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A Monolayer-Based Lift-Off Process for Patterning Chemical Vapor Deposition Copper Thin Films Noo Li Jeon,†,‡ Paul G. Clem,†,‡,§ David A. Payne,*,†,‡,§ and Ralph G. Nuzzo*,†,‡,| Department of Materials Science & Engineering, School of Chemical Sciences, The Beckman Institute, and The Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 Received April 18, 1996. In Final Form: July 16, 1996X We describe a non-lithographic monolayer based patterning process for depositing copper thin film microstructures by chemical vapor deposition (CVD). The technique combines the microcontact printing of octadecyltrichlorosilane (OTS) monolayers, nonselective copper CVD, and mild (abrasive-free) mechanical polishing to fabricate thin film microstructures on both planar and nonplanar substrates. This technique has been used successfully to deposit copper features with sizes ranging from 5 to 250 µm on variety of technologically important substrates including indium tin oxide (ITO), titanium nitride (TiN), thermal and plasma grown SiO2, Al2O3, and glass. Patterning is effected via adhesive failure in regions modified by microcontact printing (µCP); nucleation and growth are inhibited in these regions and the copper grains which eventually form on top of the OTS monolayer remain loosely adherent and, thus, are easily removed by mechanical means. The versatility and simplicity of the µCP process as a method for surface modification combined with chemical/physical routes of thin film deposition and patterning suggest a new, defecttolerant method for fabricating thin film features with micrometer to centimeter dimensions with potential advantages over conventional subtractive patterning processes involving photolithography and chemical etching. Possible applications in the manufacturing of multichip modules (MCM-D) and more generally in microelectronic packaging and liquid crystal display (LCD) metalization are described.
I. Introduction The fabrication of modern microelectronic devices is based largely on subtractive processing methods. A complex sequence of physical and chemical processes is used in which thin films are repetitively deposited and etched. Because most deposition techniques produce continuous films, patterning is usually done after a thin film of material is deposited across the entire surface of a substrate. The fabrication of microstructures in such layers involves complex lithographic patterning steps and vigorous conditions to effect the etching of unwanted materials by either reactive ion or chemical means. Although these subtractive methods work extremely well for most materials, notable exceptions do exist. Copper, prized for its high conductivity and resistance to electromigration,1 is difficult to pattern as fine lines using reactive ion etching;2 the low throughput of ion-milling processes further complicates the design of a practical commercial process.3 It is thus of considerable interest to develop new methods for pattering copper which might simplify and minimize process steps, reduce fabrication costs, and ease environmental concerns by reducing the quantity of chemical process wastes. Such advantages might be realized by the use of selective metalization, an additive process for the fabrication of thin film microstructures. Selective Cu CVD has been demonstrated previously on insulating oxides substrates * Authors to whom correspondence should be addressed. † Department of Materials Science & Engineering. ‡ The Frederick Seitz Materials Research Laboratory. § Beckman Institute. | School of Chemical Sciences. X Abstract published in Advance ACS Abstracts, October 1, 1996. (1) Kang, H. K.; Cho, J. S. H.; Wong, S. S. IEEE Electron Device Lett. 1992, 13, 448. (2) Steigerwald, J. M.; Zirpoli, R.; Murarka, S. P.; Price, D.; Gutmann, R. J. J. Electrochem. Soc. 1994, 141, 2842-2848. (3) Hu, C. K.; Luther, B.; Kaufman, F. B.; Hummel, J.; Uzoh, C.; Pearson, D. J. Thin Solid Films 1995, 262, 84-92.
