Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2002-05-15
2003-12-30
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S025400, C134S026000, C134S028000, C134S029000, C134S034000, C134S036000, C134S041000, C134S042000
Reexamination Certificate
active
06669785
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns methods for cleaning microelectronic substrates, and particularly concerns methods for removal of photoresist layers, anti-reflective layers, etch residues, ash residues, and metallic residues from microelectronic substrates during the manufacturing of microelectronics, MEM's, and optoelectronic devices.
BACKGROUND OF THE INVENTION
Approximately one in four processing steps in manufacturing integrated circuits is a cleaning step. Manufacturing steps associated with the formation of lines and interconnects, often referred to as ‘back end of the line’, BEOL, have evolved significantly as feature sizes have continued to decrease. The advent of new low k materials and copper interconnect technologies enable the evolution of smaller feature sizes but require new and better cleaning processes. In some cases traditional cleaning processes are either ineffective or damaging toward the new materials. Hydrogen fluoride, typically aqueous, has been used at varying concentrations for traditional aqueous-based and solvent-based cleaning and stripping processes. Carbon dioxide has been described for use in cleaning integrated circuits as have mixtures of carbon dioxide and aqueous hydrogen fluoride or buffered aqueous hydrogen fluoride.
Literature of background interest includes U.S. Pat. Nos. 5,908,510, 5,976,264, 5,868,862, 6,149,828, and PCT Patent Application WO 02/15251.
A problem with aqueous cleaning techniques is that the surface tension of water makes it difficult to deliver chemistry to small feature sizes. Indeed, if water can get into to very small features, it is difficult to subsequently remove. Some new materials incorporate smaller features where aqueous cleaning systems are incompatible. For such materials, CO
2
cleaning is advantageous: the lack of surface tension facilitates penetration into and rinsing of small features, the swellability of some materials in CO
2
facilitates delivery of chemistry at interfaces, the density “tunability” of CO
2
gives a wide window of process variables, and CO
2
is generally considered to be environmentally benign. Unfortunately, there is currently no good way to deliver HF in CO
2
.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a method of cleaning a microelectronic substrate, comprising: providing a cleaning fluid, the cleaning fluid comprising an adduct of hydrogen fluoride with a Lewis base in a carbon dioxide solvent; and then cleaning the substrate by contacting the substrate to the cleaning fluid for a time sufficient to clean the substrate.
In some embodiments, the adduct is formed in situ, such as by adding anhydrous hydrogen fluoride to a carbon dioxide fluid containing the Lewis base (particularly an amine), so that the adduct of the hydrogen fluoride and the Lewis base is formed in situ in the carbon dioxide.
In some embodiments, the Lewis base has a pKa of at least 5. In some embodiments, the Lewis base is an amine, such as is pyridine, poly(vinylpyridine), or triethyl amine.
In some embodiments, the cleaning fluid is nonaqueous. The carbon dioxide may be liquid or supercritical carbon dioxide. The cleaning step may be preceded by, followed by, or both preceded and followed by the step of cleaning or rinsing the substrate with a rinse fluid, the rinse fluid comprising, consisting essentially of or consisting of liquid or supercritical carbon dioxide. In some embodiments, the rinse fluid may further comprise one or more cosolvents.
In some embodiments, the substrate has a photoresist layer formed thereon, and the cleaning step removes photoresist from the substrate.
In some embodiments, the substrate has etch residue deposited thereon, and the cleaning step removes etch residue from the substrate.
some embodiments, the substrate has ash residue deposited thereon, and the cleaning step removes ash residue from the substrate.
In some embodiments, the substrate has metal residue deposited thereon, and the cleaning step removes metal residue from the substrate.
In some embodiments, the substrate comprises a dielectric layer such as a low k dielectric material containing an oxide, photoresist or etch residue formed thereon, and the cleaning step partially removes the oxide, and completely removes the photoresist or etch residue from the low k dielectric material.
In some embodiments, the substrate comprises or includes an inorganic oxide containing surface carrying an adhered processing residue, and the adduct chemically etches the inorganic oxide containing surface to facilitate the removal of the adhered processing residue.
In some embodiments, the substrate is a microelectromechanical device (MEMS), which may have a plurality (e.g., two or more) mechanically interacting elements, and the cleaning step is carried out to clean the device, reduce stiction between mechanically interacting elements of the device, free a frozen or stuck element of the device, etc.
In a particularly preferred embodiment of the foregoing, the adduct is [pyridinium poly(hydrogen fluoride)], also known as hydrogen fluoride pyridine adduct or triethylamine trihydrofluoride.
A second aspect of the present invention is a fluid composition useful for cleaning a microelectronic substrate, comprising: from 0.0001, 0.0005 or to 5, 10 or 20 percent by weight of an adduct of hydrogen fluoride and a Lewis base; and from 40 or 50 to 99.999 percent by weight of liquid or supercritical carbon dioxide. The composition is aqueous in some embodiments and nonaqueous in other embodiments. The Lewis base may be as described above. The composition may further comprise from 0.001 or 0.1 percent to 30 or 40 percent by weight of a cosolvent (including combinations of cosolvents), and/or from 0.001 to 1, 3 or 5 percent by weight of a surfactant. Typically the fluid has a density of from 0.15 g/cc to 1.1 g/cc and a temperature of from 0 to 80 degrees C.
A specific embodiment of the foregoing methods may be carried out by:
(a) providing-a first (optionally but preferably nonaqueous) cleaning fluid, the first cleaning fluid comprising a single phase solution of an amine and a semi-polar to polar cosolvent in carbon dioxide;
(b) providing a second cleaning fluid, the second cleaning fluid comprising an adduct of hydrogen fluoride with a Lewis base in carbon dioxide;
(c) cleaning the substrate by contacting the substrate to the second cleaning fluid for a time sufficient to clean the substrate; and
(d) cleaning the substrate before, after, or both before and after the cleaning step (c) by contacting the substrate to the first cleaning fluid for a time sufficient to facilitate the cleaning of the substrate.
The amine may, for example, be morpholine, and the polar cosolvent may, for example, be a C1-C4 alcohol. The second cleaning fluid including the Lewis base may be as described above, and the substrates to be cleaned may be as described above.
Without wishing to be bound to any particular theory of the instant invention, it will be noted that in some embodiments the HF may clean by etching the material to be cleaned. Relative to the conventional practice of etching dielectric materials and the scope of what is the present invention, the word “etching” may be confusing. Dielectric layers are typically patterned during manufacturing by anisotropic etching, usually with reactive ions in a plasma or gas phase but liquid compositions have been disclosed. Typically, a patterned resist serves as a mask for areas of the dielectric that are not etched away. Conventionally, the resists and etch residues are then removed in either an ash and wet clean process, or by liquid stripping and cleaning processes. It is the conventional strip and clean step that is being replaced with the instant invention—not what is conventionally referred to as etching. Further, the HF compositions described herein are also useful for cleaning where oxides are not the primary dielectric composition (organic dielectrics for example, or with steps involving metal layers.) For these reasons, the minimal etching of oxide laye
DeYoung James P.
Gross Stephen M.
McClain James B.
Wagner Mark I.
Carrillo Sharidan
Micell Technologies, Inc.
Myers Bigel & Sibley & Sajovec
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