This article explores the challenges of microbump pitch scaling down to 5 mu m for chiplet applications, including thermocompression bonding (TCB) tool alignment accuracy, fabrication process limitations, coefficient of thermal expansion (CTE) mismatch, metal oxide reduction, and reliability concerns for die-to-wafer (D2W) bonding. An approach called embedded bumps, together with fluxless TCB, is introduced to mitigate the challenges. In addition, it discusses qubit, interposer, and CMOS chips integration in 2.5-D chiplet and 3-D architectures for cold and quantum computing (QC) applications, where indium is used as the solder metal, where successful bonding results for 20- mu m pitch indium bumps are shown.

In this paper we demonstrate the application of a formulated wet passivation on scaled Cu micro-bumps before Thermal Compression Bonding (TCB)process for 3D stacked-IC (3D-SIC) applications. A formulated developmental prototype chemistry from MEC Co. Ltd is applied to protect the copper (Cu) micro-bumps from oxidation during shelf life and to provide an oxide free surface for TCB and to enable solder wetting. Good solder joint and IMC formation and almost 100% electrical yield for 20μm pitch daisy chains without yield loss in reliability tests could be obtained through the application of this formulated passivating coating on these scaled Cu bumps. Furthermore, the compatible with commercial underfill (UF) material is demonstrated with no voiding and very good UF coverage observed in between 20, 10, 7 and 5um pitch micro-bumps.

GeSbTe (GST) compounds have been implemented in Phase Change Random Access Memory (PCRAM) devices. 2D scaling or stacking of PCRAM is limited by cost and therefore the development of 3D architectures is expected. A key requirement for the fabrication of this 3D architecture is the etch-back of the GST. The main objective of this study is to partially recess GST in a controllable way, leaving the surface of the GST smooth after recess. Wet isotropic recess of amorphous and crystalline blanket films as well as patterned samples was explored using commodity chemistries like APM and HPM. Due to some shortcomings of these peroxide-containing solutions, the oxidizing agent was changed from H2O2 to O3. In the ozone-containing solutions the roughness of the GST after etch-back could be controlled as well as the selectivity towards Al2O3, SiO2 and TiN ensured.

