The present invention relates to tunable resistance coatings. More particularly, the invention relates to compositions of matter and methods of manufacture of M:AlOx thin films having tunable resistance where Mo, or conducting compounds containing these metals.
This section is intended to provide a background or context to the invention that is, inter alia, recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section. Thin film materials of metal-metal oxides of nanocomposites can have many applications, including resistive layers for electronic applications, such as, for example, electron multipliers like microchannel plates, resistive memories, electro-chromic devices, biomedical devices and charge dissipating coatings on micro-electromechanical systems. A related application, U.S. Ser. No. 13/011,645, which is incorporated by reference herein, describes microchannel plate fabrication by atomic layer deposition (“ALD” hereinafter), which provide an example of how one can benefit from the tunable resistance coatings and methods of preparation described herein.
In one embodiment, thin layers of nanocomposite tungsten-aluminum oxide (W:Al2O3) with tunable resistivity can be prepared for various commercial purposes. In another embodiment, thin layers of nanocomposite molybdenum-aluminum oxide (Mo:Al2O3) with tunable resistivity can be prepared for various commercial purposes. In yet other embodiments the W in the W:Al2O3 can be replaced by WN or WCx where WCx represents a conducting material containing W and C. Similarly, the Mo in the Mo:Al2O3 can be replaced by MoN or MoCx where MoCx represents a conducting material containing Mo and C. These thin layers preferably were deposited using ALD by combining alternating exposures to disilane and tungsten hexafluoride for W deposited by ALD, or alternating exposures to disilane and molybdenum hexafluoride for Mo deposited by ALD, with alternating exposures of trimethyl aluminum and water for Al2O3 deposition by ALD. The film thicknesses were measured by using ex-situ ellipsometry, cross-sectional scanning electron microscopy, and transmission electron microscopy. The crystallinity and topography were examined using X-ray diffraction and atomic force microscopy, respectively. The composition of the composite layers was investigated by X-ray photoelectron spectroscopy, X-ray fluorescence, and Rutherford backscattering, and the electrical conductivity was evaluated using current-voltage measurements. The microstructure of the films was evaluated using transmission electron microscopy. The W:Al2O3 and Mo:Al2O3 nanocomposite layers were smooth as revealed by atomic force microscopy, uniform in thickness according to ellipsometry, and showed an amorphous nature via X-ray diffraction scans. Transmission electron microscopy revealed the microstructure to consist of metal nanoparticles embedded in an amorphous matrix. Elemental analysis confirmed the presence of W, Al, O, F, and C in the W:Al2O3, and Mo, Al, O, F, and C in the Mo:Al2O3 and in both cases these elements were distributed homogenously throughout the films as determined by X-ray photoelectron spectroscopy depth profiling. The growth rate varied between 1.1-5 Å/cycle depending on the precursor ratio, the metal precursor, as well as sequence ALD precursors. The nature of ALD precursor dose pulses sequencing demonstrated a significant influence on the electrical properties of the desired W:Al2O3 or Mo:Al2O3 composite materials. To understand the film growth and electrical properties of W:Al2O3 and Mo:Al2O3 layers, in-situ quartz crystal microbalance (QCM) measurements were performed during the W (Mo),Al2O3 and W (Mo):Al2O3 ALD. The electrical properties for various compositions of W (Mo):Al2O3 nanocomposite layer were studied and advantageous attributes identified for a variety of commercial applications.
