Single-photon avalanche diodes (SPADs) are high-performance light-sensitive sensors operating in low-light condition. Si-SPADs manufactured through standard CMOS fabrication process have advantages in terms of manufacturing cost, low power consumption, device shrinkage, and process stability compared to SPADs on custom fabrication. A deeper multiplication using deep n-well (DNW) improves key performances of Si-SPAD such as dark count rate (DCR) and photon detection efficiency (PDE). Here, the guard ring (GR) must be included for deep junction SPAD because light detection efficiency is lowered due to premature edge breakdown (PEB) generated by strong electric field at the edge. PEB affects not only the characteristics but also the manufacturing uniformity. Therefore, the DNW should be carefully designed to show better performance and stability for Si-SPADs. In this paper, the effects of electrical characteristics such as current-voltage (I-V) curve, DCR, off leakage, and breakdown voltage, and process stability on DNW implanted SPAD with GR variation are analyzed using actual fabricated SPAD measurement data and the calibrated technology computer-aided design (TCAD) simulated results. When the deep multiplication junction is formed using the higher ion implantation energy, the penetration effect and the process instability can be generated and it can also weaken the GR effect, which prevents PEB caused by having a stronger electric field than the multiplication zone. In addition, it is verified to prevent the risk of designing a Si-SPAD and die-to-die variation due to DNW implantation. Based on the results, deep junction design scheme for high resolution and mass production can be suggested.
Plasma is widely used in etching, deposition, ashing, and ion implantation processes in the manufacturing processes of semiconductor and display devices. Recently, the role of plasma in semiconductor processes is becoming important because the pattern with high step coverage and aspect ratio is required as the semiconductor process is scaled. In particular, plasma-enhanced atomic layer deposition (PE-ALD) is recently highlighted with excellent deposition uniformity compared to chemical vapor deposition (CVD) and physical vapor deposition (PVD) technologies. The density and the state of plasma during the process cannot always remain constant and can be changed by process variables and unpredictable process random fluctuations. Since this can cause yield drop and decrease in productivity, the methodology for monitoring and diagnosing the abnormality of plasma in real time during the process is essentially required. In this paper, the plasma monitoring using the optical emission spectroscopy (OES) in PE-ALD equipment to analyze the characteristics of the process variables. Based on the diagnosis results, the optimal process variable values were proposed, and a process performance predictive model is introduced by analyzing the correlation between variables. Based on the modeling results, the modeling output for the final deposited thickness can be predicted by the initial deposition rate, which can be developed as a virtual metrology system application. In addition, by applying this proposed virtual metrology scheme for the advanced process control (APC), it is possible to estimate the process output without whole wafer measuring, thereby improving the time and cost losses and the wafer-to-wafer variation in the semiconductor manufacturing industry.
Single photon avalanche diodes (SPADs) manufactured through the standard CMOS process have a major advantage in reducing the cost and expendability in comparison with the SPAD made with the custom process.
SPAD is a single photon sensitive diode using the avalanche phenomenon and operated in Geiger-mode which applies a voltage higher than the breakdown voltage of the device. Therefore, SPAD is exposed to a higher voltage than other devices and has a high electric field in the multiplication region.
In SPAD operating with such a high electric field, the guard ring prevents edge breakdown and serves to focus the electric field on the intended multiplication region. Therefore, the optimized guard ring structure is required for the high efficiency SPAD designs. The deep virtual guard ring is designed to cope with deeper multiplication regions formed by deep n-well and p-well, thus providing higher photon detection probability (PDP) and enhanced response at a longer wavelength.
In this paper, the four possible Silicon-based SPAD candidates of different deep virtual guard rings formed by the combination of shallow trench isolation (STI) and p-substrate layer fabricated through standard CMOS process are investigated and their electric characteristics of the SPAD, such as the current-voltage (I-V) characteristic, and optical characteristics, such as dark count rate (DCR), and PDP, are measured.
In addition, TCAD simulations are used to verify the characteristic variation by analyzing the electric field profiles. Based on the results, the optimized structure of the SPAD with the deep virtual guard ring can be proposed.
A red-emitting external cavity diode laser (ECDL) module was designed to increase the slope efficiency and reduce the bandwidth by tilting the solitary laser diode (LD) 90 deg. This tilt resulted in parallel polarization, which yielded high-slope efficiency and also produced a favorable geometry that minimized the area of the back-focused beam, thereby facilitating selection of a specific wavelength. A ray-tracing simulator was used to optimize optical parameters such as the back focal length of the collimating lens, the cavity length, and the grating’s groove density. Based on the optimized structure, an ECDL module package was designed for thermal control by using autodisk computer-aided design tool. The resulting module obtained high-slope efficiency and narrow-bandwidth emission of red light, making it suitable for potential application as a light source for a commercial three-dimensional holographic system. The module achieved the narrow bandwidth of 80 pm and the slope efficiency of 0.81 W/A, which compared favorably with the output power of 0.8 to 0.9 W/A of commercial solitary LDs.
External cavity diode laser with broad-area laser diode is operated up to the output power of 160 mW at the injection current of 850 mA and the bandwidth of 80 pm at a wavelength of 648 nm in external cavity. High slope efficiency of output power and narrow bandwidth using broad-area laser (BAL) diode, the width of active layer in the slow axis is too broad to select a specific wavelength. In this paper, more efficient wavelength selection method is investigated by confirming the tendency of grating grooves and designing to set up the wavelength dispersion direction along the fast axis of a solitary laser diode (LD) geometrically. Thus, the tunable external cavity diode laser module by using BAL diode is designed with an overall size of 49 mm x 52 mm x 48.5 mm. From injection current in the range of 650-900 mA, ECDL showed excellent wavelength locking behavior without a non-shift of the peak wavelength. Here, the tuning range is 4 nm with maintaining the narrow bandwidth of 80 pm and up to the output power of 100 mW. A side-mode-suppression of 36.5dB is also achieved at the output power of 160 mW and the injection current of 850 mA.
We present a review of the characteristics of several different types of high speed InGaAs/InP avalanche photodiode (APD)s that we have developed for different guard ring depth and for different main p-n junction shape. The APD structure that we propose consists of a greatly reduced width in InP multiplication layer and a high doping concentrated electric field buffer layer, where we also adopted a floating guard ring and a shaped main junction with recess etching for a reliable operation of an APD. We obtained high reliability APDs, which are tested for two-dimensional gain behavior and for accelerated life tests by monitoring dark current and breakdown voltage. The gain and bandwidth product of the best of our APDs was measured as high as 80 GHz.
We present an overview on the progress of InP/InGaAs based Hi-Lo APD's, which are important for long-haul optical fiber communications. Much of recent research efforts have been focused on improving the operation reliability, the gain- bandwidth (GB) product, and reducing the excess noise factor. To achieve a high GB product and a reliable operation, the reduction of the thickness of the multiplication layer and an optimum design of the internal electric field distribution are essential. The concept of the planar InP/InGaAs APD is very important from this perspective and the Hi-Lo APD's are expected to play an important role.
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