Plasma polymerized methylsilane. II. Performance for 248 nm lithography

The advent of integrated metrology (IM) for lithography critical dimension (CD) control has been widely discussed and debated. A number of factors are pushing chip makers in the direction of IM implementation, including shrinking line widths and decreasing CD budgets, higher throughput Litho cells, escalating cost and impracticality of stand-alone CD metrology, and reducing overhead (or non value-add) time. These factors combine to make the question of IM for CD control "when" rather than "if". Scatterometry can provide a wealth of information about structures on a wafer including CD, sidewall angle, and film thickness for various layers. Although this information unquestioningly provides additional insight into the lithography process, in the end, the rate of IM implementation depends on its return on investment (ROI). In this paper, we discuss the implementation of integrated Optical Digital Profiling (iODPTM) on an advanced lithography track (Tokyo Electron CLEAN TRACK LITHIUSTM). Included are discussions of lithography trends, metrology requirements, and IM data flow and analysis. Various strategies for IM implementation are presented along with their associated ROIs.

It is vital to control Critical Dimension (CD) within a wafer and pattern profile in photolithography process. We have previously reported our evaluation results with chemically amplified resists that one of the causes of pattern profile fluctuation is a change in resist film composition before exposure such as non-uniform distributions of additives (photo-acid generator (PAG), quencher) concentration and casting solvent etc.; and thus resist film property control is essential to suppress these factors [1]. This is also true for thin resist film in finer line process and with top surface imaging. In the same paper [1], we have reported that a straightforward method to understand a change in film property is to check the amount of thickness loss by developing unexposed film after post apply bake (PAB). This method can be applied to thin film as well. We created unexposed films with the thickness range of 50-900nm by changing the total solid content (TSC) in resist and spin speed at resist coating. The amount of thickness loss significantly increased with sub-200nm thickness; the film property of which was quite different from that of 200nm-or-over thickness. Moreover, pattern line edge roughness (LER) as well as pattern surface roughness was prominent with 100nm-thick film even when we used a resist which has an ability to create good patterns on film with a thickness of 400nm. This is because the film quality diminishes in bulk below a certain thickness, while the property on the surface or interface layer predominates. Then we studied Scan coating to control thin film property. In Spin coating, chemical liquid dispensed on static wafer is spread by spinning the wafer and solvent is evaporated to form a film. On the other hand, in Scan coating, wafer remains static even after chemical liquid is dispensed and the wafer is dried under reduced pressure [2]-[7]; which means the thinner evaporation rate is slower than that in Spin coating and film property control may be easier. We, therefore, expect that Scan coating is a possible method to control CD and pattern profile. In this study, we compared the process performance and film property of KrF resist films by Scan and Spin coatings and examined the film composition control.

The significant optical absorption of most currently available commercial single layer 193 nm resists, even at a coating thickness of 0.4 micrometer, implies increased sensitivity to process control fluctuations of the kind that negatively impact critical dimension (CD) uniformity, process latitude, resist sidewall profile, and line edge roughness. These problems, although less severe on reflective substrates, are particularly acute on wafers with bottom anti-reflection coatings (BARCs), which are useful in CD control. With different intensity of light reaching different levels in the resist film on a BARC, a gradient is thus established in the extent of the chemical amplification reactions on which semiconductor lithography is based. The result is the familiar sloped sidewall profile and poor CD uniformity after the resist is developed. Further, with most of the photoacid generators and the polymer resins in the 193 nm resists having very low quantum efficiencies and significant absorption at 193 nm, respectively, most of the absorbed light in the resist is used up in energy dissipative processes, instead of in generating photoacids which catalyze the chemical amplification chemistry of these resists. One approach to overcome this absorption problem is to use significantly thinner resist films, but etch considerations preclude such option as these materials do not have very good etch stability. The purpose of this paper is to quantitatively assess the impact of absorption on the process control of sub- 0.15 micrometer features patterned on a full field ASML 193 nm scanner, interfaced to a TEL MARK-8 track. Optical properties of different resist films/BARC stack combinations are characterized by UV spectroscopic ellipsometry and broad band spectrometry, and sidewall profiling is done by atomic force microscopy.

