| 摘要 |
PURPOSE: A method for forming a tri-well of a semiconductor device using a BF2 ion implantation and a multi-step annealing is provided to prevent the lowering of the electrical characteristics of the device due to a remaining fluorine(F), and to prevent the increase of leakage current while driving the device. CONSTITUTION: Isolation films(2) confining a device region is formed with a LOCOS process on one side of a P-type substrate(1), and then a screen oxide is formed on a surface of the P-type substrate. Then, the first photo resist pattern is formed to confine a region to form an NMOS on the P-type substrate. An N-well(5) is formed in the P-type substrate by implanting an N-type impurity into the revealed P-type substrate and then annealing it. The second photo resist pattern is formed to reveal a part of the N-well on the P-type substrate. Then, a P-well(7) is formed in the N-well by implanting BF2 into the N-well and annealing it. After removing the second photo resist pattern and the screen oxide, an annealing is performed to remove the remaining fluorine(F) in the P-well through two steps. The first annealing is performed at a low temperature of 450-600 deg.C for 1-12 hours, and the second annealing is performed at a high temperature of 900-1200 deg.C for 10-60 seconds by a RTP(Rapid Thermal Process) method.
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