There is actually a fair amount of material. My first three thoughts are : (1) that it is not profitable to consider whether corporations are metaphysical persons. There is no firm, clear, consensual answer to the question : 'What is a person ?' Referring, that is, to the sort of entity you and I are. Since we are unclear about this basic, metaphysical concept of a person, we are unlikely to make much progress on whether corporations are persons too.
(2) Corporations might be 'moral persons' in the sense that they can possess rights, privileges, duties.
(3) They might also be 'moral agents' in the sense that they are morally accountable, responsible, capable of causing blameworthy harm and subject to punishment.
Some references might be of better help (though I've listed Scruton and Finnis last they offer a good discussion which you needn't read first but would be well-advised to include in your early reading - Scruton is a philosopher who is also a qualified lawyer and Finnis is a qualified lawyer who is also a philosopher) :
1 Rita C. Manning, 'Corporate Responsibility and Corporate Personhood', Journal of Business Ethics, Vol. 3, No. 1 (Feb., 1984), pp. 77-84.
2 Martin Kusch, 'The Metaphysics and Politics of Corporate Personhood', Erkenntnis (1975-), Vol. 79, Supplement 9: GROUP AGENCY AND COLLECTIVE
INTENTIONALITY (2014), pp. 1587-1600
3 Daniel Lipton, Corporate Capacity for Crime and Politics : Defining Corporate Personhood at the Turn of the Twentieth Century', Virginia Law Review, Vol. 96, No. 8 (December 2010), pp. 1911-1964.
4 Kevin Gibson, 'Toward an Intermediate Position on Corporate Moral Personhood', Journal of Business Ethics, Vol. 101, Supplement 1: Responsibility Beyond CSR
(2011), pp. 71-81.
5 Michael J. Phillips, 'Corporate Moral Personhood and Three Conceptions of the Corporation', Business Ethics Quarterly, Vol. 2, No. 4 (Oct., 1992), pp. 435-459.
6 Peter French, 'The Corporation as a Moral Person', American Philosophical Quarterly 16 (1979), 207-215.
7 Alisdair Maclntyre, 'Corporate Mondernity and Moral Judgement: Are they Mutually Exclusive?', Ethics and the Problems of the 21st Century, ed.
K. E. Goodpaster and K. M. Sayre (University of Notre Dame Press, 1979.
8 Roger Scruton and John Finnis, 'Corporate Persons', Proceedings of the Aristotelian Society, Supplementary Volume, Vol. 63 (1989), pp. 239-274.