US3426727A - Vacuum whirler for applying thin and uniform coating of an emulsion on a wafer - Google Patents

Description

Feb. 11, 1969 K 5, BALAlN ET AL 3,426,727

VACUUM WHIRLER FOR APPLYING THIN AND UNIFORM COATING OF AN EMULSION ON A WAFER Filed Oct. 21, 1965 Sheet Of 2 FIGJ FIG-3 Feb. 11, 1969 5, BALAIN ETAL 3,426,727

VACUUM WHIRLER FOR APPLYING THIN AND UNIFORM COATING OF AN EMULSION ON A WAFER Filed Oct. 21, 1965 sheet 2 or2 FIG. 6

f/ire/ifdr maxi cud wazg 7%)[63/6 VACUUM WHIRLER FOR APPLYING THEN AND 1 Claim ABSTRACT OF THE DISCLOSURE A vacuum whirler for applying a thin and uniform coating of an emulsion on a wafer, in which a rotor having a horizontal, perforated top member is carried on a vertically mounted spindle rotatively driven by a motor, wherein the rotor is provided with fan blades for creating, when the spindle is driven in rotation, a vacuum within the rotor causing a suction effect on the perforations in the rotor top member for holding the wafer to be coated, thus enabling a single motor to serve both for rotating the spindle and for creating the required vacuum.

This invention relates to a vacuum whirler, more particularly of the kind used for applying a thin and uniform coating of an emulsion on a wafer such as a semiconductor slice.

It is well known that the photolithographic (photornaskiug and photo etching) process is one of the key processes in the manufacture of modern semiconductor devices. In a photo-lithographic process, an important step is that of applying a very thin coating of a photosensitive emulsion, such as are available under the trade names Kodak Photo Resist and Kodak Metal Etch Resist. An essential requirement of such a coating is that it should be thin, uniform and adherent.

Said coating is usually applied by spreading the emulsion on the wafer and spinning it, so as to utilize the centrifugal force for the purpose of uni-form spreading. The technique of spreading the photo-resist by centrifugal force is preferred for accurate and fast work. In order to utilize this technique for semiconductor technology where the use of very thin and brittle substrates is encountered, a proper whirler (spinner) with a mechanism to hold the substrate by vacuum is required. Thus there is a need for a vacuum whirler which spins as Well as holds the substrate by vacuum.

The conventional vacuum whirler for the purpose mentioned has, in combination, (i) a motor to spin the rotor on which the substrate is positioned, (ii) a vacuum device including another motor to create the necessary vacuum to hold the substrates, and (iii) a high speed vacuum seal.

The conventional vacuum whirler as aforesaid suffers from various drawbacks, such as (i) that it necessitates the use of two separate motors, viz. one to spin the rotor on which the substrate is positioned, and the other to create the necessary vacuum to hold the said substrates; (ii) that it necessitates the use of a high speed vacuum seal; and (iii) that it involves a complicated design and is expensive to manufacture.

This invention has for its object improvements whereby these drawbacks may be obviated and certain additional advantages may be realised.

With this object in view, this invention consists of an improved vacuum whirler for applying a thin and uniform coating of an emulsion on a wafer, which whirler consists of a rotor mounted on a spindle adapted to be spun or rotated by means of a high speed motor, the said rotor having a perforated top on which the said wafer may be securely positioned as a result of suction of air through the said perforations, and having also a suction creating means such as a paddle wheel fan fitted on the said spindle immediately below the perforated top of the said rotor.

The improved vacuum whirler as aforesaid is provided with additional means such as those mentioned below:

(i) a housing for the vacuum whirler, including its high speed motor;

(ii) a top cover for the said housing so as to cut off completely stray light that might otherwise fall on the rotor during the formation of the coating;

(iii) a bowl for collecting extra liquid which may separate from the coating emulsion as it is spread on the wafer by centrifugal force;

(iv) a mechanical brake to stop the rotor quickly, thereby reducing the time needed for the completion of each coating operation; and

(v) levelling screws for adjusting the level of the vacuum whirler.

