Byung-Cheol Cha

Correction of Critical Dimension Uniformity on a Wafer by Controlling Back-Surface Transmittance Distribution of a Photomask

We report on a new method for correcting the critical dimension (CD) uniformity on a wafer, using a transmittance-controlled photomask with phase patterns on the back. Theoretical analysis of changes in the illumination-pupil shape with respect to the variation of the size and density of the back-surface 180°-phase contact-hole patterns and experimental results using the transmittance-controlled photomask are presented. It is shown that pattern size on the back of the photomask must be made as small as possible in order to keep the illumination-pupil shape as close as possible to the original one and to achieve as large an illumination intensity drop as possible at the same pattern density. It is demonstrated that the method is very effective for correcting the CD nonuniformity on a wafer that is induced by both CD nonuniformity of the photomask and flare in the exposure tool.

EUVL mask inspection using 193nm wavelength for 30nm node and beyond

We report inspection results of EUVL masks with 193nm wavelength tools for 30nm and 24nm half-pitch nodes. The dense line and space and contact pattern is considered to study inspection capability. The evaluation includes defect contrast variation depending on illumination conditions, defect types, and design nodes. We show many inspection images with various optic conditions. Consequently, the detection sensitivity is affected by contrast variation of defects. The detection sensitivity and wafer printability are addressed with a programmed defect mask and a production mask. With these results, we want to discuss the capability of current EUVL mask inspection tools and the future direction.

Real-time monitoring based on comprehensive analysis of the haze environment under the pellicle film

It is important to understand how the outgassed chemicals from pellicle materials are involving in various surface reactions towards haze defect formation on the mask surface during the exposure. In this work, we have analyzed the gaseous environment and the substrate surface under laser exposure in the specially designed quartz tube filled by air, or N2. We observed that various chemicals that consist of the pellicle film are outgassed from the film and then deposited or interact with other chemicals to make haze defects on the substrate surface during laser exposure. This fact can be further applied not only to the study of pellicle outgassing effect on haze defect growth mechanism but also to the development of real-time monitoring tools for the defect growth progress on the mask surface.

Evaluation of process capabilities for 50 keV with rectangular-shaped beam using computer simulation

Monte Carlo calculations, including secondary electron generation and development simulation, using a string algorithm have been carried out in order to estimate the process capabilities for a beam voltage of 50 keV with a rectangular shaped beam in electron beam lithography technology. The results for minimum resolution for the threshold energy density model and the development model were compared. A study of minimum resolution and process latitude with respect to the acceleration voltage, resist thickness, beam blur for commercial PBS resist was investigated. In addition, at 50 keV, the effects of (alpha) value, asymptotic slope at very high dose in the dissolution rate equation on minimum resolution and process latitude were examined. The results show that it is necessary to use resist with a higher (alpha) value, as well as a high acceleration voltage of 50 keV, in order to enhance process capabilities.

Dose latitude dependency on resist contrast in e-beam mask lithography

In mask-making process with e-beam lithography, the process capability is usually affected by exposure profile, resist contrast and development process. Dose latitude depends significantly on these three parameters. In this work, dose latitude between different resist contrasts has been experimentally studied as a function of linewidth, dose, beam size and over development magnitude using commercial PBS and ZEP 7000 resist on a photomask with 10 keV exposure. It has been found that ZEP 7000 resist with high contrast shows lower dose latitude, more sensitivity to the variation of linewidth, dose and beam size except for over development magnitude due to its relatively longer development time.

Evaluation of the practical use of GHOST technique for various e-beam resists

In this paper we present results of the application of the GHOST technique to the practical use with 10 keV system. Three commercial e-beam resists which include ZEP7000, PBS, and EBR9 HS31 are selected for comparisons. The background dose equalization by the GHOST technique was found to be effective in reducing the proximity effect. It is generally assumed that exposure contrast degradation due to secondary exposure with largely defocused beam for the GHOST technique, especially at boundary between pattern pixel and nonpattern pixel, leads to poor CD uniformity. Thus, we examined CD uniformity variations as a function of with and without the GHOST technique for three e-beam resists .And we also reported the comparison of proximity effect correction quality for three resists by looking at CD linearity in order to investigate relationship between proximity effect and resist contrast.

