High‐Aspect‐Ratio Parallel‐Plate Microchannels Applicable to Kinetic Analysis of Chemical Vapor Deposition

Abstract

growth rates within the 3D features are in proportion to the concentrations of fi lmforming species (i.e., a source precursor or intermediate species generated from a precursor), under the assumption that the deposition reaction on the surface follows fi rst-order reaction kinetics, as is common in most low-pressure (LP) CVDs. In most LP-CVDs, the mean free path of the fi lm forming species is much larger than the feature size, so the governing mass-transport mechanism is Knudsen diffusion, and the gas-phase reactions consuming them are negligible. Accordingly, the growth rate profi le in the depth direction of a 3D feature can be written as a concentration profi le [ 14 ] φwhere C is the concentration of the fi lm-forming species at position x , C t is the concentration at the top (e.g., the opening) of 3D features, x is a position from the bottom, and φ is the Thiele modulus. L and S / V are the depth and the surface-tovolume ratio of the feature, respectively. k s and D are the surface reaction rate constant and diffusion coeffi cient of the fi lm-forming species, respectively. As L , S , and V are determined by the geometry of the 3D features, k s and D are the only parameters that control the thickness profi le. Thus, if we know the relationship between k s / D and the process conditions, it is possible to predict the conformality within the target 3D structures. It is also helpful to know the maximum ARs feasible with the process used. [ 15 ] To determine k s / D , we have to identify the chemical compositions of the fi lm-forming species and evaluate their D and k s in the target 3D feature under the operative condition. To identify the fi lm-forming species, ab initio computational calculation methods of gas-phase chemistry have been developed, enabling accurate prediction of the time evolutions of gas-phase species. [ 16 ] D can be also determined accurately by an empirical method, considering the operative conditions (e.g., temperature and pressure) and geometrical information about the 3D feature (e.g., mean pore size and the structural complexity, such as the tortuosity factor). [ 17,18 ] However, k s is diffi cult to determine theoretically due to many uncertainties in the ab initio computational calculation of surface chemistry (e.g., a signifi cant error in estimation of vibrational frequencies [ 19 ] ). Thus, k s is often estimated by order-of-magnitude. [20][21][22][23] A method is proposed to fabricate a high-aspect-ratio (HAR) microchannel with a microscopic gap and AR of more than 1000:1 applicable to a test structure for kinetic analysis of chemical vapor deposition (CVD). It has a parallelplate structure and is formed concisely by sticking a planar Si substrate and a patterned Si or silicon-on-insulator (SOI) substrate fabricated by single-step etching, by clamping them. The resulting feature exhibits a uniform gap and smooth surface morphology along its depth. When CVD is conducted into this HAR microchannel, the sticking probability ( η ) of fi lm-forming species can be detected by analyzi...

Conformal and Stoichiometric Chemical Vapor Deposition of Silicon Carbide onto Ultradeep Heterogeneous Micropores by Controlling the Initial Nucleation Stage

“…The bare HAR microchannels were prepared using a method described elsewhere, 17 and are shown in Figure 1(a). The manufacturing procedure is as follows: part of the Si substrate is shallow-etched by reactive-ion etching, followed by stacking with another planar Si substrate.…”

“…Here, adding arbitrary underlayers to the vertical 3D test structures is not feasible because it imposes conformal deposition of the underlayer materials onto the micropores. By contrast, conformal deposition of underlayer materials onto a lateral HAR 3D test structure that we developed (denoted a microchannel 17 ) is possible because it is assemblable, and underlayers can be formed uniformly before assembling the microchannel. Note that numerous studies on conformal CVDs and ALDs to date assumed that the film formation started simultaneously at the beginning of the gas supply at all locations (i.e., at inlet and bottom of the trench, upstream and downstream of the reactor).…”

“…To design a conformal CVD process, a clear understanding of gas-phase and surface reaction kinetics and transportation of film-forming species is essential. New approaches for evaluation of the surface reaction kinetics of CVD (e.g., the Microcavity method , ) and the similar technique of atomic layer deposition (ALD) − have been developed using Si-based 3D test structures containing well-defined micrometer-scale trenches with ARs of over 100:1. − SiC-CVD has been conducted on Si microtrenches, and film-thickness decays along the trench depth have been analyzed to obtain the η values. − Combined with the time evolution of the gas-phase composition starting from an MTS/H 2 mixture, and calculated using elementary reaction simulations, − precise characterization of the surface reaction of SiC-CVD has been attempted. − ,, It has been shown that SiC-CVD involves three film-forming species: a high-η species (η ≈ 10 –2 ; probably CH 2 SiCl 3 ), a middle-η species (η ≈10 –4 ), and a low-η species (η ≈ 10 –6 ; MTS). ,, Furthermore, we have demonstrated conformal SiC-CVD via selective trapping of high-η species by using a sacrificial layer . Although the above experiments were conducted solely on heterogeneous Si surfaces due to the limited availability of test structures, the Si underlayers promoted the initial nucleation of SiC-CVD; thus kinetic studies on SiC-CVD during the continuous film-formation stages were successful.…”

Production of high‐aspect‐ratio rectangular‐lumen microtube by gas‐assisted microextrusion

“…Similarly, for micromold injection, the plastic devices bear quite high temperature and pressure in the thermal bonding step, which is also prone to collapse the rectangular channel. Though clamping can be used instead of permanent bonding to preserve the high-aspect-ratio channels, [23] it also makes the device complex, which limits the application of such microchannels compared to compact rectangular microtubes. Considering the intrinsic pullback of the above two-step methods for producing high-aspect-ratio rectangular microchannels, the airassisted microextrusion is very advantageous as a onestep method.…”

Nano crystalline diamond MicroWave Chemical Vapor Deposition growth on three dimension structured silicon substrates at low temperature

“…Application of the NCD deposition methods to industrial application requires deposition on structured substrates, with high aspect ratio features to determine the process's limitations. In addition, threedimensional patterned substrates are a useful tool for the study and modelling of CVD growth [15][16][17], which is still not fully understood. Floter et al [18] in 1995, reported a strong dependence of the nucleation density on the orientation of the surface when bias pre-treatment of structured Si substrate was employed.…”