Reuven Falah

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.

Advanced edge roughness measurement application for mask metrology

With decreasing Critical Dimensions (CD), the negative influence of line edge roughness (LER) and line-width roughness (LWR) on CD uniformity and mean-to-target CD becomes more pronounced, since there is no corresponding reduction of roughness with dimension reduction. This applies to wafer metrology as well as to mask metrology. In order to better understand the types of roughness as well as the impact of the CD-SEM roughness measurement capabilities on the control of the mask process, the sensitivity and accuracy of the roughness analysis were qualified by comparing the measured mask roughness to the design for a dedicated LER test mask. This comparison is done for different LER amplitude and periodicity values and for reference structures without nominal LER using the built-in CD-SEM algorithms for LER characterization.

Halftone PSM inspection sensitivity of OPC line/space pattern for 150-nm generation

The process of manufacturing and inspecting 150nm generation reticles, incorporating RETs - Resolution Enhancement Technologies - is discussed. Some of the RETs applied at the lithography stage while exposing the wafer, such as OAI - Off Axis Illumination, others RET are being incorporated into the reticle, such as OPC - Optical Proximity Correction - and PSM - Phase Shift is discussed. Many relevant aspects are discussed in this paper such as the ability to produce those critical layers while keeping good CD linearity, and the ability to detect OPC related defects with current reticle inspection technology.

High-transmission PSM inspection sensitivity

Manufacturing of reticles, which combine both OPC and PSM, is becoming more and more challenge. Materials cost is high, several accurate writing processes are needed and repair is almost impossible. This makes inspection a critical and very complicated process. This study describes an inspection of a test vehicle consisting of 55 cells targeted for sub- wavelength design rule technology. This study describes an inspection of the 55 cells test plate targeted for 0.17 micrometer design rule technology. The plate is written on a MoSi layer with 18% transmission for 248 nm lithography. The MoSi has higher transmittance in I-line and G-line that reduces the contrast between the MoSi and the glass (relative to the usual contrast in binary plates). The technique for inspection by Applied Materials RT8000ES 436nm die-to-database is described. The technique is based on expansion of the reduced dynamic range of gray level that results from the lower contracts, re-gaining the inspection capability. This paper reviews the results of G-line versus I-line inspection of high transmission PSM and describes the method of the sensitivity verification including CD defects analysis.

CAD-based line/space mix-up prevention for reticle metrology

This paper describes a method to automatically distinguish between line and space for 1:1 line space patterns in mask metrology. As the number of measurements typically performed on a reticle is significantly higher than on a wafer, automated CAD based CD-SEM recipe creation is essential. Such recipes typically use synthetic pattern recognition targets instead of SEM based pattern recognition targets. Therefore, a possible different contrast between lines and spaces on a mask cannot be utilized for distinguishing lines from spaces. We demonstrate an algorithm solution based on the analysis of the SEM waveform profiles to identify potential L/S mix-ups and correct them automatically. The solution allows fully automated CAD based offline recipe creation with a high success rate of distinction between lines and spaces for 1:1 pitch cases without the necessity of editing recipes on the tool in advance of performing the measurements.

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.

Inspection of aggressive OPC using aerial image-based mask inspection

Inspection of aggressive OPC represents one of the major challenges for todays mask inspection methodologies. Systems are phased with high-density layouts, containing OPC features far below the resolution limit of conventional inspection systems. This causes large amounts of false and nuisance defects, especially on production applications. The paper presents the use of Aera193, a new inspection system using aerial imaging as inspection methodology.

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.

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.