Shallow Trench Isolation Using PECVD Nitride and Fluorine Plasma

The patent replaces the wet chemical etching process (phosphoric bath) with a plasma-based dry etching process. This substitution eliminates the bathlife variation problem inherent in wet chemistry, providing consistent and controllable nitride layer removal without affecting pad oxide thickness. The plasma process offers precise endpoint detection and uniform etching rates.

The patent changes the etching mechanism from chemical (wet) to physical-chemical (plasma). By adjusting plasma parameters such as power, pressure, and gas composition, the process achieves selective and controlled nitride removal. This parameter change enables precise control over etch depth and rate, maintaining pad oxide integrity while removing deposited nitride.

The patent replaces the phosphoric bath wet etching process with plasma-based dry etching. This substitution provides better process control through real-time endpoint detection and eliminates the uncontrolled overetching that occurs with wet baths. The plasma process allows precise termination exactly when nitride is removed, preventing pad oxide damage.

The plasma etching process incorporates real-time feedback through endpoint detection methods such as optical emission spectroscopy or reflected power monitoring. This feedback mechanism automatically terminates the etch process when the nitride layer is completely removed, preventing any overetch that would damage the underlying pad oxide. The system self-regulates based on process conditions.

The patent extracts or removes the harmful backside nitride deposits that form during LPCVD batch processing. By eliminating these deposits through the plasma process or selective removal, the substrate stress and potential damage caused by thermal expansion mismatches are prevented. This extraction maintains the benefits of batch processing while removing the harmful byproduct.

The patent converts the potentially harmful backside nitride deposition into a beneficial or neutral outcome. The plasma processing conditions are controlled to prevent backside deposition, or the deposits are selectively removed without affecting the frontside device performance. This transforms a process defect into a controlled parameter.

The patent changes the deposition and etching parameters to achieve better control over nitride layer quality and thickness. The plasma-based process provides more uniform deposition and etching, reducing defects that limit device scaling. By adjusting plasma power, pressure, and gas composition, the process maintains isolation performance while enabling smaller feature sizes.

The patent uses plasma (ionized gas) instead of liquid chemicals for the etching process. This pneumatic approach provides better control over the etching front, reduces particulate contamination, and improves uniformity across the wafer. The gas-phase process enables better scaling to smaller dimensions with fewer defects.