In pathfinder magic an arcane spellcaster can memorize a lower level spell into a higher level spell slot if they wish.
Eg use a 3rd level spell slot to memorise a 2nd level spell.
Does this include cantrips?
Arcane Spells Wizards, sorcerers, and bards cast arcane spells.
Compared to divine spells, arcane spells are more likely to produce
dramatic results.Spell Slots: The various character class tables show how many spells
of each level a character can cast per day. These openings for daily
spells are called spell slots. A spellcaster always has the option to
fill a higher-level spell slot with a lower-level spell. A spellcaster
who lacks a high enough ability score to cast spells that would
otherwise be his due still gets the slots but must fill them with
spells of lower levels.
Best Answer
There's nothing prohibiting you from preparing a 0-level spell (cantrip) in a higher level slot [1]. The rules state the spells are "cast like any other spell", with the notable exception that "...they are not expended when cast and may be used again" [2]. Per the RAW, this would equally apply even if it was prepared in a higher level slot. Cantrips don't have any restrictions otherwise (and the only distinction from non-cantrip spells is, in fact, a benefit).
The question I have though, and this is admittedly just out of curiosity, but why would you want to waste a valuable higher level slot on something as mundane as a cantrip?
SOURCE
[1] http://paizo.com/prd/magic.html ("Preparing Wizard Spells")
[2] http://www.d20pfsrd.com/classes/core-classes/wizard#TOC-Cantrips