| 摘要 |
A plasma etch process for etching BPSG employing two primary etchants at low flows and pressures, and a relatively low temperature environment within the etch chamber, which includes a fluorine scavenger in the form of silicon. The two primary etchant gases are CHF3 and CH2F2, delivered at flow rates on the order of between about 10 and 40 sccm for CHF3 and also between about 10 and 40 sccm for CH2F2. Small quantities, on the order of 10 sccm or less, of other gases such as C2HF5 and CF4, may be added. A variant of the inventive etch process employing only CHF3 during a second phase thereof may be useful in providing a "punch", or dimple, at the contact bottom extending into the pristine substrate silicon under the BPSG and, optionally, other layers, and can be used to etch through both BPSG layers and a nitride films to contact a word line (or the like) thereunder wherein the contact so formed has a reduced taper as it passes through the nitride film above the word line resulting in a desirable, larger contact dimension. The system chamber temperature as defined and controlled at the roof over the wafer and the ring surrounding the wafer, the roof being held at about 115 DEG C to 150 DEG C and preferably about 140 DEG C, and the ring at about 200 DEG C to 250 DEG C, and preferably at about 200 DEG C. The temperature of the chuck supporting the wafer is maintained between about -10 DEG C and 30 DEG C. Chamber pressure is maintained at least at about >0.67 Newtons per square meter (5 mTorr), preferably >/=2.67 Newtons per square meter (20 mTorr), and most preferably between about 2.67 and 8.68 Newtons per square meter (20 and 65 mTorr). |
