Integration issues of (Ba,Sr)TiO3 thin films in high density devices

Recent progress to overcome integration issues related with (Ba,Sr)TiO3 films are presented. Firstly, ternary barrier material, Ti0.7Al0.3N deposited by reactive sputtering is shown to have superior oxidation resistance than TiN through the test using contact string pattern where Pt is deposited as a electrode. Ti0.7Al0.3N barrier is able to keep stable contact resistance below 100 Omega even under oxidizing condition where the temperature is 550 degreesC and oxygen partial pressure is 7.6 Torr. If rapid thermal annealing is used, annealing temperature without oxidation of Ti0.7Al0.3N can be increased by about 100 degreesC. Ti0.7Al0.3N is thought to be the promising one which can endure during post-annealing process. Secondly, electroplating technology is employed to fabricate the stack capacitor of Pt that has been known to be very difficult to etch. 500 Angstrom -thick Pt is used as a seed layer and very thick Pt is selectively grown on the seed layer by the electroplating. The Pt height can be controlled by changing the electroplating time, so we can make stack Pt over 8000 Angstrom. Thirdly, low temperature deposition process for MOCVD BST film is developed. The equivalent oxide thickness of about 3.5 Angstrom is obtained on Pt electrode when BST thickness is 150 Angstrom. BST film is deposited at 420 degreesC and annealed at 700 degreesC under oxidizing atmosphere. It is suggested that a new two step annealing consisting of high temperature annealing under inert atmosphere and low temperature annealing under oxidizing atmosphere is very effective to achieve the high dielectric constant and low leakage current of BST films at the same time. It is also adequate for preventing the barrier oxidation. BST film with Toxeq. of 5.2 Angstrom and low leakage current is obtained by annealing at 650 degreesC under N-2 followed by annealing at 550 degreesC under O-2. Electrical properties of BST deposited on side-wall of Pt concave capacitor is evaluated. The concave capacitor with about aspect ratio 3 shows the same capacitance and leakage current as the planar capacitor, which implies that BST composition and thickness is uniform on the side-wall. It is concluded that BST films on Pt electrode can be applied to real device.