Method of etching using hydrofluorocarbon compounds

Details Method of etching using hydrofluorocarbon compounds Method of etching using hydrofluorocarbon compounds

2000-05-11

2002-08-06

Turner, Archene (Department: 1775)

Etching a substrate: processes

Nongaseous phase etching of substrate

C216S036000, C216S053000, C216S108000, C216S109000

Reexamination Certificate

active

06428716

ABSTRACT:

FIELD OF INVENTION
The present invention relates generally to dry etching and cleaning. More specifically, this invention relates to the use of a family of hydrofluorocarbon compounds for the plasma etching of semiconductor materials.
BACKGROUND OF THE INVENTION
Semiconducting devices are manufactured by the repetitive application of four basic operations to a wafer, namely: layering, patterning/etching, doping, and heat treatments. Of particular interest herein is patterning/etching which involves the selective removal of material from the surface of the wafer. More specifically, material is removed by applying a photoresist to a wafer's surface in a particular geometric pattern selectively and then exposing the wafer to a chemical etchant. Those areas of the wafer that are covered by the photoresist are protected from the etchant, while those that are left exposed are removed to some degree by the etchant. Consequently, material is removed in a geometrical pattern as defined by the photoresist. The term “etching” refers to this selective removal of material.
There are basically two types of etching, wet and dry. Wet etching involves the use of liquid corrosive reagents that react with the unprotected material on the wafer's surface and form soluble products which are then carried away by a solvent. Dry etching refers to plasma and plasma-generated methods which employ energetic gas molecules, ions, and/or free radicals that remove material from a wafer's unprotected surface either chemically by reacting with the material, or physically by bombarding the surface. This plasma process can be used also to clean surfaces of reactors and other apparatus used in the manufacture of semiconductors. Thus, discussion directed to etching and etchants herein applies also to cleaning applications. Other terms commonly applied to these plasma processes include plasma etching, reactive-ion etching, high-density plasma etching, ion milling, reactive ion milling, chemical ion beam etching, and sputter etching. Recently, the industry has been moving away from wet etching and toward dry etching due to the more refined patterning control the latter offers.
As the semiconductor industry moves toward dry etching, environmental concerns grow over the use and disposal of the etching chemicals used and the by-products which are formed. In etching, a portion of the etching chemical tends not to react and exits in the effluent from the reaction, along with various reaction by-products. Venting of such etching chemicals is coming under increased scrutiny.
Traditional etching chemicals, such as, for example, carbon tetrafluoride, hexafluoroethane, perfluoropropane, nitrogen trifluoride, bis(trifluoromethyl) disulfide, and sulfur hexafluoride, and their perfluorinated by-products, such as carbon tetrafluoride and hexafluoroethane, have relatively high Global Warming Potentials. Global Warming Potential (herein “GWP”) refers to a compound's ability, relative to CO
2
, to contribute to global warming. GWP is a calculated value based on a compound's estimated atmospheric lifetime and its ability to absorb infrared radiation. GWPs are reported by the Intergovernmental Panel on Climate Change (IPCC) for different time horizons, with a 100-year horizon being the most common. As used herein, a GWP is based on a 100-year horizon unless otherwise stated. Increasingly, governments and international treaties are requiring that the venting of such high-GWP chemicals be reduced or eliminated. As a consequence of these restrictions, the commercial-availability of these chemicals for semiconductor fabrication is suffering.
Currently, attempts to alleviate the environmental concerns associated with plasma etching and cleaning fall into one of four categories: (1) optimizing etching and/or cleaning processes such that lower amounts of GWP chemicals are emitted into the atmosphere; (2) recycling etching and/or cleaning chemicals from an exhaust stream so that they can be disposed of properly or reused without atmospheric emissions; (3) abating etching and/or cleaning chemicals in exhaust streams by chemical reaction or burn boxes which incinerate and render the unreacted etching and/or cleaning chemical effluents inoffensive, particularly with regard to GWP; and (4) selecting or developing various replacement chemicals for etching and/or cleaning duty. Regarding the first approach, advancements in optimizing the etching and cleaning processes to reduce releases are being made continuously; however, the advancements are not capable of reducing emissions to acceptable levels. Regarding the recycling and abating approaches, although emissions can be reduced, the cost of implementation is relatively high, and, again, the reduction levels still tend to be inadequate. Therefore, replacing the traditional etching chemicals with environmentally-acceptable substitutes appears to be a solution that should be considered.
Accordingly, a need exists for etching compositions which have acceptable performance, but which do not contribute significantly to global warming when by-products or unreacted chemicals are vented to the atmosphere. The present invention fulfills this need among others.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention identifies a family of hydrofluorocarbon (HFC) compounds which are useful in plasma etching and which are environmentally acceptable. More specifically, the family of HFC compounds includes compounds having the following formula:
C
x
H
y
F
z
  (1)
wherein:
x=3, 4 or 5;
2x≧z≧y;
and
y+z=2x+2
These compounds are referred to herein as “etchant compounds.” Unlike conventional etching compounds where perfluorocarbons/perfluorochemicals (PFCs) or other highly-fluorinated compounds are preferred for their reactivity, in the present invention, HFC etchant compounds having two or more hydrogen atoms are preferred for their lower GWP and their increased selectivity. As used herein, “selectivity” refers to the ability of an etchant to etch one material at a different etch rate than another material.
One aspect of the invention is the provision of a method for etching using one or more of the above-identified HFC etchant compounds. In a preferred embodiment, the method comprises subjecting a material under plasma etching conditions to an etching composition comprising at least an etchant compound of Formula (1).
Another aspect of the invention is the provision of a composition comprising one or more of the above-identified HFC etchant compounds. In a preferred embodiment, the composition comprises an etchant compound of Formula (1), and another material, different from the etchant compound, to enhance or modify the etching characteristics of the etchant compound.
The various aspects of the present invention relate to the use of the HFC compounds of Formula (1) as etchant compounds. In a preferred embodiment, the HFC etchant compound is fluorinated such that the fluorine to hydrogen ratio is no less than 1.5 (z≧1.5y). More preferably, the HFC etchant compound is a fluorinated propane (x=3), and still more preferably, the etchant compound is selected from the isomers of hexafluoropropane and pentafluoropropane, wherein z is 6 and 5, respectively. In an even more preferred embodiment, the etchant compound is 1,1,1,3,3,3-hexafluoropropane (herein “HFC-236fa”) or 1,1,1,3,3-pentafluoropropane (herein “HFC-245fa”). The most preferred etchant compound is HFC-245fa.
Even though the HFC etchant compounds for use in the present invention have a fluorine to carbon ratio no greater than 2 to 1 (as set forth in Formula (1)) which is less than traditional etchants, it has been found that these etchant compounds, nevertheless, etch a wide variety of materials. In fact, as shown in the examples below, HFC-245fa, which has a fluorine to carbon ratio of 5:3, etches some materials more rapidly than its more-fluorinated counterpart HFC-236fa, which has a fluorine to carbon ratio of 2:1.
Examples of materials that can be etched by the

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