Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-08-31
2003-12-09
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S003000, C438S239000, C438S396000, C438S685000, C438S686000, C438S681000, C427S099300, C427S252000
Reexamination Certificate
active
06660631
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preparation of iridium- and platinum-containing films on substrates, particularly on semiconductor device structures.
BACKGROUND OF THE INVENTION
Films of metals and metal oxides, particularly the heavier elements of Group VIII, are becoming important for a variety of electronic and electrochemical applications. For example, high quality RuO
2
thin films deposited on silicon wafers have recently gained interest for use in ferroelectric memories. Many of the Group VIII metal films are generally unreactive toward metal oxides, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of certain of these metals also possess these properties, although perhaps to a different extent.
Thus, films of Group VIII metals and metal oxides, particularly the second and third row metals (e.g., Ru, Os, Rh, Ir, Pd, and Pt) have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories. Furthermore, they may even be suitable as the plate (i.e., electrode) itself in capacitors. Iridium oxide is of particular interest as a barrier layer because it is very conductive (30-60 &mgr;&OHgr;-cm) and is inherently a good oxidation barrier.
Capacitors are the basic charge storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs). It is important for device integrity that oxygen and/or silicon not diffuse into or out of the dielectric material. This is particularly true for ferroelectric RAMs because the stoichiometry and purity of the ferroelectric material greatly affect charge storage and fatigue properties.
The electrodes in a DRAM cell capacitor must protect the dielectric layer from interaction with surrounding materials, including interlayer dielectrics (e.g., BPSG), and from the harsh thermal processing encountered in subsequent steps of DRAM process flow. In order to finction well as a bottom electrode, the electrode layer or layer stack acts as an effective barrier to the diffusion of oxygen and silicon. Oxidation of the underlying silicon will result in decreased series capacitance, thus degrading the cell capacitor. Platinum is one of the candidates for use as an electrode material for high dielectric capacitors.
Platinum, alone, however, is relatively permeable to oxygen. One solution is to combine (e.g., alloy) the platinum with rhodium to enhance the barrier properties of the layer. Physical vapor deposition (PVD) of a Pt—Rh alloy has been shown by H. D. Bhati et. al., “Novel high temperature multi-layer electrode barrier structure for high-density ferroelectric memories,”
Applied Physics Letters
, 71, pp. 719-21 (1997), to provide an improvement over pure Pt for electrode applications. Also, physical vapor deposition (PVD) of a Pt—Ir alloy has been shown in JP 09162372.
Many storage cell capacitors are formed using high aspect ratio openings. PVD deposition (e.g., sputtering) does not deliver a layer which is sufficiently conformal for formation of an electrode within such a small high aspect ratio opening.
Thus, there is a continuing need for methods and materials for the deposition of metal-containing films, such as iridium- and platinum-containing films, which can function as barrier layers, for example, in integrated circuits, particularly in random access memory devices.
SUMMARY OF THE INVENTION
The present invention is directed to methods for forming films, particularly in the manufacture of a semiconductor device, such as a ferroelectric device, and devices (e.g., capacitors, integrated circuit devices, and memory cells) containing such films. The methods involve forming films containing both iridium and platinum on substrates, such as semiconductor substrates or substrate assemblies during the manufacture of semiconductor structures. The film can be a pure platinum-iridium film, an oxide film, a sulfide film, a sulfide film, a selenide film, a nitride film, or the like. Typically and preferably, the iridium- and platinum-containing film (i.e., platinum-iridium film) is electrically conductive. The resultant film can be used as a barrier layer or electrode in an integrated circuit structure, particularly in a memory device such as a ferroelectric memory device. The platinum-iridium film (i.e., layer) overcome some of the problems associated with the use of platinum alone as an electrode material.
In the context of the present invention, the term “metal-containing film” includes, for example, relatively pure films of iridium and platinum (typically, in the form of alloys or solid solutions), as well as mixtures or alloys with other Group VIII transition metals such as rhodium, nickel, palladium, iron, ruthenium, and osmium, metals other than those in Group VIII, metalloids (e.g., Si), or mixtures thereof. The term also includes complexes of iridium and platinum with other elements (e.g., O, N, and S).
One preferred method of the present invention involves forming a film on a substrate, such as a semiconductor substrate or substrate assembly during the manufacture of a semiconductor structure. The method includes: providing a substrate (preferably, a semiconductor substrate or substrate assembly); providing a precursor composition that includes one or more complexes of the formula:
L
y
IrY
z
, (Formula I)
wherein: each L group is independently a neutral or anionic ligand; each Y group is independently a pi bonding ligand selected from the group of CO, NO, CN, CS, N
2
, PX
3
, PR
3
. P(OR)
3
, AsX
3
, AsR
3
, As(OR)
3
, SbX
3
, SbR
3
, Sb(OR)
3
, NH
x
R
3−x
, CNR, and RCN, wherein R is an organic group and X is a halogen; y=1 to 4; z=1 to 4; x=0 to 3; providing a precursor composition that includes one or more platinum complexes; and forming a platinum-iridium-containing film from the precursor compositions on a surface of the substrate (preferably, the semiconductor substrate or substrate assembly), wherein the platinum-iridium-containing film has the formula platinum(x):iridium(1−x), wherein x is in the range of about about 0.99 to about 0.01. Preferably, the precursor composition that includes one or more complexes of the formula L
y
IrY
2
is the same as the precursor composition that includes one or more platinum complexes.
In certain embodiments, the process is carried out in a nonhydrogen atmosphere (i.e., an atmosphere that does not include H
2
). In other embodiments, preferably Y and L do not include halogen atoms, and more preferably, L is not a cyclopentadienyl ligand when Y is a CO ligand. Using such methods, the complexes of Formula I are converted in some manner (e.g., decomposed thermally) and deposited on a surface to form a metal-containing film. Thus, the film is not simply a film of the complex of Formula I.
Preferably, the precursor complexes are neutral complexes and may be liquids or solids at room temperature. Typically, however, they are liquids. If they are solids, they are preferably sufficiently soluble in an organic solvent or have melting points below their decomposition temperatures such that they can be used in flash vaporization, bubbling, microdroplet formation techniques, etc. However, they may also be sufficiently volatile that they can be vaporized or sublimed from the solid state using known vapor deposition techniques including chemical vapor deposition and atomic layer deposition techniques. Thus, the precursor compositions of the present invention can be in solid or liquid
Jr. Carl Whitehead
Mueting Raasch & Gebhardt, P.A.
Pham T
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