V V Aristov, S V Dubonos, R Ya Dyachenko, B N Gaifullin, V N Matveev, H Raith*,
Institute of Microelectronics Technology, Academy of Sciences,
A technology micro/nanostucturing based on e-beam lithography, plasmo-chemical etching and electrochemical deposition is developed. It allows to create structures in organic resist on substrate of predefined profile with vertical sizes in range 50nm-5um and 50nm-1mm in lateral direction (Fig.3). Metal replicas was created by electro-chemical deposition (Fig.4). The replicas were used then as a stamp for fast transferring of relief in soft material (polymer) (Fig.5).
We expect application in optoelectronics, optical processing, creation of zone plates and other diffractive optical elements (calculated holograms).
We submit a method for creation of structures with designed profile in a resist, first results on transferring a profile in a substrate and copying (printing) in soft material (polymers). By this way a designed profiles with vertical sizes in range 10nm-1000nm and with lateral sizes in range 10nm-1mm may be created.
Today there is an increasing demand for producing real three-dimensional structures, such as blazed gratings, Fresnel lenses, diffractive optical elements, computer generated holograms, lens arrays and etc. In these cases the total area has to be exposed with a continuously variable dose, which of course needs proximity correction as well - but this was not available up to now. All established methods for proximity correction aim to correct for two-dimensional structures. Most of them just take care for an absorbed dose of 100% inside the exposed structures not considering the dose distribution outside, which is below the 100% level. Characteristic sizes of the optical elements mentioned above belong to range 100nm-10um so proximity effect correction is a crucial point of the whole design and technological chain.
The method of "Simple Compensation" introduced by Aristov et al  has been developed to a very powerful tool for correction and simulation of proximity effects [2,3,4] which led to the widely used software package "PROXY".
If we assume as usual the proximity function I(x,y) consists of two Gaussians with convential parameters , and
If a structure Q is presented as a set of rectangles (polygons) Qi (Q=Q1+Q2+Q3+ ...) and absorption dose distribution D(x,y) is defined as D(x,y)=D0=100% inside structure Q and zero outside then the method of "Simple Compensation" for exposure T at point (x,y) may be written (in equivalent to  form)
An aim of the above correction procedure is to obtain D(x,y)=D0=100% inside structure Q and as less as possible outside.
We extended this numerical calculation method for 3D correction , where each element of the exposed structure is assigned by a required (designed) absorbed dose D. Proximity 3D correction leads then to an exposure dose distribution T allowing to produce on all places the required absorbed dose. "3D correction" looks very similar to the "simple compensation" and consists of sequential steps. "3D correction" establishes that dose is not constant inside structure but is actually spatially distributed D(x,y).
On practice we proceeded as following. Using graphical editor a stepwise relief was design, H(x,y) As an example (Fig.1a) consider a simple structure representing a phase graiting designed for polymer (PMMA) with refractive coefficient n=1.49. Then required absorbed dose D(x,y) just by considering the resist contrast was calculated (thick line on Fig.1b).
After that an improved exposure time T1 was calculated
We used such a procedure in iteration.
5-10 iteration are sufficient to obtain self-consisted exposure time distribution T(x,y). On Fig.1b the final distribution of exposure dose T(x,y) after 3D correction is shown by thin line. It demonstrates nontrivial changes in compare with naive noncorrected distribution proportional to D(x,y).
Technological chain, examples and testing
"PROXY-WRITER" was used to expose all these irregular. After exposure with T(x,y)and development we obtained as examples stairs, linear and circular zone plates with good reproducing of designed structure with up to ten levels in PMMA resist of micron thickness on Si wafer (Fig.3). As the next step we transferred the resist relief in rigid material by electro-chemical deposition of Cu (Ni) (Fig.4). The final step was mechanical printing in polymer material (Fig.5). Results of optical testing of created lenses showed focus spot about 5um with good efficiency.
1) V.V.Aristov, A.A.Svintsov, S.I.Zaitsev,
Microelectronic Engineering 11 (1990) 641-644
Fig.2. Technological chain apart from e-beam exposure with 3D correction, development includes electrochemical deposition of metal for obtaining rigid replicas, mechanical printing for producing copies from soft material.
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