Memory cells comprising a Phase Change Material (PCM) are the building blocks of fast and non-volatile memory devices called Phase Change Random Access Memory (PCRAM) [1-3]. The working principle of this memory involves data retention in the form of a phase (amorphous or crystalline) and the set and reset can be done by Joule heating to induce an amorphous-to-crystalline or crystalline-to-amorphous transition respectively. Some chalcogenide materials experience this thermally driven phase change, GeSbTe (GST) being one of those alloys extensively studied. GST has also been adopted for the fabrication of the 1st generation X-point memory [4] and might be adopted in a 2nd generation X-point memory of a four-layer PCM structure [5]. However, this 2D scaling or stacking of PCRAM is limited by cost and therefore the development of 3D architectures is envisaged for decreasing the cost/bit [6]. A key requirement for the fabrication of this 3D architecture is the conformal deposition and etch-back of GST. Dry plasma etching might be limited to anisotropic recess while isotropic lateral recess is needed. Therefore, wet isotropic etching might be the process of choice. A few chemical solutions have been proposed in previous studies. Cheng et al. showed that GST could be etched in HNO3 but with a very high etch rate and with an unwanted surface composition change due to different oxidation and dissolution rates of the metalloids [7]. Wang et al. demonstrated that basic wet etching solutions led to a slower etch rate and a much smoother surface compared to acidic wet etching solutions [8]. Deng et al. showed a switch in the etch rate order between crystalline and amorphous GST depending on the H2O2 concentration in TMAH [9]. In this work, we present a controllable partial recess solution that leaves the GST surface smooth after recess. Wet recess of amorphous and crystalline blanket films, as well as patterned samples, was initially explored using the commodity chemistries Ammonium Peroxide Mixture (APM) and (Hydrochloric Peroxide Mixture) HPM. The etching of GST in HPM as a function of the H2O2 concentration was monitored by ICPMS and showed a well-controlled etch rate. However, some shortcomings of these H2O2-containing solutions, like roughness and selectivity, lead to a change of oxidizing agent from H2O2 to O3. In the O3-containing solutions, the selectivity towards Al2O3, SiO2, and TiN could be secured. The impact of the dissolved O3 concentration on surface roughness and etch rate as well as the uniformity of this wet etching process were assessed on a single wafer tool. Finally, the bulk and surface GST composition and oxidation post-recess were verified through XPS and ERD. REFERENCES: [1] D. Loke et al., “Breaking the Speed Limits of Phase-Change Memory.” Science, 2012, 336, 6088, 1566. [2] K. Ding et al., “Recipe for ultrafast and persistent phase-change memory materials.” NPG Asia Mater 12, 63, 2020. [3] F. Rao et al., “Reducing the stochasticity of crystal nucleation to enable sub-nanosecond memory writing.” Science, 2017, 358, 6369, 1423. [4] [internet] https://www.techinsights.com/blog/intel-3d-xpoint-memory-die-removed-intel-optanetm-pcm-phase-change-memory [5] [internet] https://www.techinsights.com/blog/memory/intels-2nd-generation-xpoint-memory [6] [internet] https://www.imec-int.com/en/imec-magazine/imec-magazine-october-2017/in-pursuit-of-high-density-storage-class-memory [7] H.Y. Cheng et al., “Wet-Etching Characteristics of Ge2Sb2Te5 Thin Films for Phase-Change Memory.” IEEE Trans. Magn., 41, 2, 2005. [8] L. Wang et al., “Basic Wet-Etching Solutions for Ge2Sb2Te5 Phase Change Material.” J. Electrochem. Soc., 157, H470, 2010. [9] C. Deng et al., “XPS study on the selective wet etching mechanism of GeSbTe phase change thin films with TMAH.” Proc. of SPIE, 8782, 87820N, 2012.

Wet etching offers an advantage as a soft, damage-less method to remove sacrificial material with close to nanometer precision which has become critical for the fabrication of nanoscale structures. In order to develop such wet etching solutions, screening of etchant properties like selectivity and (an)isotropy has become vital. Since these etchants typically have low etch rates, sensitive test structures are required to evaluate their etching behavior. Therefore, scaled-down single-crystalline Si (c-Si) and SiGe (c-SiGe) wagon-wheels were fabricated. First, the sensitivity of the c-Si wagon-wheels to detect anisotropic behavior of crystalline silicon in the alkaline etchants TMAH and NH4OH was demonstrated. Distinctive wagon-wheel patterns, characteristic for each material/etchant pair, were observed by top-down scanning electron microscopy (SEM) after anisotropic wet etching. Similar trends in crystallographic plane-dependent etch rates were obtained for both Si(100) and Si(110) substrates. Secondly, the etching of both c-Si and c-Si75Ge25 wagon-wheels in a typical selective etchant, peracetic acid (PAA), was evaluated. c-Si75Ge25 etching in PAA resulted in isotropic etching. Selectivity values were calculated based on two methods: the first by measurement of the sidewall loss of the spokes of the wagon-wheel, the second, indirect method, through measurement of the spoke retraction lengths. Both methods give comparable values, but the latter method can only be used after a certain critical etching time, after which the spoke tips have evolved toward a sharp tip.

In next-generation EUV imaging for foundry N5 dimensions and beyond, inherent pitch- and orientation-dependent effects on wafer level will consume a significant part of the lithography budget using the current Ta-based mask. Mask absorber optimization can mitigate these so-called mask 3D effects [1-3]. Last year at the SPIE Photomask and EUVL conference [4,5], EUV mask absorber change is recognized by the community as key enabler of next-generation EUV lithography. Through rigorous lithographic simulations we have identified regions, based on the material optical properties and their gain in imaging performance compared to the reference Ta-based absorber [6]. In addition, we have established a mask absorber requirement test flow to validate the candidate material to the full mask supply chain. In this paper we discuss in more detail Te- and Ru- based alloys which cover these different improvement regions. Candidate materials are evaluated on film morphology, stability during combined hydrogen and EUV loading, and thermal and chemical durability. The EUV optical constants are measured by EUV reflectometry, and preliminary results of plasma etching are shown to enable patterning.