S0743-7463(96)00377-0 CCC: $12.00
patterned with metal seed layers.4,5 The reported processing window for selective deposition is very narrow and limited to a low-pressure regime (10-100 mTorr).6 Silating agents also have been used to passivate the oxide layers on these patterned substrates. Even so, it is found that the quality of the selective deposition achieved depends critically on the cleaning procedures used, and the deposition rates achieved are still not comparable to that of blanket (i.e., nonselective) deposition.4 In a previous study, we demonstrated that monolayers of octadecyltrichlorosilane (OTS) patterned by a printing technique direct the deposition of copper to areas not modified by the monolayer.7 The OTS monolayers formed chemically and thermally robust barriers for inhibiting nucleation and growth, thus promoting selective copper deposition over a wide, albeit still limited, range of experimental conditions. This report is but one of a growing number of papers which describe the use of monolayers as templates for the fabrication of microstructures.8-16 Ultrathin films of organic molecules, in particular self(4) Gelatos, A. V.; Jain, R. M.; Mogab, C. J. MRS Bull. 1994, 19, 49-54. (5) Jain, A.; Gelatos, A. V.; Kodas, T. T.; Hampden-Smith, M. J.; Marsh, R.; Mogab, C. J. Thin Solid Films 1995, 262, 52-59. (6) Chiou, J. C.; Juang, K. C.; Chen, M. C. J. Electrochem. Soc. 1995, 142, 177-182. (7) Jeon, N. L.; Nuzzo, R. G.; Xia, Y.; Mrksich, M.; Whitesides, G. M. Langmuir 1995, 11, 3024-3026. (8) Kumar, A.; Biebuyck, H. A.; Whitesides, G. M. Langmuir 1994, 10, 1498-1511. (9) Wilbur, J. L.; Kumar, A.; Kim, E.; Whitesides, G. M. Adv. Mater. 1994, 6, 600-604. (10) Tiberio, R. C.; Craighead, H. G.; Lercel, M.; Lau, T.; Sheen, C. W.; Allara, D. L. Appl. Phys. Lett. 1993, 62, 476-478. (11) Chan, K. C.; Kim, T.; Schoer, J. K.; Crooks, R. M. J. Am. Chem. Soc. 1995, 117, 5875-5876. (12) Dressick, W. J.; Calvert, J. M. Jpn. J. Appl. Phys. 1993, 32, 5829-5839. (13) Calvert, J. M. J. Vac. Sci. Techonol. B 1993, 11, 2155-2163. (14) Calvert, J. M.; Chen, M. S.; Dulcey, C. S.; Georger, J. H.; Peckerar, M. C.; Schnur, J. M.; Schoen, P. E. J. Electrochem. Soc. 1992, 139, 1677-1680. (15) Marrian, C. R. K.; Perkins, F. K.; Brandow, S. L.; Koloski, T. S.; Dobisz, E. A.; Calvert, J. M. Appl. Phys. Lett. 1993, 64, 390-392. (16) Ross, C. B.; Sun, L.; Crooks, R. M. Langmuir 1993, 9, 632-636.
© 1996 American Chemical Society
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Figure 1. A selectively deposited copper thin film on ITO. The substrate was patterned with a OTS SAMs by µCP. The 3000 Å thick Cu film was deposited at 175 °C at a rate of ∼200 Å/min at total chamber pressure of 300 mTorr. In order to maintain selectivity shown here, the deposition conditions were kept at low pressure and low deposition rate (low precursor flux). The smallest features evident in this micrograph are 5 µm in size.
assembled monolayers (SAMs), have been widely investigated in recent years as a surface imaging layer for deep UV lithography and as a resist for scanning tunneling microscopy (STM) based lithography.15,16 It is typical to design the SAM such that a specific area can be activated toward deposition via a selected area lithographic exposure. This latter process design is reminiscent of the more traditional applications of organosilanes as adhesion promoters, where monolayers with functional tail groups are utilized to promote chemical bonding interactions with a deposited film.17 In this paper, a new, defect-tolerant technique is reported for patterning CVD Cu thin films. Inspired by lift-off processing,18 we exploit the weak interfacial interactions occurring between the metal and a patterned OTS monolayer to effect the patterning without resort to chemical etching. Using microcontact printing (µCP) in combination with a very mild mechanical polishing step, we show that high-resolution Cu features can be reproducibly fabricated over a large area by CVD with extremely high throughput. This approach for patterning CVD copper thin films overcomes many of the more significant limitations of selective CVD processes, including slow deposition rates, high defect densities, and limited pro(17) Plueddemann, E. P. Silane Coupling Agents; Plenum: New York, 1982. (18) VLSI Technology; Sze, S. M., Ed.; McGraw-Hill: New York, 1988.
