摘要:

The ability to create patterns of specific silane monolayers by deep ultraviolet lithography has been previously demonstrated, and preliminary attempts have been made to use these patterns to control adhesion and outgrowth of neurons and other types of mammalian cells. Here we report characterization of the mechanisms involved in these photoinitiated processes and their utility in various strategies for creating patterns for biologically relevant systems. We have divided the mechanisms into three general classes. The first is surface photolysis of the silane monolayer, which appears to proceed by a purely photochemical mechanism. The second mechanism involves direct photochemical conversion of a terminal functional group on a silane monolayer into a species with altered properties, e.g., the conversion of a thiol to a more oxidized form that inhibits the subsequent adhesion of proteins. The third is a photolytic degradation of the monolayer. The mechanisms have been probed by x‐ray photoelectron spectroscopy, ellipsometry, and wettability measurements. One result of these investigations has been the development of better strategies to create patterns. Controlled growth of hippocampal neurons on high resolution patterns is presented as demonstration of the efficacy of these strategies in spatially dictating cell adhesion. These results have important implications in designinginvitroculture systems to study well‐oriented neuronal systems.

ISSN:0734-2101    

DOI:10.1116/1.578844

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Reactive ion etching processes, currently in use in microstructure fabrication, often use more than one feed gas and more than one reactive etching specie. An example is the use of gases containing both chlorine and fluorine. These processes have been developed empirically with little understanding of the detailed surface science. Directed beam measurements have been carried out using mixed chlorine‐fluorine chemistries and an unexpected enhancement of the F‐atom etching of Si by molecular chlorine has been observed.  

ISSN:0734-2101    

DOI:10.1116/1.578845

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Application of the method of characteristics to the general case of ion or plasma etching is reviewed, yielding a topography evolution algorithm which is simultaneously accurate, flexible, and efficient. The behavior of initial slope discontinuities is computed by mapping the characteristic locus in the region of the discontinuity and removing any closed loops which appear in the locus. The new method is shown to produce profiles which satisfy the required entropy and jump conditions for any given variation of etching rate with surface slope, while allowing the use of longer integration time steps than conventional methods. Previously published ‘‘string’’ algorithms [W. G. Oldham, S. N. Nandgaonkar, A. R. Neureuther, and M. O’Toole, IEEE Trans. Electron DevicesED‐26, 717 (1979); A. R. Neureuther, C. Y. Liu, and C. H. Ting, J. Vac. Sci. Technol.16, 1767 (1979)] are compared to the new method, and are shown to be capable of generating correct profiles only under limited conditions, i.e., for specific etching behaviors or if slope discontinuities are artificially removed.

ISSN:0734-2101    

DOI:10.1116/1.578846

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

To investigate the reaction layer dynamics of ion‐assisted etching we have measured the time response of product formation in an ultrahigh vacuum beam‐surface experiment on a time scale ranging from 100 μs to 1000 s. Both the step function response and the delta function response are investigated. For the latter the pseudorandom cross correlation method is used. The system investigated is the classic Si(100)/XeF2/Ar+example, at low flux conditions of 0.6 ML/s XeF2and 0.04 ML/s Ar+ions at 1 keV energy. We observe a consistent picture of the fourfold action of the bombarding ions. First, on a 1 ms time scale and shorter, the release of tightly bound intermediate radical species such as SiF and SiF2by physical sputtering, i.e., by momentum of the impinging ions, is the main effect. Second, on a time scale of 40 ms, we observe ion‐enhanced formation of SiF4, most likely by the influence of ion bombardment on a rate limiting step in the reaction chain such as the formation of SiF4from SiF3. Third, on a time scale of 4 s, there is a redistribution of intermediate SiFxproducts in the reaction chain, both in depth profile and in absolute density. Finally, on an even longer time scale, detectable after some 10 s at an ion bombardment of 0.04 ML/s, the production of vacancies and/or broken bonds as reactive sites deep in the substrate becomes important, as observed by a long‐term enhanced etch rate after switching off the ion beam. The results are consistent with a model that for low temperatures (T<600 K) the disproportionation reaction, 2 SiF3→SiF4+SiF2, is the rate limiting step, while at high temperatures (T≳700 K) the reaction step leading from SiF2to SiF3plays this role.

