In this paper, we study the feasibility of using a new system to set up offline critical dimension scanning electron
microscope (CDSEM) recipes for both litho and etch processes monitoring in a foundry environment before first silicon.
We will automatically create CDSEM measurement recipes based on CAD design data (2) and litho illumination
information. The main advantages of having recipes setup done through this method as compared to performing recipe
creation on the CDSEM tool itself are the reduction in CD-SEM tool usage and more importantly, the availability of the
recipes before the first wafer is being processed in lithography resulting in a faster of cycle time for new devices.
To facilitate our objective, a new feature was implemented in the design to provide a universal global alignment (GA)
feature under both optical and SEM view. The global alignment serves two functions: to minimize device-to-device and
layer-to-layer optical variation. It synchronizes design (CAD) and wafer coordinate systems. With this universal
alignment feature available across all production layers of interest, we can fully automate recipe creation process from
design to production.
Optical proximity correction (OPC) plays a vital role in the lithography process for critical dimension (CD) control.
With the shrinking of the design rule, CD is more sensitive to lithography process, so the task for OPC becomes more
challenging. Flare, or stray light, is an added incoherent background intensity that will detract from lithography system
performance, CD control and process latitude. The impact of flare on lithographic imaging and its correction through
OPC has been the subject of increased investigation.
In this paper, the flare effects on CD variation by changing the total image intensity are discussed. The flare map is
obtained by running the flare model on the mask layout. Based on the flare map, flare test patterns are designed and flare
test reticle is written. After collecting wafer silicon data with CD SEM, flare model is verified and the flare impacts on
the across chip line width variation (ACLV) are presented. With the existence of flare, CD bias across different areas of
the cell could be measured. As CD varies by a comparatively wider range than optical proximity range, it could not be
corrected by existing OPC model. Based on the analysis of flare model and the experiment results, applications on flare
correction are discussed by using OPC.
The objective of this work is to demonstrate a simple Linear Superposition approach to creating an optimized illumination scheme from commonly available apertures (e.g. conventional, annular, quadrupole, dipole, etc.) that meet a variety of lithographic process metrics. Previous authors have demonstrated a variety of approaches to optimize the illumination for a given lithographic process. One common example is to use an optimized illumination for a specific pitch range and breaking the exposure into multiple reticles designed to print only nested or isolated features. A second example that has been widely demonstrated is to develop a single custom illuminator, which requires long lead times for delivery and a large capital investment. The true on-wafer performance of this custom illuminator can only be determined post-installation, providing limited ability to verify the simulation work a priori. The linear superposition method described here produces an optimal illumination scheme for a given photolithographic process. The success of this approach is due to the acceptably small nature of the electric field interaction terms between individual illumination modes allowing a multiple-exposure system to model a composite source. Images from optimized sub-components can be added to generate a composite image that is superior overall to any one process alone. After each exposure in a multiple exposure system there is a latent image that is only developable after a specific energy or dose level has been surpassed. It is the additive process of these latent images that creates the composite image. The composite image has the additive properties of the sub-components according to their dose fractions. Once the optimal process and dose split have been determined, it is straightforward to create a composite aperture to produce the same process by a single exposure. The composite aperture is the addition of the multiple sub-components with the relative transmission of each related to the illuminated surface area for systems designed to deliver uniform brightness. This approach produces superior pattern fidelity and an optimized common lithography process without the pitfalls of any one of the sub-component illumination modes.