a) shows quartz crystal microbalance (QCM) measurements performed during Al2O3 ALD various precursors exposure steps;
a) shows mass add-on on QCM during ALD W deposition in various precursor exposure steps;
a) shows QCM measurements recorded during the successive ALD of Al2O3, W, and then Al2O3 thin films along with indications of when the ALD precursors were introduced;
a) shows the average mass/ALD cycle for the traces in
a) shows growth rate of W:Al2O3 deposited on Si(100) vs. W % ALD cycles and
a) shows an X-ray diffraction scan of the W:Al2O3 system vs. W % ALD cycles for W:Al2O3 layers which were deposited on fused quartz substrates and
a) shows cross-sectional high-resolution (HR) transmission electron microscopy (TEM) analysis of (30% W:70% Al2O3) ALD cycle composite layer capped with 6 nm Al2O3: Cross section HRTEM micrograph;
a) shows sputter-XPS scans of (30% W:70% Al2O3) ALD cycles composite layer for Al 2p;
a) shows an XPS scans of an as grown W:Al2O3 sample with of (30% W:70% Al2O3) ALD cycles and
a) shows microstructure and conformality of the W:Al2O3 system: scanning electron microscopy (SEM) image of W:Al2O3 on micro-capillary glass plate substrates;
a) shows mass uptakes on QCM during W:Al2O3 composite layer grown with (25% ALD W:75% ALD Al2O3)=3x(H2O-TMA)−1x(Si2H6—WF6) precursor exposures sequence; mass uptake versus time with precursor dose times indicated;
a) shows QCM mass for one super cycle (25% W:75% Al2O3) ALD cycle condition for various ALD precursor sequence: THSW;
a) shows a current-voltage (IV) curve of a film;
a) shows ln(R) vs. Temperature where R is resistance and
a) shows AFM images of an ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3); and
a) shows a top down TEM image of an ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3) with a thickness of 760 Angstrom on a Si substrate; and
a) shows a cross sectional TEM (XTEM) image of an ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3) with a thickness of 760 Angstrom thickness on a Si substrate;
a) shows a photograph of an ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3) with a thickness of 760 Angstrom deposited on a 12″×12″ glass substrate;
a) shows a thickness contour map for 400 cycles with 5% Mo;
a) shows a longitudinal (through the film) current/voltage plot of ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3) with measurements performed at 26 locations on a 300 nm wafer (see
a) shows transverse resistivity from a Mo:Al2O3 tunable resistance composite layer deposited with (10% ALD Mo:90% ALD Al2O3) beginning with Mo and Al2O3;
a) shows an SEM image of an ALD Mo:Al2O3 tunable resistance composite layer deposited with (8% ALD Mo:92% ALD Al2O3) on an inside surface of a form borosilicate glass array and
a) shows Mo atomic % versus Mo % of cycles for a Mo:Al2O3 tunable resistance film coating from X-ray fluorescence; and
a shows longitudinal resistivity and
a shows QCM data showing linear growth of material using alternating TMA and WF6 exposures at a mass deposition rate of 295 ng/cm2/cycle; Red lines (“r”) indicate TMA exposures, green lines (“g”) indicate WF6 exposures, blue lines (“b”) indicate mass, and purple line (“p”) shows reactor pressure, and
The tuning of thin film electrical resistance can be done by mixing the conducting and insulating components in a precise controlled manner in composite materials. Schematic of such mixing and the resistivity (ρ) range of thin film composite materials is shown in
The physical, electrical and chemical properties of nanocomposite thin films can be tuned by adjusting the relative proportions of the constituent materials. Amongst various thin film processes, atomic layer deposition (ALD) is a preferred technique for growing complex layers in a precisely controlled manner with many unique advantages. ALD is based on a binary sequence of self-limiting chemical reactions between precursor vapors and a solid surface. Because the two reactions in the binary sequence are performed separately, the gas phase precursors are never mixed; and this eliminates the possibility of gas phase reactions that can form particulate contaminants that might produce granular films. This strategy yields monolayer-level thickness and composition control. The self-limiting aspect of ALD leads to continuous pinhole-free films, excellent step coverage, and conformal deposition on very high aspect ratio structures. ALD processing is also extendible to very large substrates and batch processing of multiple substrates.
