Dry multilayer inorganic alloy thermal resist for...

Details Dry multilayer inorganic alloy thermal resist for... Dry multilayer inorganic alloy thermal resist for...

2000-07-17

2003-11-04

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Electron beam imaging

C430S270100, C430S312000

Reexamination Certificate

active

06641978

ABSTRACT:

TECHNICAL FIELD
The technical field to which this invention pertains is the creation of multilayered inorganic films which can react thermally to create structures for patterning layers applicable both to lithographic processes, such as those used in integrated circuit fabrication, and the making of images in thin films, such as is required in creating optical masks.
BACKGROUND OF THE INVENTION
Integrated circuit and semiconductor devices are built using microfabrication lithographic techniques to pattern many layers of conductors, insulators or semiconductors. In lithography a masking layer, called a resist, is deposited on the device substrate and exposed by optically projecting an image onto its surface. For optically sensitive resists (photoresists) a chemical reaction changes the resist. Typically after development the areas exposed to the light will be removed, while those not exposed will remain creating a raised pattern of resist on the surface (a reverse or negative resist process is also possible). This raised pattern protects parts of layers below so that when exposed to an etching environment (for example acids, etching gases or plasmas or ion beams) the areas under the remaining resist are protected from etching, while those without resist are preferentially removed. This resist layer is then striped or removed leaving a transferred raised pattern from the mask in the layer on the substrate. The patterned layer may be used directly as defined or in turn may be used to pattern a layer below it on the substrate, either for additional etching processes, or other operations (for example creating doped patterns with impurities, or growing patterned oxide layers). Repeated processes of layer deposition and resist lithographic patterning are used to create everything from simple single layer structures to complex integrated circuits.
Indeed the very photomasks used in the optical lithographic process are created by directly writing with a focused laser or electron beam spot a pattern into a resist on an optically transparent substrate, usually coated with a thin absorbing layer. That resist pattern then defines the etching of the lower layer, patterning the absorbing and non-absorbing areas on the transparent substrate creating the mask used in other lithographic processes.
Current lithographic processes typically use organic based photoresists which are applied as liquids to a substrate or wafer which is then spun at high speeds so that interaction of rotational, gravitational forces, surface tension and viscosity creates a controlled thickness of resist. The film is then baked to remove solvents before the photolithographic exposure. The photoresist is then developed using a wet chemical processes that dissolves the unwanted resist away. After the lithographic etching processes the photoresist is stripped (often in an oxygen plasma etcher or with liquid strippers). However it is very hard to remove all the organics added by the resist, and there is always the danger of other outside contaminants. Hence very aggressive chemical cleans, such as the industrial standard RCA clean, must be used to remove these organics. This combination of steps: cleaning, deposition or growth of a layer, photolithographic definition, etching and resist stripping is repeated for each layer and pattern to make the final circuit of even the simplest device. These cleaning processes are very time, energy and material consuming. Resist contamination left behind is a common source of defect creation in integrated circuit processes.
In contrast to the wet organic photoresists and their related cleanups most other processes in modern microfabrication are dry, often vacuum based procedures. Many types of deposition (plasma sputtering, Chemical Vapour Deposition (CVD), ion implant) and etching processes (Plasma, Reactive Ion Etching (RIE)) use low-pressure techniques that introduce much fewer contaninants into the processes.
In addition to contamination problems organic resists are very wavelength sensitive. Current optical exposure systems use Ultra Violet (UV) Excimer lasers operating at 248 nm wavelength as the light source, producing short (5-20 nsec.) pulses of high power for exposure to create the small structures needed. Resists for the current 248 nm wavelengths will not work for the future generations of exposure systems which currently plan to use 193 nm, 150 nm or even shorter wavelengths to make structures smaller than 0.1 microns. Furthermore, at those shorter wavelengths and high power pulses many organic resist materials are damaged (photoablated) because the energy of the UV light tears apart the molecules of the organics. This photoablation can cause problems with materials deposited on the exposed optics.
These problems have suggested that a switch to inorganic based dry resist processes would provide significant advantages. Firstly, a dry resist process would permit devices to be fabricated mostly in a vacuum based environment, allowing transfer from a dry based deposition (for example sputter deposition) to the dry inorganic resist coating, to the exposure, etching (say plasma etching) to the resist stripping processes. This would keep devices much cleaner, offering less source of contamination, and hence potentially reducing the rate of defects. Secondly the removal of the organics from the resists may significantly reduce the number of cleans needed in process steps with savings in time, materials and energy. Thirdly many organic resists are thermally activated, that is the optical exposure creates a local temperature rise, which in turn creates the inorganic reaction for the development. Thermal resists, especially those using metal-based inorganics, can be less wavelength sensitive and operate at very short wavelengths. Fourthly metal-based inorganics can avoid the photoablation effect down to very short wavelengths. Fifthly thermally reacted inorganics can show different optical characteristics after exposure than before. Thus the exposed areas can be identified before the development processes. This allows errors in exposure to be corrected.
Finally Gelbart and Karasyuk have shown that with thermal resists and a special multiple exposure modification existing optical exposure systems could substantially decrease the minimum size structures they can build. Current exposure systems are diffraction limited by their optics and need to use shorter wavelengths (193 nm and 150 nm) to pattern structures below 0.1 to 0.07 microns. However Gelbart and Karasyuk show that by use of a multiple exposure modification to existing (248 nm) systems resolution below 0.1 microns may be possible and below 0.1 micron with shorter wavelengths. This multiple exposure system only works for resists that do not follow the law of reciprocity. The law of reciprocity says that total exposure is integrated over time, meaning that two exposures at half-threshold have the same outcome as one exposure at full threshold; in either case the resist will be fully developed. Thermal resists react when the resist is heated above a certain temperature and do not follow reciprocity. Thus, if a thermal resist is heated to just below the threshold, allowed to cool, and then heated a second time to the same point, it will remain unexposed. In a microfabrication exposure system, UV light arrives in pulses of a few tens of nanoseconds spaced hundreds of microseconds apart. This means that there is sufficient time for the material to cool between UV exposures. By comparison standard photoresists follow the law of reciprocity and a multiply exposure system produces the same result as a regular exposure.
While thermal inorganic resists offer these advantages previous art has shown these resists have, until now, had significant problems, especially with their sensitivity. Janus in U.S. Pat. No. 3,873,341 proposed an amorphous iron oxide based film as a thermal resist. When heated by the optical exposure system the amorphous iron oxide is crystallized if the local temperature exceeds 820° C. The crystallized iron oxide area

Affiliated with

Also associated with

Rating

Dry multilayer inorganic alloy thermal resist for... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dry multilayer inorganic alloy thermal resist for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dry multilayer inorganic alloy thermal resist for... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3148707