GB2175278A - Avoiding drips in liquid dispensing - Google Patents

Abstract

A chemical dispense system particularly for dispensing photo-resist, a viscous liquid, onto silicon wafers includes a filter 3 in the supply line 2 to a dispense nozzle 1 and means for introducing suction between said filter and said dispense nozzle at the cessation of dispense. The last-mentioned means in the embodiment illustrated consists of a flask 5 normally evacuated to a lowered pressure connected to the point between the filter and the dispense nozzle via a control valve 7, which may be a time controlled solenoid valve; a throttle valve 6 may also be present. Flask 5 is connected to suction via 10, but may be emptied via valve 13 using high pressure gas from 9 via changeover valve 11. <IMAGE>

Description

SPECIFICATION Improvements in or relating to liquid dispensing system This invention relates to liquid dispensing systems and in particular to liquid dispensing systems for dispensing viscous liquids which require to be filtered shortly before dispensing.

One example of a system as described above is a system used for dispensing photo-resist onto silicon wafers in micro-chip manufacture. The photoresist is of course used as a medium for defining patterns. The photo-resist is pumped from a reservoir to a dispensing nozzle through a filter close to the nozzle.

After the dispense the wafer is spun so as to eject most of the photo-resist, leaving only a thin film on the wafer surface. It is most important that there should be no drips from the dispense nozzle whilst this is happening. A conventional method of guarding against such drips is to use a bellows pump which dispenses a controlled volume of photo-resist. The return stroke of the pump is used to suck back a small quantity of photo-resist from the nozzle tube thus tending to prevent drips from forming. However, the necessity to include a filter in the line adjacent the nozzle introduces a problem because the pressure difference across the filter must be reversed before any suck-back can occur. Thus a relatively large quantity of photo-resist, a viscous liquid, has to be sucked back very quickly into the pump if drips are not to be formed at the dispense nozzle.

Furthermore, the fact that the filter is being stressed in alternate directions makes it difficult to support the filter membrane and the life of the lastmentioned is very considerably shortened compared to the life of a similar membrane exposed to pressure in one direction only.

One object of the present invention is to provide an improved liquid dispensing system in which the above difficulties are avoided.

According to this invention a liquid dispensing system comprises means for passing liquid to be dispensed to a dispense nozzle via a filter and means for introducing suction between said filter and said nozzle whereby to inhibit the formation of drips at said nozzle when dispensing ceases.

Preferably said last-mentioned means comprises a sealed flask connected to a point in the supply line from said filter to said dispense nozzle via a valve and means for reducing the pressure within said flask. With an arrangement as described above said valve is normally closed during at least a substantial part of the time during which dispensing is taking place and opened shortly in advance of the cessation of dispensing whereby to create said drip inhibiting suction.

Preferably said flask includes means for draining off accumulated surplus liquid and preferably again said means for reducing the internal pressure of said flask comprises a changeover valve by means of which said flask may either be exposed to a source of vacuum or to a source of high pressure gas (such as air or nitrogen) whilst said flask is being drained.

Preferably between said first-mentioned valve and said point in the line between said filter and said dispense nozzle is an adjustable throttle valve.

Preferably said system is a system for dispensing photo-resist onto a silicon wafer in a microchip manufacturing process.

The invention is illustrated in and further described with reference to the accompanying drawing which is a schematic diagram of one photoresist dispensing system in accordance with the present invention.

Referring to the drawing, a dispense nozzle 1 is mounted to dispense photo-resist onto a silicon wafer (not represented) as known per se in a micro-chip manufacturing process.

Nozzle 1 is supplied with photo-resist from a pump (not shown) via line 2 within which is a filter 3. Filter 3 is mounted closely adjacent the nozzle 1 in order to achieve adequate filtering and in fact the distance separating the filter outlet and the wafer surface upon which photo-resist is to be dispensed in this example is but two to three centimetres.

A second line 4 joins line 2 in a T-junction between the outlet of the filter 3 and the nozzle 1.

Line 4 discharges into a sealed flask 5. Within line 4 between the T-junction with line 2 and the flask 5 are, sequentially, a throttle valve 6 and solenoid valve 7.

Also connected to the flask 5 is a third line 8 which is connectable either to a source 9 of high pressure air or nitrogen or a source 10 of vacuum by means of a changeover valve 11.

The base of the flask 5 is also provided with a drain tube 12 normally closed off by a solenoid drain valve 13.

During normal dispensing operations solenoid valve 7 is shut and changeover valve 11 is set to vacuum so that the flask 5 is under reduced pressure. Towards the end of the dispense, solenoid valve 7 is opend and photo-resist is sucked from the dispense nozzle 1 through the throttle valve 6 and into the flask 5. Normally control of solenoid valve 7 is accomplished by means of a time switch (not shown). The aforementioned time switch and throttle valve 6 are adjusted to provide optimum operation.

As and when required, the accumulation of photo-resist within the flask 5 is emptied by opening drain valve 13 and setting changeover valve 11 to its other position in which high pressure air or nitrogen from source 9 is fed into the flask 5. During this operation the solenoid valve 7 is of course shut. If desired a suitable solvent may be mixed with the high pressure gas available from source 9 so as to rinse down the interior of the flask 5 and the drain tube 12 and valve 13.

Whilst the draining operation may be carried out manually, as will be appreciated this may be arranged to operate automatically after a given number of dispense cycles.

It will be noted that with the system illustrated the flow through the filter is always in one direc tion, as is the flow through the suck-back system.

This last-mentioned tends to avoid contamination being contributed by the suck-back system. Being independent of the main supply pump, the suckback system lends itself to precise tuning for optimum operation.

Claims (1)

1. A liquid dispensing system comprising means for passing liquid to be dispensed to a dispense nozzle via a filter and means for introducing suction between said filter and said nozzle whereby to inhibit the formation of drips at said nozzle when dispensing ceases.

2. A system as claimed in claim 1 and wherein said last-mentioned means comprises a sealed flask connected to a point in the supply line from said filter to said dispense nozzle via a valve and means for reducing the pressure within said flask.

3. A system as claimed in claim 2 and wherein said valve is normally closed during at least a substantial part of the time during which dispensing is taking place and opened shortly in advance of the cessation of dispensing whereby to create said drip inhibiting suction.

4. A system as claimed in claim 2 or 3 and wherein said flask includes means for draining off accumulated surplus liquid.

5. A system as claimed in any of claims 2 to 4 and wherein said means for reducing the pressure within said flask comprises a changeover valve by means of which said flask may either be exposed to a source of vacuum or to a source of high pressure gas whilst said flask is being drained.

6. A system as claimed in any of claims 2 to 5 and wherein between said first-mentioned valve and said point in the line between said filter and said dispense nozzle is an adjustable throttle valve.

7. A system for dispensing photo-resist onto a silicon wafer in a micro-chip manufacturing process as claimed in any of the above claims.

8. A system for dispensing photo-resist onto a silicon wafer in a micro-chip manufacturing process substantially as herein described with reference to the accompanying drawing.

New claims or amendments to claims filed on 7.8.85 Superseded claims 1 New or amended claims: Claim 1

1. A liquid dispensing system comprising a source of pressurised liquid to be dispensed, means for passing said pressurized liquid to a dispense nozzle via a filter and means for introducing suction between said filter and said nozzle whereby to inhibit the formation of drips at said nozzle when dispensing ceases.