Tellurium (Te) is one of the elements with highest extinction coefficient κ at the 13.5 nm extreme-ultraviolet (EUV) wavelength. It is being considered as an alternative absorber material for binary photomasks in EUV lithography. The absorber material is required to remain chemically stable during EUV exposure, at elevated temperatures up to 150 °C, during mask cleaning, and in the low hydrogen pressure environment that is present in the EUV scanner. However, Te is known to react with oxygen and hydrogen, forming less EUV absorbing TeO2 and more volatile H2Te, respectively. Since the melting temperature of Te is only 449.5 °C at normal pressure, alloying Te with a more stable metal might result in a high κ material that will remain thermally and chemically stable over a wider range of operating conditions. In this paper, the authors report on the stability assessment of metal telluride (M-Te) alloys for the EUV absorber material. They combined Te with high κ metals, noble metals, and etchable metals. High κ and noble M-Te materials are both thermally more stable than etchable M-Te, but they cannot be patterned easily for use in an EUV photomask. High κ M-Te exhibits polycrystal morphology at room temperature compared to quasiamorphous noble M-Te though both can crystallize at a higher temperature. Hydrogen stability and cleaning solution stability of M-Te materials are improved considerably compared to Te, but their higher surface reactivity cannot be completely mitigated without the addition of an inert capping layer. Furthermore, etchable M-Te alloys are easily oxidized during deposition, resulting in lower electron density and hence lower κ. Nevertheless, M-Te alloys may be a way to stabilize Te for usage as the EUV absorber material.

A qualitative and semi quantitative analysis of anisotropic etching of silicon nanostructures in alkaline solutions was done. Dedicated nanostructures were fabricated on 300mm wafers and their geometric change during wet etching was analyzed, stepwise, by top down SEM or TEM. We challenge the previously described wagon wheel technique towards nanodimensions and describe the pros and cons of the technique using relevant experimental conditions. The formation of specific geometric patterns are explained by the face-specificity of the etch rates. Clear differences in anisotropy were revealed between pillars etched in KOH or in TMAH, and for wagon wheels etched in TMAH or in NH4OH. Finally etch rates were extracted for the different types of crystal planes and compared.

Gate All-Around (GAA) is considered a key design feature for future CMOS technology. SiGe vs. Si selective etch is required for Si nanowire formation in GAA. It is confirmed the selective SiGe removal with commodity chemical (mixtures of hydrofluoric acid (HF), hydrogen peroxide (H2O2) and acetic acid (CH3COOH, HAc)), however the thick oxidized layer on Si NW was observed after commodity chemical process, which is indicated the significant Si NW loss. On the other hand, the formulated mixture ACT® SG-101, which is focusing on SiGe oxidizer, chemical pH, solvent polarity & corrosion inhibitor for chemical concept, was performed higher selectivity and lower Si loss than commodity chemical. The formulated mixture has also been used to form an inner spacer for cavity etch scheme and confirmed uniform cavity etch and inner spacer filling on topological test structure.

The introduction of Co into MOL and BEOL requires a robust wet clean, especially the optimization of the Co rinsing step seems to be critical. The wafer rinsing solutions with a precisely controlled pH and oxidizing additive have been developed to suppress the Co corrosion. In addition, the mechanism of passivation and corrosion of the cobalt surface as well as the passivation stability is discussed.

