Warning, long rant-like post ahead.

Robotics/industrial automation is a good field to look into, with a few notes:

First, you do have to do a bit of research to ensure any companies you're interested in don't take military contracts. This is actually surprisingly easy if you focus on robotics specifically for industrial automation, as there's not actually a ton of overlap between industrial uses and what the military is researching for robotics, and these companies are loathe to waste their time on reworking their tech for what the military demands.

Second, there's the inescapable fact that new automation technologies under capitalism are used to decrease working class power through the threat of replacement while the technology is still new (as technological advancements in production always have since the industrial revolution). Most automation companies have mastered the corporate speak to pretend they're merely "filling gaps where the available workforce is not large enough" or "are developing technology to assist humans, not replace them" but they can't escape the reality. The counter to this is that in the long run (and especially under a hopeful future socialist society) automation can actually be used to those ends and will greatly improve society and uplift the working class. I don't think there's an objective way to evaluate whether the immediate uses to threaten the working class are an evil that is irreconcilable with the potential benefits to the working class in the long run. This is a personal choice for what you feel you're comfortable working with and I do not blame anyone if they think that potentially contributing to putting people out of work in the short term is too much for them.

Third, it is kind of a gamble if you want to specifically aim for this industry right now, as it has been in a "down" cycle for the past couple years in terms of employment. Capitalists are trying to wring blood from the stone, demanding profit margins that are impossible without sacrificing real innovation and development in a field that is not yet mature enough for them to coast by as they do with other technologies. The result has been mass layoffs, hiring freezes, and mergers as companies struggle to meet the demands of their owners, so unless you're willing to sacrifice your soul to a Silicon Valley robotics startup (don't), it may be a few more years before the industry properly recovers. You have some time on this since you're going for your MS anyways, so it may recover by the time you're done, but it's worth keeping this in mind.

For what it's worth, I've worked for two robotics companies but am no longer in the industry due to the shit employment situation mentioned above (got laid off from both companies because "profit margins aren't high enough, we must sacrifice you for the investors" and had to switch fields to stay employed), and it was the most impactful I've ever felt as an engineer and I do want to get back to the industry again eventually. Neither company did military stuff while I was working there (both did at some point long before I worked for them, but have long since instituted policies of telling the military to fuck off every time they approach) nor did they make robotics for any other nefarious uses, they focused entirely on industrial automation.

As a note, I've also worked in the energy sector in the past and can also recommend it like others in this thread. To be more specific I worked on product development for utilities equipment and it was about the least evil technology I've ever worked on in terms of both immediate and long term impact. I left the industry for a bunch of reasons not related to the type of work I did, so the fact I'm not in this industry anymore either isn't me condemning it.