Analysis of ion beam induced damage and amorphization of 6H-SiC by raman scattering

Raman scattering analysis of damaged SiC layers obtained by 200 keV Ge⁺ ion implantation into 6H-SiC has been performed as a function of the implanted dose (up to 10¹⁵ cm⁻²) and annealing temperature (up to 1500°C). The results obtained show the presence of three different damage levels: low damage level (doses ≤3 × 10¹² cm⁻²), medium to high damage level (doses between 10¹³ and 10¹⁴ cm^-2), and formation of a continuous amorphous layer for doses higher than the amorphization threshold of 2–3 × 10¹⁴ cm⁻². Moreover, at doses of about 10¹⁴ cm⁻² (below the amorphization threshold) amorphous domains are already observed. The Raman spectra indicate the existence of structural differences between the amorphous phase at doses below and above the threshold. After annealing, there is a residual damage which cannot be removed even at the highest annealing temperature of 1500°C. Differences in residual damage between the samples implanted at doses of 10¹⁴ and 10¹⁵ cm^-2 and annealed at the highest temperatures are observed from the peaks in the 1000–1850 cm^-1 spectral region. Finally, annealing at the highest temperature is required to observe the complete disappearance of the amorphous bands.     

Defect-engineering in SiC by ion implantation and electron irradiation

Three examples are given, which show that ion implantation and electron irradiation can drastically modify the electrical properties of SiC and SiC-based MOS capacitors. (1) It is demonstrated that sulphur ions (S⁺) implanted into 6H-SiC act as double donors with ground states ranging from 310 to 635 meV below the conduction bandedge. (2) Co-implantation of nitrogen (N⁺) - and silicon (Si⁺) - ions into 4H-SiC leads to a strong deactivation of N donors. Additional experiments with electron (e⁻)-irradiated 4H-SiC samples (E(e⁻) = 200 keV) support the idea that this deactivation is due to the formation of an electrically neutral (N_x-V_C, y)-complex. (3) Implantation of a surface-near Gaussian profile into n-type 4H-SiC followed by a standard oxidation process leads to a strong reduction of the density of interface traps D_it close to the conduction bandedge in n-type 4H-SiC/SiO₂ MOS capacitors.     

The influence of dose and protecting mask on electrically active defects induced by ion implantation in silicon

We present a study of electrically active defects induced by ion implantation, for two dopants: arsenic and phosphorous. Our analysis technique is Deep Level Transient Spectroscopy (D.L.T.S.). We have studied the generation of defects by direct implantation, and indirect implantation, that is through an SiO₂ layer. We follow the defect spectrum evolution for different doses (10⁸ to 10¹⁴ atoms/cm²) and for different annealing temperatures (from room temperature up to 800° C). The comparison of our results with other published ones allows us to improve the knowledge about the role of a protecting oxide layer, the influence of moderate thermal annealing, and the effect of oxygen on deep centers produced by ion bombardment.     

Electrical characterization of defects introduced during electron beam deposition of W Schottky contacts on n-type 4H-SiC

We have studied the defects introduced in n-type 4H-SiC during electron beam deposition (EBD) of tungsten by deep-level transient spectroscopy (DLTS). The results from current-voltage and capacitance-voltage measurements showed deviations from ideality due to damage, but were still well suited to a DLTS study. We compared the electrical properties of six electrically active defects observed in EBD Schottky barrier diodes with those introduced in resistively evaporated material on the same material, as-grown, as well as after high energy electron irradiation (HEEI). We observed that EBD introduced two electrically active defects with energies E_C – 0.42 and E_C – 0.70 eV in the 4H-SiC at and near the interface with the tungsten. The defects introduced by EBD had properties similar to defect attributed to the silicon or carbon vacancy, introduced during HEEI of 4H-SiC. EBD was also responsible for the increase in concentration of a defect attributed to nitrogen impurities (E_C – 0.10) as well as a defect linked to the carbon vacancy (E_C – 0.67). Annealing at 400 °C in Ar ambient removed these two defects introduced during the EBD.     

