As Charles T. on this post answered:
Create a Lightning Component that implements
lightning:isUrlAddressable and create a link button that navigates to
that component's Lightning URL, passing enough parameters to have the
info you need (record ID for example). This will show full-screen
rather than as a modal. Also note that the component will have to
handle changes to v.pageReference to ensure it behaves correctly if a
user navigates to it a second time in the same session.
Consequently, contrary to what Manish Anand says above, you don't have to embed the Lightning Component in a Lightning App. In fact, you can call Lightning Components not just from record detail buttons but also list buttons. Personally, I call lightning:isUrlAddressable Lightning Components constantly from related lists to navigate to subtabs with Lightning Component child object tables for easier management of child records. See the list button example below with two parameters passed in.
Button or Link URL:
Display Checkboxes (for Multi-Record Selection): false
For instructions on how to use
pageReference, see here.