cessing windows. We further demonstrate that this process can be used to promote the efficient filling of vias and trenches on substrates bearing nonplanar topologies. II. Experimental Section The copper CVD precursor, CuI(hfac)(vtms) (copper hexafluoroacetylacetonate vinyltrimethylsilane), was obtained as a gift from the Schumacher Co. (Carlsbad, CA). Indium tin oxide (ITO) substrates were obtained as a gift from Donnelly Applied Films (Denver, CO). Titanium nitride substrates (600Å thick sputtered TiN on Si) were obtained as a gift from Hyundai Electronics Ltd. Octadecyltrichlorosilane (OTS) was obtained from Aldrich and used without further purification. The PDMS stamps used for microcontact printing OTS-SAMs were fabricated according to a previously reported procedure.8,13,14,19 The substrates (TiN, ITO, SiO2, Al2O3, and glass) were washed with deionized (DI) water, acetone, and 2-propanol and dried with stream of Ar. The dried substrates were placed in a UV/ozone generator for 5-10 min to remove trace organic contaminants (and in some instances effect very thin oxide growth)20,21 immediately prior to microcontact printing with the OTS solution. A solution of OTS in dry hexane (10 mM) was used as the “ink”. The OTS solution was applied to the PDMS stamp using a photoresist spinner (3000 rpm for 30 s) and dried (19) Kumar, A.; Whitesides, G. M. Appl. Phys. Lett. 1993, 63, 20022004. (20) Vig, J. R. J. Vac. Sci. Technol. A 1985, 3, 1027-1034. (21) Zazzera, L. A. PhD Thesis, University of Minnesota, 1994.
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Jeon et al. based lift-off patterning. The latter polishing step was carried out with either a wetted cotton-felt polishing pad or a cotton Q-tip. The copper deposited on the SAM-modified regions was so loosely adherent that polishing on a wet (2-propanol) felt for few seconds was sufficient to reveal the patterns carried in the SAM.
III. Results and Discussion
Figure 2. Schematic outlines of the procedures used to pattern copper thin films on planar (a) and nonplanar (b) substrates. First, patterned SAMs of OTS are formed on the substrate surfaces by µCP. This is then followed by nonselective copper CVD using CuI(hfac)(vtms). Mild polishing after CVD reveals the patterned copper features strongly adhearing to the underivatized regions of the substrate (or filling the vias and trenches as in the case of the nonplanar substrates (b)). in a stream of Ar for ∼30 s. The stamp was brought into contact with the substrate (by hand) and held in place for ∼30 s. This procedure, in our hands, routinely yields OTS thin films with ∼25-30 Å mass coverages on the substrates examined in this work. Detailed structural characterizations of these films will be reported separately.22 After printing, copper thin films were deposited by CVD using CuI(hfac)(vtms) (copper hexafluoroacetylacetonate vinyltrimethylsilane) as the precursor. The chemical vapor deposition experiments were carried out in a home-built, cold-wall reactor. The reactor is a stainless steel chamber which is pumped by a diffusion pump to a base pressure of e1 × 10-7 Torr. Copper films were typically deposited on 1 in.2 substrates. The substrates were cleaned with DI water and 2-propanol and finally dried with a stream of Ar before loading them into the reactor. The CuI precursor was carried into the reactor using Ar as the carrier gas (flow rate of 5-150 sccm) and delivered to the susceptor region where the substrate was held between 150 and 300 °C. The temperature of the susceptor was regulated to within (2 °C using a programmable power supply. A typical deposition took ∼10-20 min to carry out. The chamber pressure was maintained at a preset value (between 100 mTorr and 1 Torr) using a throttle valve. Film thicknesses were determined by profilometry. Patterned copper films were characterized by electron and optical microscopy, energy dispersive X-ray analysis, X-ray photoelectron, and Auger electron spectroscopies. Two distinct methods of copper patterning were investigated: (1) use of low-flux and low-pressure CVD conditions to achieve and access the limits of directed selective deposition using µCP, and (2) high-flux, high-pressure blanket deposition of copper, followed by mild, nonabrasive polishing to achieve a monolayer(22) Jeon, N. L.; Nuzzo, R. G. Manuscript in preparation.