In one embodiment, thin films of W:Al2O3 nanocomposites were synthesized by combining tungsten (W) and aluminum oxide (Al2O3) using ALD processes. The ALD processes for both W and Al2O3 are known (also for Mo:Al2O3 to be discussed hereinafter. In addition, the ALD of W:Al2O3 nanolaminates comprised of alternating, distinct layers of these two materials has been explored, and these nanolaminates have been utilized as thermal barrier coatings and X-ray reflection coatings. In contrast to this previous work on nanolaminates, the instant invention in general focuses on synthesizing, characterizing, and testing nanocomposites where the W or Mo and the Al2O3 components do not exist in distinct layers but are more intimately mixed such that the domains of these materials do not exhibit bulk-like properties or structures (examples will be provided hereinafter). Furthermore, the W or Mo domains are comprised of discrete nanoparticles which are not in direct contact with one another. This offers the opportunity to develop very different materials with unique properties that are unlike any other constituents known in the art.
One exemplary use of these methods is to develop tunable resistive coatings using ALD for application in microchannel plate (MCP) electron multipliers. In this application, the ALD resistive layer serves to generate a uniform electrostatic potential along the MCP pores. The W:Al2O3 system was selected as a preferred article for a number of reasons. ALD W has a very low electrical resistivity of ρ=˜10−5Ω-cm while ALD Al2O3 is an excellent insulator with a resistivity of ρ=1014Ω-cm, and this contrast offers the potential for an extremely wide range of tunable resistance. In addition, ALD Al2O3 has a high breakdown electric field and this attribute is beneficial in high voltage devices such as MCPs. Both the W and Al2O3 ALD processes can be performed under similar conditions, and this simplifies the process of synthesizing composite layers. In addition to the wide variance in electrical properties, W and Al2O3 have very different physical and chemical properties. As a result, by adjusting the proportion of W in the Al2O3 matrix, we expect that the optical, mechanical, and physical properties of the W:Al2O3 composite layers can be broadly tuned.
Al2O3 ALD can be accomplished using alternating exposures to trimethyl aluminum (TMA) and H2O according to the following simplified binary reaction sequence:
Al—OH*+Al(CH3)3→Al—O—Al(CH3)2*+CH4 (a)
Al—CH3*+H2O→Al—OH*+CH4 (b)
where the asterisks denote the surface species. Both (a) and (b) reactions are self-limiting and terminate after the consumption of all the reactive surface species. During reaction (a), TMA reacts with surface hydroxyl species, AlOH*, and deposits surface AlCH3* species liberating methane. In reaction (b), H2O reacts with the surface methyl species to form new Al—O bonds and rehydroxylate the surface while again liberating methane. Repeating the (a)-(b) reactions results in the linear ALD of Al2O3 films at a rate of ˜1.3 Å/cycle.
The ALD of single-element films requires a different surface chemistry than the surface chemistry employed for binary compounds like Al2O3. For W ALD, one of the reactants is a sacrificial species that serves as a temporary place holder in the AB-AB-AB . . . binary reaction sequence. This sacrificial species is removed during the subsequent surface reaction. The W ALD film growth using Si2H6 and WF6 is accomplished by two self-limiting surface reactions described by the following simplified equations:
WSiHyFz*+WF6→W—WFx*+SiHF3 (c)
WFx*+Si2H6→W—WSiHyFz*+SiHF3+H2 (d)
where the asterisks denote the surface species.
During reaction (c), WF6 reacts with the sacrificial silicon surface species, WSiHyFz*, and deposits WFx species. In reaction(d), Si2H6 strips fluorine from the tungsten surface species, WFx*, and reforms the sacrificial silicon surface species. The reaction stoichiometry is kept undefined because the exact identity of the surface species is not known. Furthermore, the reactions are unbalanced for simplicity. Repeating these surface reactions (c) and (d), the W ALD grows linearly.