ISSN:0734-2101    

DOI:10.1116/1.578847

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A systematic study of etching of Si(100) and Si(111) and Ar+bombarded Si(100) (surface with defect sites) with chlorine has been carried out. We have compared the reactivity of atomic and molecular chlorine, and studied the effect of translational and vibrational excitation of the etchant on the etch rate. Similar etch rates were obtained on the Si(100) and Si(111) single crystal surfaces. On both surfaces the major etch products were SiCl4atTs<500 K and SiCl2atTs≳600 K. Some SiCl desorption was obtained atTs≳1100 K. We have outlined the conditions under which the etch rate, at constant incident flux, is adsorption and desorption limited. On the Si(100) and Si(111) surfaces we found that when the etch rate is reaction limited, higher etch rate can be obtained with atomic chlorine than with molecular chlorine. In the adsorption limited regime, translational excitation of both atomic and molecular chlorine results in a higher etch rate than that obtained with slow atomic and molecular chlorine. Vibrational excitation of Cl2does not result in an enhancement of the etch rate on the single crystal surfaces studied. In the desorption limited regime the etch rate is primarily determined by the surface temperature. The nature of the etchant particles does not have a significant effect. On Ar+bombarded Si(100), we obtained a small increase in the etch rate with translationally and vibrationally excited Cl2, and comparable enhancement is obtained with Cl2that is only translationally excited. The difference in the etch properties of the single crystalline and Ar+bombarded silicon surfaces points to the importance of surface defects in etching. The present results show that at room temperature the low etch rate of silicon single crystal surfaces with chlorine, as compared to etching with fluorine, is due to the low formation rate of volatile surface products.

ISSN:0734-2101    

DOI:10.1116/1.578848

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Etching of high aspect ratio patterns induces a phenomenon known as reactive ion etching (RIE) lag, i.e., a large feature etches faster than a smaller one. This effect is studied for oxide etched in a high density plasma excited by electron cyclotron resonance using different fluorocarbon gases. The magnitude of the RIE lag is correlated with the deposition rate of fluorocarbon film on an unbiased sample, showing that chemical effects are important to understand the mechanisms of RIE lag in high density plasmas.

ISSN:0734-2101    

DOI:10.1116/1.578849

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Etching of high aspect ratio patterns induces reactive ion etching (RIE) lag. This effect is studied for oxide features etched in a high density plasma excited by electron cyclotron resonance using different fluorocarbon gases. A new RIE lag model is proposed which depends on the assumption that the oxide etch rate is, as on a blanket sample, strongly influenced by the deposition of fluorocarbon film on the oxide surface during the etching process.

ISSN:0734-2101    

DOI:10.1116/1.578850

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A combined instrument has been developed for the investigation of plasma deposited or etched surfaces which couples a versatile chemical reaction chamber on‐line with a surface analytical system. The plasma can be generated either by microwave (2.45 GHz) or radio frequency (13.56 MHz) excitation, with and without magnetic field assistance. The surface analytical part of the instrument is equipped with monochromatized x‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry. Auxiliary energy or mass spectroscopic techniques can be applied where necessary. All spectroscopies can be performed while the sample is heated or cooled. We report on the general design and the performance of the instrument, as well as first applications in the fields of polymer analysis and bioengineering.

ISSN:0734-2101    

DOI:10.1116/1.578851

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Amorphous hydrogenated carbon (a‐C:H) films prepared by plasma polymerization can contain chemical species due not only to the process gas species, but species from prior processes in the deposition chamber. Our studies showed that standard O2etching/ cleaning processes done prior to plasma film formation will affect future film deposition rate measurements and carbonyl group formation. Additionally, substrate etching by polymer forming gas species is shown through the 956 cm−1negative peak in the IR spectrum.

ISSN:0734-2101    

DOI:10.1116/1.578852

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The photochemistry of solid, free‐standing films of poly(tetrafluoroethylene) (PTFE) and poly(hexafluoropropylene–tetrafluoroethylene) (FEP) was investigated by monitoring the neutral photodesorption products produced upon irradiation with synchrotron radiation (5–50 eV). CF3, C2F5, C3F5, C3F7, and C4F7were the predominant species observed in the mass spectra of the irradiated polymers. Oligomers at least as large as 293 amu (C7F12) were also detected. Distinct differences are observed in the photodesorption yields and time responses of the yields based on the energy of the initial excitation. An edge jump at 22 eV in the photon‐stimulated desorption spectra of both PTFE and FEP films is assigned to the ionization of the C(2s) states of the polymers. The energy dependence of the photodesorption yields is accounted for by considering two separate reaction pathways.

ISSN:0734-2101    

DOI:10.1116/1.578853

出版商:American Vacuum Society    

年代:1994

数据来源: AIP