With "have", you need the past participle -- "become". "Became" is the past tense.
Student or Learner
What is the correct form, have become, have became? Thanks.
Welcome to the forums, Evelyne.
Please note that a better title would have been have become/have became.
Extract from the Posting Guidelines:
'Thread titles should include all or part of the word/phrase being discussed.'
If you click on "Reference" at the top of the page, you can look at the listings for irregular verbs. "Become" is listed there.
Here is the link: http://www.usingenglish.com/reference/irregular-verbs/
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.