Processing and characterization of a-Si:H photoresists for a vacuum-compatible photolithography process

The vision of achieving a completely in-vacuum process for fabricating HgCdTe detector arrays is contingent on the availability of a vacuumcompatible photolithography technology. One such technology for vacuum photolithography involves the use of amorphous-hydrogenated Si (a-Si:H) as a photoresist. In this work, we deposit a-Si:H resists via plasma-enhanced chemical-vapor deposition (PECVD) using an Ar-diluted silane precursor. The resists are then patterned via excimer laser exposure and development etched in a hydrogen plasma where etch selectivities between unexposed and exposed regions exceed 600:1. To determine the best conditions for the technique, we investigate the effects of different exposure environments and carry out an analysis of the a-Si:H surfaces before and after development etching. Analysis via transmission electron microscopy (TEM) reveals that the excimer-exposed surfaces are polycrystalline in nature, indicating that the mechanism for pattern generation in this study is based on melting and crystallization. To demonstrate pattern transfer, underlying CdTe films were etched (after development of the resist) in an electron cyclotron resonance (ECR) plasma, where etch selectivities of approximately 8:1 have been achieved. The significance of this work is the demonstration of laser-induced poly-Si as an etching mask for vacuum-compatible photolithography.     

等离子刻蚀a-Si:H/a-C:H超晶格

本文介绍了 C_yF_(14)+ O_2等离子刻蚀 a=Si:H/a-C:H 超晶格的工艺原理及方法,简便可行.     

塑料基底a-Si∶H TFT制备技术

采用PECVD工艺,在300℃下在50μm厚的Kapton E高分子塑料片上制备了底栅结构a-Si∶H TFT阵列(20×20)。用傅里叶变换红外光谱仪表征了a-Si∶H薄膜的结构,用二探针法和四探针法分别表征了a-Si∶H薄膜和n+a-Si∶H薄膜的电导率。a-Si∶H薄膜中的H(原子数分数)约为15.6%,H主要以Si H和Si H2基团的形式存在,其电导率为8.2×10-7~8.8×10-6S/cm;n+a-Si∶H薄膜的电导率为3.8×10-3S/cm。所制备的TFT具有以下性能:Ioff≈1×10-14A,Ion≈1×10-9A,Ion/Ioff≈105,Vth≈5V,μ≈0.113cm2/(V.s),S≈2.5V/dec,满足TFT-LCD等平板显示器件的开关寻址电路要求。     

p-Si TFT栅绝缘层用SiN薄膜的研究

以NH3和SiH4为反应源气体,采用射频等离子体增强化学气相沉积(RF-PECVD)法在多晶硅(p-Si)衬底上沉积了一系列SiN薄膜,并利用椭圆偏振测厚仪、超高电阻-微电流计、C-V测试仪对所沉积的薄膜作了相关性能测试.系统分析了沉积温度和射频功率对SiN薄膜的相对介电常数、电学性能及界面特性的影响.分析表明,沉积温度和射频功率主要是通过影响SiN薄膜中的Si/N比影响薄膜的性能,在制备高质量的p-Si TFT栅绝缘层用SiN薄膜方面具有重要的参考价值.     

Effects of nitrogen trifluoride on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon films

The effects of nitrogen trifluoride (NF₃) on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon (DLC) films were investigated. The addition of NF₃ increases the deposition rate of DLC film due presumably to the removal of activated hydrogen species by the fluorine radical (F⁻). Diamond-like carbon films deposited in a methane/NF₃ mixture have a higher refractive index, a lower bulk resistivity, and a lower optical bandgap compared to films deposited in pure methane due to a lower hydrogen content in the films. Moreover, the bulk resistivity of methane/NF₃ DLC films remains constant for annealing temperatures below 400°C. Thus, DLC films deposited with NF₃ are more stable than DLC films deposited without NF₃.     

Scalability of dry-etch processing for small unit-cell HgCdTe focal-plane arrays

A combination of mechanical experiments and fabrication of very-long-wavelength infrared (VLWIR) HgCdTe-infrared detectors has been used to investigate the interaction between various unit-cell design and dry-etch process variables on final unit-cell dimensions and detector performance. Etch rate, which determines the process time required to achieve a specified etch depth, was found to be a function of both the trench width opening used to delineate an individual detector element in a focal-plane array (FPA) and the mesa profile observed during etching. Current-voltage (I-V) probe data at 78 K demonstrated the successful fabrication of 30 μm unit-cell, VLWIR-HgCdTe diodes with mesa delineation performed by dry etching. The breakdown performance of these diodes is sensitive to trench width and dry-etch process time.     

