Simple and inexpensive method and device for measuring concentration and rate of change of a crystal etchant gas, such as HF or DF gas

A method for determining concentration of a gas in a chamber, said gas having ability to act as a crystal etchant, said method comprising the steps of;

• subjecting a crystal having an initial mass to a crystal erosion process by the gas;
• determining the crystal resonant frequency, said crystal resonant frequency changeable during the crystal erosion process as a result of a decrease in the initial mass of said crystal occurring during the crystal erosion process;
• and
• calculating a change in the crystal resonant frequency to determine the concentration of the gas.

A device for determining concentration of a gas in a chamber, said gas having ability to act as crystal etchant, said device comprising:

• a crystal comprising an AT-cut quartz crystal placed in the chamber and subjected to erosion by the gas;
• determining means, coupled to said crystal, for determining the crystal resonant frequency, said crystal resonant frequency changeable during the crystal erosion, the determining means comprising:
• an oscillator comprising a Colpitts oscillator;
• and
• a crystal resonant frequency detector for obtaining and demodulating the crystal resonant frequency from the oscillator and supplying the crystal resonant frequency to the calculating means, the crystal resonant frequency detector comprising an FM demodulator;
• and
• calculating means, coupled to said resonant frequency determining means, for calculating a change in the crystal resonant frequency to determine the concentration of the gas, the calculating means having means for calculating a change in the gas concentration, a rate of change in the gas concentration, and means for averaging the calculated gas concentration.

A device for determining concentration of a gas in a chamber, said gas having ability to act as crystal etchant, said device comprising:

• a crystal comprising an AT-cut quartz crystal placed in the chamber and subjected to erosion by the gas;
• determining means, coupled to said crystal, for determining the crystal resonant frequency, said crystal resonant frequency changeable during the crystal erosion, the determining means comprising a Colpitts oscillator;
• calculating means, coupled to said resonant frequency determining means, for calculating a change in the crystal resonant frequency to determine the concentration of the gas;
• and
• an electronic box for storing the means for determining the crystal resonant frequency and the crystal, wherein the electronic box comprises;
• a crystal holder for holding the crystal, said crystal holder having:
• a plurality of electrodes;
• a mounting means for attaching the crystal to the electronic box and providing easy replacement of the crystal;
• a protective cover with windows over the crystal;
• a battery supply;
• and
• a crystal resonant frequency detector for obtaining the crystal resonant frequency from the oscillator, demodulating and supplying the crystal resonant frequency to the calculating means.

A method for determining concentration of a gas in a chamber, said gas having ability to act as crystal etchant, said method comprising the steps of:

• subjecting a crystal to erosion by the gas, wherein the crystal comprises an AT-cut quartz crystal;
• determining the crystal resonant frequency, said crystal resonant frequency changeable during the crystal erosion, the step of determining the crystal resonant frequency being performable in a device selected from the group consisting of an oscillator, an electronic box, and combinations thereof, said electronic box having a crystal holder for holding the crystal, said crystal holder having a plurality of electrodes, and a mounting means for attaching the crystal to the electronic box and providing easy replacement of the crystal;
• obtaining the crystal resonant frequency from the device selected from the group consisting of an oscillator, an electronic box, and combinations thereof, demodulating and supplying the crystal resonant frequency to a calculating means;
• calculating a change in the crystal resonant frequency to determine the concentration of the gas;
• calculating the gas concentration, proportional to the change in the crystal resonant frequency;
• calculating a change in the gas concentration, proportional to the change in the crystal resonant frequency;
• and
• calculating a rate of change in the gas concentration, proportional to the change in the crystal resonant frequency.