Patterned SAMs prepared by µCP provide a useful means to effect patterned materials deposition. The present report is concerned with exploring the utility of such SAMs to serve as the basis for a lift-off patterning method for metal thin films prepared by CVD. This latter application follows closely the methods reported earlier by us for patterning thin ceramic films deposited by solgel methods.25 We have also described in an earlier report the use of µCP SAMs to effect patterned CVD growth of metals.7 Since this earlier report appeared, we have been able to greatly improve the selective deposition chemistries for Cu. We therefore start this report with a brief examination of this latter deposition method to provide a better benchmark against which to compare the liftoff-based patterning method. In our hands, the results achieved were insensitive to the substrate choice and, as such, we use several different materials to develop this comparison and establish the generality of the method. Selective Deposition. Figure 1 shows (method 1) copper features deposited selectively on a 1 in.2 ITO substrate (magnification ×10). As described above, the selective deposition was achieved in two steps: (a) patterning of the ITO surface with an OTS monolayer prepared by microcontact printing and (b) low-pressure copper CVD. It is striking that the maskless patterning process routinely yields high-resolution features (as small as 0.5 µm) over large areas. The sizes of the copper features deposited in the present demonstration (Figure 1) range from 5 to 250 µm. We note that features with sizes ranging from 0.5 µm to 1 cm have been successfully deposited using stamps constructed from different masters; the smaller features (e1 µm) are more difficult to reproduce with the fidelity shown here, however. This appears to reflect limitations of the printing process which are as yet poorly understood. The patterned OTS monolayer serves to direct the deposition to areas of the substrate not modified by the SAM. Other published reports have shown similar results for selective depositions effected via a vapor phase passivation of the oxide surfaces present on a metalpatterned substrate.7,23,24 The process window for selective deposition appears to be wider for this deposition system than those previously described; however, further work is needed to clarify this point in a more quatitative way. Be this as it may, the deposition is carried out at what must still be considered a slow rate to maintain the selectivity. For example, the 3000 Å thick copper film shown in Figure 1 was deposited at 175 °C with a low total chamber pressure (300 mTorr) and at a slow deposition rate of ∼200 Å/min. In summary, µCP based selective deposition appears to have several potential advantages of interest for processing. First, the depositions can be performed in wider process window than that previously reported. Second, the process does not require metal catalyst seed layers and eliminates the need for additional patterning and cleaning protocols.4-6,23,24 Third, due to its use of printing (23) Jain, A.; Kodas, T. T.; Jairath, R.; Hampden-Smith, M. J. J. Vac. Sci. Technol. B 1993, 11, 2107-2113. (24) Jain, A.; Farkas, J.; Kodas, T. T.; Hampden-Smith, M. J.; Gelatos, A. V.; Marsh, R.; Mogab, C. J. Mater. Res. Soc Symp. Proc. 1993, No. 315, 105-109.
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Figure 3. Patterning a nonselectively deposited copper thin film on TiN: (a) as deposited and (b) after polishing with a wet felt pad. The 1 µm thick film was deposited at a substrate temperature of 250 °C and chamber pressure of 1 Torr. The deposition rate was ∼800 Å/min. The patterning is achieved via a monolayer-based “lift-off” after the blanket deposition is completed.
