The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Principles of Lithography

A method is provided for reducing Critical Dimension (CD) non-uniformity in creating a patterned layer of semiconductor material. Two masking layers are respectively created, the first masking layer comprising a main pattern, an isolated pattern and a dummy pattern, the second masking layer exposing the dummy pattern. Methods of compensating for optical proximity effects and micro-loading, as provided by the invention, are applied in creating the first masking layer. The patterned first masking layer is transposed to an underlying layer creating a first pattern therein. The second masking layer removes the dummy features from the transposed first pattern, creating a second pattern therein comprising a main pattern and an isolated pattern to which compensation for optical proximity effects and micro-loading have been applied. The second pattern serves for additional etching of underlying semiconductor material.

New method to reduce CD non-uniformity in IC manufacturing

Aspects of the present invention provide for a novel photomask for patterning features for an integrated circuit, the photomask including masked features having interior nonprinting windows. In some embodiments, the interior nonprinting window is an alternating phase shifter, while the area surrounding the masked features transmits light unshifted. In other embodiments, the interior nonprinting window transmits light unshifted, while the area surrounding the masked features is an alternating phase shifter. Thus any arrangement of features can be patterned with no phase conflict.

Photomask features with interior nonprinting window using alternating phase shifting

An electronically programmed mask is connected to an electronic device, such as a processor. In operation, a mask design is first entered into the processor. The processor controls a display of an image on the electronically programmed mask, wherein the display replicates conventional type masks. The electronically programmed mask is designed such that the display presented on its screen provides optical contrast and characteristics that are easily changed or reprogrammed by the processor. Electronically controlled masks provide the same patterns as mechanical type masks without requiring rigid, permanent type structures to form a desired pattern.

Electrically programmable photolithography mask

In this paper, wafer level experimental results on the characteristics of a low-k1 submicron lithography processes using binary mask and deep ultraviolet (DUV) wavelength (248 nm) printing tool will be discussed. In the study, we investigated the nonlinear response of wafer resist critical dimension (CD) at different pitches to the mask CD. The CD nonlinearity is due to the combination of relatively poor optical aerial image quality at low-k1 imaging and resist processes. Operating a lithographic process at this nonlinear region presents an issue since only limited process windows are available. In addition, it requires both proximity correction for larger features on the mask and tighter mask CD control. The later requirement, in practice, is rather difficult to achieve with current mask technology. In order to avoid operating low-k1 lithography processes at CD nonlinear region, improvement of aerial image quality is obviously needed. Although aerial image quality improvement can be achieved with different advanced lithographic enhancement techniques such as phase shift masks and off- axis illumination, there are different process issues related to each of the techniques as well. With conventional illumination source and binary mask, one of the option left to enhance aerial image quality is mask biasing. Our experimental results show that by positively biasing the mask, i.e., mask chrome CD line dimension is larger than targeted resist CD, CD nonlinearity for low-k1 processes can be improved. For low- k1 processes, the isofocal bias of different feature sizes (different k1 factor) was also found to be different. A strong dependence of isofocal bias on pitch was observed. Again, mask biasing can help to shift the isofocal CD of critical dimensions to the target CD. However, in our study, we found that for certain resist, opposite mask biases are required to achieve CD linear response and zero isofocal bias. In this case, tradeoffs between mask CD control, proximity effect, and process window need to be considered.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Sub-micron low-k1 imaging characteristics using a DUV printing tool and binary masks

A mask having a pattern to modify a circuitry feature that has been exposed in a radiation sensitive layer by transmitting modifying radiation to a region of the radiation sensitive layer containing the exposed circuitry feature is described. The mask may reduce subwavelength distortions and proximity effect distortions of the exposed circuitry feature. The mask may be used to manufacture a semiconductor device having circuitry that is based on the modified circuitry feature.

Modifying circuitry features in radiation sensitive layers with active secondary exposure masks

An apparatus comprising a mask having an active device area and a moat The moat substantially surrounds the mask active device area and has a width greater than a plasma specie diffusional length A method comprising depositing a layer of resist on a mask substrate having transparent and opaque layers; and exposing the resist layer to radiation The radiation is patterned to produce features within an active device area The radiation is also patterned to produce a moat substantially surrounding the active device area having a width greater than a plasma specie diffusional length

Photomask frame modification to eliminate process induced critical dimension control variation

Ultra high numerical aperture (NA) enables extension of ArF lithography for the 45 technology node and beyond. The resulting changes in design rules drives feature sizes on the mask into the sub-wavelength regime. As 2-beam imaging techniques (off-axis illumination and alternating phase shift mask) are required for strong resolution enhancement in low-k1 lithography, traditional scalar and paraxial approximations used for optical image modeling are no longer valid in the ultra high NA regime. Vector and thick-mask based models are required to account for topographic effects and large angles of incident light at the reticle plane in ultra-high NA systems. Although vector-based imaging theory is well understood, experimental validation is required to ensure the appropriate topographical and optical parameters are being used. To address these issues, finite-difference time-domain rigorous electromagnetic simulation are compared to experimental measurements of the polarization dependent diffraction efficiencies on advanced optical reticles. Based on these results, the impact of mask induced polarization to vectorial imaging latitude is assessed. The impact of polarization purity, mask absorber profile, and Fresnel effects through the pellicle on process window and OPC are also discussed.

Vectorial effects in subwavelength mask imaging

A method for forming small repeating structures, such as contact holes, is disclosed. The method comprises using a phase shift mask to perform a first exposure of a photoresist layer formed atop of a substrate. The phase shift mask includes etched regions and unetched regions. Next, the position of the phase shift mask is adjusted relative to the photoresist layer. A second exposure through the adjusted phase shift mask is performed on the photoresist layer. The photoresist is developed and is used as a mask for etching the substrate. After etch, the photoresist is stripped and cleaned. The resulted small sub-wavelength pattern is formed from the disclosed technique.

Jeff Farnsworth

Papers

Sub-micron low-k1 imaging characteristics using a DUV printing tool and binary masks

Modifying circuitry features in radiation sensitive layers with active secondary exposure masks

Photomask frame modification to eliminate process induced critical dimension control variation

Vectorial effects in subwavelength mask imaging

Exposed phase edge mask method for generating periodic structures with subwavelength feature