FR2597372A1 - CENTRIFUGATION RESIN SPREADING METHOD AND APPARATUS - Google Patents

Abstract

The invention relates to the fabrication of integrated circuits. In photoengraving operations, it is necessary to spread resins, particularly photosensitive resins. Such spreading is carried out by centrifugation after deposition of a resin droplet. For semiconductor wafers of large diameter, the tangential speed of the wafer is very high which causes breaks in the inherent flatness of the spread resin layer. This phenomenon is corrected by carrying out the centrifugation in a rarefied atmosphere.

Description

METHOD AND APPARATUS FOR SPREADING
RESIN BY CENTRIFUGATION
The present invention relates to an apparatus intended for spreading a layer of photosensitive or electrosensitive resin, on semiconductor wafers of large diameter.

 In the processing of semiconductor wafers, it is necessary to cover the surface of the wafer with a layer of photosensitive or electrosensitive resin to achieve, by photographic or electrographic process, the definition of patterns reserved for subsequent plasma etching operations, reactive ion etching, ion machining or ion implantation.

 Currently this operation is carried out by centrifugation of a small amount of resin deposited in the center of the wafer itself placed horizontally on the plate of a centrifuge.

 The centrifugal force removes the excess resin and produces a thin film of 1 to 3 microns thick, the thickness of which depends in the cases currently being tested on wafers of diameter up to 150 mm, the viscosity of the product and the speed of rotation.

 The equilibrium is reached after a time t of the order of 20 to 30 seconds for rotation regimes of 5000 to 10000 revolutions / minute.

 The empirical expressions given for the final thickness do not to date involve the radius of the insert.

 In the analyzes carried out, the forces applied to the film are also limited to the viscosity and to the centrifugal force and therefore do not take into account the resistance of the air which may have a non-negligible tangential component.

 A simple calculation shows that for a wafer with a diameter of 200 mm, for a rotation speed of 8000 to 9000 revolutions / minute, the tangential speed at the periphery reaches more than 300 km / h. The forces caused by the friction of the air during spreading of the resin film cannot therefore be neglected.

 These forces are likely to cause disturbances at the periphery during the rotation, modifying the thickness of the film locally. More particularly, the presence of a not perfectly flat topology, commonly encountered in the manufacture of semiconductors, could lead to film ruptures or to defects located mainly on the edges of the wafers.

 The object of the invention is to provide a new method and apparatus for spreading a layer of resin on large diameter semiconductor wafers.

 The method according to the invention consists in centrifuging the resin in an atmosphere at a pressure much lower than atmospheric pressure.

 The corresponding centrifugation apparatus therefore essentially comprises a centrifugation chamber in which the atmosphere can be rarefied.

 The apparatus may include, to guarantee a better quality of the atmosphere of the room, an entry airlock and an exit airlock.

The entry airlock and the exit airlock can be made up of the same unit and moreover the same entry / exit airlock can supply several treatment chambers. All these various configurations are part of the invention described below.

 Only the basic version comprising a bedroom and two airlocks, one at the entrance and the other at the exit, will be described more precisely.

The invention will be better understood on reading the following description and with the help of the figures given in the appendix:
FIG. 1 is a view in vertical section of the chamber and of the two airlocks,
- Figure 2 is a horizontal sectional view of the chamber and the two airlocks.

 The semiconductor wafers are represented at 1 2 and 3 respectively in the entry airlock, in the main chamber and in the exit airlock.

 The main chamber 4 has two lateral openings 5 and 6 for the inlets and outlets of wafers, constituted by vacuum valves of the guillotine type or the like allowing isolation between the entry airlock 7 and the exit airlock 8.

 Each of the airlocks has its vacuum valve for communication with the atmosphere, allowing an external device of the shuttle, spatula or other type to bring the plates in and out from the outside to the entry airlock and from the exit airlock to the 'outside.

These valves are referenced 9 at the inlet and 10 at the outlet.

 In each airlock a device 11 of the shuttle or spatula type with parallelogram deformation or the like allows the opening of the valves 5 or 6 to transfer the plates from one of positions 1 to 3 to the next.

 This movement can be reversed by program for measurements, for example, contamination rates.

 This transfer device, not shown in the vertical section, is shown in the horizontal section in two extreme positions corresponding to the grip, for example of the wafer 1 and to the removal of the wafer 2.

 The main chamber 4 is placed under vacuum by a main pumping group 12 connected to the chamber 4 by an isolation valve 13.

 The wafer 2 is located during its processing in position marked 2bis inside a bowl-shaped enclosure 14. The support of the wafer 16 connected to the motor 17, goes up and down to perform the necessary functions. The motor assembly 17 can be located outside the chamber.

 The enclosure 14 is used to collect the excess resin expelled by centrifugation. This resin flows through the channel 18 to a recovery container 19 isolated by a valve 20 from the chamber 4.

 Furthermore, the enclosure 14 is connected to a pumping group 21, isolated by a valve 22 from the chamber 4, to create a differential pressure between the enclosure 14 and the main chamber.

 The chamber 4 which can open upwards by lifting the cover 23, has at its upper part orifices 24 which carry the nozzles for dispensing the necessary products; for example: resin, solvent, adhesion promoter, and neutral or oxidizing gas to purge the chamber or to allow the atmosphere to be controlled. These distribution nozzles for spreading a better quality film can be mounted on mobile devices of the rotary arm or tangential displacement type.

 The invention therefore provides an apparatus making it possible to overcome the problems encountered during the centrifugation of semiconductor wafers. It goes without saying that many modifications can be made to the device described without departing from the scope of the invention.

 A preferred order of magnitude for the pressure inside the chamber during centrifugation is a few torr. A fully acceptable range is 0.1 to 100 torr.

Claims (3)

 1. A method of spreading resin by centrifugation on a flat surface, characterized in that the centrifugation is carried out in an atmosphere at a pressure much lower than atmospheric pressure.  2. A method of spreading resin by centrifugation on a flat surface according to claim 1 characterized in that the pressure is of the order of some torr.  3. Apparatus for implementing the method according to claim 1, characterized in that it comprises a chamber for receiving the flat surface to be centrifuged and pumping means for rarefying the atmosphere in this chamber to a lower value at atmospheric pressure.