Sputter deposition is a physical vapor deposition method of thin film deposition in which a high-purity source material (called a cathode or target) is subjected to a gas plasma (typically argon). The energetic atoms in this gas plasma collide with the target material and knock off source atoms which then travel to the substrate and condense into a thin film.
|Materials||Ag, Al, Al2O3, Au, Cr, Cu, Fe, Ge, Ni, Pt, SiO2, Ti, TiO2, Zn|
Method of operation
Sputtering is not typically done on liftoff samples or shadow masks. Therefore it is typically done as a blanket deposition that will be patterned and etched later if patterning is needed. Samples should be clean and vacuum-safe and should be able to handle a small amount of plasma heating. It is recommended that if there is any organic processing done to samples that they are cleaned in an oxygen plasma.
Samples are introduced into a vacuum chamber (either loaded in a vented chamber or sent in from a loadlock) with the proper source target materials. The sample is heated and etched before deposition if the process requires it. Ar is then introduced to the chamber until a desired sputtering pressure is reached and then power is applied the targets to strike a sputtering plasma. The target power is then ramped up slowly while being shielded from the samples by a shutter. Once the pre-sputter sequence is finished, the shutter opens and the deposition is timed to achieve the desired thickness of film. The shutter closes, power is ramped down and the sputtering Ar gas is pumped out. Multiple films may be run by repeating this process with a different source targets. The samples are then removed from the chamber and the tool is pumped back to a low base pressure.
This section requires expansion.
Figures of merit
The figures of merit are described in the generic PVD page
Responses of figures of merit with parameter changes
Deposition Rate, Stress, Resistivity and Step Coverage
Although many films (especially reactive films and insulating compounds) may vary in their response, typical sputtering variables can be summarized in this trend chart:
Uniformity is set by the material being deposited and the geometry of the system: throw distance, target size, substrate rotation and deposition angle.
- In sputtering, uniformity is determined by throw distance and the shape of the deposition cone.
- In the PVD 75 and Lab 18 tools, smaller sources eject material from the face of a 3" target that is angled to cover around 1/2 of the substrate area. The substrate is rotated to coat the entire area. Varying the angle will vary the throw distance and change the amount deposited on the center and edge. The supplies have a set throw angle that is optimized for best uniformity.
- In the ALN tool, the wafer is centered over two targets which are larger than the substrate. Uniformity can be only be adjusted using the DC supply which raises and lowers the power to the center target.
The following materials can be deposited using Magnetron[clarification needed] sputter deposition at the LNF.
The LNF has 4 sputter deposition tools
Endeavor M1 Aluminum Nitride Sputter Tool
- Materials deposited: AlN, Al
- The Endeavor M1 tool is designed specifically for Piezoelectric AlN on either 4" or 6" wafers. It is a high temperature process that works only on certain substrates with specific seeding materials and the handler is designed to process both 4" (via 6" carrier) or 6" wafers.
- Materials Deposited: Al2O3, ITO, Mo, Si, SiO2, Si3N4, Ta, Ta2O5, Ti, TiO2
- Lab 18-1 is a loadlocked magnetron sputter tool used for depositing less common metals, insulators, optical and semiconductive films. It has a variable-gated turbo pump and more sensitive gas flows that allow it to run more sensitive gas ratios (<1%) for reactive sputtering. It has a DC supply for conductive materials and RF supplies for electrically insulating materials. Deposition rates vary by material but are generally much slower for RF depositions. The tool supports 5 materials at a time, rotated using the 18-1 Target Change Calendar
- Materials: Al,Cr,Au,Ir,Ni,Pt,Ag,Ti
- Lab 18-2 is a loadlocked magnetron sputter tool used for mostly for depositing common and precious metals. The tool supports 5 materials at a time, rotated using the 18-2 Target Change Calendar
PVD 75 Sputter Tool
- Materials deposited: Al2O3, Al, Cr, Cu, Si, SiO2, Si3N4, Ni, Ag, Ti
- The PVD 75 tool is designed specifically for point of use processing of materials not allowed or not currently in the Lab 18 tools. It is an open loop (non-loadlocked) tool with easier-to-change targets. Qualified users can change targets when they vent the chamber to load their samples.