Qualitative analysis of haze defects

We created haze defects on the PSM mask surface using ArF haze accelerator while the mask was previously cleaned by SPM and SC1 solutions. Then we directly analyzed the defects on the surface using TOF-SMS. The comprehensive analysis of TOF-SIMS signifies that the defects mainly consist of hydrocarbons, Na, K, Cl, F, Mg, Al, etc., which have probably come from previous procedures, fab environments, storage materials, handling steps, or pellicle materials. This fact implies the exclusion of sulfate or ammonium ions from the mask surface should not be enough for the realization of haze-free PSM masks. In addition, complete removal of residual hydrocarbons deposited through previous procedures and perfect protection against environmental contaminants from fab air, storage materials, handling steps, or pellicle materials should be further accomplished.

Monitoring system of CD error analysis for the 90-nm node mask manufacturing

CD(Critical Dimension) Non-Uniformity on a mask is normally separable into global and local CD errors by means of their error sources. In general a global CD error trend on a mask shows the properties of each process. On the other hand, local CD errors on a mask are pretty much random and caused from mainly measurement errors, LER(Line Edge Roughness), and litho-shot errors. However, because of its difficulty to pin point the sources of errors and correct them, the local CD errors are required more attention. A Global CD error trend on a mask can be classified into several groups. One originating from vacuum delay, lithography error, bake and etch process will cause a side error trend on a mask. Others are fogging, radial trends of develop, and etch loading. In order to classify all those global CD errors and local CD errors, the proper monitoring mask must be required. The works on this paper mainly focalize on minimizing global CD error trends on a mask by separating and analyzing error components with proper monitoring system of each process. We therefore, provide a monitoring mask designed for efficiently representing global and local CD errors in more detailed fashion which can analyze CD errors of each process and make feed-back to each process in order to improve each process of mask manufacturing.

Pellicle process effects in critical dimension fluctuation

In this article, we will analyze in-field uniformity (IFU) fluctuation of linewidth on wafer considering errors related to mask pellicle process. As gate linewidth becomes smaller, the controllability of in-field uniformity (IFU) plays a key role in wafer manufacturing yield. IFU depends on various lithography parameters including mask CD (critical dimension) uniformity, MEEF (mask error enhancement factor), exposure margin, focus margin, transmittance, flare and illumination uniformity. Although the short term repeatability of IFU is manageable, various parameters which affect IFU are still changing. During the wafer process, mask re-pellicle process is unavoidable due to haze contamination. For this reason, mask pellicle process including cleaning should be carefully controlled to achieve the long-term IFU stability on wafer as well as exposure machine (optic), resist coating (resist property). This paper will discuss the various experimental works including IFU correlation on wafer in terms of optic stability, resist stability and mask pellicle process. CD uniformity data on mask and IFU data on wafer is obtained from optical measurement tool to reduce measurement error disregarding local CD variation.

Analysis of in-field uniformity on wafer considering exposure margin and MEEF

In this article, we analyzed in-field uniformity (IFU) on wafer considering exposure margin [linewidth variation (nm) per % exposure dose variation (%)] and the MEEF (mask error enhancement factor). As gate linewidth becomes smaller, the controllability of in-field uniformity (IFU) plays a key role in wafer manufacturing yield. IFU depends on various lithography parameters including mask CD (critical dimension) uniformity, MEEF, exposure margin, focus margin, transmittance, flare and illumination uniformity. In real world, the combination of wafer exposure machine and mask characteristics should be carefully considered to achieve better IFU on wafer. This presentation discusses the various experimental works including CD uniformity on mask, IFU on wafer, MEEF, exposure margin and wafer exposure machine. CD uniformity data on mask and IFU data on wafer is obtained from optical measurement tool to reduce measurement error disregarding local CD variation. Even though one handles a unit pattern, various MEEF exists in a unit pattern in case of complex pattern. In addition, the MEEF varying with the area across one mask degrades IFU on a wafer. IFU on a wafer is predictable using mask CD uniformity and exposure margin mean. Variation of exposure margin is the measure of stability of photo process. In manufacturing devices, mask and Litho. Tool should be well harmonized to achieve better IFU and a higher manufacturing yield. The photo process including resist process should be well controlled to get stability, as well as mask CD uniformity.