However, the initial nucleation of ALD Al2O3 on the ALD W surface, or the ALD W on the ALD Al2O3 surface may not have the same growth behavior as for the pure materials on themselves. The self-limiting surface reaction discussed above change as compared to the pure Al2O3 and W due to mixing of the four precursors TMA, H2O, WF6, and Si2H6 during the growth of W:Al2O3 composite layers. This is due in part to the fact that the ALD Al2O3 surface is hydroxyl-terminated, and does not have the appropriate fluorine species required for the W ALD. Similarly, the ALD W surface is fluorine terminated and does not bear the hydroxyl species needed for the Al2O3 ALD. These four precursors can be introduced on the substrate by in different orders resulting in the formation of various functional groups such as —OH, —WF3, —SiHx, —Al(CH3), —AlFx on the already partially or fully deposited layer and can result in a complex ALD chemistry. Furthermore, it is possible that atoms present in the precursor ligands, such as C, H, or F, as well as Si from the sacrificial disilane, may be incorporated into the ALD composite film as a result of the unique surface chemistry that occurs upon transitioning between the W and Al2O3 ALD. In addition, the nucleation delay for Al2O3 and W ALD film growth may affect the resulting film growth and the roughness. The roughness (surface area) of each individual layer can affect the nucleation of the W or Al2O3 processes. This nucleation process will affect the composition and growth-per-cycle of the tunable resistance coatings, and therefore will influence the electrical properties. Various aspects of the ALD synthesis of W:Al2O3 composite layers were examined with variation of composition of the W:Al2O3 layers. The physical and electrical properties of W:Al2O3 composite layers are discussed hereinafter.
In a preferred method the W:Al2O3 composite layer depositions were carried out in a hot wall viscous flow reactor ALD reactor. The W:Al2O3 composite films were deposited on n-type Si(100), fused quartz, glass substrates and high aspect ratio (60:1) borosilicate glass micro-capillary plates. Prior to ALD process all the substrates degreasing was performed using a 10 min dip ultrasonic acetone cleaning. For Al2O3 growth, Al(CH3)3 [TMA] was obtained from Sigma-Aldrich with a 97% purity and deionized (DI) H2O vapor were used as the precursors. For W ALD, tungsten hexafluoride (WF6, Sigma Aldrich, 99.9%) and disilane (Si2H6, Sigma-Aldrich, electronic grade 99.995%) were used as precursors. All precursors were maintained at room temperature at ˜20° C. The background N2 flow was set to 300 sccm which gives a base pressure of 1.0 Torr in the ALD reaction chamber and was measured by a heated MKS Baratron 6298 model. The precursors TMA and H2O were alternately pulsed in the continuously flowing N2 carrier flow using high speed computer controlled pneumatic valves in the desired ALD sequence. During the TMA and H2O dosing, pressure transient increases of ˜0.2 Torr for TMA and ˜0.3 Torr for H2O were observed when the reactants were introduced into N2 carrier flow. Similarly, during the Si2H6 and WF6 dosing into the N2 carrier gas flow, pressure transient increases of 0.25 Torr for Si2H6 and 50 mTorr for WF6 were seen. The results below utilized the optimized process conditions and precursor dose timing sequences for the pure W and Al2O3 ALD processes. The main experimental conditions for ALD are summarized in Table 1.
An in-situ quartz crystal microbalance (QCM) study was performed for the various ALD processes Al2O3, W and W:Al2O3 with a different mixture of ALD cycle ratios. QCM mass gains were recorded for each case. Front sided polished QCM sensors were obtained from Colorado Crystal Corporation. The QCM housing is located inside the uniformly heated reaction zone of the ALD flow tube reaction chamber. The Maxtek BSH-150 sensor housing was modified to provide a slow nitrogen purge of 10-20 sccm over the back of the quartz crystal sensor. This nitrogen purge prevents reactant gases from entering the QCM housing and depositing material on the back surface of the QCM sensor. By preventing this deposition, the QCM yields absolute mass measurements. In addition, the nitrogen purge allows QCM measurements during the ALD of conducting materials such as W. These conducting materials would otherwise electrically short the QCM sensor and prevent oscillation. Mass uptake data was recorded every 0.1 s, and this data was processed to obtain the net mass change from each ALD cycle in the cases of Al2O3, W and W:Al2O3 composites with various ALD cycles ratio.
