Shirley Hemar

Aerial image-based inspection of binary (OPC) and embedded-attenuated PSM

The paper presents a revolutionary technology to inspect advanced contact layers. Instead of finding defects based on a size-dependent defect specification, defects are found according to their impact at the wafer CD result. The inspection methodology used is aerial imaging. The main advantage of this method is that only defects, which actually affect the wafer result, will be detected and classified. The paper presents first inspection results on contact layers designed for the 130nm and 90 nm technology node.

Inspecting alternating phase shift masks by matching stepper conditions

The paper presents a new technology to inspect alternating phase shifting masks. Instead of finding defects based on a size-dependent defect specification, defects are found according to their impact at the wafer CD result. The inspection methodology used is aerial imaging. Phase effects are taking into account inherently. The main advantage of this method is that only defects, which actually affect the wafer result, will be detected and classified. The paper presents first inspection results on alternating phase shifting test masks designed for the 70nm generation.

Aerial-image based inspection of AAPSM for 193-nm lithography generation

The inspection of alternating phase shifting masks is still one of the major challenges in state-of-the-art mask making. Main issue is that phase defects cannot easily be identified by inspection systems using an inspection wavelength different form the target exposure wavelength. The paper presents inspection results using the Aera193, an aerial image based mask inspection system.

CD uniformity control using aerial image-based mask inspection

The industry roadmap for IC manufacturing at design rules of 90nm and below foresees low k1-factor optical lithography at 193nm exposure wavelength. The mask error enhancement factor (MEEF) describes the phenomenon in which errors in the mask critical dimensions (CDs) are not transferred to the wafer in direct proportion to the optical reduction value of the lithography system. In the low-k1 area, the MEEF becomes a significant problem, as it consumes a larger than anticipated percentage of the CD tolerance budget. As a result mask CD uniformity requirements have been tightened significantly to find MEEF-related CD defects prior to the first printing at the wafer fab. The challenge for todays mask inspection methodology lays in the way defects are detected. Conventional mask inspection detects defects according to their dimensions on the mask. Finding MEEF-related CD defects is a challenge as these defects are often caused by CD deviations close to metrology resolution. The paper investigates CD uniformity control using aerial image based mask inspection. The fundamental difference to todays inspection methodology is that a defect is detected based on its impact onto the aerial image projected by the given mask. In order to emulate the aerial image, lithography condition like Numerical Aperture and illumination need to be known to the inspection system. As a large portion of the MEEF is based on the lithography exposure system, MEEF defects can be detected.

Aerial-image-based off-focus inspection: lithography process window analysis during mask inspection

The industry roadmap for IC manufacturing at design rules of 90nm and below foresees low k1-factor optical lithography at 193nm exposure wavelength. Aggressive model-based OPC are being used more and more frequently in order to achieve the extremely tight mask CD specifications required by 90nm technology node. State-of-the-art mask inspection is challenged to detect CD defects close to metrology resolution. Inspection of OPC is critical; OPC feature dimensions are usually near or below the resolution limits of mask exposure. In addition, chrome defects can be semitransparent and change the intensity of light on the wafer. In this paper aerial-image based mask inspection is investigated and presented. The concept inspects a given mask based on its aerial image with selected wafer exposure conditions, thus “finds only defect which will print”. This paradigm shift in mask inspection philosophy provides the unique opportunities of verifying and controlling the entire aerial image generated by the inspected mask. As reticle enhancement techniques like OPC are designed to enhance the aerial image of a mask, this concept offers a comprehensive way of inspecting these techniques. The inspection is shifted from detecting every single minor change on mask to detecting what on mask could possibly impact the printing image quality on the wafer. In this paper an advanced application of aerial-image based mask inspection is discussed in more detail. As a standard, the Aera193 uses the best-focus aerial image for defect detection. From HNA mask inspection it is a well-known fact, that shifting the inspection off-focus, can provide a more sensitive detection. In the csase of aerial-image based inspection, going off-focus can be compared with lithography exposure out of focus. In other words, the lithography process window will be taken into account for defect detection. This methodology provides additional important information ·Understand process window printability of defects detected at best-focus ·Detect additional defects, which may print at the borders of the process window. This information is of extreme value for wafer lithography and may help by decisions about lithography process and mask usage. Focus of the paper is to analyze the application of aerial image-based off-focus inspection. Advanced OPC test plates are used to analyze detection at best and off-focus. The inspection results are compared to actual wafer results. Wafer lithography benefit is discussed.

Inspecting Alternating Phase Shift Masks by Matching Stepper Conditions

The paper presents a new technology to inspect alternating phase shifting masks. Instead of finding defects based on a size-dependent defect specification, defects are found according to their impact at the wafer CD result. The inspection methodology used is aerial imaging. Phase effects are taking into account inherently. The main advantage of this method is that only defects, which actually affect the wafer result, will be detected and classified. The paper presents first inspection results on alternating phase shifting test masks designed for the 70nm generation.

New approach to improve CD uniformity based on mask quality

CD uniformity is one of the key discussion topics in the ramp-up process of new technologies. The impact of mask quality is getting more and more attention in this process. The paper presents improving wafer CD uniformity control by application of new reticle CD qualification procedure. The new procedure is based on combining conventional CD metrology and Linewidth Bias Monitor (LBM) as a standard part of mask inspection.

150-nm DR contact holes die-to-database inspection

Using a failure analysis-driven yield enhancements concept, based on an optimization of the mask manufacturing process and UV reticle inspection is studied and shown to improve the contact layer quality. This is achieved by relating various manufacturing processes to very fine tuned contact defect detection. In this way, selecting an optimized manufacturing process with fine-tuned inspection setup is achieved in a controlled manner. This paper presents a study, performed on a specially designed test reticle, which simulates production contact layers of design rule 250nm, 180nm and 150nm. This paper focuses on the use of advanced UV reticle inspection techniques as part of the process optimization cycle. Current inspection equipment uses traditional and insufficient methods of small contact-hole inspection and review.

In-line verification of linewidth uniformity for 0.18 and below: design rule reticles

Mask making process development and control is addressed using a reticle inspection tool equipped with the new revolutionized application called LBM-Linewidth Bias Monitoring. In order to use the LBM for mask-making process control, procedures and corresponding test plates are a developed, such that routine monitoring of the manufacturing process discloses process variation and machine variation. At the same time systematic variation are studied and either taken care of or taken into consideration to allow successful production line work. In this paper the contribution of the LBM for mask quality monitoring is studied with respect to dense layers, e.g. DRAM. Another aspect of this application - the detection of very small CD mis-uniformity areas is discussed.

Innovative approach for concurrent CD-uniformity monitoring and reticle inspection

In this paper a new approach of concurrent CD-uniformity monitoring is presented. This is achieved by using the Linewidth Bias Monitoring (LBM) tool, which utilizes data collected during the reticle inspection to concurrently generate real-time line width monitoring with superb precision without affecting inspection time or results. The capabilities of the LBM are presented by a specially designed test-plate, establishing the tool precision and repeatability. Analysis of case studies based on various production plates demonstrates the contribution to process control and mask fidelity.