Name: fabrication of low temperature carbon nanotube vertical interconnects compatible with semiconductor technology
Uploaded: 2015-12-07T13:00:00
Description: Watch this Scientific Journal Video about Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology at JoVE.com

Part of the work has been performed in the project JEMSiP_3D, which is funded by the Public Authorities in France, Germany, Hungary, The Netherlands, Norway and Sweden, as well as by the ENIAC Joint Undertaking. The authors would like to thank the Dimes Technology Centre staff for processing support.

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in this fabrication process are acutely toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when working with equipment, chemicals or nanomaterials, including the use of engineering controls (fume hood) and personal protective equipment (safety glasses, gloves, cleanroom clothes).
1. Alignme...

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Figure 1 displays a schematic overview of the structure fabricated in this work, and which was used for the 4-point probe measurements. As the potential is measured through probes carrying no current, the exact potential drop (VH-VL) over the central CNT bundle and its contacts to the metal can be measured. Bigger diameter CNT bundles are used to contact the bottom TiN layer from the contact pads, in order to reduce the total resistance for the current forcing probes and maximize th...

Copper and tungsten, the metals which are currently used for the interconnects in state-of-the-art very-large-scale integration (VLSI) technology, are approaching their physical limits in terms of reliability and electrical conductivity1. While down-scaling transistors generally improves their performance, it actually increases the resistance and current density of the interconnects. This resulted in interconnects dominating the integrated circuit (IC) performance in terms of delay and power consumption2.
Carbon nanotubes (CNT) have been suggested as alternative for Cu and W metallization, especially for vertical interconnects (vias) as CNT can easily been grown vertical3. CNT have been shown to have excellent electrical reliability, allowing an up to 1,000 times higher current density than Cu4. Moreover, CNT do not suffer from surface and grain boundary scattering, which is increasing the resistivity of Cu at the nanometer scale5. Finally, CNT have been shown to be excellent thermal conductors6, which can aid in the thermal management in VLSI chips.
For successful integration of CNT in VLSI technology it is important that the growth processes for the CNT is made compatible with semiconductor fabrication. This requires the low temperature growth of CNT (&#60; 400 &#176;C) using materials and equipment which are considered compatible and scalable to large scale manufacturing. While many examples of CNT test vias have been demonstrated in the literature7,8,9,10,11,12,13,14, most of these use Fe as catalyst which is regarded as a contaminant in IC manufacturing15. Besides, the growth temperature used in many of these works is much higher than the upper limit of 400 &#176;C. Preferably CNT should even be grown below 350 &#176;C, in order to allow integration with modern low-&#954; dielectrics or flexible substrates.
Here we present a scalable method for growing CNT at temperatures as low as 350 &#176;C using Co as catalyst16. This method is of interest for fabricating different electrical structures consisting of vertically aligned CNT in integrated circuits, ranging from interconnect and electrodes to super capacitors and field emission devices. The Co catalyst metal is often used in IC manufacturing for the fabrication of silicide&#8217;s17, while TiN is an often used barrier material7. Moreover, we demonstrate a process for fabricating CNT test vias while only using techniques from standard semiconductor manufacturing. With this, CNT test vias are fabricated, inspected by scanning electron microscopy (SEM) and Raman spectroscopy, and electrically characterized.

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			<td style="width:291px;">Comments/Description</td>
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			<td height="21" style="height:21px;width:307px;">Si (100) wafer 4&#34;</td>
			<td style="width:188px;">International Wafer Service</td>
			<td style="width:119px;"></td>
			<td>Resisitivity: 2-5 m&#937;-cm, thickness: 525 &#181;m&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Ti-sputtertarget (99.995 % purity)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Al (1% Si)-sputtertarget (99.999 % purity)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Co (99.95 % purity)</td>
			<td style="width:188px;">Kurt J. Lesker</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">Chemicals</td>
			<td style="width:188px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td>Comments/Description</td>
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			<td height="21" style="height:21px;width:307px;">SPR3012 positive photoresist</td>
			<td style="width:188px;">Dow Electronic Materials</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">MF-322 developer</td>
			<td style="width:188px;">Dow Electronic Materials</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">HNO3 (99.9 %)</td>
			<td style="width:188px;">KMG Ultra Pure Chemicals</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">HNO3 (69.5%)</td>
			<td style="width:188px;">KMG Ultra Pure Chemicals</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">HF 0.55%</td>
			<td style="width:188px;">Honeywell</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:307px;">Tetrahydrofuran</td>
			<td style="width:188px;">JT Baker</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Acetone</td>
			<td style="width:188px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">ECI3027 positive photoresist</td>
			<td style="width:188px;">AZ</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Tetraethyl orthosilicate (TEOS)</td>
			<td style="width:188px;">Praxair</td>
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			<td height="21" style="height:21px;width:307px;">Gasses</td>
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			<td style="width:119px;">Catalog Number</td>
			<td>Comments/Description</td>
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			<td height="21" style="height:21px;width:307px;">N2 (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">O2 (99.9999%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">CF4 (99.9970%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">CL2 (99.9900%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">HBr (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:307px;">Ar (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">C2F6 (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">CHF3 (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">H2 (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">C2H2 (99.6000%)</td>
			<td style="width:188px;">Praxair</td>
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			<td height="21" style="height:21px;width:307px;">Equipment</td>
			<td style="width:188px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td>Comments/Description</td>
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			<td height="21" style="height:21px;width:307px;">EVG 120 coater/developer</td>
			<td style="width:188px;">EVG</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">ASML PAS5500/80 waferstepper</td>
			<td style="width:188px;">ASML</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">SPTS &#937;mega 201 plasma etcher</td>
			<td style="width:188px;">SPTS</td>
			<td style="width:119px;"></td>
			<td>Used for Si and metal etching</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">SPTS &#931;igma sputter coater</td>
			<td style="width:188px;">SPTS</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Novellus Concept One PECVD</td>
			<td style="width:188px;">LAM</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Drytek 384T plasma etcher</td>
			<td style="width:188px;">LAM</td>
			<td style="width:119px;"></td>
			<td>Used for oxide etching</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">CHA Solution e-beam evaporator</td>
			<td style="width:188px;">CHA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">AIXTRON BlackMagic Pro CVD tool</td>
			<td style="width:188px;">AIXTRON</td>
			<td style="width:119px;"></td>
			<td>Carbon nanotube growth</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Philips XL50 scanning electron microscope</td>
			<td style="width:188px;">FEI</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Tepla 300</td>
			<td style="width:188px;">PVA TePla</td>
			<td style="width:119px;"></td>
			<td>Resist plasma stripper</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Avenger rinser dryer</td>
			<td style="width:188px;">Microporcess Technologies</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Leitz MPV-SP reflecometer</td>
			<td style="width:188px;">Leitz</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Renishaw inVia Raman spectroscope</td>
			<td style="width:188px;">Renishaw</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Agilent 4156C parameter spectrum analyzer</td>
			<td style="width:188px;">Agilent</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Cascade Microtech probe station</td>
			<td style="width:188px;">Cascade Microtech</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
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fabrication of low temperature carbon nanotube vertical interconnects compatible with semiconductor technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

The design of the measurement structure used in this work can be found in Figure 1. By employing such a structure the measurement of the CNT bundle resistance and the metal-CNT contact resistances can be determined accurately, as probe and wire resistances are circumvented. The resistance of the bundle is a measure for the quality and density of the CNT bundle. In order to determine the contact resistance bundles of different lengths should be measured.
A typical SEM image of ...

Watch this Scientific Journal Video about Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology at JoVE.com

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

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