High-precision feedback control for ion sculpting of solid state features
The invention provides a method for controlled fabrication of a solid state structural feature. In the method, a solid state structure is provided and the structure is exposed to an ion beam, under fabrication process conditions for producing the structural feature. A physical detection species is directed toward a designated structure location, and the rate at which the detection species proceeds from the designated structure location is measured. Detection species rate measurements are fit to a mathematical model, and the fabrication process conditions are controlled, based on the fitted detection species rate measurements, to fabricate the structural feature.
1 . A method for controlled fabrication of a solid state structural feature, comprising:
providing a solid state structure;
exposing the structure to an ion beam under fabrication process conditions for producing the structural feature;
directing a physical detection species toward a designated structure location;
measuring a rate at which the detection species proceeds from the designated structure location;
fitting detection species rate measurements to a mathematical model; and
controlling the fabrication process conditions based on the fitted detection species rate measurements to fabricate the structural feature.
2 . The method of claim 1 wherein measuring detection species rate comprises making a measurement of count of the species as the species proceeds from the designated structure location.
3 . The method of claim 1 further comprising storing detection species rate measurements.
4 . The method of claim 1 further comprising adjusting the mathematical model based on the fitted detection species rate measurements.
5 . The method of claim 1 wherein fitting detection species rate measurements comprises fitting a selected number of previously acquired detection species rate measurements.
6 . The method of claim 1 wherein the mathematical model includes parameters reflecting characteristics of the fabrication process.
7 . The method of claim 1 wherein the mathematical model is a polynomial expression.
8 . The method of claim 1 wherein the mathematical model is a statistical average of previously acquired detection species rate measurements.
9 . The method of claim 1 wherein controlling the fabrication process conditions is based on determining if a preselected detection species rate has been met.
10 . The method of claim 9 wherein if a preselected detection species rate has been met, then the ion exposure is continued without further measurement of detection species rates.
11 . The method of claim 9 wherein if a preselected detection species rate has been met, then the fabrication process conditions are adjusted to complete the structural feature fabrication.
12 . The method of claim 1 wherein controlling the fabrication process conditions is based on determining if measurement of detection species rates is to be continued.
13 . The method of claim 1 wherein controlling the fabrication process conditions is carried out during the ion exposure.
14 . The method of claim 1 wherein the ion exposure comprises periodic ion exposure with a duty cycle of an ion packet duration and a nonexposure duration.
15 . The method of claim 14 wherein controlling the fabrication process conditions comprises controlling ion packet duration.
16 . The method of claim 14 wherein controlling the fabrication process conditions comprises controlling ion exposure duty cycle.
17 . The method of claim 1 wherein controlling the fabrication process conditions comprises controlling ion energy.
18 . The method of claim 1 wherein controlling the fabrication process conditions comprises controlling ion species.
19 . The method of claim 1 wherein controlling the fabrication process conditions comprises controlling structure temperature.
20 . The method of claim 1 wherein controlling the fabrication process conditions comprises controlling process pressure.
21 . The method of claim 1 wherein controlling the fabrication process conditions comprises terminating exposure of the structure to the ion beam at a time when the fitted detection species rate measurements indicate completion of the structural feature fabrication.
22 . The method of claim 1 wherein the physical detection species comprises ions.
23 . The method of claim 1 wherein the structure comprises a semiconductor substrate.
24 . The method of claim 1 wherein the structure comprises a membrane.
25 . The method of claim 1 wherein the structure comprises a substrate including a layer in which the structural feature is to be fabricated.
26 . The method of claim 1 wherein the structural feature is an aperture in the structure and the designated structure location is through the aperture.
27 . The method of claim 26 wherein the aperture comprises an array of apertures.
28 . The method of claim 26 wherein the fabrication process conditions are selected to reduce an initial aperture diameter.
29 . The method of claim 26 wherein the fabrication process conditions are selected to increase an initial aperture diameter.
30 . The method of claim 26 wherein the fabrication process conditions are selected to etch the aperture in the structure.
31 . The method of claim 1 wherein the structural feature is a gap between at least two structural edges and the designated structure location is through the aperture.
32 . The method of claim 31 wherein the fabrication process conditions are selected to reduce an initial gap in the structure.
33 . The method of claim 31 wherein the fabrication process conditions are selected to increase an initial gap in the structure.
34 . The method of claim 1 wherein the physical detection species is directed toward a designated structure location during ion beam exposure of the structure.
35 . The method of claim 1 wherein the physical detection species is directed toward a designated structure location at a time when the structure is not exposed to the ion beam.