Machining oｎ Rear Surface of a Silicon Substrate by an Infrared Femtosecond Laser via Non-linear Absorption Processes
Machining oｎ Rear Surface of a Silicon Substrate by an Infrared Femtosecond Laser via Non-linear Absorption Processes
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红外飞秒激光非线性吸收过程对硅基片背面进行加工
DOI：
10.1016/j.procir.2016.02.191
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Yoshiro ITO
中科院分区：
文献类型：
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作者：
Khanh Phu LUONG;Rie TANABE;Yoshiro ITO
硅（Si）是一种广泛用于现代技术如微电子学、MEMS和光子学的半导体材料。Si在可见光到近红外波长区域中是不透明的材料，但它透射任何长于1127 nm的光，这对应于其1.12 eV的带隙能量。因此，Si可以被认为是用于长于1127 nm的辐射的透明材料。本文提出了一种新的硅激光微加工方法，提高了加工效率、精度和灵活性。使用的Si基板的厚度为320 μm，并且通过100倍红外物镜透镜将1552 nm的飞秒激光聚焦在基板的后表面上。然而，仅形成浅槽：其深度约为170 nm或更小。预期当激光聚焦在Si背面上时，激光与蚀刻剂接触，由于激光照射引起的温度升高，将发生湿蚀刻。因此，为了提高加工速率，我们尝试了使用KOH溶液作为蚀刻剂的激光辅助背面湿法蚀刻。最大槽深增加到3 μm以上。研究了激光辐照条件对加工槽的影响。结果表明，相当分散的值，并表明，最大的槽深并不总是在高能量沉积条件下产生。其中一个原因可能是由于Si和KOH之间的化学反应形成氢气泡，这阻碍了Si和KOH的接触。
Silicon (Si) is a semiconductor material widely used in modern technologies such as microelectronics, MEMS, and photonics. Si is an opaque material in visible to near-infrared wavelength region but it transmits any light longer than 1127 nm, which corresponds to its band gap energy of 1.12 eV. Therefore, Si can be considered as transparent material for radiations longer than 1127 nm. Here we have proposed a new laser microprocessing method of Si, which increases the efficiency, accuracy and flexibility in machining. The thickness of the Si substrate used was 320 μm and a femtosecond laser at 1552 nm was focused by a 100x infrared objective lens on the rear surface of the substrate. However, only a shallow groove was formed: its depth was approximately 170 nm or less. It is expected that when the laser is focused on the Si rear surface, where it is contacting with an etchant, wet etching will occur due to the temperature rise caused by the laser irradiation. Therefore, to increase the machining rate, we tried laser-assisted backside wet-etching using KOH solution as the etchant. The maximum groove depth was increased to more than 3 μm. The effects of laser irradiation conditions on machined grooves were examined. The results achieved showed rather scattered values and indicated that the maximum groove depth was not always produced at high energy deposition conditions. One of the reasons might be the formation of hydrogen bubbles from the chemical reaction between Si and KOH, which block the contact of Si and KOH.