1. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Sputtering Procedures Lecture 11 G.J. Mankey gmankey@mint.ua.edu

2. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Targets and Substrates We will use native oxide coated Si wafers--the surface is basically glass (amorphous SiO x ). Currently Si(100) is less expensive than glass. Si(100) is easy to cleave along high symmetry planes to make smaller samples. The four targets are Ta, Cu, permalloy (Ni 80 Fe 20 ), and silicon nitride (Si 3 N 4 ). We will produce single layers, superlattices and multilayers for characterization using the methods available in the center. First the fluxes will be calibrated, then the test samples will be fabricated.

3. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Procedure Load targets--2" diameter disks of the pure materials. Cleave substrates and mark for later lift-off of film for thickness measurement. Load substrates. Initiate pump down procedure. After crossover point is reached, you may leave the room until the starting pressure is reached (hours). Deposit thick films at stable pressure and power for a measured deposition time for flux calibration. Load new substrates and measure thicknesses with the profilimeter. Deposit films with specific thicknesses using the flux calibration data.

4. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Suggested Samples Effect of Ta underlayer on permalloy and Cu crystal texture. Smooth versus rough layers for AFM comparison. A multilayer with high optical contrast for ellipsometry study. Thin permalloy films with different capping layers. Superlattices for x-ray reflectivity (High Z/Low Z)xn for high x ray contrast. Single crystal Cu or permalloy on H-Si(100).

5. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Ta Underlayers Ta bonds strongly to the SiOx substrate and forms a smooth polycrystalline bcc(110) close packed surface with a moderately high surface energy. For growth of metals with a low surface energy on a high surface energy substrate, layer by layer growth is expected sing the energy is minimized by forming a completely wetted surface. The thermodynamically-favored surface for fcc metals is the close-packed (111) surface. The layers will be poycrystalline with random in-plane orientations.

6. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Smooth vs. Rough Films Cu has a higher surface free energy than SiOx and Cu does not mix with SiOx at room temperature. The surface energy will be minimized by forming droplets or agglomerated islands of Cu on the surface. These islands will be on the nanoscale with size dependent on the amount of material deposited and the deposition conditions. Subsequent growth of another thin film material on the surface may have conformal roughness.

7. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Optical Contrast The optical reflectivity of materials depends on the electronic structure within a few electron volts of the Fermi energy. For metals, the probing depth of radiation is called the skin depth. In general, the color of a metal-semiconductor or metal-insulator composite film will depend on the size of metal particles in the film (see: http://www.ifh.ee.ethz.ch/~martin/res50.en.html for a discussion).

8. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Skin Depth where:  = permeability (4  10 -7 H/m), note: H = henries =  *s  = pi ss = skin depth (m)  = resistivity (  *m)  = radian frequency = 2  *f (Hz)  = conductivity (mho/m), note: mho [ ] = siemen [S] Example: Copper @ 10 GHz ref: http://www.rfcafe.com/references/electrical/skin_depth.htm

9. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Capping Layers Does oxidation of bare permalloy surface affect the magnetization? Is Cu an effective cap layer? Ta? Si3N4? How long does it take a film to corrode?

10. Center for Materials for Information Technology an NSF Materials Science and Engineering Center High XRR Contrast Multilayers Ta/Si3N4 does not meet the surface energy criteria for producing smooth interfaces. Ta/Cu multilayers are a better candidate. The larger the period (layer thicknesses) the better. Ta/Cu also has technological importance (ref: http://www.eps.org/aps/meet/APR02/baps/abs/S53 70004.html) What thickness should we use for the four-period superlattice?

11. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Cu on H-Si(100) Epitaxial growth of Cu on Si by magnetron sputtering H. Jiang, T. J. Klemmer, and J. A. Barnard Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487-0209 E. A. Payzant High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6064 Epitaxial Cu films were grown on H-terminated Si(100), Si(110) and Si(111) substrates by magnetron sputtering. The epitaxial orientation relationships and microstructural characteristics of the Cu films were studied by x-ray diffraction (XRD) including the conventional -2 mode, rocking curve and pole figures, as well as by transmission electron microscopy. The results of both pole figure and electron diffraction reveal the epitaxial orientation relationship of the Cu/Si epitaxial system is as follows: Cu(100)/Si(100) with Cu[010]//Si[011]; Cu(111)//Si(110) with Cu[10]//Si[001] and Cu[10]//Si[001] which are twin related; and for the Cu/Si(111) system the Cu film grows primarily in the epitaxial relationship of Cu(111)/Si(111) with Cu[10]//Si[11]. It is shown by XRD that Si(110) is a more favorable substrate than Si(111) for the epitaxial growth of Cu(111). An ultrathin Cu(111) film (up to 2.5 nm) with high epitaxial quality can be grown on Si(110). The epitaxial relationships of the Cu/Si are discussed on the basis of geometrical lattice matching, including the invariant-line criterion and the superlattice area mismatch rule. ©1998 American Vacuum Society.

12. Center for Materials for Information Technology an NSF Materials Science and Engineering Center UHV Three basic rules: 1.Never go home before the pumps are running. 2.Find the leak. 3.Fix the leak.

13. Center for Materials for Information Technology an NSF Materials Science and Engineering Center Nuts and Bolts Rule 4: Fix it yourself! Rule 5: If in doubt, ask. Some repair jobs required a complete disassembly and reassembly—in one working day!

14. Center for Materials for Information Technology an NSF Materials Science and Engineering Center VUV Physics For a “run” at the LSU/CAMD synchrotron the system has to be assembled at the beamline port in one day. This involved lifting two chambers to the stand with a crane, carefully positioning them, assembly, pumpdown and bake.

15. Center for Materials for Information Technology an NSF Materials Science and Engineering Center The Team Two or three people working together can accomplish the task. The grad students are the tech people.