The Semiconductor Industry Association (SIA) has placed stringent requirements on Next GenerationLithography mask critical dimension (CD) control. A new chemically amplified (CA) positive resist,Shipley XP2040D was evaluated for mask making application. This resist exhibited an extraordinary postexposure bake (PEB) sensitivity, less than 0.6 nm/ C, along with a sub-50 nm resolution. The PEB stabilityin ambient was larger than 4.5 hours and the line-edge-roughness (LER) was less than 2.9 nm. 1. INTRODUCTION Critical dimension (CD) control and uniformity for a SCALPEL mask must be kept within 7 nm (3 ) inorder to meet the SIA Roadmap requirement for 70 nm NGL mask fabrication [1]. Chemically amplified(CA) resists have been considered for NGL mask patterning because of their high resolution, high electronexposure sensitivity and etch selectivity. However, CD variation due to the PEB sensitivity of CA resistcomplicates the mask making process and needs to be minimized.Previous Finite Element Analysis modeling indicates there are PEB temperature gradients across a 200 mmSCALPEL mask and within each membrane of the mask. The thermal variations are due to the combinedcomplex three-dimensional mask structure coupled with the thermal gradients associated with the bakechamber environment. These gradients were experimentally confirmed through the measurement of criticalfeatures across various membranes on the mask array. A CD uniformity of 8-10 nm for inter-membrane and4-7 nm for intra-membrane was observed using a CA negative-tone resist, NEB22[2]. This CD variationwas mainly attributed to the large PEB sensitivity of the resist ( ~8 nm/ C).In order to meet the 7 nm SIA mask budget, CD non-uniformity due to thermal variations must be reduced.One way to minimize the influence of this thermal effect is to use low PEB sensitivity resists. This paperreports on the performance of Shipley XP2040D positive CA resist for 200 mm SCALPEL maskfabrication using the Leica VB6HR 100 KeV e-beam exposure system.

Dual Damascene (DD) process has been implemented in manufacturing semiconductor devices with smaller feature sizes (<EQ 0.20 micrometer), due to increased use of copper as a metal of choice for interconnects. Copper is preferred over aluminum due to its lower resistance which helps to minimize the effects of interconnect delays. Via first DD process is the most commonly used process for manufacturing semiconductor devices since it requires less number of processing steps and also it can make use of a via fill material to minimize the resist thickness variations in the trench patterning photolithography step. Absence of via fill material results in non-uniform fill of vias (in isolated and dense via regions) thus leading to non-uniform focus and dose for exposure of the resist in the deep vias. This results in poor resolution and poor critical dimension (CD) control in the trench-patterning step. When a via fill organic material such as a bottom anti- reflective coating (BARC) is used, then the resist thickness variations are minimized thus enhancing the resolution and CD control in trench patterning. Via fill organic BARC materials can also act as etch blocks at the base of the via to protect the substrate from over etch. In this paper we review the important role of via fill organic BARCs in improving the efficiency of via first DD process now being implemented in semiconductor manufacturing.

Argon (Ar) ion implantation into resist pattern was investigated and the remarkable improvement of the etchingresistance was confirmed on various films such as tungsten, aluminum copper, silicon oxide and silicon nitride. The possibility to make resist thickness thinner was proven. Ion dose more than 1E15/cm2 was necessary toobtain a sufficient effect, so that shrinking of resist thickness and pattern width occurred simultaneously. Thedependence of pattern shrinking on the line width was observed. Line width uniformity within a wafer was improved because of high etching resistance by ion implantation process. Line edge roughness (LER) of resist pattern was also reduced by ion implantation and smooth etched pattern could be formed. Although same effects were obtained for ArF resist, the shrinkage of ArF resist after ion implantation was more than that of KrF resists. The improvements in etching resistance and critical dimension (CD) control will be discussed in this article. KEYWORD: ion implantation, etching resistance improvement, pattern shrinking, line edge roughness, CD

