Aerosol substrate cleaner

Details Aerosol substrate cleaner Aerosol substrate cleaner

1997-12-30

2001-12-25

Stinson, Frankie L. (Department: 1746)

Cleaning and liquid contact with solids

Apparatus

With plural means for supplying or applying different fluids...

C134S102200, C134S105000, C134S902000

Reexamination Certificate

active

06332470

ABSTRACT:

BACKGROUND
1. Technical Field
This invention relates to semiconductor device manufacturing, and more particularly to the post chemical mechanical polishing (CMP) cleaning of semiconductor substrates.
2. Background Information
During the manufacture of semiconductor devices, after particular manufacturing steps, it is desired or required to remove contaminant particles. If not removed, such particles may cause defects in the device being manufactured or otherwise interfere with the manufacturing process.
For example, integrated circuits are typically formed on silicon wafers by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. After a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. The substrate may be periodically planarized via a process such a chemical mechanical polishing. This method typically includes the mounting of the substrate on a carrier or polishing head and the placing of the exposed surface of the substrate against a rotating polishing pad. A polishing slurry, which may include chemically-reactive agents and/or abrasive particles, may be introduced to facilitate the polishing. The polishing leaves the surfaces of the substrate contaminated with polishing byproducts typically including silica, alumina, or other abusive particles from the slurry as well as a variety of other particles. Other residues from the polishing include the slurry itself, and often rubber or lubricant residue left by the carrier on the unpolished surface of the substrate.
A variety of methods and apparatus have been used or proposed for substrate cleaning after CMP. Broadly characterized, these include immersive and spray techniques. One immersive technique involves placing the substrates in an alkaline solution of ammonium hydroxide, water and hydrogen peroxide, and subjecting the solution to ultrasonic agitation to remove contaminants. The substrates may then be rinsed and dried.
Prominent among spray techniques are a variety of cryogenic techniques. Such techniques require the use of a high pressure gas and frequently may include the introduction of a cleaning agent. The cleaning agent is frozen by the expansion of the gas through a nozzle and is thus impinged upon the surface of the substrate as a spray of frozen particles. Cryogenic methods typically make intensive use of the gas which may prove expensive.
Somewhat intermediate of the immersion and spray methods are methods which involve directing a stream of liquid onto a substrate surface being cleaned. A liquid cleaning agent is sprayed from a high pressure nozzle, with an associated high kinetic energy, for dislodging small particles from the surface. Such methods may make intensive use of the cleaning agent, with a relatively large droplet or jet size as compared with the size of the particles being removed. Thus, in addition to the high cost of the high volume of cleaning agent, expensive high pressure pumps may be required and the cleaning agent may need to be filtered to avoid damage to the substrate. Accordingly, it is desirable to provide a substrate cleaning system and method which is efficient in its use of consumable products such as cleaning agent and does not present high equipment costs.
SUMMARY
In one aspect, the invention is directed to a method for cleaning a substrate. A substrate is provided having first and second generally flat faces. A source of pressurized carrier gas is provided. A source of cleaning agent in liquid form is provided. A flow of the carrier gas is directed along a flow path from the source upstream to the substrate downstream. The cleaning agent is introduced to the flow of carrier gas at least at a first location along the flow path so as to form a vapor of the cleaning agent. The vapor is condensed to form droplets of cleaning agent in the flow at a second location along the flow path, downstream of the first location. The flow of carrier gas containing the droplets is caused to impinge on at least the first face of the wafer so as to clean the first face of debris. Implementations of the inventive method may include one or more of the following. The introduction of the cleaning agent may include bubbling the carrier gas through a body of cleaning agent in liquid form. The body of cleaning agent may be heated to a temperature above an ambient temperature. The vapor may be condensed by externally cooling the flow of carrier gas. The flow of carrier gas containing the droplets may be caused to impinge on both the first and second faces of the substrate and on a substrate perimeter.
In another aspect, the invention is directed to an apparatus for cleaning a substrate. The apparatus includes a source of pressurized carrier gas and a body of cleaning agent in liquid form. A first conduit directs the carrier gas from the source to the body of cleaning agent. A second conduit carries the flow of the carrier gas away from the body of cleaning agent. The flow carried by the second conduit includes cleaning agent in vapor form acquired from the body of cleaning agent. A nozzle is coupled to the second conduit for causing flow of carrier gas containing droplets of the cleaning agent to impinge at least a first face of the substrate.
Implementations of the inventive apparatus may include one or more of the following. The apparatus may include a heater for heating the body of cleaning agent to a temperature above an ambient temperature. The apparatus may include a cooling unit cooling the flow of carrier gas containing cleaning agent vapor. The first conduit may extend into the body of cleaning agent. The first conduit may terminate in a sparger, the sparger emitting bubbles of the carrier gas into the cleaning agent. The body of cleaning agent may be contained within a vessel and the second conduit may extend from a headspace within the vessel, the headspace containing carrier gas and cleaning agent in vapor form. The carrier gas may be compressed air or compressed nitrogen. The carrier gas may be introduced to the body of cleaning agent at a pressure of approximately 80 psi. The cleaning agent may comprise a solution of approximately 5% NH
4
OH in deionized water. Impingement of the droplets on the first face of the substrate may act so as to remove residue from the chemical mechanical polishing operation from the first face of the substrate.
According to a further aspect, the invention provides an apparatus for cleaning byproducts of chemical mechanical polishing from a face of a substrate. The apparatus includes an inlet, a mixing unit and a nozzle. The inlet receives the flow of carrier gas. The mixing unit introduces a cleaning liquid into the flow of carrier gas at a location wherein the pressure of the carrier gas is less than 100 psi above an ambient pressure. The nozzle directs the flow of carrier gas to impinge the face of the substrate with droplets of the cleaning liquid.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.


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