Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Reexamination Certificate
2000-04-06
2001-06-12
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C392S387000, C392S394000, C392S399000
Reexamination Certificate
active
06245151
ABSTRACT:
DESCRIPTION
1. Field Of The Invention
This invention relates generally to an apparatus and method for vaporization of a liquid precursor for transport to a deposition zone, e.g., a chemical vapor deposition (CVD) reactor. More particularly, the present invention relates to a liquid delivery system of such type, in which the pressure upstream of the vaporization means is controllably maintained at a level commensurate with highly efficient operation of the liquid delivery system.
2. Description Of The Related Art
In the formation of thin films, layers and coatings on substrates, a wide variety of source materials have been employed. These source materials include reagents and precursor materials of widely varying types, and in various physical states. To achieve highly uniform thickness layers of a conformal character on the substrate, vapor phase deposition has been used widely as a technique. In vapor phase deposition, the source material may be of initially solid form which is sublimed or melted and vaporized to provide a desirable vapor phase source reagent. Alternatively, the reagent may be of normally liquid state, which is vaporized, or the reagent may be in the vapor phase in the first instance.
In the manufacture of advanced thin film materials, a variety of reagents may be used. These reagents may be used in mixture with one another in a multicomponent fluid which is utilized to deposit a corresponding multicomponent or heterogeneous film material. Such advanced thin film materials are increasingly important in the manufacture of microelectronic devices. For such applications and their implementation in high volume commercial manufacturing processes, it is essential that the film morphology, composition, and stoichiometry be closely controllable. This in turn requires highly reliable and efficient means and methods for delivery of source reagents to the locus of film formation.
Examples of advanced thin film materials include refractory materials such as high temperature superconducting (HTSC) materials including YBa
2
Cu
3
O
x
, wherein x is from about 6 to 7.3, BiSrCaCuO, and TlBaCaCuO. Barium titanate, BaTiO
3
, and barium strontium titanate, Ba
x
Sr
1−x
TiO
3
, have been identified as ferroelectric and photonic materials with unique and potentially very useful properties in thin film applications of such materials. Ba
x
Sr
1−x
Nb
2
O
6
is a photonic material whose index of refraction changes as a function of electric field and also as a function of the intensity of light upon it. Lead zirconate titanate, PbZr
1−x
Ti
x
O
3
, is a ferroelectric material whose properties are very interesting. The Group II metal fluorides, BaF
2
, CaF
2
, and SrF
2
, are useful for scintillation detecting and coating of optical fibers. Refractory oxides such as Ta
2
O
5
are coming into expanded use in the microelectronics industry; Ta
2
O
5
is envisioned as a thin-film capacitor material whose use may enable higher density memory devices to be fabricated.
Thin films comprising the Group II metal fluorides, BaF
2
, CaF
2
, and SrF
2
, are potentially very useful as buffer layers for interfacing between silicon substrates and HTSC or GaAs overlayers or between GaAs substrates and HTSC or silicon overlayers, and combinations of two or all of such metal fluorides may be employed in forming graded compositions in interlayers providing close lattice matching at the interfaces with the substrate and overlayer constituents of the composite. For example, a silicon substrate could be coated with an epitaxial layer of BaF
2
/CaF
2
, SrF
2
/CaF
2
, or SrF
2
/CaF
2
/BaF
2
, whose composition is tailored for a close lattice match to the silicon. If the ratio of the respective Group II metal species in the metal fluoride interlayers can be controlled precisely in the growth of the interlayer, the lattice constant could be graded to approach the lattice constant of GaAs. Thus, a gallium arsenide epitaxial layer could be grown over the metal fluoride interlayer, allowing the production of integrated GaAs devices on widely available, high quality silicon substrates. Another potential use of such type of metal fluoride interlayers would be as buffers between silicon substrates and polycrystalline HTSC films for applications such as non-equilibrium infrared detectors. Such an interlayer would permit the HTSC to be used in monolithic integrated circuits on silicon substrates.
BaTiO
3
and Ba
x
Sr
1−x
Nb
2
O
6
in film or epitaxial layer form are useful in photonic applications such as optical switching, holographic memory storage, and sensors. In these applications, the BaTiO
3
or Ba
x
Sr
1−x
Nb
2
O
6
film is the active element. The related ferroelectric material PbZr
1−x
Ti
x
O
3
is potentially useful in infrared detectors and thin film capacitors well as filters and phase shifters.
Chemical vapor deposition (CVD) is a particularly attractive method for forming thin film materials of the aforementioned types, because it is readily scaled up to production runs and because the electronic industry has a wide experience and an established equipment base in the use of CVD technology which can be applied to new CVD processes. In general, the control of key variables such as stoichiometry and film thickness, and the coating of a wide variety of substrate geometries is possible with CVD. Forming the thin films by CVD permits the integration of these materials into existing device production technologies. CVD also permits the formation of layers of the refractory materials that are epitaxially related to substrates having close crystal structures.
CVD requires that the element source reagents, i.e., the precursor compounds and complexes containing the elements or components of interest must be sufficiently volatile to permit gas phase transport into the chemical vapor deposition reactor. The elemental component source reagent must decompose in the CVD reactor to deposit only the desired element at the desired growth temperatures. Premature gas phase reactions leading to particulate formation must not occur, nor should the source reagent decompose in the lines before reaching the reactor deposition chamber. When compounds are desired to be deposited, obtaining optimal properties requires close control of stoichiometry which can be achieved if the reagent can be delivered into the reactor in a controllable fashion. In this respect the reagents must not be so chemically stable that they are non-reactive in the deposition chamber.
Desirable CVD reagents therefore are fairly reactive and volatile. Unfortunately, for many of the refractive materials described above, volatile reagents do not exist. Many potentially highly useful refractory materials have in common that one or more of their components are elements, i.e., the Group II metals barium, calcium, or strontium, or the early transition metals zirconium or hafnium, for which no or few volatile compounds well-suited for CVD are known. In many cases, the source reagents are solids whose sublimation temperature may be very close to the decomposition temperature, in which case the reagent may begin to decompose in the lines before reaching the reactor, and it therefore is very difficult to control the stoichiometry of the deposited films from such decomposition-susceptible reagents.
In other cases, the CVD reagents are liquids, but their delivery into the CVD reactor in the vapor phase has proven impractical because of problems of premature decomposition or stoichiometry control.
When the film being deposited by CVD is a multicomponent substance rather than a pure element, such as barium titanate or the oxide superconductors, controlling the stoichiometry of the film is critical to obtaining the desired film properties. In the deposition of such materials, which may form films with a wide range of stoichiometries, the controlled delivery of known proportions of the source reagents into the CVD reactor chamber is essential.
In other cases, the CVD reagents are liquids, but their delivery into the CVD reactor in the vapor phas
Bhandari Gautam
Brestovansky Dennis F.
Advanced Technology & Materials Inc.
Bueker Richard
Hultquist Steven J.
Zitzmann Oliver A. M.
LandOfFree
Liquid delivery system comprising upstream pressure control... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid delivery system comprising upstream pressure control..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid delivery system comprising upstream pressure control... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2498950