Figure 4. Scanning electron micrographs of a copper thin film deposited on a SiO2/Si substrate (a), and an OTS-modified SiO2/Si surface (b). The micrographs were taken from a single sample. A continuous film of copper is formed on the nonderivatized region of the surface as compared to the sparse, disconnected copper nuclei seen in the OTS-modified areas. These microstructures are representative of Cu films grown on all samples studied in this work (TiN, ITO, Al2O3, and glass). A higher magnification micrograph showing the sharp boundary formed between the copper deposited on either the functionalized or unfunctionalized regions of a TiN substrate (c).
as the means of generating a pattern, it is possible to imagine its extension to very large format substrates (i.e., large flat panel displays) to which projection-based lithography is poorly suited. Despite these advantages, achieving faster deposition rates and reducing the number of defects generated remain issues of significant interest. It is to these issues that we now turn our attention. Monolayer-Based Lift-Off Patterning. In our previous work on the patterning of sol-gel derived oxide thin films,25 we showed that the presence of an OTS monolayer between the sol-gel derived ceramic thin film and substrate allowed facile removal of material from the functionalized areas. Thus it was found that the deposition of a variety of oxides on monolayer-patterned surfaces, when combined with nonabrasive polishing, enabled the direct fabrication of micrometer-scale patterned oxide features appropriate for device applications. We were inspired by this work to investigate similar adhesion effects for metal thin films (Cu in this report) deposited (25) Jeon, N. L.; Clem, P. G.; Nuzzo, R. G.; Payne, D. A. J. Mater. Res. 1995, 10, 2996-2999.
by CVD under nonselective conditions. As we show below, a similar postdeposition polishing results in the selective deadhesion of Cu from the SAM functionalized regions of the substrate. This provides the basis for a new liftoff patterning process for Cu based on microcontact printingsa high throughput, waste minimizing method which eliminates the need for postdeposition chemical etching. A schematic outline of the procedure used is shown in Figure 2. We first use microcontact printing to pattern an OTS monolayer; this can be done on either a planar (Figure 2a) or nonplanar (Figure 2b) substrate. Copper is then deposited nonselectively on the modified substrate using the CuI(hfac)(vtms) reagent; temperatures as high as 275°C and pressures greater than 1 Torr have been used successfully (see below). Nonabrasive polishing is then employed. The pattern definition which results from selective deadhesion is due to the presence of the patterned monolayer underneath the Cu thin film; it is this latter step which finds the closest analogy in lift-off processing. The use of µCP in this instance offers potential advantages,
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Figure 5. (a) Optical micrographs of a nonplanar SiO2-Si substrate. The letters and squares are formed by 1.0 µm deep channels cut into the plasma-grown SiO2 layer using conventional microfabrication techniques. The top-most surface of this substrate is functionalized with an OTS monolayer. (b) A nonselectively deposited copper film showing a bright, highquality copper film filling the recessed regions of the substrate and a dull copper deposit on the outer OTS functionalized region. (c) The sample after removing the loosely adhering copper deposits by mechanical polishing. The copper is removed using a cotton-felt pad wetted with 2-propanol, leaving behind the patterned copper features filling the recessed regions.
however, viz., the metalization needed for the filling of vias and trenches. Since the excess material in this case is easily removed without the use of abrasive polishing compounds, higher throughput might be achieved in production level chemical mechanical polishing (CMP) processes. We discuss this latter issue in greater detail below. The result achieved for a prototypical blanket deposition of Cu on a SAM-modified TiN substrate is shown in Figure 3a. It is evident that the coherence of the Cu film is very poor, with many features of the SAM-derived pattern being
Jeon et al.
