Elizabeth Wolfer

New spin-on metal hardmask materials for lithography processes

Since the critical dimensions in integrated circuit (IC) device fabrication continue to shrink below 32 nm, multilayer stacks with alternating etch selectivities are required for successful pattern transfer from the exposed photoresist to the substrate. Inorganic resist underlayer materials are used as hard masks in reactive ion etching (RIE) with oxidative gases. The conventional silicon hardmask has demonstrated good reflectivity control and reasonable etch selectivity. However, some issues such as the rework of trilayer stacks and cleaning of oxide residue by wet chemistry are challenging problems for manufacturability. The present work reveals novel spin-on underlayer materials containing significant amounts of metal oxides in the film after baking at normal processing conditions. Such an inorganic metal hardmask (MHM) has excellent etch selectivity in plasma etch processes of the trilayer stack. The composition has good long term shelf life and pot life stability based on solution LPC analysis and wafer defect studies, respectively. The material absorbs DUV wavelengths and can be used as a spin-on inorganic or hybrid antireflective coating to control substrate reflectivity under DUV exposure of photoresist. Some of these metal-containing materials can be used as an underlayer in EUV lithography to significantly enhance photospeed. Specific metal hard masks are also developed for via or trench filling applications in IRT processes. The materials have shown good coating and lithography performance with a film thicknesses as low as 10 nm under ArF dry or immersion conditions. In addition, the metal oxide films or residues can be partially or completely removed by using various wet-etching solutions at ambient temperature.

Progress in spin-on metal oxide hardmask materials for filling applications

It is well known that metal oxide films are useful as hard mask material in semiconductor industry for their excellent etch resistance against plasma etches. In the advanced lithography processes, in addition to good etch resistance, they also need to possess good wet removability, fill capability, in high aspect ratio contacts or trenches. Conventional metal containing materials can be applied by chemical vapor deposition (CVD) or atomic layer deposition (ALD). Films derived from these techniques have difficulty in controlling wet etch, have low throughput and need special equipment. This leads to high costs. Therefore it is desirable to develop simple spin-on coating materials to generate metal oxide hard masks that have good trench or via filling performances using spin track friendly processing conditions. In this report, novel spin-on type inorganic formulations providing Ti, W, Hf and Zr oxide hard masks will be described. The new materials have demonstrated high etch selectivity, good filling performances, wet removal capability, low trace metals and good shelf-life stability. These novel AZ® Spin-on metal hard mask formulations can be used in several new applications and can potentially replace any metal, metal oxide, metal nitride or silicon-containing hard mask films currently deposited using CVD process in the semiconductor manufacturing process.

Novel spin-on metal hardmask materials for filling applications

Hardmasks are indispensable materials during pattern transfer to the desired substrates in the semiconductor manufacturing process. Primarily there are two types of hardmask materials - organic and inorganic - and they can be coated onto substrates or underlying materials either by a simple spin-on process or by more expensive methods such as chemical vapor deposition (CVD), atomic layer deposition (ALD) and sputtering process. Most inorganic hardmasks such as SiO2, SiON, SiN and TiN are deposited using the CVD process. Future nodes require hardmasks with high etch resistance as the designs move from horizontal to vertical (3D). We have reported novel spin-on metallic hardmasks (MHM) with comparable or higher etch resistance than SiO2.1-2 In addition to high etch resistance, they are easy to remove using wet etch chemicals. The spin-on process offers high throughput and commonly used spin tracks can be utilized; thereby reducing overall process costs when compared with CVD. Via-fill performance is also an important attribute of hardmask materials for these future nodes. Organic spin-on materials, both siloxane- and carbon-based, are used in filling applications of deep via or deep trench fill, such as those found in LELE double-patterning schemes. Inorganic materials deposited by either chemical vapor deposition (CVD) or atomic layer deposition (ALD) have higher resistance to oxygenated plasma than organic materials, but are hindered by their poor filling performance. Therefore, novel tungsten (W) containing MHM materials having both good filling performance and higher resistance to oxygenated plasma than organic materials would be of value in some filling applications. The present paper describes specific metal oxides useful for filling applications. In addition to basic filling performance and etch resistance, other properties such as optical properties, outgas and shelf life via forced aging etc. will be discussed.

Image Reversal Trilayer Materials and Processing

Image reversal trilayer (IRT) combines three lithographic patterning enhancement approaches: image reversal, spin on hard masks, and shrink for recess types of features. With IRT, photoresist imaging is done directly on top of the carbon underlayer. Thick IRT-Carbon Hard Masks (CHM) films provide effective antireflection with high NA lithography and are more etch resistant than common photoresist. IRT-Silicon Hard Masks (SiHM) can be coated over the resist patterns in the lithography track. IRT etching reverses the resist pattern into the IRT-SiHM and transfers this image to the IRTCHM. The recessed patterns in the IRT-CHM are smaller than the CD of the photoresist feature from an inherent shrinking capability of the IRT-SiHM. Continuous improvements to both IRT-SiHM and IRT-CHM have been made. Silicon contents in IRT-SiHM have been pushed as high as possible while not impacting other important properties such as stability, coating quality and resist compatibility. Newer polysiloxane IRT-SiHM no longer require resist freezing prior to coating. Carbon contents in IRTCHM have been pushed as high as possible while maintaining solubility and a low absorption which is important when resist imaging is done directly on top of the IRT-CHM. Feasibility of this image reversal trilayer process was previously demonstrated on L/S and pillar gratings. Recent work focused on nonsymmetrical 2D gratings and simultaneous patterning of L/S gratings at different pattern densities. Particular emphasis is given to pattern density effects which are applicable to any top-coating image reversal process. This paper describes the lithography, pattern transfer process and 2nd generation hard mask materials developed for IRT processing.

