Method and apparatus for the fabrication of ferroelectric films
View Patent ↗The present invention is related to methods and apparatus for processing weak ferroelectric films on semiconductor substrates, including relatively large substrates, e.g., with 300 millimeter diameter. A ferroelectric film of zinc oxide (ZnO) doped with lithium (Li) and/or magnesium (Mg) is deposited on a substrate in a plasma assisted chemical vapor deposition process such as an electron cyclotron resonance chemical vapor deposition (ECR CVD) process. Zinc is introduced to a chamber through a zinc precursor in a vaporizer. Microwave energy ionizes zinc and oxygen in the chamber to a plasma, which is directed to the substrate with a relatively strong field. Electrically biased control grids control a rate of deposition of the plasma. The control grids also provide Li and/or Mg dopants for the ZnO to create the ferroelectric film. A desired ferroelectric property of the ferroelectric film can be tailored by selecting an appropriate composition of the control grids.
1. A consumable control grid for supplying a dopant in a plasma deposition process for producing a ferroelectric film, the control grid comprising:
an electrical connection adapted to allow the control grid to sustain an electrical bias;
a substantially planar conductor wherein at least a surface of the substantially planar conductor comprises the dopant of the ferroelectric film; and
openings defined within the conductor adapted to allow the passage of plasma products.
2. The consumable control grid as defined in claim 1 , wherein the substantially planar conductor corresponds to a wire screen, and where the openings defined within the conductor corresponds to spacing between wires of the wire screen.
3. The consumable control grid as defined in claim 1 , wherein the surface of the substantially planar conductor includes a zone refined material.
4. A plasma assisted chemical vapor deposition system for depositing a ferroelectric film on a substrate, the system comprising:
a heater adapted to heat the substrate to a first temperature;
a first mass flow controller for introducing zinc to an interior of an electromagnetic excitation chamber;
a second mass flow controller for introducing oxygen to the interior of the electromagnetic excitation chamber;
means for ionizing the zinc and the oxygen to form a plasma with microwave power; and
at least one grid comprising one or more dopants, which, in combination with zinc and oxygen, form the ferroelectric film, where the grid is positioned in proximity to the substrate, and where the grid is biased to a negative electric potential.
5. The system as defined in claim 4 , further comprising means for propelling the plasma towards the substrate with a magnetic field.
6. A plasma assisted chemical vapor deposition system adapted to deposit a ferroelectric film on a substrate, the plasma assisted chemical vapor deposition system comprising:
a chamber configured to introduce gases that form an oxide on the substrate, wherein the chamber is further configured to ionize the gases to plasma; and
a grid in the chamber formed from a dopant material for the oxide, where the grid is configured so as to sputter dopant material off of the grid and to dope the oxide, where a combination of the oxide and the dopant material provide ferroelectric properties, and where the grid is configured to control a rate of deposition.
7. The plasma assisted chemical vapor deposition system as defined in claim 6 , wherein the plasma assisted chemical vapor deposition process is an electron cyclotron resonance chemical vapor deposition process.