Method and apparatus for reducing aspect ratio dependent etching in time division multiplexed etch processes
View Patent ↗The present invention provides a method and an apparatus for reducing aspect ratio dependent etching that is observed when plasma etching deep trenches in a semiconductor substrate through an alternating deposition/etch process. A plurality of different sized features on the substrate are monitored in real time during the alternating deposition/etch process. Then, based on the information received from the monitor, at least one process parameter is adjusted in the alternating deposition/etch process to achieve equivalent etch depths of at least two different sized features on the substrate.
1. A method for reducing aspect ratio dependent etching in a plasma etching process, the method comprising:
placing a substrate in a vacuum chamber;
setting a desired etch depth difference of different sized features on said substrate;
depositing a passivation layer on said substrate by means of a plasma;
removing at least a portion of said passivation layer by means of a plasma;
etching a material from said substrate by means of a plasma;
performing a process loop of repeating the deposition step, the removal step, and the etch step;
monitoring the etching of said different sized features on said substrate in real time;
measuring a current etch depth difference between said different sized features based on said monitoring step;
comparing the current etch depth difference of said different sized features on said substrate to said desired etch depth difference of said different sized features on said substrate;
adjusting the process loop step based on said comparison step, thereby minimizing the differences in the etch depth between the monitored different sized features on said substrate; and
removing the substrate from the vacuum chamber.
2. The method of claim 1 wherein said monitoring step further comprising:
generating an initial signal from a differential interferometer;
evaluating said initial signal prior to initiating said process loop step;
generating a process signal from said differential interferometer during said process loop step;
comparing said process signal to said initial signal; and
terminating the process loop step when said process signal is about equal to said initial signal.
3. The method of claim 1 wherein said etch step further comprises a plurality of sub-steps.
4. The method of claim 1 wherein said etch step further comprises at least one isotropic sub-step.