The word "以至于" is formed by sequentially combining the character "以", which functions as a preposition indicating cause or means, with "至", a verb meaning "to reach" or "to arrive at", and then "于", a preposition that introduces a target or extent. This structure literally conveys "in order to reach to", and as a fixed phrase, it serves as a conjunction that links a cause or action to its resulting degree or outcome, thus expressing "to such an extent that".