AVS 45th International Symposium
    Thin Films Division Tuesday Sessions
       Session TF-TuM

Paper TF-TuM5
Process Monitoring of Hemispherical-Grained Polysilicon Thin Films for DRAM Applications

Tuesday, November 3, 1998, 9:40 am, Room 310

Session: Thin Films for Sensing and Data Storage
Presenter: A. Bivas, KLA-Tencor Corporation
Authors: C. Hayzelden, KLA-Tencor Corporation
A. Bivas, KLA-Tencor Corporation
C.L. Ygartua, KLA-Tencor Corporation
K.C. Chan, KLA-Tencor Corporation
Correspondent: Click to Email
The fabrication of hemispherical-grained (HSG) polycrystalline silicon was developed to increase the surface area (and storage capacitance) of Dynamic Random Access Memory (DRAM) devices. The increase in surface area (typically 2.4 x) is extremely sensitive to processing conditions. Therefore, to obtain high yields, process monitoring is of great importance. The use of spectroreflectometry and spectroscopic ellipsometry, described in this paper, provides a non-destructive method to monitor film fabrication. Using these two measurement technologies, the intensity and polarization state of the light reflected from the wafer surface is measured and analyzed over the wavelength range 220 to 800 nm. In the measurement analysis, a polysilicon layer is frequently modeled as a mixture of several materials, using the Effective Medium Approximation (EMA). Using the EMA model, with a composition of crystalline silicon, amorphous silicon, and a percentage of "voids", the analysis of measurement data yields values of the optical parameters (refractive index, extinction coefficient) and effective thickness of the HSG layer. In this paper, we present capacitance data from a series of HSG-processed wafers and report the observed correlation with the measured variables: percentage of "voids", effective thickness and optical parameters. The most appropriate variables to report for accurate process control will be discussed.