Browse Prior Art Database

Integrated Circuit Wafer Temperature Detector

IP.com Disclosure Number: IPCOM000089503D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 5 page(s) / 97K

Publishing Venue

IBM

Related People

Ehrlich, RF: AUTHOR [+2]

Abstract

In automated integrated circuit fabrication lines, it is very important to monitor wafer temperatures at various processing steps optically on a moving wafer mounted on a susceptor of refractory material, such as a graphite boat.

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Integrated Circuit Wafer Temperature Detector

In automated integrated circuit fabrication lines, it is very important to monitor wafer temperatures at various processing steps optically on a moving wafer mounted on a susceptor of refractory material, such as a graphite boat.

The wafer temperature is obtained by sighting on the wafer with an automatic optical pyrometer. The output of the pyrometer is monitored by the computer that displays the reading in degrees centigrade. The computer reading, however, will only occasionally be taken from the wafer. This is the case because the product is moving from one end of the reactor to the other end while the optical sensor is stationary. The reading, therefore, will depend on the target area that is in focus when the reading was taken. The graphite boats will appear hotter than the wafers.

Fig. 1 is a typical profile seen by a stationary optical pyrometer during a run. There are only two 1-1/4'' wafers shown in the figure as well as the surfaces of the boats that hold these wafers. Note that the reading decreases when the target varies from the boat surface to the surface of the wafer, and it reaches its lowest point in the neighborhood of the center of the wafer.

The wafer temperature detectos contains two major components: I. Hardware with the following functions: --Amplify low level signal (0-50 mv) produced by the optical sensor. --Detect minimum and maximum peaks of this signal. --Hold the minimum peak. --Set up latches to be used in the software logic. II. Software with the following functions: --Makes a logic decision whether or not to accept the minimum peak. --Resets the hardware at the start of a new cycle. --Provides for operator's display of data. --Updates set point for computer control. Hardware Operation.

Fig. 2 is a block diagram of the Wafer Temperature Detector hardware. Fig. 3 contains output wave forms of major components. The detector contains the following major components: --Signal conditioners (A(1), A(2), A(6)) --Minimum peak detector (A(3), A(4), A(5)) --Maximum peak detector (B(1), B(2), B(3)) -- Latches (L(1), L(2))

The function of the minimum peak detector that is employed in conjunction with the signal conditioners is to obtain the wafer temperature. The maximum detector and the latches are used by the software logic to decide whether the reading is from a wafer and should be accepted or from a boat and should be rejected. Minimum Detector.

The output of the optical sensor is amplified and filtered by A(1). Before the signal is fed to the minimum detector, it is level shifted by A(2). The negative gate A(3) allows the input to charge the hold amplifier A(4) to the most negative input value. This voltage changes polarity, and then it is fed back to the gate by means of A(5). When the fed-back voltage equals or is less than the input value, the gate cuts off. At this time, the most negative input value will be stored by the hold amplifier. After anoth...