The thicknesses of W:Al2O3 layers were determined using spectroscopic ellipsometry measurements on the Si monitor coupons. The ellipsometry film thicknesses were supported by cross-section scanning electron microscopy (SEM) analysis and transmission electron microscopy (TEM). Annealing of W:Al2O3 composite layers were performed at 400° C. in 500 sccm flowing Ar condition for 4 hrs. at a pressure of 1 Torr. The microstructure and conformality of W:Al2O3 layer coatings on Si substrates and high aspect ratio glass micro-capillary plates were examined by cross-sectional scanning electron microscopy (SEM) using a Hitachi model 4700. The electrical I-V characteristics and thermal coefficient of resistance (TCR) of W:Al2O3 layers were measured using a Keithley Model 6487 pA/V source. Electrical measurements were done using either micro probes or Hg-probe contact method. The resistance stability test was performed for several days under constant applied potential in vacuum.
Prior to ALD growth W:Al2O3 composite layers, pure Al2O3 and W layers growth was studied by ALD. Thickness series samples were prepared and characterized. The in-situ quartz crystal microbalance (QCM) was performed during the pure Al2O3 and W ALD films growth.
QCM measurements were performed during Al2O3 ALD at 200° C. using TMA and H2O with the timing sequence: (1-10-1-10). These conditions were chosen from the ALD growth saturation studies. Under these conditions
ALD of W performed on QCM at 200° C. with the repetition of a ALD precursors cycle Si2H6 (dose)-N2(purge)-WF6(Dose)-N2(purge) with precursor timings of (1-10-1-10)s. These conditions were chosen from the ALD growth saturation studies. W growth directly on Si(100) substrate has shown poor adhesion whereas Al2O3 passivated Si(100) substrate shows good adhesion with W layer.
Prior to W:Al2O3 composite layers growth, the QCM data were collected for the steady state ALD growth of Al2O3—W:Al2O3 with the precursor sequence of n(TMA-H2O)-m(Si2H6—WF6)-n(TMA-H2O) where n and m are the desire number of cycles and shown in
In
The first cycles of Al2O3 mass uptake on the W surface was noted to be high ˜68 ng/cm2, which is ˜1.8 times more than the steady state growth condition 37 nm/cm2/ALD cycle (
Control over the electrical properties of W:Al2O3 composite layers is preferably accomplished by adjusting relative ratio of the W to Al2O3 ALD cycles. The QCM study was performed at 200° C. for various compositions of the W:Al2O3 ALD cycles using the precursor sequence n[x(TMA-N2—H2O—N2)+y(Si2H6—N2-WF6—N2)] where the % W cycles, y/(x+y)*100, can vary between 0-100; and n is adjusted to control the film thickness. The precursors were dosed for 1 s followed by a 10 s N2 purge.
Thickness series samples of W:Al2O3 system with % W ALD cycles variations were deposited under similar conditions on Si(100) and thicknesses measured spectroscopic ellipsometry.
As deposited pure Al2O3, pure W as well as composite W:Al2O3 layers were uniform and smooth over the 300 mm Si substrate area. These layers were analyzed by X-ray diffraction analysis shown in
Cross-section TEM samples were analyzed at Evans Analytical Group (EAG). TEM ready samples were prepared using the in-situ FIB lift out technique on an FEI Strata Dual Beam FIB/SEM. The samples were capped with a protective layer of carbon prior to FIB milling. The samples were imaged with a FEI Tecnai TF-20 FEG/TEM operated at 200 kV in bright-field (BF) TEM mode, high-resolution (HR) TEM mode, high-angle annular dark-field (HAADF) STEM mode and nano-beam diffraction (NBD) mode.