The need to characterize line edge and line width roughness in patterns with sub‐50 nm critical dimensions challenges existing platforms based on electron microscopy and optical scatterometry. The development of x‐ray based metrology platforms provides a potential route to characterize a variety of parameters related to line edge roughness by analyzing the diffracted intensity from a periodic array of test patterns. In this study, data from a series of photoresist line/space patterns featuring programmed line width roughness are measured by critical dimension small angle x‐ray scattering (CD‐SAXS). For samples with designed periodic roughness, CD‐SAXS provides the wavelength and amplitude of the periodic roughness through satellite diffraction peaks. For real world applications, the rate of decay of intensity, termed an effective “Debye‐Waller” factor in CD‐SAXS, provides an overall measure of the defects of the patterns. CD‐SAXS data are compared to values obtained from critical dimension scanning electron microscopy (CD‐SEM). Correlations between the techniques exist, however significant differences are observed for the current samples. A tapered cross sectional profile provides a likely explanation for the observed differences between CD‐SEM and CD‐SAXS measurements.

The need to print smaller feature sizes has led to the shift from 248nmto193nm lithography. The disadvantages of 193nm ArF single-layer resist materials, such as lower depth of focus and lower etch resistance, have made thin-film imaging (TFI) techniques an attractive alternative. In the bilayer (comprised of an image layer and an underlayer) approach, a form of TFI, O2-based plasma chemistries are used for the transfer etches whereby oxidation of silicon in the image layer provides the required etch resistance. However, use of oxygen results in profile and critical dimension (CD) control issues. While gas additives have helped minimize these problems, there are other accompanying disadvantages. In this work, the feasibility of a non-O2-containing NH3-based plasma etch chemistry was evaluated. Effects of additive gases, such as N2, H2, and C2H4, were investigated. Surface analysis of the resist showed that nitrogen from the gas phase was incorporated in the surface of the image layer during the etch, and the etch resistance increased with this nitrogen content. Gas phase analysis showed that the relative N2H species density in the system was correlated with the nitrogen incorporated in the image layer, and is thus believed to govern the etch resistance of the image layer. The underlayer etch behavior was correlated with that of the atomic hydrogen species density. The effect of the additives on the cross section profiles and line edge roughness were studied. The highest CD biases were obtained with H2 as the additive, while near-zero CD biases were attained with C2H4 as the additive. Also, with the C2H4 additive, minimum line edge roughness and smoothest profiles were obtained.

Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.

The resist materials are evaluated using their resolution, line edge roughness (LER), and sensitivity. However, the evaluation of chemically amplified resists is tricky because of the trade-off relationships between resolution, LER, and sensitivity. In this study, we investigated a chemically amplified resist with a fullerene matrix by analyzing the dose-pitch matrices of line width and LER. The effective quencher concentration of the fullerene resist obtained by the analysis was higher than those of typical polymer-type resists. This suggests that the quantum efficiency of acid generation in the fullerene matrix is slightly lower than those of polymer-type resists. The effective reaction radius was 0.06 nm, which was smaller than those of polymer-type resists. The proportionality constant between LER and the chemical gradient of the fullerene resist was smaller than those of polymer-type resists, probably owing to its molecular size.

In order to meet the challenging patterning requirements of the 14 nm node, the semiconductor industry has implemented use of negative tone develop (NTD) and other tone inversion techniques on wafer to enable use of bright field masks which provide an improved lithography process window. 1,2,3 Due to e-beam write time and mask pattern fidelity requirements, the increased use of bright field masks means that mask makers must focus on improving the performance of their negative tone chemically amplified resist (NCAR) processes. In addition, the move to heavy use of bright field masks is introducing new challenges for mask makers. Bright field masks for 14 nm critical layers are required to have opaque sub-resolution assist features (SRAFs) as small as 50 nm while at the same time having across mask critical dimension uniformity (CDU) of less than 2 nm (3 sigma) to meet the 2014 ITRS targets. 4 Achieving these specifications is particularly difficult for bright field contact and via level masks. This paper will survey the performance requirements for NCAR resists for building 14 nm critical level masks. As part of this survey, the results of current commercially available and development NCAR resists will be compared. The study will focus on key elements of the resist process pertaining to line edge roughness, pattern fidelity, minimum feature size, and critical dimension control through density with differences in resist type, sensitivity, and thickness. In addition, use of a novel flow cell test apparatus for detailed study of the develop loading performance of the NCAR resists will be described. Data showing the current capability of these NCAR materials as well as remaining 14 nm node performance gaps and issues will be presented.

