Optimising the usage of SEM Sputter Targets

Introduction
In an SEM sputter coater for coating non-conductive SEM samples, a plasma is created at a vacuum level of around 2x10-1 to 2x10-2 mbar by applying a high voltage between the grounded sample stage and the target. Argon is used as sputter gas and the gas pressure is maintained by using an adjustable needle valve to control the flow of Argon gas whilst the chamber is being pumped at the same time. It is advisable to flush the vacuum chamber twice with Argon gas before setting the required vacuum level. Argon is an inert gas and will not react with the sample or the target materials. It is also a relatively heavy gas and therefore more effective for sputtering. In modern sputter coaters a magnet is used in the target head (behind the target) to contain the plasma close to and in front of the target. A grounded dark space shield surrounds the target head.
The plasma consists of positive Argon ions and electrons. The positive Argon ions bombard the target to remove materials which is subsequently deposited on the specimen (and other parts of the sample chamber). In well designed systems, the electrons are mainly collected by the dark shield.
In some applications, such as gold coating non-conductive samples for table top SEMs, air can be used as process gas.


Sputter parameters

When using a sputter coater,  there are multiple variable parameters which influence the deposition rate, sputter process and coating quality:

  • Sputter current
  • Sputter voltage
  • Pressure (vacuum) in the sample chamber
  • Distance from target to sample
  • Sputter gas
  • Target thickness
  • Target material
  • Sample material(s)

With so many different variables, it is near to impossible to calculate the deposition rate. It is better to use a thickness monitor to measure the actual deposited coating thickness.
Note: Sputter rate is measure of the amount of material removed from the target. Deposition rate is the amount of target material deposited on the sample surface.


Optimising the usage of a sputter target and reducing sputter target costs
In modern DC magnetron sputter coaters, an annular magnet behind the target contains the plasma in a doughnut shape and the high voltage used is below 1 kV. This creates a highly efficient sputtering process with few electrons reaching the sample surface with no thermal damage. The drawback of this design is a preferred area on the target where target material is removed; it resembles a race track. Only a small percentage of the target is used before the plasma has “eaten” through the target. This signifies that the sputter target needs to be replaced, although only a small amount form the target is effectively used to coat the sample. Here are some simple and easy tips to increase the usage of a sputter target:

  • Reduce the distance from target to sample – a shorter distance results in higher deposition rates
  • Reduce the coating thickness – resistivity of sample materials can differ greatly. A coating thickness just enough to enable non-charging imaging is all that is needed. No need to coat each sample with a shiny gold layer
  • Use a thickness monitor to measure the optimum coating thickness – this will lead to substantial cost savings
  • Coat multiple samples in a coating cycle – one or twelve samples uses the same amount of material from the target
  • Reduce the pressure of Argon in the sample chamber – less argon causes less scattering and more efficient coating with lower loss to the sample chamber walls
  • Consider using a different low cost coating material when possible. For low and medium magnifications, Silver is an excellent low cost alternative (and can be removed easier as well)
  • Use Argon instead of air as sputter gas – argon is more efficient
  • Clean the target surface outside the racetrack area – maintain conductivity of the complete target area
  • Use thicker targets – twice the thickness results in approximately 15% more material and thicker targets are less expensive per weight resulting in in an overall cost efficiency of 25-30%.



SEM Supplies

TEM Supplies

Calibration

Sample Preparation

AFM / SPM

  Product Menu with Images
  SEM Sample Stubs
  Carbon Tabs
  Sample Stub Adapters
  SEM Stage Adapters
  SEM Sample Holders
  SEM Preparation Stands
  Filaments / Cathodes
  Silicon Finder Grid
  Gatan 3View Pins
  FEI Volumescope Pins
  SEM Stub Storage Boxes
  Phenom Supplies
  JEOL NeoScope Supplies
  Hitachi TM Series Supplies
  Field & Lab Sampler Kits
  FlowView liquid sample Kit

Instruments

  Acoustic Enclosures
  Cressington SEM coaters
  TEM Sample Prep
  Diaphragm Pump
  Rotary vacuum Pump
  Precision diamond saw  
  TEM Grids
  TEM Support Films
  Silicon Nitride Films
  K-Kit Wet Cell Holder
  Graphene Films
  TEM Grid Boxes
  Cryo Grid Boxes
  TEM Sample Staining
  3mm Embedding Tubes
  Filaments/Cathodes
  Eyelash Manipulators

Cryo Supplies

  Cryo Grid Boxes
  Other Cryo Supplies

FIB Supplies

  FIB Lift-out Grids
  FIB Low Profile Stubs
  FIB Grid Holders
  FIB Pre-tilt Holders
  FIB Pre-tilt stubs
  FIB Grid Boxes
  SEM / FIB Magn. Calib.
  SEM Res. Test Spec.
  EDS / WDS Calibration
  TEM Calibration
  AFM / SPM Calibration
  LM Magn. Calibration

Vacuum Supplies

  Vacuum Gauges
  KF/NW Vacuum Parts
  KF/NW Vacuum Hoses
  ISO Vacuum flange parts
  Vacuum Oil and Grease
  Vacuum Sealant
  Diaphragm Pump
  Rotary vacuum Pump
  Vacuum Sample Storage
  Vacuum Pick-Up Pens

Sample Coating Supplies

  Sputter Targets
  Carbon Rods & Fibers
  Quartz QCM Crystals
  SEM Sample Coating Fluid

Evaporation Supplies

  Thermal Evaporation Sources
  Evaporation Materials
  Supports & Substrates
  SEM Preparation Stands
  Tweezers
  Probes & Picks
  Applicators & Swabs
  Plastic Transfer Pipettes
  Cutting Tools / Scissors
  Conductive Paint/Cement
  Conductive Tapes & Tabs
  Non-Conductive Adhesives
  Sample Storage
  Hand Tools
  Sorting Wire Mesh
  Preparation Surfaces
  Cleaning / Gloves
  Conductive Metal Powders
  Metallographic Sample Prep
  AFM/SPM Discs
  AFM/SPM Disc Pick-up Tool
  AFM/SPM Holders
  AFM/SPM Disc Storage
  Cantilever Tweezers
  AFM/SPM Discs Tweezers
  Nano-Tec Mica Discs
  HOPG Substrates

Light Microscopy

  Correlative Cover Slips
  Glass Microscope Slides
  Glass Cover Slips
  Quartz Microscope Slides
  Quartz Cover Slips
  Black Metal Slides
  Slide Storage Boxes
  LM Calibration
  Plastic Transfer Pipettes
  Optical Lens Tissue
  Glass Petri Dishes
  Digital Microscope
  PTFE Beakers