a—SiNx：H薄膜对a—Si：H TFT阈值电压的影响

介绍了测定a－Si：HTFT闽值电压的实验方法。重点研究了改变a－SiNx：H薄膜淀积时反应气体NH3／SiH4流速比以及a－SiNx:H膜厚对a－Si：HTFT阈值电压的影响。对实验结果进行了分析。实验结果表明：a－Si:HTFT的阈值电压随a－SiNx：H的膜厚增加而增大；增大X－SiNx：H薄膜淀积时NH3／SiH4气体流速比，可明显减小a-Si:HTFT的阈值电压。     

Dependence of Threshold Voltage of a-Si:H TFT on a-SiN_x:H Film

ＤｅｐｅｎｄｅｎｃｅｏｆＴｈｒｅｓｈｏｌｄＶｏｌｔａｇｅｏｆａ－Ｓｉ：ＨＴＦＴｏｎａ－ＳｉＮｘ：ＨＦｉｌｍ①ＸＩＯＮＧＺｈｉｂｉｎ，ＷＡＮＧＣｈａｎｇ’ａｎ，ＸＵＺｈｏｎｇｙａｎｇ，ＺＯＵＸｕｅｍｅｉ，ＺＨＡＯＢｏｆａｎｇ，ＤＡＩＹｏｎｇｂｉｎｇ，Ｗ...     

PECVD a—Si：H薄膜对TFT有源矩阵性能的影响及其淀积工艺研究

分析了a－Si：HTFT有源层──a－Si：H薄膜质量和厚度对于a－Si：HTFT关键性指标（通断电流比、阈值电压、响应时间、开口率）的影响，深入、详细地研究了PECVD衬底温度、RF功率和频率、气体流量和反应室气压等淀积工艺参数对a—Si：H薄膜组分、结构的影响，并在实验的基础上给出了它们之间的关系曲线，确定了最佳淀积工艺参数，从而获得了高性能的7.5cm372×276象素a－Si：HTFT有源矩阵。     

Dependence of Threshold Voltage of a-Si:H TFT on a-SiNx:H Film^①

The relation between threshold voltage for hydrogenated amorphous silicon thin film transistors(a-Si:HTFTs)and deposition conditions for hydrogenated amorphous silicon nitride(a-SiNx:H)films is investigated.It is observed that the threshold voltage,Vth,of a-Si:HTFT increases with the increase of the thickness of a-SiNx:H film,and the threshold voltage is reduced apparently with the increase of NH3/SiH4 gas flow rate ratio.     

An a-Si:H vacuum-compatible photoresist process for fabricating device structures in HgCdTe

A process for transferring patterns into HgCdTe epilayers using a hydrogenated amorphous silicon (a-Si:H) photomask has been demonstrated. a-Si:H films were grown using plasma enhanced chemical vapor deposition (PECVD). A latent image of a projected mask pattern was created at the a-Si:H surface by ultraviolet enhanced oxidation in the load lock of the PECVD vacuum chamber. This image was transformed into a mask by hydrogen plasma removal of the unexposed areas. A hydrogen plasma etch selectivity value greater than 500:1 for oxide and a-Si:H allows patterns as thick as 700 nm to be generated. a-Si:H masks were used to create arrays of mesas in planar HgCdTe epilayers by etching in an electron cyclotron resonance (ECR) plasma reactor. Etch selectivity between a-Si:H and HgCdTe during an ECR hydrogen plasma etch was measured to be greater than 18:1. R_oA values > 10³ were obtained for mid-wavelength infrared diodes made from HgCdTe heterojunctions using a-Si:H masks.     

氢化非晶硅中光致亚稳性退化的物理机制

关于氢化非晶硅(a-Si:H)中光致亚稳性退化(Staebler-Wronski效应)虽已进行了大量研究,但对其物理机制至今还是不清楚的,已有物理模型都有它自己的困难.本文指出,光激产生的导带电子与价带空穴通过Si-H弱键的无辐射复合时放出的Si-H 局域模振动声子使Si-H键自身断裂而造成硅悬挂键——SW缺陷.该模型可以定性解释我们所知道的重要实验事实.     

用逐层淀积法制备a－Si∶H薄膜

本文用逐层淀积法制备了ａ－Ｓｉ：Ｈ薄膜，研究了生长速率、子层厚度及氢等离子体处理对薄膜性质的影响，结果指出：不同条件下的氢等离子体处理不仅可以使淀积的样品发生从非晶到微晶的相变，而且可以使费米能级的位置向上或者向下移动，在较低的淀积速率及较小的子层厚度下淀积，并配合以适度的氢等离子体处理，可以得到具有较高光电灵敏度及稳定性的ａ－Ｓｉ：Ｈ薄膜。     

a-Si:H薄膜的磁场诱导红外光谱变化的研究

本文研究了在磁场作用下a—Si:H薄膜的红外光谱的变化,发现了2000cm~(-1)硅氢振动模向2100cm~(-1)硅氢振动模的直接转变,并且在这种变化中键合氢的含量不变。提出了Si—H……Si弱耦合模型。     

