Noise filter for backside helium signal

Details Noise filter for backside helium signal Noise filter for backside helium signal

2002-08-21

2004-08-17

Picard, Leo (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C438S714000, C209S235000

Reexamination Certificate

active

06778875

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processing of semiconductor wafers in general and more particularly to the elimination of false processing errors due to erratic noise in the PID control of backside helium.
BACKGROUND OF THE INVENTION
Backside cooling by helium controls the rate and uniformity of etching in a dry non-isotropic etching process of thermal silicon layers. Helium pressures are found in the two to twenty Torr range.
U.S. Pat. No. 5,624,582 issued to Cain teaches in a dry non-isotropic etching employing wafer backside cooling by means of helium gas flow to the backside of the wafer holder wherein the helium gas pressure is greater than about three Torr. The control system that controls the processing has many sensors including a sensing control for the flow of the helium. As with any alarm system, most of the alarms can initiate a process stoppage that in a great many instants ruins the wafer being processed.
U.S. Pat. No. 5,753,566 issued to Hwang, teaches the use of heated helium that is heated to a temperature between about 70° C. and about 100° C. This gas is circulated to the back surface of the work-piece to bow the work-piece forming a vaulted space there below. The pressure of the helium is between about 200 milliTorr and about 600 milliTorr above the work-piece and the pressure in the vaulted space below the work-piece is between eight and fourteen Torr. The use of helium as a cooling gas is to prevent the wafer from overheating.
U.S. Pat. No. 5,968,278 issued to Young et al. teaches an improved etching procedure that uses three processing steps to vastly improve the High Aspect Ratio “HAR”, the high depth to width ratio, opening profile and improved under-layer selectivity. In each of the three processes backside helium is used for cooling and is in the pressure range between ten and fourteen milliTorr.
U.S. Pat. No. 6,254,398 issued to Chen, teaches a process having a two-cycle, dry etching procedure. The first cycle performs using a first set of dry etching conditions, not robust enough to result in etching of exposed material, but robust enough to allow the activation, and operation, of a backside helium alarm procedure. The backside helium alarm procedure is used to monitor particle count in the dry etching chamber. If the particle counts observed via use of the backside helium alarm procedure during the non-etching, first cycle are high, the dry etching procedure is interrupted. After cleanup of the dry etching chamber, the same samples, with a re-worked photoresist, are again subjected to the two-cycle, dry etching procedure.
SUMMARY OF THE INVENTION
In Automatic Pressure Control (APC) of Super Etching (Super-E) backside helium, the APC has a high-speed response for helium supply pressure or pumping speed change. So if the Proportional-Integral-Derivative (PID) control unit in the APC does not optimize or if the DC power supply has noise, the helium flow reading will have a spike noise appear. When the spike noise helium flow has been detected by the system during the process, the system will trigger an alarm to abort the process. This alarm is known as the “B/S helium alarm”. In addition this alarm has serious problems around Super-E high RF power and high magnet process design environment.
These and other problems are readily solved by a special T-type R/C filter design in a semiconductor wafer-processing controller having a plurality of voltage inputs for receiving various regulated dc voltages to operate the controller. A helium gas input operatively connected to a source of helium gas and a helium gas output operatively connected to a wafer-processing chamber.
PID helium pressure controller is operatively connected to at least two of the voltage inputs and operates to control the flow of helium gas from the source to the helium gas output. The PID controller is responsive to the flow for generating a helium flow pulsed signal. A filter is responsive to the helium flow pulsed signal from the PID controller for reducing the amplitude of the pulsed signal when the pulsed signal has a duration less than a predetermined value and non-responsive to all other pulsed signals. The output of the filter is a filtered helium flow signal.
An alarm control unit is operatively responsive to the filtered helium flow signal for generating an alarm signal when the flow of helium gas has at least one measurable transient pulse signal greater than a first amplitude and with a time period between the predetermined value and a second value, the alarm signal is adaptable to interrupt the wafer fabricating process.


REFERENCES:
patent: 5624582 (1997-04-01), Cain
patent: 5753566 (1998-05-01), Hwang
patent: 5968278 (1999-10-01), Young et al.
patent: 6254398 (2001-07-01), Chen
patent: 6424880 (2002-07-01), Goder et al.

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