3D NAND staircase CD control by using interferometric endpoint detection
Embodiments of the present disclosure provide methods for forming stair-like structures in manufacturing three dimensional (3D) stacking of semiconductor chips. In one example, a method includes performing a trimming process on a substrate to trim a patterned photoresist layer disposed on a film stack from a first width to a second width in a processing chamber, performing an etching process to etch a portion of the film stack exposed by the trimmed patterned photoresist layer, directing an optical signal to a surface of the trimmed patterned photoresist layer continuously during the trimming and the etching process, collecting a return reflected optical signal reflected from the trimmed patterned photoresist layer, determining a change of reflected intensify of the return reflected optical signal as collected; and calculating a photoresist thickness loss based on the change of the reflected intensity.
1. A method of determining a photoresist trimming process endpoint comprises:
directing an optical signal to a surface of a patterned photoresist layer disposed on a film stack formed on a substrate in a processing chamber;
performing a trimming process on the substrate to trim the patterned photoresist layer disposed on the film stack from a first width to a second width in the processing chamber, wherein the patterned photoresist layer exposes a portion of the film stack uncovered by the patterned photoresist layer during the trimming process;
performing an etching process to etch a portion of the film stack exposed by the trimmed patterned photoresist layer;
continuously directing the optical signal to the surface of the trimmed patterned photoresist layer during the trimming and the etching process;
collecting a return reflected optical signal reflected from the trimmed patterned photoresist layer;
determining a change of reflected intensify of the return reflected optical signal as collected;
calculating a photoresist thickness loss based on the change of the reflected intensity; and
determining an endpoint for each trimming process based on the photoresist thickness loss as calculated after each etching process.
2. The method of claim 1 , the change of reflected intensity is obtained by computing a ratio of the reflected intensity or the derivative of the reflected intensity with respect to time obtained during the photoresist trimming process with a reflected intensity obtained from the referenced waveform from a referenced substrate.
3. The method of claim 2 , wherein referenced substrate is a bare-silicon wafer.
4. A method of determining a photoresist trimming process endpoint comprises:
directing an optical signal to a surface of a patterned photoresist layer disposed on a film stack formed on a substrate in a processing chamber;
performing a trimming process on the substrate to trim the patterned photoresist layer disposed on the film stack from a first width to a second width in the processing chamber, wherein the patterned photoresist layer exposes a portion of the film stack uncovered by the patterned photoresist layer during the trimming process;
performing an etching process to etch a portion of the film stack exposed by the trimmed patterned photoresist layer;
repeatedly performing the trimming process and the etching process;
continuously directing the optical signal to the surface of the trimmed patterned photoresist layer during the repeated trimming and the etching process;
collecting a return reflected optical signal reflected from the trimmed patterned photoresist layer; and
analyzing the return reflected optical signal to calculate a photoresist thickness loss; and
determining an endpoint for each trimming process based on the photoresist thickness loss as calculated after each etching process.
5. The method of claim 1 , wherein determining the change of reflected intensify of the return reflected optical signal further comprises:
analyzing a waveform indicating the reflected intensity change over different wavelengths obtained during the photoresist trimming process.
6. The method of claim 2 , further comprising:
obtaining a nominal reflectivity from the referenced waveform from the reference substrate.
7. The method of claim 6 , further comprising:
extracting a minimal pattern from the nominal reflectivity.
8. The method of claim 7 , wherein the minimal pattern is fringes shown in the waveform.
9. The method of claim 1 , the photoresist layer has similar lateral and vertical trimming rates.
10. The method of claim 1 , wherein the film stack includes a multi-material layer made from repeated pairs of layers.
11. The method of claim 10 , wherein each repeated pair includes a first layer that is a dielectric layer and a second layer that is a dielectric layer or a conductive layer.
12. The method of claim 11 , wherein the first layer is a silicon oxide layer and the second layer is a silicon nitride layer.
13. The method of claim 1 , wherein the optical signal comprises:
generating a plasma within the processing chamber.
14. The method of claim 1 , wherein the photoresist trimming process and the etching process may be repeatedly performed to gradually trim dimension of the photoresist layer in each trimming process cycle to form stair-like statures in the film stack.