US 5,717,608 A · Electro-optical board assembly for measuring the temperature of an object surface from infra-red emissions thereof, including an automatic gain control therefore

Abstract

An automatic gain control technique integrates samples of an incoming analog signal a controlled amount of time so that the magnitudes of the samples lie within the desired input window of an analog-to-digital converter or other signal processing device. The values of the samples are then determined from a combination of the output of the signal processing device and their integration time. This is utilized in a system for determining the temperature of a surface of an object, without contacting the surface, by measuring the level of its infra-red radiation emission. A particular application of the system is to measure the temperature of a semiconductor wafer within a processing chamber while forming integrated circuits on it. The measuring system is configured on a single printed circuit board with an extra height metal heat sink structure to which a cooling unit is mounted. A photodetector and a circuit chip which performs the signal integrations are mounted within the cooling unit and operated at a uniform temperature. The combination of the variable time integration and cooling techniques greatly increases the signal-to-noise ratio of the measuring system. This allows surface temperature measurements to be made down to about 250.degree. C. by measuring object emissions at slightly less than one micron in wavelength, conditions which provide signal levels which are normally too weak to measure accurately.

Claims23

Dependent claims

A method of measuring the temperature of an object from a level of intensity of infra-red radiation emitted by the object, comprising:

positioning a photodetector to receive said infra-red radiation emission, thereby to generate an electrical signal proportional thereto,
periodically integrating said electrical signal, a characteristic of the individual integrations being controllable,
applying the integrated signal to an analog-to-digital converter having an optimum input signal range,
controlling said characteristic of the individual integrations in order to maintain the integrated signal within said optimum input signal range, and
determining the temperature of the object from both a value of said characteristic and an output of said analog-to-digital converter.

2 more elements

A method of measuring a characteristic of a surface of an object being heated by lamps which emit infra-red radiation with a time varying ripple component, comprising:

detecting a combination of radiation reflected by a surface of the object from the lamps and radiation emitted by said surface in a manner to obtain a first electrical signal proportional thereto,
directly detecting the lamp radiation in a manner to obtain a second electrical signal proportional thereto,
digitizing each of the first and second electrical signals by a method which comprises:
periodically integrating said electrical signal, the time of the individual integrations being controllable,
applying the integrated signal to an analog-to-digital converter having an optimum input signal range,
controlling the time of the individual integrations in order to maintain the integrated signal within said optimum input signal range, and
obtaining digital values of said electrical signal from both the time of the individual integrations and an output of said analog-to-digital converter,
determining a magnitude of a time varying component in each of said first and second electrical signals after digitation thereof, and
combining at least the time varying components of said first and second digitized electrical signals in a manner to determine said object surface characteristic.

6 more elements

Dependencies are inferred from the claim text.

Electro-optical board assembly for measuring the temperature of an object surface from infra-red emissions thereof, including an automatic gain control therefore

Life of this patent

Electro-optical board assembly for measuring the temperature of an object surface from infra-red emissions thereof, including an automatic gain control therefore

Life of this patent

Abstract

Claims23