Negative Tone Development Process Research Articles

Cluster sampling and scalable Bayesian optimization with constraints for negative tone development resist model calibration

As the semiconductor technology node continues to shrink, achieving smaller critical dimension in lithography becomes increasingly challenging. Negative tone development (NTD) process is widely employed in advanced node due to their large process window. However, the unique characteristics of NTD, such as shrinkage effect, make the NTD resist model calibration more complex. Gradient descent (GD) and heuristic methods have been applied for calibration of NTD resist model. Nevertheless, these methods depend on initial parameter selection and tend to fall into local optima, resulting in poor accuracy of the NTD model and massive computational time. In this paper, we propose cluster sampling and scalable Bayesian optimization (BO) with constraints method for NTD resist model calibration. This approach utilizes cluster sampling strategy to enhance the capability for global initial sampling and employs scalable BO with constraints for global optimization of high-dimensional parameter space. With this approach, the calibration accuracy is significantly enhanced in comparison with results from GD and heuristic methods, and the computational efficiency is substantially improved compared with GD. By gearing up cluster sampling strategy and scalable BO with constraints, this method offers a new and efficient resist model calibration.

Wafer CD Uniformity Improvement in Negative Tone Development Process

WCDU (wafer critical dimension uniformity) has become one of the most momentous factors in the resist process for mass production. Non-uniform WCDU, CD value changes from wafer center to edge, can occur in resist process despite tight critical dimension uniformity (CDU). In this paper, the resist components and the resist process conditions that influence on WCDU variation in negative tone development (NTD) process will be discussed. WCDU was measured with various parameters to understand the causes of current performance.

Necessity of resist model in source mask optimization for negative tone development process

As the semiconductor technology node comes to 14 nm and below, using bright-field exposure with negative tone development (NTD) has been a dominant lithographic solution for metal and contact layers, which has benefits of larger process windows and higher image contrasts than positive tone development (PTD). For PTD, a resist model is usually optional in source mask optimization (SMO) because optical models with aerial image blur can predict resist behaviors in most cases. However, NTD has much stronger resist effects, such as resist shrinkage and two-dimensional-effect-induced local stress. It has been suggested that the calibrated resist model is strongly required in the SMO of NTD process. We clarify this issue—the necessity of resist model in SMO for NTD process. First, we analyze the mismatch between simulation and experimental data when the aerial image blur is only used to simulate resist effects. Second, we present the calibration flow of resist model. Finally, we use the calibrated resist model to check the test pattern and run the SMO. The result demonstrates that the simulation data have the same tendency with experimental data, and the model has a good prediction on NTD resist behaviors under different conditions.

Optimization of resist parameters to improve the profile and process window of the contact pattern in advanced node

Typically, the printing of contact patterns uses a dark-field (DF) mask in combination with a positive tone resist and positive tone development (PTD) process. PTD, which has a mature process and simulation model, had been widely applied in high-volume manufacturing. For the low aerial image quality of a DF mask in advanced node, PTD is substituted by negative tone development (NTD), which uses a positive tone resist and bright-field mask. Due to the high cost and immature simulation model of NTD process, it is worthwhile to extend PTD to some critical patterns. With the purpose of improving the resist profile and process window (PW) of the contact pattern with a PTD process in advanced node, an optimization method combined with the idea of a genetic algorithm is put forward. For performance of the optimized resist under the conditions of best focus and best dose, an evaluation based on the through pitch square contact patterns with the critical dimension (CD) fixed at 50 nm has been provided. The generalization performance of the optimized resist is also analyzed by a systematic method, which contains the resist profile and PW simulation on the base of through CD and through pitch contact patterns. The above simulation results verify the effectiveness and validity of the proposed optimization method.

(Invited) Negative Tone Development Process and Resist Materials with ArF Immersion Exposure Process

Negative tone development (NTD) process was proposed as a good candidate to obtain good quality in resist pattern for trench and contact hole (C/H) pattern with ArF immersion resist process. Advantages of NTD compared to positive tone development (PTD) process are discussed in detail. High volume manufacturing capabilities, mainly in the performances of CD uniformity and defectivity, are discussed. The challenges in resist material are addressed, and the material design strategies and new resist materials are introduced.

Potential applications of negative tone development in advanced lithography

Advanced lithography requires resolution enhancement techniques (customized illumination mode, litho friendly design), and alternative process flow schemes (double exposure, double patterning) in order to meet the requirements of the ITRS technology roadmap and to extend the applications of a full-field scanner with a 1.35 numerical aperture (NA) that represents the physical limit of water-based immersion ArF lithography.Today, one of the most interesting alternative processes uses the patterning inversion through a negative tone development (NTD) process step. Traditionally, the patterning (contacts or trenches) is done by using a dark field mask in combination with positive tone resist and positive tone development (PTD). By using a solvent-based developer (NTD) and a bright field mask, the same features can be transferred into a positive resist with the benefit of better image contrast and, consequently, better line width roughness (LWR) and resolution.In this work we have explored the potential applications of NTD for trenches and contact holes for the 45nm technology node requirements and beyond. The NTD process is a promising option considering the impact on process window, LWR, CD uniformity and defectivity. The experimental result of this alternative approach to print critical dark field levels in an advanced lithography boundary has been explored.

