TurboDisc c h a m b e r , m a i n t e n a n c e is significantly reduced. Many E M C O R E users report doing hundreds of runs prior to scheduled maintenance and cleaning. For the use of phosphorus materials this provides an improvement in historically hazardous system cleaning problems. For production environments the reduced maintenance contributes to improved throughput and cost reduction. The flexibility o f the TurboDisc system is highlighted by the ability of a large TurboDisc

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doping simultaneously in a wide range of materials (see Table I}. E M C O R E and its customers routinely achieve better than 1% thickness uniformity as shown in Figure 4. For device designers achieving uniform doping as measured by sheet resistivity is important. Disilane doping of GaAs at carrier concentration in the low 10 TM cm -3 has been demonstrated to yield sheet resistivity with variat{ons of less than 0.5%. Most advanced device designers require multiple layers with stringent conditions not only on uniformity, but also for an abrupt transition between layers. Figure 5 shows TEM micrographs of lnP-based ternary; quaternary quantum wells with excellent uniformity across one of multiple 50 mm wafers. The interface transition in this structure as well as other optoelectronic structures have been measured by E M C O R E users to be one atom layer. The special uniformity of optical properties can be easily measured with various mapping techniques. Figure 6 shows the wavelength variation in one of multipie wafers in l n G a P grown in a TurboDisc system with a standard deviation of only 0.7 nm. E M C O R E is proud of the fact that its customers have routinely exceeded its own in-house materials demonstrations. This has always been the major goal of the company.

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EMCORE, a Global Company Figure 6. Wavelength variation in one

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system to be configured to "behave' as a small system. Using E M C O R E ' S FlowFlange, it is possible to change reactant flow distributions to allow growth on single wafers for development purposes and then to return to the conditions for maximum capacity production. This reduces material costs for development and preserves the integrity of the d e v e l o p m e n t process for favorable manufacturing.

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a uniform t e m p e r a t u r e and flow patterns with the precise reactant control associated with the FlowFlange contributed to excellent uniformity of thickness composition and

The success of any company is the market acceptance of its products. On this basis E M C O R E has clearly demonstrated that the world of" lII-V materials was ready for its TurboDisc concept. With a p p r o x i m a t e l y 100 systems sold around the world, Emcore believes it has the largest in-

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stalled base of multiple wafer systems for III-V applications. Its commitment to the multiwafer capability is reflected in the fact that 92% of its units handle three or more 50 mm wafers. As a US-based start-up, its largest number of installed systems is in the American market but it has grown rapidly in Asia, where it has sold 30 units. As the only nonJapanese equipment supplier to successfully penetrate the difficult Japanese market area, E M C O R E has also sold systems in Korea and Taiwan. Its presence in Europe, although quite recent, has been highlighted by multiple system sales to the Thomson group in France, and Siemens in G e r m a n y . The flexibility o f the E M C O R E T u r b o D i s c system for diverse applications and device requirements is shown in Figure 7. EMCORE's success in world sales can certainly be attributed to its technology, but its business approach plays an important role also. E M C O R E clearly focused on customer requirements. Customers find that E M C O R E can provide not just the TurboDisc system, but also the process and materials support necessary to rapidly achieve materials and device results. Although each E M C O R E system contains the basic T u r b o D i s c technology, E M C O R E customizes its system designs to meet each individual customer requirement for safety and process and then uses its internal applications laboratory to develop c u s t o m e r specific device structures. With a commitment to customer success, E M C O R E m a i n t a i n s a strong relationship with its customers through a worldwide network of E M C O R E Users Groups. EMCORE works with local customers

to arrange non-proprietary information exchange and technology updates. With the recent addition of Dr Alan Thompson to the E M C O R E staff, a special department devoted to customer applications and engineering has been created to enhance an already strong customer-oriented focus. EMCORE's customers find that the ability to focus their internal resources on their business interests and goals rather than system development represents a significant market a d v a n t a g e to t h e m , since EMCORE's systems have a continuous upgrade capability. EMCORE's business success and growth in world markets have earned it significant recognition. In 1992 it received the World Trade Award for its meteoric growth in export sales to 80% of revenues. In 1992 the company was awarded the Small Business Administration Award for contributions to US exports. Dr Norman E. Schumaker, founder and president of E M C O R E , was appointed by the Governer of New Jersey to the New Jersey Commission on Science and Technology to assist the state in the development of effective policy for technology business development. Recently, the American Electronics Association selected Dr Schumaker as Businessman/Entrepreneur for 1993 in New Jersey during its 50th anniversary celebration. Dr Schumaker was also elected a National Director of the AEA.

can provide large t h r o u g h p u t of wafers due to their short total cycle time (ref. article in III-Vs Review, Vol. 5, No.3, 1992), E M C O R E has responded to customer requests for larger systems to address large scale commercial market requirements. These new systems have capacities ranging from 13 to 26 wafers 50 mm in diameter or 3 to 7 wafers 100 mm in diameter and can produce the same material uniformities achieved in the earlier designs. The demand for increasing volumes of wafers and increasing emphasis on throughput has led to E M C O R E to introduce the first MESC-compatible MOCVD system configuration. This configuration allows the use of standard silicon wafer handling technology for III-V materials with the associated reduction of particulates and costs. In a similar fashion, E M C O R E now offers a TurboDisc 'kit' that allows current M O C V D users to adapt E M C O R E technology to their present gas handling systems. This 'kit' was developed in response to customer desires to upgrade their outmoded and inefficient deposition systems to current 'state-of-the-art' technology at a much lower price, than replacing a whole system. E M C O R E has forged a unique direction in MOCVD technology and represents, pardon the pun, a 'revolutionary' company. E M C O R E is certainly a company to watch. Contact. E M C O R E Corporation, Marketing Department, 35 Elizabeth Avenue, Somerset NJ 08873, USA. Tel." [1] (908) 271-9090 Fax." [1] (908) 271-9686.

EMCORE's evolution A changing world market requires a continuously changing response to customer requirements. Although E M C O R E systems with stainless steel chambers and UHV loadlocks

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