mass is energy per c square $m=E/c^2$ energy is made up of photons but what made up photon itself? what made up a single photon?
Replay to comment: but as we can see in history early phyisicists though that atom in non-fissionable (thats why they called it atom), now we call photon elementary but it may be a composite particle!, why not?
Photons are elementary particles, so they aren't made of anything. What does this mean? This means that a photon is an entity with the right mass, spin, electric charge and so on
everything depends on how you observe it or may be how you want to observe it.
$c$ is a constant and not light, if you target the photons you do need to pass to Planck's formulation $\hbar\dots$.
But to your question: it depends how how you observe them!
Photons can be observed as superpositioned waves. Photons can be also observed as particle. Photons are the elementary superpositioned waves or particles of light - or better say they are themselves light! Photons are indeed elementary superpositioned waves or particles that package energy.
The formula above says that photons would have also a mass equivalent. However it does not say how and under which condition you may convert photons in your lab to mass particles.
But what makes up a single photon? My favorite answer would be: the probability of meeting it at a location or with a certain energy.
Hope this helps.
Pair Production confirms that radiation (photon) has corpuscular properties. a highly energetic photon, interacting with a nucleus, disappears and produces an electron and a positron.