visible. This illustrates the significant heterogeneity of the activated nucleation rates for deposition on this surface. Profilometry revealed that copper film in the non-SAM bearing regions was 1 µm thick (this particular film was deposited at a substrate temperature of 250 °C and chamber pressure of 1 Torr). At the significantly higher deposition rate of 800 Å/min used here, the presence of the OTS monolayer was not enough to maintain selectivity, although some regions with sparse copper coverage reveal a recognizable pattern underneath. In this regard, then, the deposition is best regarded as being a highly defective selective deposition. The significant level of defects not withstanding, a mild polishing on a cotton felt wetted with 2-propanol sufficed to reveal the intricate patterns of the copper features as is illustrated by the micrograph shown in Figure 3b. Features with dimensions ranging 5 to 250 µm are clearly visible in this image. The resolution of the features obtained was similar to that achievable by directed selective deposition. SEM analyses showed that the copper thin films deposited on the monolayer-modified regions are markedly different from those deposited on nonmodified areas. Macroscopically, the films forming on the nonmodified regions of the substrate appear bright and metallic and stand in marked contrast to the dull non-lustrous appearance of the films growing on monolayer-modified areas. This directly reflects the differences in the underlying grain structure. The SEM images shown in parts a and b of Figure 4 are for representative Cu thin films deposited on a Si(100) substrate bearing an ∼30 Å thick native oxide overlayer. The micrographs were taken of suitable regions from a single sample. Figure 4c shows a higher magnification micrograph which reveals the sharp boundary and line edge definition seen between copper deposited on the unfunctionalized and OTS functionalized regions of a TiN substrate. The grain size is similar in both regions, a feature reflective of the controlling influence of precursor flux and substrate temperature on this structural feature. The density of nuclei/grains is very different in the two regions, however. These qualitative aspects of the microstructure are representative of those found for films deposited on TiN, ITO, SiO2, Al2O3, and glass. As noted above, the density of the growth nuclei is the most significant difference noted between copper deposited on modified and unmodified regions. On the unmodified substrate surface, the copper is seen to nucleate rapidly and more uniformly, forming a continuous film of higher quality. It is known that, for CVD with this reagent, single metal atom sites are sufficient to initiate grain growth26 and that the nucleation rate is not substrate dependent for the materials of interest here.23 The present results suggest that the reactive sticking probability of the reagent must be significant in the unmodified regions. In contrast, sparse nucleation occurs on monolayer-modified areas, suggesting that the interactions occurring between the precursor and the OTS surface are at best weak. Several groups have shown that monolayers terminated with a variety of functionalized tail groups interact strongly with the coinage metals and that this interaction is correlated with both higher nucleation densities and more continuous film growth at lower mass-coverages of metal.27-31 The kinetic control evidenced here is thus one (26) Jeon, N. L.; Nuzzo, R. G. Langmuir 1995, 11, 341-355. (27) Allara, D. L.; Hebard, A. F.; Padden, F. J.; Nuzzo, R. G.; Falcone, D. R. J. Vac. Sci. Technol. A 1983, 1, 376-382. (28) Dunaway, D. J.; McCarley, R. L. Langmuir 1994, 10, 35983606. (29) Czanderna, A. W.; King, D. E.; Spaulding, D. J. Vac. Sci. Technol. A 1991, 9, 2607-2613. (30) Tarlov, M. J. Langmuir 1992, 8, 80-89.
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Figure 6. (a) Scanning electron micrograph of a patterned Cu film that fills the recessed regions of a nonplanar substrate. (b) An energy dispersive X-ray analysis Si elemental map of the region shown in (a) (the bright regions represent Si). (c) complementary energy dispersive X-ray analysis of a Cu elemental map (the ∼1 µm thick copper film filling the recessed areas is revealed as the bright areas).
