Absolute Calibration of Sims Depth Profiles of a-SiN x :H/a-Si:H and a-SiO x :H/a-Si:H Multilayers
- PDF / 847,872 Bytes
- 4 Pages / 414.72 x 648 pts Page_size
- 42 Downloads / 161 Views
a-SiNx:H/a-Si:H AND a-SiOx:H/a-Si:H MULTILAYERS
Jianwei Li, Jan M. Chabala, Riccardo Levi-Setti Enrico Fermi Institute and Department of Physics The University of Chicago 5640 S. Ellis Ave., Chicago, IL 60637 ABSTRACT We calibrated secondary ion mass spectrometry (SIMS) depth profiles of a-SiNx:H/a-Si:H and aSiOx:H/a-Si:H multilayer samples by comparing them to high-spatial-resolution SIMS maps of cross sections through the layers. Both profiles and images were acquired with a focused scanning 45 keV Ga+ ion microprobe. During depth profiling an area gating technique was used to improve depth resolution. At the beginning of the profile the resolution was 8 nm. By cutting the multilayer films at a small angle through the layers, we obtained SIMS images of cross sections through these multilayer samples. The resolution along the expanded direction is about 10 nm. By comparing the depth profiles and the cross section images, we determined the ionbeam-induced atomic mixing in the samples, as a function of depth and the sputtering yield for each layer.
INTRODUCTION Ion beam sputtering/SIMS is commonly used for in-depth analysis of semiconductor multilayer materials. However, the depth resolution of SIMS sputter profiles can be strongly influenced by atomic mixing of the target atoms and sputter induced surface topography, especially when the primary ion energy is higher than 10 keV. Chemical effects, such as the presence of oxide, can also influence the appearance of SIMS depth profiles. The differing sputter yields and erosion rates for each layer presents additional difficulties in determining the true depth. We show in this presentation that SIMS depth profiles can be calibrated by comparison with high-spatial-
resolution SIMS maps of cross sections through the multilayer films.
EXPERIMENTS Both depth profiles and images of Si-based multilayers were acquired with a scanning ion microprobe (SIM) at the University of Chicago. A 45 keV primary ion beam, extracted from a Ga+ liquid metal ion source, is focused to a spot of diameter in the range 20-70 nm with the current between 2-30 pA. 1 ,2 The secondary ions were discriminated by a double focusing magnetic mass spectrometer and detected by an ETP thin film electron multiplier. The multilayers, on 7059 Coming Glass substrates, were prepared by alternating the feed gases in PECVD deposition. One sample is a-SiNx:H/a-Si:H multilayer film, consists of alternating 7 nm hydrogenated amorphous silicon nitride (a-SiNx:H), here x is about 1.3, total 21 layers and 20 layers of 20 nm hydrogenated amorphous silicon (a-Si:H). The second sample is a-SiOx:H/aSi:H multilayer sample, 27 layers of 42 nm siliconoxidide (a-SiOx:H), x is about 1.9, and 26 layers of 28 nm silicon (a-Si:H). A thin gold layer was placed over each sample to prevent initial sample charging. Charging during the profiles is not a problem. To improve depth resolution, a raster-gating technique was used. The beam was scanned in a spiral pattern and the signal gated to accept the central 10 % of the scanned regi
Data Loading...
