Strongly depends on the team you intern under. Don't expect any team to offer you a PPO straightaway after your first internship, but if you do decent work and the team thinks that you'll be a good fit with them, they'll definitely call you back for call-back internships. The "procedure" for the same would be to signal to the team that you're interested in working there as an associate. Best returns would be by signalling the same to SAs and/or Partners (provided you've interacted with them beforehand).