Lithography radiation sensitivity

Enhanced radiation sensitivity may be designed into polymer molecules by incorporation of radiation sensitive groups,and this is an important aspect of research in e beam lithography. 

Resists used to define circuit patterns are radiation-sensitive and may be either positive- or negative-working. As a result of the fine lines, there has been movement away from optical lithography and into the mid- or deep-uv regions. Developmental work has also been focused on electron beam, x-ray, and ion-beam exposure devices and resists (9,10). 

Lithography is the process of generating a stencil or pattern in a radiation-sensitive material. The stencil subsequently serves as a mask to permit... 

Acrylate resists such as polymethylmethacrylate (PMMA) have been used extensively in electron beam lithography because of their excellent resolution and contrast, despite their limited dry etch resistance and low sensitivity (1). Copolymers of PMMA, containing chemical groups more sensitive to radiation induced degradation, have also been studied and have shown up to a four-fold improvement in sensitivity (2). One approach has been to form a crosslinked gel, in-situ on the wafer, which contains radiation sensitive crosslinks and leads to improved sensitivity and improved contrast during development (3-7). 

In addition to the binary classification based on the imaging tone, resists can be divided on the basis of their design into 1) one-component and 2) multi-component systems (Fig. 4). One-component resists consist of pure radiation-sensitive polymers that must combine all the necessary attributes as mentioned above, and have long lost ground. The modern advanced lithography is ex-... 

Today, the reach of Maxwell s electromagnetic theory extends all the way to lithography, where it guides the choice and usage of optical elements of lithographic exposure tools, as well as the interaction of these optical elements and radiation-sensitive resist materials with lithographic exposure radiations. 

It should be emphasized that one-component resists consisting of pure radiation-sensitive materials, which in modern times are comprised primarily of polymers that combine all of the necessary attributes of a resist, have now fallen out of favor. In contrast, modern advanced lithography relies almost exclusively on the multicomponent design concept in which resist functions are provided by separate components, comprising the resin/bmder on the one hand, and the photoactive compounds on the other. In these multicomponent systems, the resins/ binders are polymers and are typically inert to radiation, but can undergo radiation-induced reactions initiated by the photoactive components of the resists. ... 

The object of semiconductor lithography is to transfer patterns of ICs drawn on the mask or reticle to the semiconductor wafer substrate. The transfer is carried out by projecting the image of the reticle with the aid of appropriate optical elements of an exposure tool onto a radiation-sensitive resist material coated on the semiconductor wafer, typically made of silicon, and stepping the imaging field across the entire wafer to complete a layer. The shape of the IC pattern transferred to the wafer substrate is dependent entirely on the wafer layer being patterned. Examples of patterns include gates, isolation trenches, contacts, metal interconnects, and vias to interconnect metal layers. An advanced CMOS (complementary... 

Thick-film lithography refers to the processes used to make thick films of photoresist, i.e., typically thick film is used to refer to films that are 5-100 pm (p) thick, and subsequently produce relief patterns in those Alms. The photoresist is a radiation-sensitive material that is applied to a substrate surface, exposed to radiation to create a physiochemical change in the exposed regions, and washed in a developer solution to produce the desired physical relief patterns. 

Lithography relies on radiation-sensitive polymers called resists. When irradiated, these materials undergo chain scissioning, cross-linking, molecular rearrangement, or other process that creates a solubility difference between the irradiated or exposed areas of the polymer and the nonirradiated or unexposed areas... 

Detection limits for various elements by TXRF on Si wafers are shown in Fig. 4.13. Synchrotron radiation (SR) enables bright and horizontally polarized X-ray excitation of narrow collimation that reduces the Compton scatter of silicon. Recent developments in the field of SR-TXRF and extreme ultra violet (EUV) lithography nurture our hope for improved sensitivity down to the range of less than 10 atoms cm ... 

Sensitivity and contrast are conveniently measured experimentally by exposing areas of resist of known size to varying radiation doses and measuring the film thickness remaining after development for each area. In the case of negative resists, gel is not formed until a critical dose, denoted as the interface gel dose Dp, has been reached. At this dose no lithographi-... 

The conventional approach has been to take resists which were developed for electron lithography and apply them to x-ray lithography. To a first order, there is a strong correlation between the sensitivity of resist systems (positive or negative) to electron beam radiation and their corresponding sensitivity to x-ray radiation. Figure 11 shows a plot of the 20 kV electron beam sensitivity in... 

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