19DECEMBER 2022$19.35 billion in 2020 and predicts this growing at a rate of 8.9percenta year to reach $23.93 billion by 2026. However, as transistor density increases and semiconductor processes scale down to deliver new architectures at ever-smaller technology nodes, ensuring reliable PVD presents a growing number of challenges to semiconductor manufacturers. Among these are the need to better control the film morphology and ensureprecise deposition of thinner and thinner films inside high-aspect-ratio features. What's more, a focus on maximum yield and productivity means such deposition must not only be accurate, but also must be done at very high speed in systems with maximum uptime. Fine control of the plasma used in the sputtering system combined with optimized arc management ­ including quick recovery from arc conditions while maintaining process and plasma ­is needed to ensure the highest-quality coatings, maximize throughput, minimize the potential for damage to the target surface and extend the time between scheduled-maintenance shutdowns.With today's PVD processes commonly deploying single- or dual-magnetron reactive sputtering techniques that require pulsed-DC power, how the power is delivered, managed, and monitored is fundamental to meeting the needs outlined above. Choice of plasma power generator, therefore, is a critically important consideration for any PVD semiconductor fabrication process. Pulsed-DC PowerThe intimate connection between the power supply and the plasma, and the influence the supply can have on plasma deposition has long been recognized. Pulsed DC has been used in reactive sputtering applications because the pulsed-DC waveform allows for inherent charge build-ups to clear during the off times. A controllable reverse voltage has improved on this for reactive sputtering with pulsed-DC power in which the periodic reversal of voltage clears charge build-up more effectively during a pulsing. This has grown in popularity thanks in part to its ability to reduce or prevent arcing created by charge build-ups.In principle, pulsed DC is based on a shift in voltage or current from one power level to another or a shift in voltage from one polarity to the opposite, the latter being known as bipolar pulsed DC. Pulses can, in theory, be square or half sinusoidal. In practice, however, waveforms are impacted by factors such as nonlinearities of the plasma and, therefore, the shapes of the resulting power waveforms can be very complex. Controlling these waveforms by managing the power supply output is one of the keys to fine tuning the sputtering process. With the most recent bipolar pulsed-DC power supply technologies, the level of waveform control available to manufacturers has increased considerably, allowing for control of both the dV/dt and dI/dt of the waveform.So, what are the criteria that manufacturers should consider when selecting a pulsed-DC power supply? Clearly, one of the first considerations will be the power rating demanded by the application and today's pulsed-DC power supplies are now able to offer powers up to around 60kW. Maximum pulsing frequency and frequency configurability will also be an important factor, and supplies with frequencies that can be configured from 5to 150 kHz are increasingly available.Peak voltages and safe operating area (SOA) will need to be taken into account and, depending on the process setup, how the power supply is cooled ­ air-cooled, water-cooled, or a hybrid approach ­ will also be important. However, as PVD processes become more complex, it is the approach to waveform management and arc control that is beginning to dominate the selection criteria for plasma power generators.Waveform ControlExamples of the latest developments in waveform control can be found in the Advanced Energy® Ascent® AP (advanced pulsing) family of power supplies for single- and dual-magnetron sputtering applications.Operating with powers up to 30 kw, these supplies have been specifically designed to optimize outputs and deliver precise and repeatable sputtering of thin films by combining a patented pulsing technology with a variety of additional parameters for real-time control ­ even when plasma impedance changes abruptly. The AP waveform delivers boost voltage, reverse voltage control, and advanced pulse shaping with precise frequency control in 1 kHz increments up to 150 kHz and duty cycles down to 60Percent. Dead time delay between pulses can be configured from 0 to 1µs. The result is a system that allows manufacturers to fine-tune the process for tailored film morphologies and desired film properties. Figure 1 shows an example of the waveform at the power supply output and the resulting waveform at the plasma in a single-magnetron sputtering application. The reverse portion Figure 1: Waveform control in a single-magnetron sputtering application (diagram from Ascent® AP datasheet)
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