N3-functionalized monolayers on silicon wafer substrates are prepared via the controlled vapor-phase deposition of 11-azidoundecyltrimethoxysilanes at reduced pressure and elevated temperature. The quality of the layer is assessed using contact angle, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and ellipsometry measurements. At 60 °C, longer deposition times are needed to achieve monolayers with similar N3 density compared to depositions at 145 °C. The monolayers formed via the vapor phase are denser compared to those formed via a solvent-based deposition process. ATR-FTIR measurements confirm the incorporation of azido-alkyl chains in the monolayer and the formation of siloxane bridges with the underlying oxide at both deposition temperatures. X-ray photon spectroscopy shows that the N3 group is oriented upward in the grafted layer. Finally, the density was determined using total reflection X-ray fluorescence after a click reaction with chlorohexyne and amounts to 2.5 × 1014 N3 groups/cm2. In summary, our results demonstrate the formation of a uniform and reproducible N3-containing monolayer on silicon wafers, hereby providing a functional coating that enables click reactions at the substrate.

For the Ge nanowire formation in a gate-all-around (GAA) integration scheme, a selective etch of Si0.5Ge0.5 or Si0.3Ge0.7 selective to Ge is considered. Two wet process approaches were evaluated: a boiling TMAH as a commodity chemistry is compared with a formulated chemistry using a multi-stack SiGe/Ge layer as a test vehicle. The boiling TMAH exhibits an anisotropic etch of the SiGe whereas the formulated semi-aqueous chemistry removes the sacrificial SiGe by an isotropic etch which makes the process suitable for a Ge nanowire release process.

The Gate All-Around device architecture requires the formation of semiconductor nanowires. As an example SiGe nanowires can be formed by the selective removal of rSi in a Si-SiGe fin-shaped stack. In this paper we will show how alkaline solutions can be used for the selective removal of Si to SiGe and SiGe to Ge. We will also show that the anisotropy of the SiGe alkaline etch is not an extension of Si, even at low to moderate Ge concentrations (Ge ≤ 50%).

Protein phosphatase-1 (PP1) is a major protein Ser/Thr phosphatase in eukaryotic cells. Its activity depends on two metal ions in the catalytic site, which were identified as manganese in the bacterially expressed phosphatase. However, the identity of the metal ions in native PP1 is unknown. In this study, total reflection X-ray fluorescence (TXRF) was used to detect iron and zinc in PP1 that was purified from rabbit skeletal muscle. Metal exchange experiments confirmed that the distinct substrate specificity of recombinant and native PP1 is determined by the nature of their associated metals. We also found that the iron level associated with native PP1 is decreased by incubation with inhibitor-2, consistent with a function of inhibitor-2 as a PP1 chaperone.

Silicon solar cells are the dominating technology in photovoltaics (PV) industry and have a market share of more than 85% of the modules produced for roof top installations.

An investigation of the surface chemistry of In0.53Ga0.47As in HCl/H2O2 solution for etching in the low etch rate range (<0.1-10 nm min(-1)) is described. Kinetic studies using inductively coupled plasma - mass spectrometry showed a surprizing result: the etch rate decreased with increasing chloride concentration, suggesting chlorine termination of the surface. This was confirmed by a determination of the relative chlorine coverage using total reflection X-ray fluorescence. These results are supported by contact angle measurements and surface oxide analysis with X-ray photoelectron spectroscopy. Reaction schemes based on chemical and electroless mechanisms are presented to help understand the surface chemistry. The etch rate range and the favorable surface roughness after etching as determined by atomic force microscopy show that this HCl/H2O2 system is an excellent candidate for advanced CMOS processing. (C) 2014 The Electrochemical Society. All rights reserved.

The cumulative installed solar power generation has been rising exponentially over the past decade. This has lead to a concomitant rise in production capabilities, leading eventually to excess production capabilities and rapid price declines per unit. In order to compete with the standard electricity generation the cost of solar panel production and installation needs to decrease even further. At the same time the solar panel and cell makers need to be able to keep a healthy margin. A crucial element in this exercise is a close control on the Cost of Ownership (CoO) of a solar cell / panel fabrication site.