KEYWORDS: Etching, Plasma etching, Plasma, Climate change, Gases, Transistors, Power consumption, Front end of line, Sustainable technology, CMOS technology
The semiconductor industry is aware of its high resource consumption and overall impact on the environment and is working to minimize it. Especially, the use of perfluorocarbons (PFC) during the dry etching and deposit steps of device manufacturing is a major concern because of the extremely high global warming potential (GWP) and lifetime of most of those compounds. Consequently, plasma etching significantly contributes to CO2 emissions for sub-28nm technologies on Scope 1 and 2 emissions. Currently, CEA-Leti is developing a 10nm node on FDSOI (Fully Depleted Silicon On Insulator) technology. In this framework, we present Life Cycle Assessment (LCA) of etching processes for FDSOI transistor technologies. A comparison of impacts between the 28nm node and 10 nm one is then conducted for FEOL and MEOL processes. Finally, based on these results, some eco-innovation proposals are discussed.
N-on-p extrinsically doped MWIR HgCdTe material and photodiodes have been developed to benefit from the expected reduction of the Auger generation in the p-type absorbing layer. Samples with two doping levels have been characterized using dark current, current noise, Hall effect and PhotoLuminescence Decay (PLD) measurements. The dark current and PLD measurements are consistent with a reduction of the Auger generation quantified by the ratio between the Auger 1 and 7 recombination coefficients 𝛾 around 10. The corresponding dark current in the sample with the lowest doping level was slightly higher than in typically p-on-n photodiodes. The low frequency noise, characterized by a Tobin coefficient below 10-5, is lower than the values reported for other MWIR HgCdTe photodiodes at the same dark current density. The low dark current and dark current noise show on the high potential of such photodiodes to form focal plane array that can be operated at high operating temperature without degradation of the image quality.
In the last decade, IR imaging detector trend has gone for smaller pixels and larger formats. Most of the time, this scaling is carried out at given total sensitive area for a single focal plane array (FPA). As an example, QVGA 30µm pitch and VGA 15µm pitch exhibit the exact same sensitive area. SXGA 10µm pitch tends to be very similar as well. This increase in format is beneficial to image resolution. However, this scaling to even smaller pixels raises questions because the pixel size becomes similar to the IR wavelength but also to typical transport dimensions in the absorbing material. Hence, maintaining resolution for such small pixel pitches requires a good control of the modulation transfer function (MTF) and quantum efficiency (QE) of the array, while decreasing the pixel size. This might not be obtained just scaling the pixel dimensions. As an example, bulk planar structures suffer from excessive lateral diffusion length inducing pixel-to-pixel cross talk and thus degrading MTF. Non-bulk semiconductor materials such as colloidal quantum dots might exhibit much smaller cross talk due to weak transport properties, but it usually strongly degrades the accessible QE. On the other side, mesa structures might minimize cross-talk physically separating pixels, but also tends to degrade the QE due to non-negligible pixel fill factor shrinking down the pixel size. This paper intend to discuss those issues, taking into account different material systems and structures, in the perspective of expected future pixel pitch IR FPAs. This paper also introduces an important issue in this context: how to reliably measure the MTF of those small pitch detectors. As an answer to this question we will share our first investigations of MTF measurement using the electron beam of an SEM instead of a photon beam (EBIC measurement)
SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. This is the result of strong and continuous development efforts to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. On one hand the advanced performances of Sofradir product rely on a strong partnership with CEA-LETI materialized in a common laboratory named DEFIR.
On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.
SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. This is the result of strong and continuous development efforts to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. On one hand the advanced performances of Sofradir product rely on a strong partnership with CEA-LETI materialized in a common laboratory named DEFIR. On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.
Bayer filter arrays are commonly added to visible detectors to achieve multicolor sensitivity. To extend this approach to the infrared range, we present frequency selective surfaces that work in the mid-infrared range (MWIR). They are easily integrated in the device fabrication process and are based on a simple operating principle. They consist of a thin metallic sheet perforated with apertures filled with a high-index dielectric material. Each aperture behaves as a separate resonator. Its size determines the transmission wavelength λ. Using an original approach based on the temporal coupled mode theory, we show that metallic loss is negligible in the infrared range, as long as the filter bandwidth is large enough (typically <λ/10). We develop closed-form expressions for the radiative and dissipative loss rates and show that the transmission of the filter depends solely on their ratio. We present a prototype infrared detector functionalized with one such array of filters and characterize it by electro-optical measurements.
Multicolor detection capabilities, which bring information on the thermal and chemical composition of the scene, are desirable for advanced infrared (IR) imaging systems. This communication reviews intra and multiband solutions developed at CEA-Leti, from dual-band molecular beam epitaxy grown Mercury Cadmium Telluride (MCT) photodiodes to plasmon-enhanced multicolor IR detectors and backside pixelated filters. Spectral responses, quantum efficiency and detector noise performances, pros and cons regarding global system are discussed in regards to technology maturity, pixel pitch reduction, and affordability. From MWIR-LWIR large band to intra MWIR or LWIR bands peaked detection, results underline the full possibility developed at CEA-Leti.
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