As the design rule is decreased rapidly, tighter critical dimension (CD) control is highly requested in photomask process. Accordingly, instead of wet etching to make an isotropic pattern, dry etching has been increasingly applied for an anisotropic pattern transfer in order to get an accurate critical dimension (CD). Since the dry etching process was employed for the fabrication of photomask, particles in plasma reactor has been a big issue. It is being currently recognized that the splinters of polymers, defectively stunk on the reactor wall leading to the particles as plasma is ignited by radio-frequency (RF) power. Hence, wet cleaning used to be performed for the purpose of removing the particle source. Nevertheless, this method is not able to remove particles perfectly in the plasma reactor. Frequently the number of the particle is not changed before and after wet cleaning, particularly in ICP reactor. In this paper, we studied the characteristics of the plasma chemistry and the behavior of ions in ICP reactor. The origin of the particle generation was investigated by the analysis of the composition and configuration of particles. Finally, solutions will be suggested to reduce the particle with low damage on the insulator based on the above studies.
In photomask manufacturing, etch loading effect is one of the most serious problems. The equal size of isolated clear patterns, each of which is surrounded by different pattern density, can show different CD (critical dimension) results after Cr etching process. Furthermore, as the feature size decreases and pattern density increase, the burden of Cr loading effect in mask fabrication is more enlarged than ever. In this paper, we will present the new method for approaching to the loading free process in photomask Cr dry etch.
As the feature size of integrated circuits decreases, it is difficult to have a good resolution with an ordinary lithography technology. Resolution enhancement technologies (RETs), therefore, become prominent way to achieve better resolution. Among various RETs, Phase Shift Mask (PSM) can be one of the most useful technologies in these days and especially Chrome-Less Mask (CLM) or Phase Edge PSM (PE-PSM) is used for utilizing strong effect of PSM technology. In manufacturing the CLM or PE-PSM, the quartz layer of the photomask should be etched to 2480 in depth which is the equivalent value in phase, 180°. But quartz etch is one of the difficult processes in photomask manufacturing due to the absence of stopper layer. Moreover, the depth uniformity should be controlled within the tolerance of 5°. But there are etch rate variations from center to edge positions within the 6-inch mask area which originates from the deficit of plasma uniformity. As a result, phase deviation in those area occurs after quartz etch up to several degrees in phases and this problem makes the manufacturing of CLM or PE-PSM difficult. We thought there would be some relations between etch rate uniformity and hardware, such as focus ring which is used for confinement of plasma species. Various experiments, therefore, were executed with regard to the type of focus ring (shape, and height). As a result, the outstanding tendencies which show the relations, can be obtained. On this paper, the detailed descriptions of the experiments and their results will be presented.
The introduction of ArF lithography in device manufacturing has been studied with a low k1-factor. There are a number of issues that must be resolved to ensure the successful implementation of this technology. Such issues include the reduction in resist thickness and organic bottom anti-reflective coating (BARC) due to the characteristics of ArF resist with lower etch resistance in comparison with that of KrF. Requirements of a suitable high-performance of thin organic BARC material include chemical reactions with sub-layer, simulation for the minimization of reflectance, faster etch rate, and compatibility with resist. The optimum refractive index (n) and the extinction coefficient (k) of thin organic BARC are simulated to match the optical properties of substrates. These values are satisfied with the reflectance less than 2% at 1st minimum. In the case of SiN sub-layer with acid absorption capability, it is confirmed that the chemical reaction with thin organic BARC has an effect on line edge roughness (LER) and pattern profile. Also, the degree of these effects is dependent upon the acidity of thin organic BARC. In this paper, it is shown that the application of thin organic BARC to sub-90nm patterning in ArF lithography is very feasible and adaptable in the view of lithographic and etch performance.
As the feature size of integrated circuits shrinks, the demands for the critical dimension (CD) uniformity on wafers are becoming tighter. In the era of low k1, moreover, mask CD uniformity should be controlled even more stringently due to the higher mask error enhancement factor (MEEF). Mask CD non-uniformity can originate from several sources which include photomask blanks and mask-making processes (exposure, post-exposure bake (PEB), development, and etch processes). Analyzing the CD error sources and eliminating the origins are very important tasks in optimization of mask-manufacturing processes. In this paper, we focus on the side error in mask CD uniformity and present a simple method for separating and evaluating the origins. Especially, quantitative analysis of the side errors induced by photomask blanks and mask-making processes, respectively, is given. Photomask blanks are found to be one of the main sources of the side error and it is shown that the temperature distribution of the PEB process during the ramp-up as well as the stable period should be maintained uniformly for chemically amplified resist (CAR) blanks in order to reduce the process-induced side error.
An analytical approach to X-phenomenon in alternating phase-shifting masks is given in the framework of the thin-mask approximation. We present an analytical expression for the focus-dependent intensity imbalance between 0° and 180° phase regions when there exists relative phase error. It is shown that X-phenomenon results from the interference between 0th diffracted order, which originates from the phase error and has an in- or out-of-phase component with respect to the ±1st diffracted orders depending on the defocus directions, and the ±1st diffracted orders. Dependences of the intensity imbalance on the phase error and the duty ratio of the structure are given.
The demands for shrinking critical dimension (CD) and for tight control of CD uniformity on photomask are rapidly increasing. To keep pace with the demands, optical pattern generators using i-line resist is expanding its capability by continuously modifying hardware and writing strategies. Aside from their advantage of high throughput and layer-to- layer alignability for phase-shifting masks (PSM), this optical process has proven to show a good capability in view of the mean-to-target (MTT) control. In this paper, we investigate the extended capability of a laser writing tool for 180nm node and below in view of process-induced limitations and systematic errors. We also discuss the effects of pattern density and of writing strategy on Cd accuracy and pattern placement error. Since MTT and CD uniformity error for 180 nm generation device are critical for wafer printing, we scrutinize process-induced limitations and systematic errors. The process-induced limitations, related to pattern density and shape, are discussed along with the football effect and iso-dense bias.
As the design rule is rapidly decreased, tighter critical dimension (CD) control is highly requested. Considering the mask error enchantment factor, higher mask quality below 8nm should be guaranteed for 0.10micrometers generation devices. Among a number of actors causing CD errors in e-beam mask fabrication, dry etching plays an important role. Therefore, it is necessary to reduce loading effect for accurate CD control. As the loading effect in the dry etching is closely related to the selectivity of Cr to resist, a clue to reduce the loading effect is to reduce loading. In this paper, we will clarify the relation mechanism between the selectivity and loading effect. We will investigate the degree of loading effect by quantifying the selectivity with different etch processes.
Resolution comparison of a CAR (positive resist) and ZEP- 7000 was investigated for 50 kV e-beam machine and dry etching process. The CAR is superior to ZEP-7000 in view of resist profile, while it is inferior in view of CD variation, after Cr dry etching. The etching results were improved using thin resist, optimizing the etching condition and process effect correction. The best performance was obtained form e-beam proximity correction. It is difficult to apply this model to a real device since it has model errors and inconvenience in data handling. Among the activities for the improvements, etch condition optimization is the most effective. A pattern fidelity issue such as edge roughness and line-end shortening remains even with a CD linearity improvement.
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