Hydrogen Atom Desorption Induced by Electron Bombardment on Si Surface
Hydrogen Atom Desorption Induced by Electron Bombardment on Si Surface
复制标题
电子轰击硅表面诱导氢原子脱附
DOI：
10.1149/06931.0035ecst
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
and Masao Sakuraba
中科院分区：
文献类型：
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作者：
Wu Li;Shigeo Sato;Hisanao Akima;and Masao Sakuraba
1.纳米尺度量子器件的发展有望为信息处理开辟新的途径。在迄今提出的各种量子器件中，固态量子比特是为现代计算机技术带来进一步发展的潜在候选器件之一。Kane提出的核自旋量子比特是嵌入Si晶格中的磷施主原子，具有弛豫时间更长和与Si LSI技术更高的工艺兼容性等优点[1]。为了在Si衬底上精确地操纵单个掺杂剂，已经提出了一种方法，该方法采用来自氢终止的Si表面上的STM尖端的电子轰击[2]，[3]。虽然已经报道了成功的实验结果，包括氢原子的解吸和磷原子的吸附与原子分辨率，但解吸的氢原子的数量和轰击的电子的数量之间的关系，这是制造的基本问题之一，还没有给出详细的。本研究针对原子光刻技术的发展，对氢原子在Si（111）表面的脱附进行了定量研究.方法首先，在NH 4F水溶液（40%）中化学蚀刻Si（111）晶片，以获得用于单原子解吸的氢终止的光滑表面[4]。为了消除腐蚀坑的产生，在腐蚀之前，使用N2鼓泡来去除溶液中溶解的O2。接下来，将晶片放入真空室中，在STM图像扫描期间，电子从STM针尖注入到表面。适当能量的隧穿电子可以破坏Si-H键，导致氢原子脱附.实验结果3.1 Si表面的平整由于Si（111）在NH_4F水溶液中的水平腐蚀速率大于垂直腐蚀速率，因此获得了平整的表面。结果表明，最佳刻蚀时间为15分钟左右.此外，FT-IR结果表明，表面被氢原子成功地封端。图1示出了氢解吸之前和之后的Si（111）的STM扫描图像。对于这种情况，通过STM扫描以+3.5 [V]和4 [nA]样品偏压进行氢解吸，并且在扫描区域中的所有氢原子被解吸。另一方面，通过STM扫描获得表面图像，用-2. 5 [V]和0.5 [nA]样本偏置。表面图像中较亮的区域（图1（B））对应于氢解吸区域，因为悬挂键增加了电导率。图2示出了作为隧穿电流和偏置电压的函数的氢解吸面积与扫描面积的比率。可以看出，解吸需要大于3.1 [V]的偏置电压，并且解吸面积近似与隧穿电流成比例地增加。我们还进行了电子轰击，没有扫描。通过在STM图像中心位置的针尖上施加电压脉冲，并控制施加电压、隧穿电流和脉冲持续时间，我们可以获得合适的实验参数，以使氢脱附面积最小化。结果表明，幅值为3.6 [V]、持续时间为70 [ms]的电压脉冲可以在约30个位置上解吸氢气.结论我们研究了电子轰击Si（111）表面引起的氢原子脱附现象，并利用STM扫描证实了脱附面积与隧穿电流成正比。我们还证明了...
1. IntroductionDevelopments of nano-scale quantum device have been expected to open new approaches for information-processing. Among the various quantum devices proposed so far, a solid state qubit is one of the potential candidate devices to bring further progress to the modern computer technology. The nuclear spin qubit proposed by Kane, which is a phosphorus donor atom embedded in a Si lattice, has advantages such as longer relaxation time and higher process compatibility with Si LSI technology [1]. To manipulate a single dopant precisely on a Si substrate, a method employing electron bombardment from an STM tip on hydrogen-terminated Si surface has been proposed [2], [3]. Though successful experimental results including desorption of hydrogen atoms and adsorption of phosphorus atoms with atomic resolution have been reported, the relation between the number of desorbed hydrogen atoms and the number of bombarded electrons, which is one of fundamental issues for fabrication, has not been given in details. In this research, we study hydrogen atom desorption on Si(111) surface quantitatively for aiming at the development of atomic lithography.2. MethodFirst, a Si(111) wafer is chemically etched in aqueous NH4F solution (40%) in order to obtain hydrogen-terminated smooth surface for single atom desorption [4]. To exclude generation of etch pits, N2bubbling has been employed prior to the etching to remove dissolved O2in the solution.Next, the wafer is put into a vacuum chamber, and electrons are injected from an STM tip to the surface during STM image scanning. Tunneling electrons with appropriate energy can break Si-H bonds resulting in desorption of hydrogen atoms.3. Experimental Results3.1 Flattening of Si SurfaceBecause the horizontal etching rate of Si(111) is larger than that of vertical one in the aqueous NH4F solution, flatter surface has been obtained. Our results show that the optimum etching time is about 15 minutes. Moreover, FT-IR result indicates that the surface is terminated by hydrogen atoms successfully.3.2 Hydrogen DesorptionFig. 1 shows STM scan images of Si(111) before and after of hydrogen desorption. For this case, hydrogen desorption was done by STM scanning with +3.5 [V] and 4 [nA] sample bias, and all the hydrogen atoms in the scanned area were desorbed. On the other hand, surface images were obtained by STM scanning with -2. 5 [V] and 0.5 [nA] sample bias. Brighter region in the surface image (Fig. 1 (b)) corresponds to the hydrogen desorption area because dangling bonds increase electrical conductivity. Fig. 2 shows the ratio of hydrogen desorption area to the scanning area as functions of the tunneling current and the bias voltage. It can be seen that bias voltage lager than 3.1 [V] is required for desorption and desorption area increases approximately in proportion to the tunneling current. We also carried out electron bombardment without scanning. By applying a voltage pulse to the tip at the center position of an STM image and controlling the applied voltage, tunneling current, and pulse duration time, we can obtained suitable experimental parameters for minimizing the area of hydrogen desorption. The results show that a voltage pulse with 3.6 [V] amplitude and 70 [ms] duration desorbs hydrogens on about 30 sites.4. ConclusionWe have studied about the desorption of hydrogen atoms on Si(111) surface caused by electron bombardment, and confirmed by utilizing STM scanning that the desorption area is proportional to the tunneling current. Also, we demonstrated that the …