以致 / 以至于: so that, to the extent that
连词 / conjunctions
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Cause，以致 + consequence (negative) | …，以至于 + extreme degree
以致 introduces an unfortunate consequence: "so that", "with the result that". Written register, often when reviewing a mistake.
以至于 marks reaching an extreme degree: "to the point that". The result can be neutral.
Don't mix it up with 以免 (so as to avoid): 以致 = the bad result happened; 以免 = you want to prevent it.
Examples
公司盲目扩大生产，以致产品卖不出去。
Gōngsī mángmù kuòdà shēngchǎn, yǐzhì chǎnpǐn mài bu chūqu.The company blindly expanded production, so its products wouldn't sell.
他没有及时还贷款，以致信用受到了影响。
Tā méiyǒu jíshí huán dàikuǎn, yǐzhì xìnyòng shòudào le yǐngxiǎng.He didn't repay his loan on time, which damaged his credit.
他太专心了，以至于没听见有人叫他。
Tā tài zhuānxīn le, yǐzhìyú méi tīngjiàn yǒu rén jiào tā.He was so focused that he didn't hear someone calling him.
Common mistakes
✗ 他很努力，以致考上了大学 → positive result: ✓ 从而/所以 考上了大学。
✗ 以致 ≠ 以免: ✗ 早点走，以致迟到 → ✓ 早点走，以免迟到。