It is clear from the
The elemental composition across the layer of the (30% W:70% Al2O3) ALD cycle condition case for an as deposited sample capped intentionally with the 60 Å Al2O3 is shown in
XPS spectra of individual elements were taken with respect to their binding energies after removing a portion of the W:Al2O3 composite layer with a sputter rate of (˜30 Å/min) and are shown in
Evidently, F1s features in
The conformality of the composite W:Al2O3 layer was studied by depositing this layer on the high aspect ratio (AR=60) micro-capillary borosilicate glass plate shown in
The precursor sequence in ALD has an important role, and this will define the functional groups present during the subsequent precursor doses.
This mass add-on for one super ALD cycle or within the super cycle is significantly lower than the steady state mass uptakes for W and Al2O3 shown in
Similar to the
A similar mass uptake was noticed for the ALD precursor sequence THWS and THSW and can relate to W growth on —OH rich surface. AlF3.3H2O can cause exposure of TMA on W which actually adds the mass shown in
Current-Voltage (I-V) characteristics of the W:Al2O3 with various compositions were measured.
Transverse (⊥) characteristics were determined by appropriate contacts where the electric field is perpendicular and longitudinal (∥) characteristics where the electric field is parallel to the W:Al2O3 composite layers I-V. In the longitudinal measurement the high surface area microchannel plate was used as well as a lithographically patterned, interdigitated comb structure comprised of gold lines contained 80000 sq and 2 μm spacing. For transverse measurements a TiN deposited Si substrate was used which makes bottom contact; and a top contact was made with a Hg drop set-up with dot size of about 812 pm.
In
The possibility of Fowler-Nordheim tunneling mechanism here is low because it normally requires very high electric field (E) for reasonable conduction which is about ˜1 GV/m. Instead of this conduction for the W:Al2O3 composite it is likely to occur through one of the two predominant conduction mechanisms for insulators, Frankel-Poole (FP) emission, which has the following form,
J∝E exp(−q(φb−(qE/πε)1/2/kBT)) (1)
or Space-Charge Limited (SCL) emission, which at high field is
J˜εμ(V2/L3) (2)
These two mechanisms have different IV behavior. At lower field the IV curve follows linear ohm's law (V=IR) whereas the I-V curve of FP emission is characterized by a straight line at large Eon a semi-log plot of J/E vs. E1/2. In contrast to this the IV curve of SCL emission has a second order dependence on E. In addition to this only FP emission will show the temperature dependence, whereas both SCL and FN tunneling will not.
a)-20(d)(2) represent electrical measurements for a W:Al2O3 layer grown with a 30% W ALD cycle condition, IV curve of a film in
To establish straight SCL emission characteristics, the data is plotted on a log-log scale
I-V behavior in the temperature range 30-130° C. were measured for (30% W:70% Al2O3) ALD cycle case sample. The resistance at different temperatures are shown in
The W:Al2O3 composite layer shows a negative temperature coefficient of resistance (PTCR) effect from 30° C. to 130° C. The PTCR effect is a very common phenomenon observed in semiconducting layers.
