Overlay accuracy is a key issue in the semiconductor manufacturing process. To achieve overlay requirements, we developed compensation functions, i.e. Enhanced Global Alignment (EGA), Super Distortion Matching (SDM), and Grid Compensation for Matching (GCM). These functions are capable to reduce all the components except local linear components caused by a wafer global deformation. In this paper we introduce a novel correction framework which includes new compensation function called Shot Correction by Grid Parameter; thereby enabling further enhancements to overlay. Using this novel framework, we show both simulation and experimental data demonstrating improved overlay accuracy.
Wafer alignment plays a significant role in the advancement of microlithography and has been constantly improved to meet various situations. As a result, its configuration is very dynamic and it sometimes requires considerable cost for process optimization.
Software has been developed which evaluates the alignment performance in a variety of conditions from the minimal data set. It allows the user to perform off-line optimization, essentially reducing the amount of interruption toward production. This article illustrates the simulation method implemented in the software, OverLay EValuation program (OLEV).
Outliers in measurement often interfere with alignment. They are caused by sudden damages in the alignment mark, and existence of particles, resist damages and so on. In a conventional way to identify outliers, the observations that have larger residual than previously determined threshold are identified as outlier. It works well only with the operator’s labor of adjusting the threshold according to the deviation of <i>ordinaries</i> (non-outliers). However, labor is a problem especially in Small-Quantity Large-Variation fabrication such as for ASIC, System-LSI and so on. A novel method for elimination of the labor has been developed. It utilizes normal mixture models whose number of components is determined based on the Maximum Penalized Likelihood (MPL) method. It can be regarded as an identification method that determines threshold adaptively using <i>ordinaries’ </i>deviation. Simulation results show that the penalty coefficient, the only parameter of the method, can be a constant in the variation of <i>ordinarie's</i> deviation. It also shows that in the absence of outliers, the accuracy of the method is comparable with the maximum likelihood estimation that is commonly considered to be the best method when the observations follow the normal distribution. The method performs better than conventional ones when there are a sufficient number of observations (no less than ten) in the standard Enhanced Global Alignment (EGA). Superiority of the adaptive method is dependent upon the probability of outlier occurrence, variation of the <i>situation</i>, the number of observations and the complexity of the model fitted to the observations.
Advanced stepper or scanner needs extremely high accuracy alignment system. This alignment accuracy is mainly affected by the errors caused by mark deformations and by optical system. To improve the alignment accuracy of our wafer alignment system called 'FIA' we have developed a method called the 'FFO'. Our studies have already shown that FFO has the effect of reducing the errors caused by mark deformations. To examine the errors caused by optical system, new approaches are adopted. In the new approaches a simulation method and a suitable experimental are used. The simulation results by the new method, Spatial Frequency Analysis of Image, show the relation between defocus and the errors caused by optical system and the superiority of FFO. Suitable experimental system brings us the same results as the simulation method. As a result, FFO also has a positive effect on the errors caused by optical system. FIA with FFO is much more accurate alignment sensor for ULSI production.
Detecting position of the wafers such as after CMP process is critical theme of current and forthcoming IC manufacturing. The alignment system must be with high accuracy for any process. To satisfy such requirements, we have studied and analyzed factors that have made alignment difficult. From the result of the studies, we have developed new optical alignment techniques which improve the accuracy of FIA (alignment sensor of Nikon's NSR series) and examined them. The approaches are optimizing the focus position, developing an advanced algorithm for position detection, and selecting a suitable mark design. For experiment, we have developed the special wafers that make it possible to evaluate the influence of CMP processes. The experimental results show that the overlay errors decrease dramatically with the new alignment techniques. FIA with these new techniques will be much accurate and suitable alignment sensor for CMP and other processes of future generation ULSI production.
As semiconductor design rules decrease, tighter tolerances are required for alignment. Improvement of the measurement algorithm can make a considerable contribution to reduction of the overlay error. An algorithm makes the alignment accuracy greatly improved that utilizes wavelet transform and uses information about image asymmetry. Experimental result using the Alignment Data Logging System shows that there is a process that the algorithm reduces the overlay error from over 100nm (3(sigma) ) to under 50nm. Two other algorithms are also introduced that are an interpolation method that reduces error from image sampling and a mark recognition method that reduces measurement failures focusing on some kinds of symmetry of the alignment mark.
Use of photons for in-situ measurements of various objects provides a number of benefits, such as precise real-time measurement with no effect on the measured objects. Our research aims to develop an in-situ measurement technology that uses the benefits of photons and is ideal for applications in production lines. We succeeded in developing a tunable laser beam source to obtain the spectral line width of 5 MHz and a continuous wavelength sweep bandwidth of 200 nm, thus achieving our initial target. We believe that these characteristics are sufficient for use in absorption spectroscopy measurement of gases. For a 2.5 - 2.7 micrometer- band quantum infrared photo detector, we achieved the initial target of D* equals 1 to 3 X 10<SUP>11</SUP> cmHz<SUP>1/2</SUP>/W (at room temperature). For a 3 - 10 micrometer-band quantum infrared photo detector, we performed a study on designing an InAsP/InP multi-quantum well light-absorbing layer.