c-axis orientation and piezoelectric coefficients of AlN thin films sputter-deposited on titanium bottom electrodes
c-axis orientation and piezoelectric coefficients of AlN thin films sputter-deposited on titanium bottom electrodes
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DOI：
10.1016/j.apsusc.2012.06.086
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发表时间：
2012-10-15
影响因子：
6.7
通讯作者：
Schmid, U.
中科院分区：
文献类型：
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作者：
Ababneh, A.;Alsumady, M.;Schmid, U.
铝靶反应溅射氮化铝(AlN)是一种有趣的化合物材料，它的制备工艺与其压电性是兼容的。要获得高的压电系数，必须先合成具有c轴取向的薄膜。除了溅射条件对AlN薄膜微结构的影响外，衬底表面条件也是非常重要的因素。本文研究了在SiO_2/Si衬底上，在2×10~(-3)~14×10~(-3)mbar范围内，在不同背压级b(p，Ti)下，直流溅射沉积350 nm厚的钛金属化对600 nm厚的AlN薄膜c轴取向和压电系数的影响。除沉积钛的等离子体功率(P-p，P-Ti=100W)外，在100%N-2气氛中，合成AlN的参数固定为P-p=1000W，b(p，AlN)=4×10~(-3)mbar。基本上，钛底层的表面粗糙度是导致高c轴取向(即在低b(p，Ti)值时)或非晶态AlN组织(即在高b(p，Ti)值时)的主要因素。在低压条件下，由于与吸附原子相关的更高的动能，获得了光滑和致密的表面特征，这在名义上不加热的衬底条件下尤其重要。当溅射气压从2×10~(-3)~14×10~(-3)mbar增加到14×10~(-3)mbar时，压电系数d(33)从2.55降到1.7 pm(-1)。当钛膜厚度减小到60 nm，从而使均方根粗糙度减小约2倍时，与AlN(002)峰相关的强度增加了约1.7倍，表明直接影响。此外，还确定了d(33)和d(31)的最大值(即3.15 pm V-1和-1.28 pm V-1)。(C)2012爱思唯尔B.V.保留所有权利。
Aluminum nitride (AlN) reactively sputter deposited from an aluminum target is an interesting compound material due to its CMOS compatible fabrication process and its piezoelectric properties. To obtain high piezoelectric coefficients it is a necessary pre-request to synthesize films with c-axis orientation. Besides the influence of sputter conditions on the microstructure of AlN thin films the condition of the substrate surface is another important factor of utmost importance. In this study, the influence of 350 nm thick titanium metallization DC sputter-deposited on SiO2/Si substrates at varying back pressure levels b(p,Ti) in the range of 2x10(-3) to 14x10(-3) mbar on the c-axis orientation and the piezoelectric coefficients of 600 nm thick AlN thin films is investigated. Besides the plasma power for Ti deposition (P-p,P-Ti = 100 W) the parameters for AlN synthetization are fixed to P-p = 1000 W and b(p,AlN) = 4 x 10(-3) mbar in 100% N-2 atmosphere. Basically, the surface roughness of the Ti bottom layer is the dominating factor resulting either in a high degree of c-axis orientation (i.e. at low b(p,Ti) values) or in an amorphous AlN microstructure (i.e. at high b(p,Ti) values). Under low pressure conditions, a smooth and dense surface characteristics is achieved due to a higher kinetic energy associated with the adatoms what is especially important at nominally unheated substrate conditions. The piezoelectric coefficient d(33) decreases from 2.55 to 1.7 pm(-1) when increasing the titanium sputter pressure from 2x10(-3) to 14x10(-3) mbar. When decreasing the Ti film thickness to 60 nm and hence, reducing the root mean square roughness by a factor of about 2, the intensity associated with the AlN (0 0 2) peak is increased by a factor of about 1.7 demonstrating the direct impact. Furthermore, the highest values for d(33) and d(31) (i.e. 3.15 pm V-1 and -1.28 pm V-1) are determined. (C) 2012 Elsevier B. V. All rights reserved.