In another embodiment of the invention involving Mo:Al2O3 (or Mo AlOx) the Mo:Al2O3 composite layer depositions were preferably carried out in a hot wall viscous flow reactor ALD reactor. The Mo:Al2O3 composite films were deposited on n-type Si(100), fused quartz, glass substrates and high aspect ratio (60:1) borosilicate glass micro-capillary plates. Prior to ALD processing all the substrates were degreased using a 10 min dip ultrasonic acetone cleaning. For Al2O3 growth, Al(CH3)3 [TMA] was obtained from Sigma-Aldrich with a 97% purity and deionized (DI) H2O vapor was used as a precursors. For Mo ALD, molybdenum hexafluoride (MoF6, Alfa Aser, 99.9%) and disilane (Si2H6, Sigma-Aldrich, electronic grade 99.995%) were used as precursors. All precursors were maintained at room temperature at ˜20° C. The background N2 flow was set to 300 sccm which gives base pressure of 1.0 Torr in the ALD reaction chamber was measured by a heated MKS Baratron 629B model. The precursors TMA and H2O were alternately pulsed in the continuously flowing N2 carrier flow using high speed computer controlled pneumatics valves in a desire ALD sequence. During TMA and H2O dosing, pressure transient increases of 0.2 Torr for TMA and 0.3 Torr for H2O when the reactants were introduced into N2 carrier flow nitrogen carrier flow. Similarly, MoF6 and Si2H6 precursors were alternately injected into N2 carrier flow. During the Si2H6 and MoF6 dosing, pressure transient increases of 0.25 Torr for Si2H6 and 50 mTorr for MoF6. The main experimental conditions for ALD are summarized in Table 4.
The thicknesses of MoAlOx layers were determined using spectroscopic ellipsometry measurements on the Si monitor coupons. Annealing of MoAlOx composite layers were performed at 400° C. in 500 sccm flowing Ar condition for 4 hrs. at pressure of 1 Torr. The film thicknesses were measured using ex-situ ellipsometry and supported by cross-section scanning electron microscopy (SEM) analysis and transmission electron microscopy (TEM). The microstructure and conformality of MoAlOx layer coatings on Si substrates and high aspect ratio glass micro-capillary plates were examined by cross-sectional scanning electron microscopy (SEM) model Hitachi 4700. The electrical I-V characteristics and thermal coefficient of resistance (TCR) of MoAlOx layers were measured using a Keithley Model 6487 pA/V source. Electrical measurements were done using either micro probes or Hg-probe contact method. The resistance stability test was performed for several days under constant applied potential in vacuum.
X-ray diffraction (XRD) analysis was performed to test deposited materials crystallinity or preferred any crystallographic phase. X-ray diffraction of as deposited MoAlOx layers deposited with 8% Mo ALD cycles shows an amorphous structure (see
To evaluated the microstructure, surface roughness and uniformity of the deposited MoAlOx materials. AFM analysis (shown in
To evaluated the across the layer microstructure, uniformity and crystallinity of the deposited materials MoAlOx films were analyzed with TEM. Top down transmission electron microscopy (TEM) image
The cross section transmission electron microscopy (XTEM) images of
The Mo:Al2O3 processes were tested on the 300 mm Si wafer as well as 12″×12″ glass substrate shown in
Transverse electrical measurements of the MoAlOx layer were performed on the 300 mm Si wafer deposited first with Mo (served as bottom contact). The schematic of the test structures on 300 mm Si wafer is shown in
The Mo:Al2O3 layers were deposited with various thicknesses and compositions. The longitudinal and transverse resistivities were measured for several samples and plotted against the % of Mo ALD cycles in Al2O3 and shown in
I-V behavior in the temperature range 30-130° C. was measured for various Mo:Al2O3 layers The resistance at different temperatures are shown in
The temperature dependence of resistance was fit to:
R=Roe
−(βT(T-To))
Where R is resistance, T is temperature and Ro is initial resistance at initial temperature and βT is the thermal coefficient of resistance.
For reference:
Commercial lead-glass MCP: βT=−0.02
Micro-machined silicon MCP: βT=−0.036
Aluminum zinc oxide coated MCP: βT=−0.06
The growth of ALD MoAlOx layer on high aspect ratio 3D structures was also evaluated. ALD MoAlOx tunable resistance coatings were prepared using 8% Mo ALD cycles on the inside surface of a porous borosilicate capillary glass array showing excellent thickness uniformity, conformality, and smoothness of the films
SEM images of ALD MoAlOx tunable resistance coating prepared using 8% Mo ALD cycles in Al2O3 on inside surface of porous borosilicate capillary glass array showing excellent thickness uniformity, conformality, and smoothness of the films.
