Germanium ALD/CVD Precursors for Deposition of Ge/GeTe Films
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1071-F09-11
Germanium ALD/CVD Precursors for Deposition of Ge/GeTe Films William Hunks, Philip S. Chen, Tianniu Chen, Matthias Stender, Gregory T. Stauf, Leah Maylott, Chongying Xu, and Jeffrey F. Roeder ATMI, 7 Commerce Dr., Danbury, CT, 06810 ABSTRACT In order to deposit conformal films in the high aspect ratio trench and via structures in future high-density phase-change memory devices, suitable ALD/CVD precursors are needed. We report on the development of novel germanium(II) metal-organic ALD/CVD precursors containing amide, cyclopentadienyl, and amidinate ligands. The physical properties, volatility, and thermal behavior of the precursors were evaluated by simultaneous thermal analysis (STA) and vapor pressure measurements. Stability studies were conducted to investigate the suitability of the precursors for use as ALD/CVD precursors for device manufacturing.
INTRODUCTION As device manufacturers continue to increase storage capacity by scaling to smaller dimensions, it is anticipated that flash memory will experience performance limitations due to its use of electrons to store data. Several groups are investigating phase-change random access memory (PRAM) as an alternative memory technology that is scalable to < 5nm and compatible with Si-based ICs [1-2]. PRAM combines the fast memory access speed of DRAM/SRAM with the non-volatile storage feature of flash. PRAM displays long-term data retention at elevated temperatures, fast read/write speeds of 5-20ns, and is capable of direct overwrites of up to 108 cycles. Digital data is stored through a thermally reversible phase transition from an amorphous state (high resistivity, binary 0) to a crystalline state (low resistivity, binary 1) with fast crystallization kinetics. For prototype PRAM devices, GST (germanium-antimony-tellurium) has emerged from the chalcogenide glasses used in the manufacturing of rewritable optical disks. However, for the high density memory arrays proposed for PRAM devices of less than 50nm, the increasing aspect ratio makes filling of the trenches and vias difficult. For conformal deposition without voids, there is a strong need to transition from physical vapor deposition (PVD) to chemical vapor deposition (CVD), which requires suitable low-temperature deposition precursors. CVD precursors explored use volatile Ge(IV) compounds that require high temperatures for deposition and give poor film conformality and morphology. Reported GST films have been deposited using CVD processes at temperatures ranging from 300-400°C using tetraallylgermane or tetraisobutylgermane co-deposited with triisopropylantimony and diisopropyltellurium. Deposited films displayed nonuniform and island growth behavior [3-7]. Similarly, co-deposition of Ge(NMe2)4, Sb(NMe2)3, and iPr2Te gave poor film morphology [8]. We describe a series of Ge(II) precursors that show enhanced low-temperature deposition characteristics, investigate their thermal stability, vapor pressure, and thin film deposition rates and contrast them to the Ge(IV) precursor Ge(NEtMe)4.
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