Are there any popes who became saints?

No, not all bishops become saints. According to these quotes
“The floor of hell is paved with the skulls of bishops.†attributed to St. Athanasius, Council of Nicaea, AD 325.

“I do not think there are many among Bishops that will be saved, but many more that perish.†attributed to St. John Chrysostom, Extract from St. John Chrysostom, Homily III on Acts 1:12.

Bishops are humans but they are also shepherds and, therefore, have a great responsibility for leadership and will be held responsible for their actions if they lead people astray.