Chucking sensor using floating ESC power supplies
Electrostatic chucks (ESCs) are used to provide a clamping force between the substrate and the pedestal during semiconductor processes. However, it is difficult to measure a chucking state of the substrate during a live process, as this usually requires invasive measurements or additional hardware to be added to the pedestal. A new technique for monitoring a chucking state electrically isolates the ESC from the system ground to create a single conductive path through the ESC power supplies, ESC electrodes, and the substrate. A floating voltage between the two power supplies may change with the chucking state of the substrate, and this voltage may be monitored to determine the real-time chucking state of the substrate. This provides an unintrusive way to monitor the ESC state in real-time during a semiconductor process at the controller without disturbing the process or modifying the pedestal.
1 . A semiconductor processing chamber comprising:
a pedestal configured to support a substrate during a semiconductor process, wherein the pedestal comprises a first electrode and a second electrode for an electrostatic chuck (ESC);
a chamber body that encloses the pedestal to form a processing region in which the semiconductor process is performed, wherein the chamber body is electrically connected to a system ground;
a first power source for the ESC that is electrically connected to the first electrode, wherein the first power source and the first electrode are electrically isolated from the system ground; and
a voltage monitor configured to provide a measurement indicative of a voltage induced on the substrate, wherein the voltage monitor is electrically connected to a first output of the first power source, and the first electrode is electrically connected to a second output of the first power source, and the voltage induced on the substrate varies based on a chucking state of the substrate.
2 . The semiconductor processing chamber of claim 1 , wherein the semiconductor process comprises a plasma-enhanced chemical vapor deposition (PECVD) process to deposit a film on the substrate.
3 . The semiconductor processing chamber of claim 1 , wherein the semiconductor process comprises depositing a carbon-based material on the substrate.
4 . The semiconductor processing chamber of claim 1 , further comprising a top-feed RF power supply that provides RF power to a plasma in the processing region, wherein the RF power is grounded through the first electrode and/or the second electrode.
5 . The semiconductor processing chamber of claim 1 , further comprising a bottom-feed RF power supply that provides RF power to a plasma in the processing region, wherein the RF power is provided through the first electrode and/or the second electrode.
6 . The semiconductor processing chamber of claim 1 , wherein the semiconductor process is performed at a temperature of between about 500° C. and about 700° C.
7 . An electrostatic chuck comprising:
a first electrode and a second electrode embedded in a pedestal configured to support a substrate during a semiconductor process, wherein the first electrode and the second electrode form a bipolar electrostatic chuck;
a first power source comprising a positive output that is electrically connected to the first electrode, and a negative output;
a second power source comprising a negative output that is electrically connected to the second electrode, and a positive output that is electrically connected to the negative output of the first power source; and
a voltage monitor that is electrically connected to the negative output of the first power source and the positive output of the second power source.
8 . The electrostatic chuck of claim 7 , wherein a connection between the positive output of the second power source and the negative output of the first power source is floating relative to a system ground.
9 . The electrostatic chuck of claim 7 , wherein a connection between the positive output of the second power source and the negative output of the first power source comprises a voltage offset that equalizes current through the first electrode and the second electrode resulting from a bias induced on the substrate.
10 . The electrostatic chuck of claim 7 , wherein the electrostatic chuck forms a continuous current path from the first power source, to the first electrode, to the second electrode, to the substrate, to the second power source, and back to the first power source.
11 . The electrostatic chuck of claim 10 , wherein the continuous current path is not connected to any free current paths to a system ground.
12 . The electrostatic chuck of claim 7 , wherein the first power source provides a positive voltage to the first electrode, and the second power source provides an equal and opposite negative voltage to the second electrode.
13 . A method of determining a chucking state of a substrate during a semiconductor process, the method comprising:
applying a first chucking voltage to a first electrode of an electrostatic chuck (ESC) in a pedestal configured to support the substrate, wherein the first chucking voltage is provided from a first output of a first power source for the ESC;
measuring a voltage at a second output of the first power source for the ESC; and
determining the chucking state of the substrate based at least in part on the voltage at the second output of the first power source for the ESC, wherein determining the chucking state of the substrate comprises determining whether the substrate is fully chucked flat against the pedestal, or whether the substrate is bowed or a gap exists between the substrate and the pedestal.
14 . The method of claim 13 , further comprising:
applying a second chucking voltage to a second electrode of the ESC in the pedestal, wherein the second chucking voltage is provided from a first output of a second power source for the ESC, and the second output of the first power source is connected a second output of the second power source.
15 . The method of claim 13 , wherein the first power source and the first electrode are floating relative to a system ground, and the voltage at the second output of the first power source is measured relative to the system ground.
16 . The method of claim 13 , wherein determining the chucking state of the substrate comprises identifying a variation in the voltage at the second output of the first power source relative to a baseline voltage indicating that the substrate is fully chucked to the pedestal.