Effect of Molecular Weights of 193nm Resist Polymers on the Negative Tone Development Process

The effect of molecular weights of 193nm resist polymers on the negative tone development (NTD) process was studied in three different solvent developers. By optimizing the polymer structures for the NTD process, it was possible to improve the dissolution rate of 193 nm resist polymers in the NTD process to give higher dissolution rate contrasts in a wide range of molecular weights. Contrary to the conventional positive tone development process, the NTD process yielded faster photospeeds with higher molecular weights. It was also found that the critical dimension uniformity (CDU) of 193 nm resists can be optimized in the NTD process by optimizing the molecular weights of the resist polymers. The optimum Mw for the best CDU was different for different developers and could be different for different resist formulations. In addition to the resist polymers and developers, it will be necessary to optimize other imaging materials for the NTD process in order to maximize the full benefits of the NTD process.

Circle Patterning Technology with Negative Tone Development for ArF Immersion Extension.

Contact hole patterning for half pitch 51nm can be achieved by single exposure for mass production and for half pitch 39nm can be achieved by Litho-Etch-Litho-Etch (LELE). Currently for half pitch 32nm there is no promising solution so far, but ouble patterning and extreme ultraviolet lithography (EUV) are still competing each other for this target. In the current situation of contact hole patterning, single exposure negative tone development (NTD) shows excellent contact hole performance on fidelity, process window and CD uniformity compared to positive tone development (PTD) and finally enables to define half pitch below 50nm. In this paper, we describe necessity for circle patterning on 3-D flash, optimization of exposure condition, upgrade status of resist and device speed of 3-D flash on negative tone development (NTD) process.

Comparing positive and negative tone development process for printing the metal and contact layers of the 32- and 22-nm nodes

A strong demand exists for techniques that extend application of ArF immersion lithography. Besides techniques such as litho-friendly design, dual exposure/patterning schemes, customized illumination, alternative processing schemes are also viable candidates. One of the most promising alternative flows uses image reversal by means of a negative tone development (NTD) step with a Fujifilm solvent-based developer. Traditionally, contact and trench printing uses a dark-field mask in combination with positive tone resist and positive tone development. With NTD, the same features are printed in positive resist using light-field masks, and consequently with better image contrast. We present an overview of NTD applications, comparing the NTD performance to that of the traditional development. Experimental work is performed at a 1.35 numerical aperture, targeting the contact/metal layers of the 32- and 22-nm nodes. For contact printing, we consider both single- and dual-exposure schemes for regular arrays and 2-D patterns. For trench printing, we study 1-D, line end, and 2-D patterns. We also assess the etch capability and critical dimension uniformity performance of the NTD process. We proves the added value of NTD. It enables us to achieve a broader pitch range and/or smaller litho targets, which makes NTD attractive for the most advanced lithography applications, including double patterning.

Materials and Processes of Negative Tone Development for Double Patterning Process

A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed to form narrow trench and contact hole patterns, which is promising for double patterning process, since it is difficult to obtain sufficient optical image contrast to print narrow trench or contact hole below 60 nm pattern size with positive tone imaging. No swelling property in the developing step realized low LWR number at 32 nm trench patterns. Uniform de-protection ratio through the depth of resist film reduced cuspy resist pattern profile causing micro-bridges at narrow trench pattern, and low frequency LWR number down to 2.4 nm. High resolution potential was demonstrated with 38 nm dense S/L under 1.35 NA immersion exposure. Better CD uniformity and LWR number of trench pattern were obtained by negative tone development (NTD) process with comparison to positive tone development (PTD) process. Excellent defect density of 0.02 counts/cm2 was obtained for 75 nm 1:1 S/L by combination of 0.75 NA dry exposure and NTD process combination. NTD process parameters impacts to defectivity were studied.

Development of Materials and Processes for Double Patterning toward 32nm Node ArF Immersion Lithography

A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed for narrow trench pattern formation, which is effective to the double trench process that is one of the candidates of double patterning process for 32 nm node semiconductor devices. No swelling property was realized in the developing step, in which the dissolution mechanism was discussed. Significantly better line width roughness (LWR) and resolution on narrow trench pattern were observed with this negative tone development compared to positive tone development. These results suggest that this negative tone development process is one of the promising candidates for double trench process.