Jin-Min Kim

Modeling and correction of global CD uniformity caused by fogging and loading effects in 90-nm-node CAR process

As critical dimensions (CDs) continue to approach the 90 nm node, it is inevitable that the industry has employed the use of chemically amplified resist (CAR) with 50 kV e-beam writing tool. However, the fogging effect by re-scattered incident electron at a high acceleration e-beam writer and the loading effect at dry etching step due to pattern density are critical issues since these effects make the variation of CD mean to target (MTT) and the degradation of CD uniformity. Tracking the CD error sources in CD uniformity and minimizing the error are very important task for high technology node mask production. In this paper, we focus on finding the source of the radial error in CD uniformity for each process step since the radial error occupy the main part of total CD uniformity. Also we present the radial error modeling using convolution equation between Gaussian CD error distributions with pattern densities. Finally, we describe the radial error correction method by phantom exposure with rectangle representing local pattern density. Fogging effect at writing process is one of the main sources of the radial error in global CD uniformity. The error by fogging effect is linearly proportional to mask pattern density, whereas loading effect at dry etch process increases the radial error in the case of the higher pattern density. The correction method using defocused beam based on our CD uniformity model effectively reduces the radial error and total error to 50% of their original value.

A new method for correcting proximity and fogging effects by using the EID model of variable shaped beam for 65-nm node

In this paper, an Energy Intensity Distribution (EID) model considering dose latitude for Variable Shaped Beam (VSB) has been developed. η values (i.e. back-scattering ratio) versus dose and process threshold have been investigated by using the EID model. Additionally, a new procedure to find optimum PEC values (η) taking into account of the process threshold is proposed through simulation. For fogging effect correction, we have adopted a Gauss model and created a new simulation algorithm to find the most suitable parameters regarding η value, process threshold, dose and the EID model.

Optimum PEC Conditions Under Resist Heating Effect Reduction for 90nm Node Mask Writing

For high-voltage vector e-beam writing systems, solving the resist heating effect problem is one of the highest priorities because it is a major factor affecting localized critical dimension (CD) uniformity. In order to write patterns for 90nm node devices, the utilization of proximity effect correction (PEC) is essential for e-beam mask writers to achieve high CD performance. In this study, the dependence of CD variation on e-beam write conditions was investigated under optimum PEC parameter conditions. Writing conditions such as current density, shot size, number of writing passes, and settling time were tested to see their affects on resist heating. Industry-standard Nippon Zeon ZEP 7000 resist was written by a Toshiba EBM-3500B 50KeV vector e-beam writer using patterns found in sub-130nm node devices. Results indicated that the main factor affecting resist heating CD variation for ZEP 7000 was in fact the e-beam writer shot size selected. Multi-pass writing was effective in reducing the CD variation, and the settling time of each shot in the EBM-3500B had very little influence.

Detection capability for chrome defect of tri-tone PSM

The semiconductor industry continuously shrink the linewidths and the smaller linewidths are easily affected by the defects. The defects have to be detected to prevent printed images on wafers. This paper will present the detection capability of current inspection machines for chrome defects on attenuated MoSiN layer and simulation results for the effect of chrome defect on attenuated layer. Two inspection machines based on i-line light source were used for comparison of detection capability for chrome defect on attenuated layer. The effect of chrome defect on attenuated MoSiN layer was evaluated with MSM 100 at 248 nm wavelength.

Etching selectivity and surface profile of attenuated phase shifting mask using CF4/O2/He inductively coupled plasma (ICP)

The selectivity and etched profile of MoSiON in high-density CF4/O2/He inductively coupled plasma (ICP) have been studied. The etched profiles of MoSiON along with the quartz surface morphologies were investigated as a function of etching parameters by scanning electron microscopy (SEM). We varied pressure from 5 mtorr to 20 mtorr and CF4 flow rate from 15 sccm to 40 sccm. A smooth quartz surface and a vertical MoSiON slope were observed under 10 sccm CF4, 15 sccm of O2 flow rate, -240 V of DC bias and 5 mtorr pressure. And the other conditions showed rough quartz surface and bad MoSiON slope. Only at the appropriate CF4/O2 Flow rate, high vapor pressure compounds inhibits nonuniform quartz etching.

