摘要:

The successful application of x‐ray lithography to a manufacturing process requires a detailed understanding of the image formation process. In a series of articles, a theoretical study of the optical processes involved in the definition of the image in proximity printing has been presented. In addition to the diffraction process, it is included here that the image formation in the very near field (microgaps) due to the guiding effects in the absorber which alters the boundary condition for diffraction and thus changes the final image pattern. Also presented here is an experimental study designed to verify the predictions of the models of image formation. Preliminary result shows a very large depth‐of‐focus for 0.25 μm features.

ISSN:1071-1023    

DOI:10.1116/1.585901

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

A resonance frequency measurement technique has been used to measure the stress at temperature of plated gold films on x‐ray mask membranes over the temperature range of 90–525 K. Room temperature tensile stress increases are observed after above room temperature anneals. Stress relaxations are measured after liquid nitrogen cools. The tensile stress increases and the stress relaxations depend upon the microstructure of the plated films. Focused ion beam imaging shows that grain growth is the dominant mechanism for the tensile stress increases observed for fine grained as‐plated gold films.

ISSN:1071-1023    

DOI:10.1116/1.585902

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

In this article some of the results on growth and application of SiC thin films for x‐ray mask substrates are presented. Aspects of the process that are relevant to the film’s use for x‐ray masks, such as growth defects, roughness, stress, and growth rate versus gas composition, growth temperature, and flow rates are discussed. There are definite regions in composition space within which the growth rate is useful and the growth defect population is minimized. The film’s internal stress is generally tensile and increases with growth temperature, although it can be made compressive by the appropriate choice of growth parameters. The SiC film’s surface roughness also decreases with growth temperature, and growth temperature/gas composition combinations exist which yield smooth films (roughness less than 200 Å) with a desirable stress (less than 300 MPa). Our SiC films are typically 20–500 Å rough (peak‐to‐peak), tensile with a stress in the range of 100–500 MPa, and grow at a nominal rate of 0.8 μm/h. The films appear to be radiation hard up to incident doses of approximately 25 KJ/cm2. The chemical‐vapor deposition system is a cold‐wall‐type with a temperature range of 1423–1673 K. The growth takes place at pressures of 100–700 Torr in a H2–C2H4–SiH4atmosphere.

ISSN:1071-1023    

DOI:10.1116/1.585903

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Most analyses of the effects of diffraction and source coherence on image quality in proximity x‐ray lithography have used Kirchhoff boundary conditions and scalar diffraction theory. In this article we treat the x‐ray absorber as a lossy dielectric and employ the vector form of Maxwell’s equations to calculate image intensity as a function of position for lines, spaces, and gratings, at 100 nm linewidths and below. We show that vector and scalar theories give different results. Simulations are done for two point sources (CuLand an Fe‐plasma) so that calculations could be compared with our experimental results. Agreement was excellent for 80 and 50 nm features at relatively large gaps. We define image contrast and show that, contrary to common intuition, it is enhanced (and spurious ringing is suppressed) as penumbral blurring is increased, reaching a maximum when the extent of blurring is somewhat larger than the minimum feature size.

ISSN:1071-1023    

DOI:10.1116/1.585904

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The implementation of x‐ray lithography requires that in‐plane distortion caused by absorber stress be eliminated (i.e., be made less than ∼10% of minimum feature sizes). As a rule of thumb, for large‐area membranes (i.e., ≥30 mm diam) stress‐induced distortion is negligible if absorber stress is kept below 108dynes/cm2(10 MPa). The most common way of determining absorber stress on membranes is to measure the out‐of‐plane deflection in a Linnik or Mireau interferometer. Out‐of‐plane deflection is caused by absorber bending moment. It is possible, in principle, for an absorber to have a stress that varies with depth in such a way that bending moment is zero but net in‐plane stress is not. To determine if there is a one‐to‐one correspondence between out‐of‐plane and in‐plane distortion, and in order to check the validity of Yanof’s model, we have developed two methods of measuring in‐plane distortion: a moiré method and a holographic interferometry (HI) method. Both require that one etch or lift‐off a grid on one surface of the x‐ray mask membrane using holographic lithography and reactive‐ion etching. On the opposite surface an x‐ray absorber is deposited and patterned. In the moiré method another holographic exposure is performed, at the same spatial period as the grid, but at a small azimuthal rotation. After development, a clear moiré pattern is formed, from which one can calculate the in‐plane distortion and corresponding absorber stress. In the HI method, the mask is placed in the standing wave produced by two intersecting laser beams. A fringe pattern can then be seen on a charge coupled device camera. The HI method provides a higher sensitivity to in‐plane distortion than the moiré method and should enable one to measure in‐plane strain at a level corresponding to in‐plane distortion below 1 nm for typical pattern geometries.

