摘要:

The production of plasma debris ejected from various solid targets heated and ionized by intense KrF laser pulses was studied. The plasma is produced by focusing a train of 50 ps KrF laser pulses to an 8‐μm‐diam spot on the surface of solid tape targets. The plasma conditions are those of interest for the generation of a point source of the keV and sub‐keV x rays for microlithography (Cu and Fe targets) and x‐ray microscopy (plastic targets). Experimental measurements of the amounts of debris produced, the statistical distribution of the debris size, and angular distribution in vacuum are presented. The results of similar measurements in a background gas of helium are also presented together with measurements of the stopping power of the gas. A large flux of micron and submicron size particles is generated in vacuum even when employing thin tape targets. The introduction of a background gas reduces the damaging influence of such particles dramatically but only if enough path length exists to stop the particles. Theoretical calculations have been carried out of the stopping power of the background gas based on Stokes law and the Newtonian theory of deceleration of particles in gas.

ISSN:0734-2101    

DOI:10.1116/1.580070

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Laser evaporation and laser ablation methods were applied to the preparation of polytetrafluoroethylene (PTFE) thin films. In the case of the laser evaporation method, PTFE targets were evaporated by a continuous wave (cw) CO2laser (10.6 μm), and fluorocarbon thin films were formed at a deposition rate of as high as 2 μm/min for a laser power of 10 W. The chemical composition and structure of the deposited film corresponded to those of a PTFE target, which was confirmed by x‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy analyses. In the laser ablation method, PTFE targets were ablated by a XeCl excimer laser (308 nm). It is found that the deposited films contained a small amount of fluorine atoms on the surface. From these experiments, the successful formation of PTFE thin films was demonstrated for the first time using cw CO2laser evaporation method.

ISSN:0734-2101    

DOI:10.1116/1.580071

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The UV laser (λ=308 nm) ablation of silicon wafers in 1 mbar ambient ammonia results in the deposition of pure and uniform film of amorphous silicon nitride. At low pressures of NH3(of several to several tens of μbar), the deposited films are a mixture of amorphous silicon nitride, amorphous nonstoichiometric silicon nitride, and amorphous silicon. The contamination with oxygen is low and is more evident at lower pressures. At ammonia pressures 0.1–1 mbar, the films also contain a certain fraction of hydrogen. Droplets of polycrystalline Si cover the surfaces of some films. This phenomenon is more important at smaller target‐collector distances and lower pressures of ambient NH3.

ISSN:0734-2101    

DOI:10.1116/1.580072

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A large areac‐axis oriented YBa2Cu3O7−xthin film was grown on a 3‐in. LaAlO3substrate using off‐axis excimer laser deposition. Substrate rotation and laser beam scan on a target enabled thickness variations less than ±4% over the 3‐in. film. The superconducting transition temperature was 88.4–90.8 K and the critical current density was in excess of 106A/cm2at 77 K under the zero magnetic field. The surface was smooth with few outgrowths, and the density of particles was 104/cm2, which is 1/100 less than that yielded on‐axis laser deposition.

ISSN:0734-2101    

DOI:10.1116/1.580073

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The Si atom density at the 3p23P2level in electron cyclotron resonance SiH4/H2and SiH4/Ar plasmas was measured as a function of total pressure from 0.6 to 3.3 Pa at a microwave power of 400 W and a SiH4flow rate of 6 sccm using ultraviolet absorption spectroscopy. Parent SiH4molecules in SiH4/H2and SiH4/Ar plasmas were found to be considerably dissociated using infrared diode laser absorption spectroscopy. The Si atom density in the SiH4/H2plasma was larger than that in the SiH4/Ar plasma, which was quite different from that in the capacitively coupled rf SiH4plasmas. Behaviors of the Si atom density are discussed on the basis of the rate equation for Si atoms. It was concluded from a comparison of the behavior of the density and generation rate of Si atoms that the diffusion loss was comparable to the reaction loss in the removal process of Si atoms in the case of H2dilution, while the reaction loss was dominant in the case of Ar dilution.

ISSN:0734-2101    

DOI:10.1116/1.580074

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Gas phase reactions of CFx(x=1−3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma were investigated at 300 W and a CHF3pressure of 0.4 Pa by adding O2to CHF3using infrared diode laser absorption spectroscopy and actinometry, respectively. By adding a small amount of O2to CHF3, the CF and CF2radical densities rapidly decreased, while the CF3radical density rapidly increased but then decreased with further addition of O2to CHF3. These reaction mechanisms in the plasma were evaluated on the basis of measurement results of CFx(x=1−3) radical and F atom densities. Under the same conditions as the measurements of radical densities, the etching rates of Si and SiO2were measured. Furthermore, the etched Si surfaces were also analyzed with x‐ray photoelectron spectroscopy. The etching mechanisms for Si and SiO2in the CHF3/O2ECR plasma were investigated by connecting these etching characteristics on Si and SiO2with the behaviors of CFx(x=1−3) radical and F atom densities. The Si etching rate was affected primarily by the concentrations of the CF and CF2radicals and F atoms in the plasma.

