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.
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.
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.
Array CD uniformity can be measured by inspection tool and showed good correlation to traditional CD measurement
such as CD-SEM and OCD. Due to the inspection tool's basic requirement which collects information over whole area
of wafer, the CD mapping from inspection images results in high spatial details within shot and along the wafer scale.
However the reflected light which comes from the interaction between sub-wavelength array pattern and illuminated
light isn't only responsible for CD variation of the illuminated area pattern. Other than lateral CD differences, thickness
variation of pattern and under layer films also result in light intensity changes on reflected light. Therefore the noise
separation other than CD variation is crucial factor on CD mapping using inspection tool. On the other hand, the
sensitivity of CD variation is dependent on the patterned layer materials and how it interacts with the polarization of
From previous study, reflection light from sub wavelength array structure contains CD variation information and gives
linear response to the structure volume change. In this paper, CD test box which has intentional CD variation is
introduced to investigate on various parameters that result in reflectivity changes. Wavelength, polarization and optical
property of patterned structure are conducted to analyze the influence to the reflectivity signal. In parallel the
experimental results are compared with simulation result using RCWA and good correlation is achieved.
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 0<sup>th</sup> 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