Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2000-01-28
2002-04-09
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S067000, C451S332000, C015S088300, C134S902000, C414S936000
Reexamination Certificate
active
06368183
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, generally, to a self-contained machine and to a method associated with that machine for cleaning and rinsing work pieces and, more particularly, to an improved system and method for brush cleaning semiconductor wafers in the presence of various solutions and then rinsing the wafers.
BACKGROUND OF THE INVENTION
Machines for polishing and machines for cleaning work pieces and disks in the electronics industry are generally well known. For example, semiconductor wafers, magnetic disks, and other work pieces often come in the form of flat, substantially planar, circular disks. In the manufacture of integrated circuits, semiconductor wafer disks are sliced from a silicon ingot and prepared for further processing. After each wafer is sliced from the ingot, it must be thoroughly polished and then cleaned, rinsed, and dried to remove debris from the surface of the wafer. Thereafter, a series of steps are performed on the wafer to build the integrated circuits in and near the wafer surface, usually including the steps of depositing or otherwise forming one or more dielectric or metal layers overlying the wafer surface. Typically, after the layers are formed on the wafer surfaces, the wafers must be planarized to remove excess material and imperfections.
After each processing step, it is often desirable to thoroughly clean, rinse, and dry the wafers to ensure that debris is removed from the wafers. Thus, a method and apparatus for quickly and efficiently cleaning, rinsing, and drying wafers is needed which facilitates high wafer throughput, while at the same time thoroughly cleaning and drying the wafers with a minimum of wafer breakage. For a discussion of existing wafer cleaning machines, see, for example, Lutz, U.S. Pat. No. 5,442,828, issued Aug. 22, 1995; Frank et al., U.S. Pat. No. 5,213,451, issued May 25, 1993; and Onodera, U.S. Pat. No. 5,357,645, issued Oct. 25, 1994.
Presently chemical-mechanical polishing and/or planarization (CMP), one method for planarizing wafers, is performed by one machine and wafer cleaning and drying is performed by another, separate machine. After a processing layer (i.e., oxide, tungsten or the like) has been formed on the surface of the wafers, the dry wafers are planarized in a CMP polishing machine. The CMP machine planarizes the wafers by removing excess material, and then typically the wafers are rinsed and placed into a wet cassette. After polishing, residual particles still reside on the wafer's surface. If these particles dry on the wafer prior to cleaning, the microelectronic structures on the wafer may be corrupted. Therefore, it is extremely important to keep the wafers wet prior to final cleaning and drying of the wafers. From the CMP machine the wet cassette is hand carried to a separate post-CMP wafer cleaning and drying machine that is typically located somewhere near the CMP machine.
This conventional practice of utilizing separate machines for wafer polishing and for wafer cleaning and drying has serious drawbacks. First, wafer manufacturers must have personnel, equipment and facilities on hand to transport wafers in a wet environment from a CMP machine to a cleaning and drying machine. Second, having separate machines for polishing wafers and for cleaning wafers consumes a significant amount of clean room space which, as one skilled in the art will appreciate, is very expensive. Third, having two separate operating systems requires operators to become familiar with two different machines and two different sets of controls.
In addition, recent wafer cleaning techniques have incorporated the use of a certain chemical cleaning agents that are difficult and/or dangerous to handle, such as highly diluted hydrofluoric acid (HF) solution, for improved cleaning of semiconductor wafers, particularly for cleaning metallic ion residue from CMP planarization of the wafer surface. HF poses substantial health and safety risks, and thus great care must be taken when designing equipment that utilizes HF to ensure against undesired escape of HF contaminated fluid or fumes. Past HF cleaning operations have been designed around the conventional dip-tank style of wafer cleaning, wherein wafers are held vertically and are immersed in a tank into which fluids, including HF, may be introduced. In such dip tank style cleaners the motion of the wafer through the fluid, the reaction of the fluid with the wafer surface, and circulation of the fluid in the tank are relied upon to clean the wafer surface.
Conventional brush box style cleaners have also been modified to accommodate the use of HF solutions in wafer cleaning. Known HF brush box cleaners introduce HF solution onto the wafer or the brushes of the brush box so that the wafer is then mechanically scrubbed in the HF solution. Because of the extremely hazardous and corrosive nature of the HF, very dilute solutions are preferable for cleaning. As a result of using dilute solutions, the cleaning time is increased. To provide for adequate cleaning and particle removal, past HF cleaners have had to either add additional brush boxes to increase HF scrubbing time, or have had to increase the wafer residence time in the brush box. One way to increase the residence time is to move the wafer through a single brush box at a reduced rate. A problem with slowing the rate at which the wafer moves through the brush box is that it becomes difficult to control the wafer feed rate when the rate becomes too low. The residence time can also be increased by rotating the wafers within the brush box. Unfortunately this adds complexity to the equipment and results in nonuniformity in the cleaned wafer surface. Adding additional brush boxes or lengthening existing boxes is also often unsatisfactory because either solution requires additional scrubbing length which, in turn, increases the overall tool footprint. The added scrubbing length also increases the amount of chemicals used in the process. Thus a need exists for an improved brush box for cleaning semiconductor wafers or other work pieces with chemical cleaning agents such as HF that safely and efficiently scrubs the work piece in the presence of the chemical cleaning agents without overly slowing the work piece feed rate, or increasing tool footprint and with minimum chemical consumption. Ideally such a brush box and cleaning method could be incorporated into an integrated apparatus and method for CMP polishing, cleaning, rinsing, and drying of work pieces.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the invention, cleaning apparatus preferably comprises a water track, cleaning stations, and a plurality of work piece staging areas. In a further embodiment of the invention, the cleaning apparatus additionally includes a rinse station and a spin dryer station. In accordance with a preferred embodiment of the invention, the cleaning apparatus comprises an input water track station, a first scrub module, a mid-station water track, and a second scrub module. Each scrub module preferably includes a brush box and a rinse station and is chemically isolated from the other scrub module. Potentially hazardous chemical cleaning fluids are contained within each module using primary and secondary containment, and chemical fumes are exhausted from each module independently.
In accordance with a further embodiment of the invention, the cleaning apparatus is combined with a planarization apparatus to form a single, integrated machine for the planarization and cleaning of work pieces. More specifically, in accordance with a preferred embodiment, a work piece is planarized in a CMP station and then is directly transferred to a cleaning apparatus of the machine. When a work piece is first loaded into the cleaning apparatus from a CMP station of the machine, the work piece is held at a first input water track staging area until a determination is made that the next processing area, the first scrub module, is clear and is ready to receive the work piece. Only then is the work piece released to that next processing
Gopalan Periya
MacErnie Jon
Trojan Daniel
Eley Timothy V.
Snell & Wilmer LLP
SpeedFam-IPEC Corporation
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