瞬态电荷收集法研究a—Si：H／a—SiN：H界面处的电子积累＊

本文介绍一种研究a-Si:H/a-SiN:H界面层电子积累特性的新方法,所用样品为Cr/a-SiN:H/a-Si:H/(n+)a-Si:H/AI.测试表明,a-Si:H/a-SiN:H界面是一个电子积累层,其电子面密度为3.2×10~(11)/cm~2,并且界面层中的电子面密度随外加电压的增加而线性增加。实验结果与理论分析相一致。     

碲镉汞干法刻蚀速率的微负载效应研究

报道了碲镉汞干法刻蚀技术的刻蚀速率的一些研究结果。在同样的刻蚀条件下,当刻蚀区域的图形面积过小,刻蚀剂不易进入刻蚀区域,生成物也不易快速转移出去,使刻蚀速率变慢,这种效应可以等效于刻蚀的微负载效应。而当刻蚀区域的面积过大,刻蚀剂很快被消耗,也会使刻蚀速率变慢,这种效应称为负载效应。采用在同一碲镉汞芯片上制作不同刻蚀面积区域进行刻蚀,比较不同刻蚀面积对刻蚀速率的影响。     

Si/a-Si:H异质结微波双极型晶体管实验研究

本文首次报道采用重掺杂的氢化非晶硅(n~+a-Si∶H)作发射极的硅微波双极型晶体管的制备和特性.该器件内基区方块电阻2kΩ/□,基区宽度0.1μm,共发射极最大电流增益21(V_(cB)=6V,I_c=15mA),发射极Gummel数G_B值已达1.4×10~(14)Scm~(-4).由S参数测得电流增益截止频率f_s=5.5GHz,最大振荡频率f_(max)=7.5GHz.在迄今有关Si/a-Si HBT的报道中,这是首次报道可工作于微波领域里的非晶硅发射极异质结晶体管.     

Determination of surface states distribution in a-Si:H using MOS tunnel Junctions

The measurement of the tunneling conductance and the ac conductance of a tunnelable MOS capacitor enables the determination of surface states distributions in semiconductors. Carrying out the measurement on hydrogenated amorphous silicon a-Si:H has revealed a non-uniform states distribution with a peak at about 0.45 eV below the conduction band edge. If the detected states are considered bulk states they appear to have a density of 10¹⁸ − 5×l0¹⁸ cm⁻³ eV⁻¹ at this peak. The agreement between the above results and states distributions obtained on a-Si:H alloys from other methods, and on materials prepared in various deposition systems, indicates that this peak is a universal property of these alloys. The latter conclusion is shown to be applicable for the determination of the doping efficiency in the alloys.     

Effects of nitrogen doping on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like-carbon films

Nitrogen-doped diamond-like carbon (DLC) or amorphous hydrogenated carbon (a-C:H) films were grown by plasma enhanced chemical vapor deposition using methane and nitrogen gases as precursors. The effects of nitrogen trifluoride (NF₃) on these nitrogen-doped DLC films were also investigated. The deposition rate decreases sharply with the addition of nitrogen in the absence of NFF₃ due to dilution, while it increases in the presence of NFF₃ due, presumably, to the reduction of activated hydrogen species by the fluorine radical (F϶. X-ray photoelectron spectra reveal a nitrogen concentration in the range of 9.3 to 13.8% in these DLC films with a C Is electron binding energy of 287-288 eV, indicating the diamond-like structure. Infrared spectra of DLC films indicate the presence of amino groups (N-H) and nitrile and/or isonitrile (C= N) groups giving strong evidence of sp carbon. Diamond like carbon films deposited in CHF₄ +NF₄ (with and without NFF₃) have a lower refractive index, a lower bulk resistivity, and a lower optical bandgap than films deposited using CHF₄ due to a lower hydrogen content in the films. Moreover, the bulk resistivity of these films decreases by over four orders of magnitude and the optical bandgap decreases from 2.65 eV to about 0.75 eV following annealing at a temperature of 500°C.     

a－S1∶H CCD的转移特性分析

本文从ａ—Ｓｉ∶Ｈ的材料特性出发，采用更为精确的ａ—Ｓｉ∶Ｈ带隙态分布模型计算了ａ—Ｓｉ∶ＨＣＣＤ的转移特性，得出了ａ—Ｓｉ∶Ｈ材料参数对ａ—Ｓｉ∶ＨＣＣＤ的动态特性影响的数值分析结果．理论结果表明，ａ—Ｓｉ∶Ｈ材料带隙中的局域态分布对ａ—Ｓｉ∶ＨＣＣＤ的转移特性有非常大的影响．而且在高频下，ａ－Ｓｉ∶Ｈ中的带尾态对ａ—Ｓｉ∶ＨＣＣＤ转移特性的影响比深局域态要大．