Development of Motorola’s InGaP HBT Process Mariam Sadaka, Darrell Hill, Fred Clayton, Haldane Henry, Colby Rampley, Jon Abrokwah, and Ric Uscola Motorola Semiconductor Products Sector 2100 E. Elliot Rd. MD EL720 Tempe, AZ 85284 Phone (480)413-3129, FAX (480)413-4453, Email: mariam.sadaka@mot.com ABSTRACT This paper reports on the development of InGaP HBT process at Motorola Compound Semiconductor One facility (CS-1) with emphasis on the process critical modules. These modules include: emitter definition by selective wet etches, base contact formation by non dielectric assisted lift-off, collector and isolation selective dry etch, and low parasitic airbridge process. Moreover, device results of both linear and saturated power applications are reported. INTRODUCTION InGaP HBT technology delivers high power density, high efficiency, superior linearity, and single supply operation. This makes the InGaP HBT an attractive solution for power amplification in portable wireless applications. Due to the rapidly increasing market share for GaAs HBTs, Motorola developed a third generation InGaP HBT in its Compound Semiconductor One facility (CS-1). Although first and second generation HBT technologies are used in the majority of HBT products, third-generation HBTs (C-doped InGaP/GaAs) offer several acknowledged advantages. InGaP HBTs have superior reliability [1- 2] due to the lower initial defect density of InGaP, and its lower defect mobility in comparison to the widely used AlGaAs. In addition because of the minimum conduction band offset between InGaP in the emitter and GaAs in the base, InGaP HBTs have improved uniformity of current gain over current [3] and temperature [4]. Furthermore, the carbon doping in the base prevents the dopant out-diffusion degradation mechanism common to the widely used beryllium doping in AlGaAs HBTs [5]. Besides superior performance and reliability, the InGaP HBT process has superior manufacturability. This paper reports on the process developed at CS-1 with emphasis on robustness of the different process modules. DEVICE FABRICATION A cross-section of the InGaP HBT device is shown in figure 1. The fabrication process includes forming a thermally stable, low resistance, low stress, non- alloyed emitter contact using sputtered TiWN. Subsequently, the emitter and ledge are defined by a series of selective wet etches. The fully depleted ledge reduces recombination currents, thus increasing the current gain, decreasing the noise, and improving the device reliability. A non-alloyed base contact is formed by a single layer lift-off process, resulting in a damage free base surface. Figure 1. A cross-section of an InGaP HBT The collector is formed by a highly selective anisotropic self-aligned dry etch. The collector contact is an alloyed NiGeAu formed by a dielectric assisted lift-off process. The devices are isolated by an anisotropic self-aligned dry etch through the subcollector. The rest of the fabrication process involves dielectric deposition and via etching. The process includes two layers of interconnect. Plated Metal1 caps the emitter, base, and collector. Metal2 is a plated airbridge. The airbridge allows managing challenging topography while helping reduce thermal resistance. After connecting all three terminals of the device, a thick nitride layer is deposited for passivation. The wafers then are mounted on sapphire substrates to prepare for the through substrate via etching. This process involves a plasma etch through the GaAs substrate stopping on gold. Gold as back metal is finally plated in the vias. PROCESS DETAILS Compound Semiconductor One was converted to 150mm wafer size to increase capacity and meet the high demand for GaAs products [6]. Thus, the current InGaP HBT process is in production on 150mm wafers. The process includes refractory emitter contacts, non-alloyed base contacts, alloyed collector Copyright 2002 GaAsMANTECH, Inc. 2002 GaAsMANTECH Conference