ISSN:0734-2101    

DOI:10.1116/1.580075

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Gas phase reactions of CFx(x=1–3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma have been investigated at 300 W and a CHF3pressure of 0.4 Pa by adding H2to CHF3. The behaviors of CFxradical densities were measured using infrared diode laser absorption spectroscopy, while F atom density was estimated with actinometry. Furthermore, the composition of fluorocarbon films deposited on the chamber walls in the CHF3/H2ECR plasma has been investigated with x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. On the basis of measurement results, the correlation between the characteristics of fluorocarbon films and the behaviors of radicals in the plasma has been investigated. The CF radical density was found to be changed by the variation of the composition, in particular F/C ratio, of the films deposited on the chamber walls. Under the same conditions as the measurements of radical densities, the deposition rates of fluorocarbon films formed on the substrate set in the downstream plasma region were measured. The behavior of CF radical density followed the deposition rates, which suggested that the CF radical played an important role for the formation of carbon‐rich fluorocarbon films in the CHF3/H2ECR plasma.

ISSN:0734-2101    

DOI:10.1116/1.580076

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The electric field distribution for an electron cyclotron resonance (ECR) cavity was measured using microcoaxial probes. Typically, two to three resonant modes are found for each plasma condition and longer cavity length provides a more stable plasma. A 30° periodicity is seen in the angular dependence of the electric field, and the peak right across the microwave input probe becomes more dominant at shorter cavity length. The longitudinal dependence of the electric field has a peak close to the middle of the cavity, and the measured field patterns agree well with the theoretical prediction. The resonant modes were identified by fitting the experimental measurements to linear combinations of electromagnetic resonant modes with characteristic length close to the cavity height. Using this method, all the modes in this ECR cavity were found to be multimode, and the resonant mode with the longest cavity length was found to be a mixing of TE314and TE611modes. Significant changes in the electric field patterns are seen when the ECR cavity is out of tune. The sensitivity of electric field distribution to ECR cavity tuning allows process control to be implemented by monitoring the changes in the electric field intensity of just a single probe position. Despite the variations in electric field distribution for different resonant modes, uniformity of photoresist etching across 15‐cm‐diam wafer is better than 5%. The good uniformity of the photoresist etching suggests that the plasma density at the wafer is uniform, probably due to the diffusion of the reactive species from the ECR source.

ISSN:0734-2101    

DOI:10.1116/1.580077

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

In this article we extend our previous analysis of a cold beam tube vacuum in a superconducting proton collider to include ion desorption in addition to thermal desorption and synchrotron radiation induced photodesorption. The ion desorption terms introduce the possibility of vacuum instability. This is similar to the classical room temperature case but is now modified by the inclusion of ion desorption coefficients for cryosorbed (physisorbed) molecules which can greatly exceed the coefficients for tightly bound molecules. The sojourn time concept for physisorbed H2is generalized to include photodesorption and ion desorption as well as the usually considered thermal desorption. The ion desorption rate is density dependent and divergent so at the onset of instability the sojourn time goes to zero. Experimental data are used to evaluate the H2sojourn time for the conditions of the Large Hadron Collider (LHC) and the situation is found to be stable. The sojourn time is dominated by photodesorption for surface densitys(H2) less than a monolayer and by thermal desorption fors(H2) greater than a monolayer. For a few percent of a monolayer, characteristic of a beam screen, the photodesorption rate exceeds the ion desorption rate by more than two orders of magnitude. The photodesorption rate corresponds to a sojourn time of approximately 100 s. The article then turns to the evaluation of stability margins and the inclusion of gases heavier than H2(CO, CO2, and CH4), where ion desorption introduces coupling between molecular species. Stability conditions are worked out for a simple cold beam tube, a cold beam tube pumped from the ends, and a cold beam tube with a coaxial perforated beam screen. In each case a simple inequality for stability of a single component is replaced by a determinant that must be greater than zero for a gas mixture. A connection with the general theory of feedback stability is made and it is shown that the gains of the diagonal uncoupled feedback loops are first order in the ion desorption coefficients whereas the gains of the off‐diagonal coupled feedback loops are second order and higher. For this reason it turns out that in practical cases stability is dominated by the uncoupled diagonal elements and the inverse of the largest first‐order closed loop gain is a useful estimate of the margin of stability. In contrast to the case of a simple cold beam tube, the stability condition for a beam screen does not contain the desorption coefficient for physisorbed molecules, even when the screen temperature is low enough that there is a finite surface density of them on the screen surface. Consequently there does not appear to be any particular advantage to operating the beam screen at a high enough temperature to avoid physisorption. Numerical estimates of ion desorption stability are given for a number of cases relevant to the LHC and all of the ones likely to be encountered were found to be stable. The most important case, a 1% transparency beam screen at ∼4.2 K, was found to have a stability safety margin of approximately 17 determined by ion desorption of CO. Ion desorption of H2is about a factor of 75 less stringent than CO. For these estimates the beam tube surface was assumed to be chemically cleaned but otherwise untreated, for example, by a vacuum bakeout or by glow discharge cleaning.

ISSN:0734-2101    

DOI:10.1116/1.580078

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Ion beam assisted deposition offers a novel and unique process to prepare diamond‐like carbon (DLC) films at room temperature with particularly good interface adhesion. This advantage is explored to deposit highly wear resistant DLC coating on AISI 52100 steel. Various bombarding species and energy are examined to optimize the process. Infrared, Raman, Auger electron spectroscopy spectra, and hardness measurements are used to characterize the structure and properties of DLC films. The friction and wear behavior of DLC films are systematically investigated by performing extensive experiments in different testing styles. It is disclosed that by means of a dynamic mixing of atoms in interfaces, a pure metal intermediate layer can tremendously improve the tribological properties of DLC films on 52100 steel. The results are optimistic and may lead to useful applications.

ISSN:0734-2101    

DOI:10.1116/1.580079

出版商:American Vacuum Society    

年代:1996

数据来源: AIP