In yet another embodiment tunable resistance coatings of Mo—Al2O3 can be deposited and the Mo content can be controlled by adjusting the percentage of Mo ALD cycles, the number of ALD Mo cycles executed consecutively, the Mo ALD precursor exposure times, and the order in which the precursors are supplied. By controlling the Mo content, the composition and structure of the films can be tailored to yield the desired resistivity.
Another method for adjusting the Mo content of the Mo:Al2O3 tunable resistance coatings is to execute multiple, consecutive Mo ALD cycles comprised of alternating exposures to Si2H6 and MoF6. For instance,
One effect of adjusting the Mo content in the Mo:Al2O3 tunable resistance coatings by controlling the number of Mo ALD cycles executed consecutively is shown in FIG. 37a and 37b.
A third method for controlling the Mo content in the Mo:Al2O3 tunable resistance coatings is by adjusting the MoF6 precursor exposure. The MoF6 precursor exposure can be adjusted by changing the dose time, the partial pressure of the MoF6 during the exposure, or both.
Yet another method for controlling the Mo content in the Mo—Al2O3 tunable resistance coatings is by adjusting the order for the ALD Mo precursors.
Another formulation for the tunable resistance coatings containing Mo is MoCx—Al2O3 where MoCx represents a material containing both Mo and carbon that results from alternating exposures to molybdenum hexafluoride (MoF6) and trimethyl aluminum (TMA). To demonstrate the viability of this precursor pair for atomic layer deposition,
In a further embodiment, tunable resistance coatings of W:Al2O3 can be deposited using alternating exposures to disilane and tungsten hexafluoride (WF6) for W ALD, and alternating exposures to trimethyl aluminum (TMA) and H2O for the Al2O3 ALD. By varying the deposition process conditions such as the percentage of W ALD cycles, the composition and structure of the films can be tailored to yield the desired resistivity.
Another formulation for the tunable resistance coatings containing W is WCx—Al2O3 where WCx represents a material containing both W and carbon that results from alternating exposures to tungsten hexafluoride (WF6) and trimethyl aluminum (TMA). To demonstrate the viability of this precursor pair for atomic layer deposition,
A film of WCx was prepared using the conditions listed in Table 9. 50 ALD cycles of WCx yielded a thickness of 400 Å as determined by ellipsometry, and the film was highly conductive with a resistivity of 3.5e-2 Ohm cm as determined using a four point probe, and was amorphous as determined using X-ray diffraction (XRD).
A WCx:Al2O3 tunable resistance film was prepared using 500 ALD cycles with 33% WCx cycle percentage at 200° C. on a silicon substrate. As shown by the XPS depth profiling measurement in
Yet another formulation for the tunable resistance coatings containing W is WN:Al2O3 where WN represents a material containing both W and nitrogen that results from alternating exposures to tungsten hexafluoride (WF6) and ammonia (NH3). Both W:Al2O3 films and WN:Al2O3 films were prepared under identical conditions on silicon and glass substrates using 500 ALD cycles with a W or WN cycle percentage of 33% at a deposition temperature of 200° C. using reactant exposure times of 1 s and purge times of 5 s. In both cases, the films were found to be uniform over the ˜30 cm length of the ALD reactor. The thicknesses, refractive indices, and resistivities for these films are presented in Table 10.
The foregoing description of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.
This application is a Continuation-In-Part of U.S. application Ser. No. 13/525,067, filed Jun. 15, 2012, incorporated herein by reference in its entirety, which is a Continuation-In-Part of U.S. application Ser. No. 13/011,645, filed Jan. 21, 2011, incorporated herein by reference in its entirety.
The United States Government has certain rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC, representing Argonne National Laboratory.
Number | Date | Country | |
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Parent | 13525067 | Jun 2012 | US |
Child | 13804660 | US | |
Parent | 13011645 | Jan 2011 | US |
Child | 13525067 | US |