90nm Node CD Uniformity Improvement Using a Controlled Gradient Temperature CAR PEB Process

Writing fogging effect in chemically amplified resist process makes critical effect on global CD distribution in the advanced 90nm node photomask with higher pattern density and smaller geometries. High contrast feature of chemically amplified resist makes difficult to correct the global CD uniformity in resist develop process compared with conventional ZEP resist. In this paper we examine the fogging effect in the combination chemically amplified resist with 50KeV writing tool and the consequential problem for production mask with higher pattern density. We will present the feasibility of the global CD uniformity correction technique in post exposure baking process using gradient temperature hotplate.

A study of storage life extension for high performance chemically amplified resist coated blanks

The importance of advanced e-beam writing system and chemically amplified resist (CAR) coated blank is increasing gradually in high-end grade photomask manufacture according to CD embodiment of 90 nm and beyond technology node requiring because of the shrinkage of design rule in the semiconductor industry. However, many studies have been reported that CAR has several troubles and especially, CAR sensitivity change is occurred by airborne molecular contamination (AMC). So, the storage life of CAR coated blank is shortened. This problem may cause the difficulty of high-end grade photomask manufacture because it is hard to secure stable mean to target (MTT) and CD uniformity by sensitivity change, T-top profile and footing profile. Therefore, the purpose of this paper is to investigate the storage life extension for high performance CAR coated blank through improvement of the packing materials. Firstly, a variety of packing materials were collected and the selected packing materials were analyzed by Automatic Thermal Desorption Gas Chromatograph/Mass Spectrometer (ATD GC/MS) and Ion Chromatograph (IC) to examine AMC generated from the packing materials. As a result, molecular condensables such as alcohols, hydrocarbons and fatty acids were detected and molecular acids and molecular bases those are NH4+, Cl-, NOx- and SOx- were also detected from the packing materials, respectively. From the above results, we selected the best packing materials which generated the least AMC and the worst packing materials which generated the most AMC. Additionally, we verified photomask process with CAR coated blanks which were packed with those packing materials with post coating delay (PCD) by 50 kV e-beam writing system. In consequence, dose to clear (DTC) showed 4.6 μC/cm2 at 0 day PCD for both of the best and the worst packing materials of CAR coated blank. After 90 days PCD, DTC variation was only 0.4 μC/cm2 for the best packing materials, but DTC variation of 4.0 μC/cm2 showed in the worst packing materials. There was 10 times difference in DTC variation between the best and the worst packing materials. As well as, the CD variation at 0.5 μm dense line presented less than 5 nm movement for 90 days PCD.

Improving lithography CD control by correcting proximity and long range variations in electron beam mask writer

In this paper, an Energy Intensity Distribution (EID) model considering dose latitude for Variable Shaped Beam (VSB) has been developed. η values (i.e. back-scattering ratio) versus dose and process threshold have been investigated by using the EID model. Additionally, a new procedure to find optimum PEC values (η) taking into account of the process threshold is proposed through simulation. For fogging effect correction, we have adopted a Gauss model and created a new simulation algorithm to find the most suitable parameters regarding η value, process threshold, dose and the EID model.

Decrease of chrome residue on MoSiON in embedded attenuated-PSM processing

In Embedded Attenuated PSMs(Phase Shift Masks), chrome residues on MoSiON, especially at the edge of a pattern, should be decreasing the phase-shift effect and it must be also causing CD(critical dimension) variations in a wafer-process. Chrome residues on MoSiON are well known being generated at second level lithography or according to performance of cleaning process before it. In this paper, we investgated the influence of treatment on Cr surface during MoSiON etch process using CF4 plasma and proposed the optimum treatment procedure to reduce the Cr residues originated form re-deposition of carbon-contained polymers in CF4 plasma.

The judgment criteria of halftone pinhole defects

As the design rule of the semiconductor devices approaches to 90nm node technology, the defect controllability of the photomask becomes critical success factor. The halftone defects generated in photomask cannot be easily judged because the results of Aerial Image Measurement System (AIMS) are flexible with the defect size and transmission. Also, the printability of halftone defect on wafer is not clear because of low sensitivity of inspection system for pinholes. In this paper, halftone defects with programmed size were fabricated by Focused Ion Beam (FIB) repair tool. We evaluated the transmission correlation of the halftone defects between printability with 248nm simulation tool and inspection machine with 365nm light source. We could make the judgment criteria of halftone defects captured by inspection machine without AIMS result from this correlation result. Inspection machines such as KLA-Tencor and Lasertec are used to verify the detectability of halftone defects. Wafer printability was simulated using AIMS fab 248. Even though the transmission of halftone defects is same, the energy intensity of large size defects is higher than that of small size.