This invention will now be more particularly described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic layout of an improved vacuum whirler according to this invention.

FIG. 2 is an isometric view of the rotor of the said whirler, including the blades of the paddle wheel fan provided for creating suction.

FIG. 3 is a section on AA of FIG. 2.

FIG. 4 is a section on BB of FIG. 3.

FIG. 5 shows the details of mechanical brake mechanism provided for stopping the rotor.

FIG. 6- is a view, partly in section, showing a modified disposition of the rotor in relation to the high speed working of the vacuum whirler.

The vacuum whirler illustrated in the drawings consists of a rotor I mounted on a spindle 2 adapted to be spun or rotated by means of a high speed motor 3, and it has a perforated top 4 having perforations 5.

Immediately below the said perforated top 4 and fitted on the said spindle 2, is a paddle wheel fan 7 with blades so shaped as to suck in air through the said perforations 5, when the spindle 2 is spun rapidly.

The perforated top 4 is adapted to hold a wafer 8 securely in position as a result of the suction created by the paddle wheel fan 7.

The said rotor 1 together with the motor 3 is provided with a metal housing 9 having a top cover 10 adapted to cut off completely stray light from falling on the said rotor 1.

A bowl 11 is provided around the perforated top 4, for collecting extra liquid which may separate from the coating emulsion as it is spread on the wafer 8 by centrifugal force.

The said vacuum whirler is provided with a brake mechanism which, as shown in FIG. 5, consists of a brake shoe 15 provided on a pivoted bent lever 16, which, at its remote end, is provided with a brake control knob 17 of a rod 18 passing through push bearings 19, and with a spring 20 which serves as the fulcrum for the operation of the said bent lever for applying the brake to the rotor 1, or for releasing the brake from the said rotor 1.

The vacuum whirler is also provided with a variac 21 whereby the speed of the high speed motor 3 may be regulated tosuit requirements, and with levelling screws 22.

It will be seen that a vacuum whirler as shown in the drawings will provide various advantages such as:

(i) That both the rotor and the suction producing means are operated by one and the same motor, and therefore, there is no need for two separate motors for operating them as in conventional whirlers.

(ii) As the wafer or like substrate will be held in position by the vacuum created underneath thereof, it will be pOssible to apply the coating on its entire surface.

(iii) It will not be necessary to provide a high speed vacuum seal.

(iv) The mechanical brake provided for stopping the rotor quickly, will economise the time needed for a complete coating process.

(v) The top cover will facilitate the utilisation of the vacuum whirler for coating very senstive photo-resist emulsions.

(vi) The variac will enable a smooth adjustment of variable and reproducible speeds of the rotor.

(vii) The design of the whirler is quite simple and compact.

Instead of mounting the rotor member directly in line with the drive motor a high speed centrifugal whirler may include a pulley and drive belt connection as shown in FIG. 6 of the drawings.

What we claim is:

1. A vacuum whirler for applying a thin and uniform coating of an emulsion on a wafer, comprising a spindle, means supporting said spindle for rotation about a vertical axis, a rotor mounted on the upper end of said spindle for rotation therewith, said rotor having fixed with respect thereto a perforated horizontal top member upon the perforated surface of which said wafer is supported and a fan member horizontally disposed beneath 4 said perforated top member and fixedly mounted on said spindle whereby to effect a vacuum beneath said perforaated top member when said spindle is rotated and whereby suction elfected through the perforations retains said wafer on the perforated surface, and means for rotating said spindle whereby to whirl said wafer and to effect said suctionretention of the water on the perforated surface.

References Cited UNITED STATES PATENTS OTHER REFERENCES IBM Technical Disclosure Bulletin Vacuum Spintable, by F. H. Masterson, vol. 5, No. 5, October 1962, pp. 7, 8.

MORRIS KAPLAN, Primary Examiner.

US. Cl. X.R.

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