Characterization of phosphorus implantation in 4H-SiC

We report the characterization of phosphorus implantation in 4H-SiC. The implanted layers are characterized by analytical techniques (secondary ion mass spectrometry, transmission electron microscopy) as well as electrical and a sheet resistance value as low as 160 Ω/□ has been measured. We have also studied the effect of annealing time and temperature on activation of phosphorus implants. It has been shown to possible to obtain low sheet resistance (∼260 Ω/□) by annealing at a temperature as low as 1200°C. High-dose (∼ 4 × 10¹⁵ cm⁻²) implants are found to have a higher sheet resistance than that on lower dose implants which is attributed to the near-surface depletion of the dopant during high temperature anneal. Different implantation dosages were utilized for the experiments and subsequently junction rectifiers were fabricated. Forward characteristics of these diodes are observed to obey a generalized Sah-Noyce-Shockly multiple level recombination model with four shallow levels and one deep level.     

Electrically active defects induced by hydrogen and helium implantations in Ge

Results of a study of electrically active defects induced in Sb-doped Ge crystals by implantations of hydrogen and helium ions (protons and alpha particles) with energies in the range from 500 keV to 1 MeV and doses in the range 1×10¹⁰–1×10¹⁴ cm⁻² are presented in this work. Transformations of the defects upon post-implantation isochronal anneals in the temperature range 50–350 °C have also been studied. The results have been obtained by means of capacitance–voltage (C–V) measurements and deep-level transient spectroscopy (DLTS).It was found from an analysis of DLTS spectra that low doses (<5×10¹⁰ cm⁻²) of H and He ion implantations resulted in the introduction of damage similar to that observed after MeV electron irradiation. The Sb–vacancy complex was the dominant deep-level defect in the lightly implanted samples. After implantations with doses higher than 5×10¹⁰ cm⁻² peaks due to more complex defects were observed in the DLTS spectra. Implantations with heavy (5×10¹³ cm⁻²) doses of both H and He ions caused the formation of a sub-surface layer with a high (up to 1×10¹⁷ cm⁻³) concentration of donors. These donors were eliminated by anneals at temperatures in the range 100–200 °C. Heat treatments of the heavy proton-implanted Ge samples in the temperature range 250–300 °C resulted in the formation of shallow hydrogen-related donors, the concentration of which was the highest in a region close to the projected depth of implanted protons. The maximum peak concentration of the H-related donors was higher than 1×10¹⁵ cm⁻³ for a proton implantation dose of 1×10¹⁴ cm⁻².     

Al掺杂6H-SiC铁磁性研究(英文)

使用物理气象沉积法生长了轻Al掺杂6H-SiC样品,并使用超导量子干涉磁强计(SQUID)对无腐蚀及腐蚀后的样品进行了测试,发现了腐蚀后的样品在室温下表现出铁磁性。经过计算,样品磁信号并非来源于腐蚀剂KOH及K2CO3。同时腐蚀后的样品形貌表明杂质聚集在腐蚀后的缺陷附近从而形成了一定的铁磁性,因此缺陷被腐蚀放大是样品形成铁磁性的主要原因。     

退火工艺对Al离子注入的4H-SiC表面形貌的影响

通过应用多次Al离子注入和CVD中的高温退火技术,在SiC片表面形成了p型层。p型层中各深度下Al的浓度均为110¹⁹cm^-3,层厚为550nm。本文应用三种不同的退火工艺对注入后的SiC进行退火。通过测量和比较表面粗糙度,发现通过石墨层覆盖来保护表面的退火工艺可以很好的阻止SiC表面在高温退火下的粗化,粗糙度保持在3.8nm。通过其他两种(在氩气保护下、在SiC保护片的覆盖下)退火工艺退火所得到的表面有明显的台阶,粗糙度分别为12.2nm和6.6nm。     

EPR studies of point defects in Cu-III–VI2 chalcopyrite semiconductors

EPR and PL spectra were measured to investigate point defects in I–III–VI₂ type chalcopyrite semiconductors where the group I element is Cu. Taking into account various optical spectra, the EPR signals observed were assigned to defect centers involving residual Fe impurities and Cu-vacancies. Some of the point defects were found to form defect-complexes.     

