Jinseok Heo

Tactile sensors using the distributed optical fiber sensors

This paper describes two kinds of the tactile sensors using the optical fiber sensors. One is the tactile sensor using fiber Bragg grating (FBG) sensor. Bragg grating inscribed in an optical fiber causes reflect of a spectral component at the Bragg wavelength. This sensor can detect external force using change of the reflective wavelength. The other is the tactile sensor using the microbending optical fiber (MBOF) sensors. The microbending of the optical fiber drives the light transmission loss from the optical fiber. Using the light loss, this sensor can also detect the external force. The structures of these type tactile sensors are very simple. The tactile sensor using FBG sensor consists of an optical fiber which has a Bragg grating and bridge type transducers, and using MBOF sensors is composed of crossed fibers in the silicone rubber. In this paper, we fabricated and evaluated both tactile sensors. The performances of both tactile sensors were verified.

Development of a Distributed Force Detectable Artificial Skin Using Microbending Optical Fiber Sensors

This article describes a skin-like tactile sensor system that can detect a distributed force using microbending optical fiber sensors. In this design, optical fibers are used both as actual force elements and as signal-transmission media. The tactile array sensor is formed by appropriately arranging fibers into two overlapping layers, forming a 2D grid of fibers. When force is imparted to a given fiber taxel, small distortions (microbends) appear in the stressed fibers, resulting in decreases in the transmitted light intensity in these fibers. A prototype sensor of this type has been fabricated and tested. Comparison with a conventional tactile sensor reveals that the proposed tactile sensor provides outstanding performance and many advantages such as water resistive characteristics, high durability, and simple wiring.

Dose performance characterization of extreme ultraviolet exposure system using enhanced energy sensitivity by resist contrast method

Characterization of the systematic and random dose errors of an extreme ultraviolet (EUV) exposure system is performed using an EUV resist as an energy sensor for fast and repeatable measurements. Dose error measurement is enabled by a critical phenomenon that occurs when the photoresist is exposed to a dose in the region between the onset dose of E1 and the clearing dose of E0 on the photoresist contrast curve, which results in enhanced sensitivity to the applied dose relative to the resist thickness. At doses near the enhanced sensitivity point, changes in the thickness of the photoresist can be detected based on the change in the reflected light intensity, and any intensity variations in a captured image of an exposed wafer can be reverse translated into the dose error of the exposure system. With a dose sensitivity that is capable of resolving approximately 0.25% of the nominal dose, it is possible to decompose the measured systematic in-band EUV dose error of the exposure system into the intrafield s...

Fast resist-activation dosimetry for extreme ultra-violet lithography

Due to the rather broad band emission spectrum of the extremely hot plasma in its extreme ultra-violet (EUV) source, an EUV lithography scanner also projects out-of-band vacuum- and deep-UV (OoB V/DUV) light on the photoresist on a wafer. As this type of uncontrolled and undesirable light can activate resist chemistry, it will impair the critical dimension uniformity of the patterns, especially across the borders of the fields. Hence, OoB V/DUV quantification technology is required in the pre-production phase. For this reason, the systematic characterization of the EUV-source emission spectrum and the spatial profile of the light as projected on the wafer is indispensable to sustain stable integrated circuit production with EUV lithography. This paper introduces an in-band EUV and OoB V/DUV dosimetry method that is based on enhanced energy sensitivity by resist contrast (EESRC). This dosimetry method is applied in an EUV lithography tool to quantitatively analyze the spatial distribution the resist activation by in-band EUV and OoB V/DUV light, under several exposure conditions. This pragmatic approach can replace the current best-practice of measuring the full spectrum of an EUV light source.

Highly sensitive and fast scanner focus monitoring method using forbidden pitch pattern

Forbidden pitches that are introduced under certain illumination conditions can have extremely narrow depth of focus (DOF), so that when a lithographic pattern is transferred to a wafer, the forbidden pitch should be removed from the layout. However, the sensitivity of this narrow DOF can be utilized to monitor focus changes in the scanner system itself. In this paper, a newly developed focus monitoring method utilizing the forbidden pitches is introduced and the sensitivity and advantages of this method are discussed in detail.

Fast mask CD uniformity measurement using zero order diffraction from memory array pattern

CD Uniformity (CDU) control is getting more concerning in lithographic process and required to control tighter as design rule shrinkage. Traditionally CDU is measured through discrete spatial sampling based data and interpolated data map represents uniformity trends within shot and wafer. There is growing requirement on more high sampling resolution for the CDU mapping from wafer. However, it requires huge time consumption for CD measurements with traditional methods like CD-SEM and OCD. To overcome the throughput limitation, there was an approach with inspection tool to measure CD trends on array area which showed good correlation to the traditional CD measurement. In this paper, we suggest a fast mask CD error estimation method using 0th order of diffraction. To accomplish fast measurement, simple macro inspection tool was adopted to cover full wafer area and scan result gives good correlation with mask uniformity data.

Advanced overlay stability control with correction per exposure on immersion scanners

In this paper, we propose advanced overlay stability control improving conventional stability control, Baseliner™ and reference wafers with new vertical structure for effective stability control. We verify improved overlay stability control experimentally by using this stability control method. Also we suggest that additional improvements can be achieved by controllable process terms. For focus stability control, we make reference wafers which can measure overlay and focus simultaneously on the same wafer to minimize monitoring wafers.

High sensitive and fast scanner focus monitoring method using forbidden pitch pattern

Forbidden pitch which is introduced under a dipole illumination condition has extremely narrow DOF (Depth Of Focus). Therefore when a lithographic pattern is transferred on a wafer the forbidden pitch should be removed from the layout. However this narrow DOF behavior can be utilized to monitor a focus of scanner systems due to its sensitiveness to focus changes. In this paper, a newly developed focus monitoring method utilizing a forbidden pitch pattern will be introduced and the benefits and sensitivity of this method will be discussed in details.