Spin-on metal oxide materials for N7 and beyond patterning applications

There is a growing interest in new spin on metal oxide hard mask materials for advanced patterning solutions both in BEOL and FEOL processing. Understanding how these materials respond to plasma conditions may create a competitive advantage. In this study patterning development was done for two challenging FEOL applications where the traditional Si based films were replaced by EMD spin on metal oxides, which acted as highly selective hard masks. The biggest advantage of metal oxide hard masks for advanced patterning lays in the process window improvement at lower or similar cost compared to other existing solutions.

Spin-on metal oxide materials with high etch selectivity and wet strippability

Metal oxide or metal nitride films are used as hard mask materials in semiconductor industry for patterning purposes due to their excellent etch resistances against the plasma etches. Chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques are usually used to deposit the metal containing materials on substrates or underlying films, which uses specialized equipment and can lead to high cost-of-ownership and low throughput. We have reported novel spin-on coatings that provide simple and cost effective method to generate metal oxide films possessing good etch selectivity and can be removed by chemical agents. In this paper, new spin-on Al oxide and Zr oxide hard mask formulations are reported. The new metal oxide formulations provide higher metal content compared to previously reported material of specific metal oxides under similar processing conditions. These metal oxide films demonstrate ultra-high etch selectivity and good pattern transfer capability. The cured films can be removed by various chemical agents such as developer, solvents or wet etchants/strippers commonly used in the fab environment. With high metal MHM material as an underlayer, the pattern transfer process is simplified by reducing the number of layers in the stack and the size of the nano structure is minimized by replacement of a thicker film ACL. Therefore, these novel AZ® spinon metal oxide hard mask materials can potentially be used to replace any CVD or ALD metal, metal oxide, metal nitride or spin-on silicon-containing hard mask films in 193 nm or EUV process.

Combinatorial process optimization for negative photo-imageable spin-on dielectrics and investigation of post-apply bake and post-exposure bake interactions

Patternable dielectric materials were developed and introduced to reduce semiconductor manufacturing complexity and cost of ownership (CoO). However, the bestowed dual functionalities of photo-imageable spin-on dielectrics (PSOD) put great challenges on the material design and development. In this work, we investigated the combinatorial process optimization for the negative-tone PSOD lithography by employing the Temperature Gradient Plate (TGP) technique which significantly reduced the numbers of wafers processed and minimized the developmental time. We demonstrated that this TGP combinatorial is very efficient at evaluating the effects and interactions of several independent variables such as post-apply bake (PAB) and post-exposure bake (PEB). Unlike most of the conventional photoresists, PAB turned out to have a great effect on the PSOD pattern profiles. Based on our extensive investigation, we observed great correlation between PAB and PEB processes. In this paper, we will discuss the variation of pattern profiles as a matrix of PAB and PEB and propose two possible cross-linking mechanisms for the PSOD materials to explain the unusual experimental results.

Photo-imageable spin-on dielectrics for TSV 3D packaging applications

Photo-imageable spin-on dielectrics (PSOD) with low dielectric constant were developed for TSV 3D packaging applications. Negative-tone PSOD with high resolution was devised to afford patterned dielectrics through simplified process, i.e. lithography and thermal annealing, in comparison to conventional CVD / Lithography / DRIE integration process. All processes employed in the PSOD fabrication are performed at low temperature (≤200°C) in order to meet the relatively low temperature constraints from conventional packaging materials.

Negative photo-imageable spin-on dielectrics: report on progress, challenges, and opportunities

From the perspectives of IC fabrication simplification, cost reduction, and waste material cutback, it is highly desirable to combine the traditional pattern formation step (lithographical processes) and the pattern transfer step (etch processes) into a single step. Photo-imageable spin-on dielectrics (PSOD) render it possible to achieve the aforementioned goal. However, the bestowed dual functionalities on PSOD put great challenges on the material design and development. PSOD needs not only to match all the performances of the advanced resists, but also to undertake all the duties of the dielectrics on the chips. We wish to report our modular approach employing Si-containing materials to address the challenge and to meet the requirements from the different material roles. This paper will also discuss the investigation and progress on lithographic performance, cure behaviors, thermal stability, and electrical and mechanical properties.

A study on effect of point-of-use filters on defect reduction for advanced 193nm processes

Bottom Anti-Reflective Coatings (BARCs) have been widely used in the lithography process for decades. BARCs play important roles in controlling reflections and therefore improving swing ratios, CD variations, reflective notching, and standing waves. The implementation of BARC processes in 193nm dry and immersion lithography has been accompanied by defect reduction challenges on fine patterns. Point-of-Use filters are well known among the most critical components on a track tool ensuring low wafer defects by providing particle-free coatings on wafers. The filters must have very good particle retention to remove defect-causing particulate and gels while not altering the delicate chemical formulation of photochemical materials. This paper describes a comparative study of the efficiency and performance of various Point-of-Use filters in reducing defects observed in BARC materials. Multiple filter types with a variety of pore sizes, membrane materials, and filter designs were installed on an Entegris Intelligent(R) Mini dispense pump which is integrated in the coating module of a clean track. An AZ(R) 193nm organic BARC material was spin-coated on wafers through various filter media. Lithographic performance of filtered BARCs was examined and wafer defect analysis was performed. By this study, the effect of filter properties on BARC process related defects can be learned and optimum filter media and design can be selected for BARC material to yield the lowest defects on a coated wafer.