in which the weakly interacting, low surface energy monolayer of OTS (-CH3 terminated) evidences a significantly higher barrier to activated growth than does the unmodified regions. We must stress, however, that the rates accelerate autocatalytically in either region once a critical nucleus is formed. What is not evident in the micrographs, and perhaps is the most important result of this work, is that the copper nucleated on the OTS surface is poorly adherent. This latter aspect facilitates the postdeposition patterning by “lift-off”. As one measure of adhesion, films deposited on OTS monolayers could be easily peeled off with Scotch tape. In contrast, films deposited on unmodified SiO2, TiN, ITO, and other substrates were strongly adherent and could not be removed by Scotch tape. The films deposited on OTS are also easily removed by mild abrasion; solvents such as acetone and 2-propanol facilitate this latter mechanical de-adhesion. OTS patterning also provides a powerful method for promoting the filling of complex features on a nonplanar substrate. An illustrative example is provided by the complete filling by Cu of the test structures shown in Figure 5. Figure 5a shows an optical micrograph of the starting substrate (patterned 1 µm thick PECVD SiO2 on Si). The top surface of the substrate was derivatized with an OTS monolayer using the procedure shown in Figure 2b. The results of a blanket deposition of copper on (a) are shown in parts b and c of Figure 5 before and after polishing, respectively. The letters and square patterns are recessed by 1 µm with respect to the outer flat regions of the PECVD SiO2. A bright, metallic copper film fills the recessed areas completely (as seen in Figure 5b). The dull optical characteristics of nonselective film growth on a SAM-modified surface characterize the material depositing on the outermost surfaces. The qualitative appearance here is similar to that of the films shown in Figure 3a. Polishing with a felt pad wetted with 2-propanol (Figure 5c) completely removes the weakly adherent copper grains which decorate the top surface of the sample. SEM analysis of cross-sectioned samples (not shown) suggests that the filling is highly efficient, with little or no void content being seen at the bottoms of the recessed regions.32 A scanning electron micrograph of this latter patterned copper thin film is shown in Figure 6a (a slightly larger region than that shown in Figure 5c is presented). The (31) Allara, D. L.; Nuzzo, R. G. U.S. Patent 4690715, 1987. (32) Jeon, N. L.; Nuzzo, R. G. Unpublished results.
bright regions correspond to the 1 µm thick copper film which completely fills the recessed regions of the substrate. Figure 6b shows an energy dispersive X-ray analysis (EDXA) Si elemental map of the same region, with Si indicated as a bright highlight. The corresponding EDXA elemental map for copper is shown in Figure 6c. Taken together, the data shown in Figures 5 and 6 clearly demonstrate the capability of OTS monolayer assisted patterning to fill holes and trenches and allow facile, selective removal of unwanted material. Current research is aimed at extending these methodologies to submicrometer via filling and will be reported separately. IV. Conclusion Microcontact printing (µCP) of octadecyltrichlorosilane (OTS) monolayers, combined with Cu CVD, provides an effective means for producing copper thin films patterned at the micrometer scale on a variety of substrates. At low deposition rates, patterned copper thin films were selectively deposited on areas not modified by the monolayer. At higher deposition rates, this selectivity is lost but the patterns are readily revealed by following the deposition process with a nonabrasive polishing step. The defect densities seen in these latter films are low and may be limited solely by the µCP process itself. Patterning is easily effected on both planar and nonplanar substrate surfaces. In particular, the capability of this technique to deposit patterned thin films directly in two (direct, selective CVD) or three (with polishing) steps offers significant potential advantages over conventional lithography based thin film patterning processes. The approach described in this paper is a general one and should be applicable to other CVD precursors, SAMs, and substrate surfaces. Most important, however, is that thin film patterning process based on µCP templated deposition, especially when used in combination with polishing, offers significant potential for applications requiring largearea, fine scale patterning. Possible applications in diverse areas of microelectronics fabrication, including MCM-D (multichip module), packaging, and LCD (liquid crystal display) metalization are envisioned. Acknowledgment. We gratefully acknowledge the support of the National Science Foundation (CHE9300995) and the Department of Energy through the Frederick Seitz Materials Research Laboratory (DEFG0291ER45439). LA960377B
