Sputter Materials

1
Sputter Materials

• Lecture 10
• G.J. Mankey
• gmankey_at_mint.ua.edu

2
The Key System

• The Key system has a stainless steel bell jar, a
  cryopump, gas supply system, four 2" targets and
  a substrate holder for six substrates.
• The cycle time is about one day--it takes a day
  to load substrates and targets and reach the
  starting pressure for deposition.
• We will use three cycles to produce a set of test
  samples.

ref www.lesker.com
3
Targets and Substrates

• The four targets are Ta, Cu, permalloy
  (Ni80Fe20), and silicon nitride (Si3N4).
• 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.

• We will use native oxide coated Si wafers--the
  surface is basically glass (amorphous SiOx).
• Currently Si(100) is less expensive than glass.
• Si(100) is easy to cleave along high symmetry
  planes to make smaller samples.

4
Si

• Si forms in the diamond structure--two
  interpenetrating fcc lattices, one displaced by
  (1/4 1/4 1/4).
• Si is semiconducting.
• The surface is an amorphous oxide similar in
  structure and composition to glass.
• A H-terminated single crystal surface can be
  produced by wet etching the oxide in HF.

http//cst-www.nrl.navy.mil/lattice/mainpage.html
5
Ta

• Tantalum is formed in the body centered cubic
  structure.
• Tantalum is a refractory metal with a high
  melting point and low reactivity so it makes a
  good "capping layer."
• The surface energy is high, so other metals with
  lower surface energy completely wet the surface.
• Ta reacts strongly with Si to form a silicide
  interface layer which bonds the film strongly to
  the substrate.

http//cst-www.nrl.navy.mil/lattice/mainpage.html
6
Cu

• Cu forms in the fcc lattice structure.
• Cu is the ubiquitous conductor, with applications
  wherever a low resistance current path is needed.
• Cu has a relatively low surface energy for a
  metal and low reactivity with SiOx.
• Cu oxidizes slowly in air, so it makes a marginal
  "capping layer."

http//cst-www.nrl.navy.mil/lattice/mainpage.html
7
Ni80Fe20

• Permalloy is a random substitutional alloy which
  forms in the fcc phase with a lattice constant
  nearly equal to that of Cu.
• Permalloy is a soft magnet, with coercivity and
  anisotropy dependent on deposition conditions.
• The surface energy is comparable to Cu with a
  moderate reactivity with Si.
• The Ni and Fe oxidize to form a nonmagnetic
  surface layer.

http//cst-www.nrl.navy.mil/lattice/mainpage.html
8
Si3N4

• Silicon nitride forms in a hexagonal phase,
  however in thin film form it is usually
  amorphous.
• It is a high temperature ceramic, with a larger
  bandgap than pure Si.
• The surface energy is comparable to SiOx-- much
  lower than that of a typical metal.
• It makes a good capping layer because it is inert.

http//cst-www.nrl.navy.mil/lattice/mainpage.html
9
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.

10
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).