Process for the fabrication of oxide 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 plasma assisted chemical vapor deposition process for forming a ferroelectric material film on a substrate, the process comprising:
generating plasma products of oxygen and metal in a plasma chamber;
propelling the plasma products towards the substrate;
providing a control grid of a dopant source material, where the control grid is disposed between the plasma chamber and the substrate such that plasma products pass through at least a portion of the control grid; and
electrically biasing the control grid to control a rate of deposition on the substrate, where the ferroelectric material film formed comprises metal, oxygen, and dopant source material sputtered from the control grid.
2. The process as defined in claim 1 , wherein the control grid comprises a wire screen.
3. The process as defined in claim 1 , wherein the dopant source material comprises lithium.
4. The process as defined in claim 1 , wherein the dopant source material comprises magnesium.
5. The process as defined in claim 1 , wherein the dopant source material comprises both lithium and magnesium.
6. The process as defined in claim 1 , wherein the dopant source material comprises a combination of lithium and magnesium, where the ratio of lithium to magnesium in the dopant source material approximately corresponds to a desired doping ratio of lithium and magnesium.
7. The process as defined in claim 1 , wherein the oxide film comprises a ferroelectric film.
8. The process as defined in claim 1 , wherein generating plasma products comprises ionizing a vaporized metal precursor and ionizing oxygen.
9. The process as defined in claim 1 , wherein the control grid is biased to about −300 to −350 Volts direct current (Vdc) relative to ground.
10. The process as defined in claim 1 , further comprising biasing the substrate within a range of about 0 to −50 Volts direct current (Vdc) relative to ground.