A resin comprising a structural unit represented by formula (I0):

##STR00001## wherein A.sup.1, A.sup.2 and A.sup.3 each independently represent a C2-C18 divalent hydrocarbon group, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each independently represent a hydrogen atom or a C1-C6 saturated hydrocarbon group, X.sup.1 and X.sup.2 each independently represent *OCO, OCOO or O, and * represents a binding site to A.sup.2 or A.sup.3.

The resist composition comprises an onium salt of sulfonic acid which has a linkage of two iodized or brominated aromatic groups as the acid generator. The resist composition offers a high sensitivity, reduced LWR and improved CDU independent of whether it is of positive or negative tone. A pattern can be formed by using the resist composition.

It is an object of the present invention to improve the curability of a resin composition and a photosensitive composition suitably employed to form e.g., a surface protecting film and an interlaminar insulating film of e.g., an electronic part, while reducing the internal stress remaining in a substrate when the composition is used to form a cured film on the substrate. The photosensitive composition includes a resin (A) having a phenolic hydroxyl group, a crosslinking agent (B1) having at least two oxazoline groups and a crosslinking agent (B2) having at least two groups represented by CH.sub.2OR (wherein R is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an acetyl group) and a photosensitive acid-generating agent (C).

Apparatuses and methods of overlay measurement are disclosed. An example apparatus includes: a substrate comprising first material; a first layer comprising second material disposed on a surface of in the substrate; a first alignment pattern including third material disposed in the first layer; and a second layer above the first layer including a second alignment pattern. A difference between refractive indexes of the second material and the third material is greater than a difference between refractive indexes of the first material and the third material.