ISSN:1071-1023    

DOI:10.1116/1.585905

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

During an x‐ray lithography proximity exposure x rays generate electrons in the resist which deposit energy along a finite range. This range combines with diffraction spreading to degrade the image resolution. The component of resolution arising from electron range is often taken as the Grun range of the most copiously generated photoelectrons, about 0.1 μm at an exposure wavelength of 10 Å. Although some experiments have shown much better resolutions, there is a widespread belief that photoelectron range limits resolution to about 0.1 μm. We have analytically modeled the distribution of energy deposited by Auger and photoelectrons. Near an edge the distribution is well‐fit by an error function. The standard deviation of this error function, which we define as the ‘‘effective range,’’ is about 0.01 μm at 10 Å in poly(methylmethacrylate) (PMMA) resist. For all energies of interest to x‐ray lithography the effective range of the electrons is much smaller than the Grun range, explaining the high‐resolution results. It is diffraction which dominates the resolution of conventional x‐ray lithography. Consequently, reducing the gap in proximity printing should produce resolutions far below 0.1 μm, while retaining all the latitude inherent in the x‐ray lithography process.

ISSN:1071-1023    

DOI:10.1116/1.585906

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

X‐ray projection lithography has recently been explored as a method for the manufacture of ≤200 nm linewidth integrated circuits. A method was previously described [J. Appl. Phys.71, 2993 (1992)] whereby projected lithographic images can be formed with x rays by means of a transmission hologram. The form of the hologram is computed by an algorithm which eliminates the unwanted signals normally present as systematic errors in in‐line holographic images. Such an approach to projection x‐ray lithography requires an x‐ray beam with very little coherence and is thus compatible with high wafer throughput schemes; in addition, image fidelity remains high even when moderately small contaminant particles block the light from small regions of the hologram. Previous example calculations involved using 5 nm x rays to illuminate a 0–1 μm thick carbon hologram located 200 μm from the wafer to produce simulated 0.06 μm linewidth images with good fidelity and with 6 μm depth of field. Presented here are simulations involving holographic masks made of 0–1 μm of tungsten operating at 1 nm wavelength with 50 μm mask‐to‐wafer gap. Such a configuration can be viewed as a future extension of the existing technology of proximity x‐ray lithography to linewidths as small as 0.02 μm.

ISSN:1071-1023    

DOI:10.1116/1.585907

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We have developed a new technique for removing opaque defects on soft x‐ray projection lithography reflection masks using ion beam etching. This technique clears the defect without damaging the multilayer mirror or introducing an absorptive element into the multilayer. Our procedure uses a thin, Si overcoat to protect the multilayers from the kinetic energy of the ion beam, reduced ion beam energy, and a Ar ion beam to avoid absorption losses. A Si ion beam could also be used in this process.

ISSN:1071-1023    

DOI:10.1116/1.585908

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We describe some key aspects of proximity x‐ray technology currently being developed at AT&T, from mask fabrication to wafer patterning. The masks are primarily based on polycrystalline Si membranes, 1 μm thick, which are formed directly on optically flat glass disks. A tungsten absorber layer is deposited on the membranes by radio‐frequency diode sputtering, withinsitustress control in the deposition chamber so that stresses ≤10 MPa are routinely achieved. Patterns are defined in an organosilicon negative resist, P(SI‐CMS), using an electron beam writing tool and a neural network based proximity correction algorithm. The patterns are transferred into metallic absorber layers by reactive ion etching in a parallel plate plasma system. Using the above procedure, we have fabricated masks with 0.25 μm features and also some test patterns with lines and spaces as small as 0.1 μm. X‐ray exposures were done with a Hampshire 5000P point source stepper, using AZ PF‐114 resist from Hoechst–Celanese.

ISSN:1071-1023    

DOI:10.1116/1.585909

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We report a detailed description of x‐ray mask technology based on SiC membrane and tungsten absorber. Amorphous SiC films were prepared using either a 100 kHz plasma‐enhanced chemical vapor deposition (PECVD) system (allowing a high throughput) or a laser ablation deposition (LAD) technique. The PECVDa‐SixC1−x:H films have a maximum Si–C bond density atx=0.5, a hydrogen content of 27 at. % and a high‐compressive stress (1 GPa). The LAD films are stoichiometric, hydrogen‐free, and under high‐compressive stress (1.4 GPa). In order to achieve the tensile stress range (20–40 MPa) required for membrane fabrication, we developed a well‐controlled rapid thermal annealing (RTA) process. At 633 nm, the resulting PECVD and LAD membranes have an optical transparency of 75% and 40%, respectively, and their corresponding biaxial Young’s moduli are 250±30 and 360±60 GPa. A novel approach using RTA for ‘‘fine tuning’’ of the tungsten stress is also proposed. Low stress (≤10 MPa) is obtained for W layers initially under compressive stress lower than 300 MPa. Finally, using an e‐beam patterning process based on a single resist layer and reactive ion etching for the pattern transfer, x‐ray masks with linewidths down to 100 nm were developed.

ISSN:1071-1023    

DOI:10.1116/1.585910

出版商:American Vacuum Society    

年代:1992

数据来源: AIP