Lam Research Corporation

Strasbaugh

Terry L Lentz

Michael R Vogtmann

Bill Kalenian

In a machine for planarizing wafers, when a spindle carrier descends over the load station, it needs a way of determining whether it should descend to a first position suitable for depositing a wafer onto the load station or whether it should descend to a lower second position suitable for acquiring a wafer that is already present on the load station. The present invention provides a way of making this determination. The load station includes three upwardly-directed nozzles for use in supporting a wafer on three separate spaced cushions of purified water. The nozzles are supplied through branch conduits from a supply main. When no wafer is present, the pressurized water meets with little resistance as it is discharged from the nozzles. Accordingly, the pressure in the branches is relatively low. In contrast, when a wafer is present the wafer partially impedes the discharge of the water from the nozzles, causing the pressure in the branches to be greater than when no wafer is present. In accordance with the present invention, the pressure in one of the branches is sensed. A low pressure indicates the absence of a wafer and signifies that the spindle carrier should descend to the first position to deposit a wafer. A high pressure indicates the presence of a wafer on the load station and signifies that the spindle carrier should descend to the lower second position to acquire the wafer.

Sensing the presence of a wafer

A nozzle that extends telescopically upward is used to elevate a wafer without contacting the wafer. The nozzle includes a stationary hollow cylinder, closed at its lower end and open at its upper end, within which a spool is disposed to slide vertically. In its lowest position the spool is spaced from the closed bottom of the cylinder, and purified water is supplied under pressure to the space. A passage extends vertically through the spool, and the water is discharged at the upper end of the spool from the passage. As a wafer is lowered toward the upper end of the spool, the wafer partially impedes the discharge, increasing the pressure in the space below the spool. The increased pressure drives the spool and the wafer upward, but the wafer never comes into contact with the wafer because the discharge of water creates a protective cushion between them.

Lifting and rinsing a wafer

A load station is used in a planarizing machine to perform several useful functions related to handling of a wafer. By centering the wafer with respect to a spindle carrier the load station interrupts the accumulation of positional errors. The load station never makes solid contact with the wafer, but instead the wafer is continually levitated on three cushions of water that are directed upwardly against the lower face of the wafer. The presence of the wafer partially impedes the flow of water from the nozzles used for levitation causing an increase in the water pressure immediately upstream of the nozzles. This increased pressure is sensed and used as an indicator of the presence of a wafer at the load station. The load station further includes a nozzle that directs a stream against the lower side of the wafer so as to elevate the wafer from the load station into the carrier.

Accurate positioning of a wafer

In one type of planarizing machine, a wafer is maintained with its fragile processed side facing downward as the wafer is passed from a robot to a load station and from the load station to a spindle carrier, and then returned from the spindle carrier to the load station to the robot. These transfers must be accomplished without anything solid contacting the downwardly facing side of the wafer. This is accomplished by supporting the wafer, while it is on the load station, on cushions of purified water. The cushions are formed at three spaced areas on the lower side of the wafer by upwardly-directed nozzles located below the wafer. The purified water is discharged with sufficient force to prevent the wafer from contacting the nozzles. The use of three separate cushions insures stability of the wafer.

Non-contacting support for a wafer

Apparatus for use in a semiconductor wafer polishing machine of a type in which the wafer is picked up and held by a suction cup effect between the wafer and a resilient diaphragm on the wafer carrier. The apparatus permits the presence or absence of a wafer on the carrier to be sensed so that this information can be used in controlling the operation of the machine. In normal operation, a vacuum is applied to a downwardly-opening plenum that is covered by a resilient diaphragm. The present invention is the addition to the wafer carrier of an air conduit opening into the plenum through an air port and connected to an orifice so that air can flow through the orifice, through the air conduit and the air port into the plenum at a rate that is slow relative to the capacity of the vacuum pump. The present invention further requires the addition of a pressure sensor for sensing the pressure in the air conduit or alternatively in the vacuum conduit. The sensed pressure in the vacuum conduit is lower in the absence of a wafer than in the presence of a wafer, and the sensed pressure in the air conduit is greater in the absence of a wafer than it is when a wafer is present.

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San Luis Obispo, CA, United States of America

Terry L Lentz