As the design rule of lithography becomes smaller, accuracy and precision in Critical Dimension (CD) and controllability of pattern-shape are required in semiconductor production. Critical Dimension Scanning Electron Microscope (CD SEM) is an essential tool to confirm the quality of the mask such as CD control, CD uniformity and CD mean to target (MTT). Unfortunately, in the case of extremely rounded region of arbitrary enclosed patterns, CD fluctuation depending on Region of Interest (ROI) is very serious problem in Mask CD control, so that it decreases the yield. In order to overcome this situation, we have been developing 2-dimensonal (2D) method with system makers and comparing CD performance between mask and wafer using enclosed arbitrary patterns. In this paper, we summarized the results of our evaluation that compare error budget between 1-dimensonal (1D) and 2D data using CD SEM and other optical metrology systems.

In 32nm/22nm advanced technology node, double patterning lithography is considered for semiconductor manufacturing. It necessitates tightened requirement of overlay measurement, i.e. to measure the position of a pattern with respect to that of a pattern in the underlying layer. The measurement target design plays a fundamental role in overlay precision and accuracy. Typical alignment target, such as bar-in-bar or box-in-box (BIB), has precision, accuracy, and size restrictions. This prompts us to look into better alignment targets. Recently, scatterometry-based metrology and profile model capability have been extended to measure multi-level grating structures. In addition, scatterometry has been shown to be the best choice for integrated metrology to perform wafer-to-wafer control. Therefore, it makes sense to consider using scatterometry for overlay measurement. In this research, the modeling analysis is performed on the spectra taken directly from a real pattern area with grating-ongrating structure. The critical dimension (CD) at the grating on top and the lateral shift between the top and the bottom gratings can be detected simultaneously. The lateral shift between the layers can be verified with the traditional overlay box. Unlike the traditional BIB target that has micrometer CD size, the CD size of the scatterometry overlay (S_OVL) target is much closer to that on the real device. So, it can much better reflect the overlay (OVL) shift on real devices. We also studied the non-model-based S_OVL measurement using a 673-nm semiconductor laser with a 10&mu;m x 20&mu;m target size, wafer-to-wafer control of CD and lateral shifts on some critical layers with grating-on-grating structure, as well as the CD and OVL variations within layer and from layer to layer for double patterning.

As pattern design rule of device shrinks, CD control becomes more critical and important especially for resistance devices. As CD (Critical Dimension) increases, CDU (Critical Dimension Uniformity) becomes worse generally. The question with this relationship is a starting point of our study. Mainly we focused on two points. One is which factor affects CDU. The other is whether CDU degradation with large CD happens at all cases or not. We have analyzed with simulation and experiment results about CDU with splitted mask layout CD under limited conditions such as same equipment, illumination and exposure dose. As a result, we will show the relationship between CD size and CDU.

Trilayer NbN/MgO/NbN tunnel junctions and Mo and NbN/sub x/ resistors fabricated over a NbN ground plane form the basis of a high performance, 10 K, superconductor integrated circuit foundry process. To produce high yield LSI and VLSI superconductor integrated circuits requires predictable device characteristics, stable, well-characterized, thin film deposition processes, and control of critical dimensions (CD). In this paper, we discuss improvements in thin film deposition processes, device characteristics, and CD control. Repeatable trilayer characteristics have been achieved through the use of feedback control of critical MgO and NbN sputtering parameters. Run-to-run variations in MgO film thickness have been reduced to less than /spl plusmn/1.0% (1/spl sigma/) using a novel computer feedback control technique. Improvements in MgO deposition uniformity and CD control of junction size have reduced across wafer I/sub c/ nonuniformity to less than /spl plusmn/10% (3/spl sigma/) and 100 junction array I/sub c/ nonuniformity on 0.5 cm chips to /spl plusmn/2% (1/spl sigma/). We report on the electrical characteristics of junctions and resistors and on component spreads and stability of our NbN foundry process.