Precision surface treatments using dense fluids and a plasma

Abstract

The present invention is a method, process and apparatus for selective cleaning, drying, and modifying substrate surfaces and depositing thin films thereon using a dense phase gas solvent and admixtures within a first created supercritical fluid antisolvent. Dense fluids are used in combination with sub-atmospheric, atmospheric and super-atmospheric plasma adjuncts (cold and thermal plasmas) to enhance substrate surface cleaning, modification, precision drying and deposition processes herein. Moreover, conventional wet cleaning agents such as hydrofluoric acid and ammonium fluoride may be used with the present invention to perform substrate pre-treatments prior to precision drying and cleaning treatments described herein. Finally, dense fluid such as solid phase carbon dioxide and argon may be used as a follow-on treatment or in combination with plasmas to further treat a substrate surface.

Description

[0001] This invention claims the benefit, under Title 35, United States Code 119 (e), of Provisional Application No. 60 / 365,788, filed Mar. 21, 2002 entitled "Precision surface treatments using dense fluids and a plasma" which is hereby incorporated by this reference.BACKGROUND OF INVENTION[0002] Smaller electronic, optical and micromechanical devices, with nano-scale device manufacturing already on the horizon, are driving the need for improved cleaning and drying technology. Smaller circuits and surface features are becoming increasingly affected by smaller surface particles and other residues (contaminations) during manufacturing operations. Moreover, many conventional wet cleaning techniques are not compatible with the shrinking device geometries and new manufacturing materials. Still moreover, the transition to larger wafer substrates such as the 300 mm platform is driving the need for increased performance and productivity in cleaning and drying processes and tools. Precision ...

AI Technical Summary

Benefits of technology

0122] In addition, and simultaneously with the application of the supercritical fluid solvent, a lower temperature zone may be established below the substrate surface to collect reacted dense fluid as a `condensed phase`, which separates readily within the process chamber due to both density and cohesive energy increases. Thus, another advantage of the present invention is that a variety of dense fluid solvent pressures, temperatures and conditions can be applied to and reacted with the surface of a substrate under isobaric conditions and using pulsation, gravity flow, or high pressure spray techniques. Moreover, another advantage of the present invention is that the process chamber does contain a significant quantity of liquefied dense fluid phase carbon dioxide or other spent dense fluid solvent at any given time. Contaminants, water and particles contained within a hemisphere below a substrate and in a very small quantity of dense fluid relative to the volume of the process chamber are much less likely to become entrained within the anti-solvent phase due to significant differences in cohesion energy, density, and viscosity. Therefore the use of a condensed-phase zone as taught herein serves as a liquid trap for reaction by-products and prevents re-deposition of contaminants onto substrate surfaces above.

0123] In another aspect of the present invention, a substrate is plasma cleaned in a supercritical argon atmosphere at a temperature which is below the critical temperature and greater than the critical pressure of ...

Problems solved by technology

Smaller circuits and surface features are becoming increasingly affected by smaller surface particles and other residues (contaminations) during manufacturing operations.

Moreover, many conventional wet cleaning techniques are not compatible with the shrinking device geometries and new manufacturing materials.

The presence of organic contaminants or particles on a substrate surface with thicknesses on the order of 0.1 microns or greater generate considerable cleaning difficulties.

The trend towards miniaturization of silicon, germanium and gallium arsenide microprocessors in the electronics industry and the emergence of new microelectromechanical systems (MEMS) manufacturing, which uses much the same microprocessor manufacturing technology, is creating new material and process challenges.

For example, the smaller dimensions create new cleaning challenges due to increasing capillary force pressures which hold process fluids within cavities, more prevalent electrostatic forces which hold micromechanical structures together, porous or complex surface topography which preclude the use of aqueous chemistries, and high aspect ratio cavities and vias which hide etch residues and particles, among others.

Moreover, new materials such as low-k films and copper lines used to fabricate smaller device geometries (line widths) are not compatible with many conventional wet processing techniques described above.

However, the compliant nature of the silicon makes it susceptible to fabrication problems.

A significant problem in the fabrication of the micromachined components is sticking of released structures to the substrate after they are dried using conventional air drying techniques.

Electrostatic forces due to electrostatic charging may cause sticking.

This is a non-equilibrium condition which usually dissipates over time or with contact between conducting surfaces.

Second, a smooth surface finish may cause stiction.

The impurities in narrow gaps formed by the suspended microstructures essentially bridge the gaps, causing the structures to stick.

Perhaps the most troublesome cause of surface stiction is liquid bridging.

Interfacial forces generated when the trapped capillary fluid dries can cause the microstructures to collapse and stick.

Moreover, conventional thermal or solvent drying of silicon IC structures such as microvias cause the cavity walls to crack as the sidewalls are pulled together during extraction or evaporation of water or high surface tension drying solvents such as methyl alcohol.

If a liquid such as water is present in small capillaries during the drying process, the surface tension exerts tremendous pressure on the sidewalls.

This stress can be high enough to cause smoothe flat interfaces to stick, or in the case of IC fabrication, microvia sidewalls to collapse.

The most significant drawbacks with the aforementioned conventional dense fluid drying techniques are very long process cycle times and the use of excessive amounts of supercritical or liquid carbon dioxide in completely flooded pressure vessels to remove only trace amounts of surface contamination (i.e., water and drying solvents).

Another drawback is that these drying methods do not effectively remove small particles and in fact can easily re-contaminate substrates which are completely bathed in the reactor fluid.

Moreover, these methods are not effective or selective for removing other liquid contaminations present on the substrate surface or trapped within pores of substrates.

Still moreover, solid contaminants such as carbon residues are not effectively removed using these conventional techniques, even when modified with organic solvents.

Most often extreme pressures are required to achieve separation.

If left on critical surfaces, these may bridge circuits, obscure light or produce other deleterious side-effects which reduce yields, that is clean dry surfaces for subsequent processing steps.

Moreover, processes described above such as cleaning, etching, drying and application of coatings are most often performed as separate operations, which greatly increases the risk of device contamination during manufacture.

This system suffers from an inability to apply thermal energy to the substrate because it lowers the solubility of ozone in solution and is essentially time-dependent and concentration-dependent solid-ozone gas interfacial reaction.

However, similar to the DIO3 process, transport of ozone of any significant concentration into micron features on the wafer surface is very limited due to the solid-ozone gas interface.

Moreover excessive agitation caused by rapid movement of water over the spinning wafer accelerates the decomposition of the ozone gas as it diffuses through the thin film boundary.

Moreover, complete drying of the substrate following cleaning by both methods is also limited due to hydration of small capillaries, vias and interstices present on the wafer.

Finally, a lack of solvent selectivity can be limiting in many resist removal applications.

This method is similar to ozonated water treatment of wafer and suffers from the same solubility and selectivity problems.

A limitation with this method is its inability to actually remove particles from the wafer.

In fact, the rapid deployment of water from the tank often transfers more particles onto the wafer.

In addition, the wafers from the quick dump tank must still undergo a drying operation, further increasing the number of particles on the wafer.

However, the spin rinse/dryer often introduces more particles onto the wafer.

Another limitation with the spin rins...

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