Novel semiconductors with controlled both single-atom number and position

在半导体中掺杂杂质原子是实现半导体器件正常功能的必要条件。到目前为止，半导体被假定在有源通道区域均匀掺杂。然而，在纳米级半导体器件中，通道区域将包含很少的掺杂原子，并且均匀分布的假设不再可行。在这种情况下，由于随机泊松分布导致的掺杂原子数的统计波动将对器件的功能产生有害影响。我们一直在开发一种单离子注入（SII）方法，使我们能够将掺杂离子一个一个地注入到半导体中，直到达到期望的数量。在本研究中，我们通过修改SII的聚焦离子束光学元件，将光束直径提高到约10nm，并通过检测单离子入射引起的漏极电流变化，实现了100%的单离子检测效率。然后，我们用SII制造了具有有序掺杂阵列的半导体器件。所得到的晶体管的电学测量表明，与常规随机掺杂分布的器件相比，具有有序掺杂阵列的器件的阈值电压（V_<th>；器件的导通电压）的器件间波动更小。我们还发现，掺杂有序的器件的V_<th>的平均值比掺杂无序分布的器件的V_<th>的平均值低2倍。我们将阈值电压的显著差异解释如下：静电电位的均匀性降低了从源极到漏极打开通道所需的电压，这允许在通道中与植入离子位置相对应的部分早期打开，并导致较低的阈值电压。必须指出的是，目前的技术是基于离子的随机分布，不能控制离子的数量和位置，而我们的方法可以控制离子的数量和位置，这种控制对于未来的纳米级半导体器件是必不可少的。少

Doping of impurity atoms into semiconductors is essential to achieving the proper function of semiconductor devices. So far the semiconductor has been assumed to be homogeneously doped in the active channel region. In the nano-scale semiconductor devices, however, the channel region will contain few dopant atoms and the assumption of uniform dopant distribution is no longer feasible. In this situation, the statistical fluctuation in dopant atom number due to random Poisson distribution will elicit deleterious effects on the device's functioning. We have been developing a single-ion implantation(SII) method that enables us to implant dopant ions one-by-one into semiconductors until the desired number is reached In this study, we have improved the beam diameter approximately 10nm by modifying the focused ion beam optics for the SII and achieved the single-ion detection efficiency 100% by detecting the change in drain-current induced by single-ion incidence. We have then fabricated semico … More nductor devices with ordered dopant arrays by the SII. Electrical measurements of the resulting transistors revealed that there are fewer device-to-device fluctuations in the threshold voltage (V_<th> ; the turn-on voltage of the device) of the devices with ordered dopant arrays than of those with conventional randomly doped distribution. We also found that the average value of V_<th> for the devices with ordered dopants is two times lower than that of the devices with a random distribution of dopants. We explain this pronounced difference in threshold voltage as follows : the uniformity of electrostatic potential lowers the voltage required to open the channel from source to drain, which allows for early turn-on in those parts of the channel that correspond to the positioning of the implanted ions and results in the lower threshold voltage. It must be noted that current technology, which is based on random distribution of ions, cannot control either the number or the positioning of the ions, while our method can control both the number and the positioning of the ions and that this control is essential for future nanoscale semiconductor devices. Less