Pt and W ohmic contacts to p-6H-SiC by focused ion beam direct-write deposition

Low resistance Pt and W ohmic metallizations to p-type 6H-SiC, using focused ion beam (FIB) surface-modification and in-situ direct-write metal deposition without annealing, are reported. FIB (Ga) surface-modification and in-situ deposition of Pt, and W showed minimum contact resistance values of 2.8 × 10⁻⁴ ohm-cm² to 2.5 × 10⁻⁴ ohm-cm², respectively. A comparison with ex-situ pulse laser deposited Pt on surface-modified areas showed comparable contact resistance values and similar behavior. Auger and secondary ion mass spectroscopy analysis showed a significant (∼4% a.c.) incorporation of Ga within a 15 nm distance from the SiC surface with surface-modification. Atomic force micros-copy studies showed that surface-modification process smooths out the SiC surface significantly.     

电子和中子辐照n型6H-SiC的光致发光谱

对用电子能量为1.7,0.5和0.4MeV的电子辐照和中子辐照后的n型6H-SiC样品进行低温光致发光研究.对于Ee≥0.5MeV电子辐照和中子辐照后的样品,首次发现了位于478.6/483.3/486.1n m的S1/S2/S3谱线.对样品进行热退火研究表明S1/S2/S3谱线在500℃下消失,而退火温度高于700℃时D1中心出现.考虑到产生C空位和Si空位所需的位移阈能以及热退火行为,说明S1/S2/S3为初级Si空位初级缺陷,而D1中心为二次缺陷.     

EPR characterization of defects in monoclinic powders of ZrO2 and HfO2

Electron paramagnetic resonance (EPR) measurements have been made on a variety of commercially available samples of the monoclinic form of the high-dielectric constant (high k) materials ZrO₂ and HfO₂ with the aim of characterizing the defects they contain. All EPR measurements were at about 9.5 GHz and at room temperature. An axially symmetric spectrum with g=1.961(2), g=1.976(2) is observed in most of the ZrO₂ samples and a similar one with g=1.940(3), g=1.970(2) is seen for most of the HfO₂ samples; they are attributed to centres involving Zr³⁺and Hf ³⁺, respectively. Their average concentration lies in the approximate range 10¹⁵–10¹⁷ cm⁻³, depending on the product specification, and, with one exception is unaffected by γ-irradiation. Grinding granules to powder and/or γ-irradiation yields further EPR spectra of defects, some of which are likely to involve oxygen, those are probably in the near surface region.     

电子和中子辐照n型6H-SiC的光致发光谱

对用电子能量为1.7,0.5和0.4MeV的电子辐照和中子辐照后的n型6H-SiC样品进行低温光致发光研究.对于Ee≥0.5MeV电子辐照和中子辐照后的样品,首次发现了位于478.6/483.3/486.1n m的S1/S2/S3谱线.对样品进行热退火研究表明S1/S2/S3谱线在500℃下消失,而退火温度高于700℃时D1中心出现.考虑到产生C空位和Si空位所需的位移阈能以及热退火行为,说明S1/S2/S3为初级Si空位初级缺陷,而D1中心为二次缺陷.     

N型6H-SiCMOS电容的电学特性

在可商业获得的 N型 6 H- Si C晶片上 ,通过化学气相淀积 ,进行同质外延生长 ,在此结构材料上 ,制备 MOS电容 .详细测量并分析了 6 H- Si C MOS电容的电学特性 ,其有效电荷密度为 4.3× 10 1 0 cm- 2 ;Si C与 Si O2 之间的势垒高度估算为 2 .6 7e V;Si C热生长 Si O2 的本征击穿场强 (用累计失效率 5 0 %时的场强来计算 )为 12 .4MV/ cm ,已达到了制作器件的要求 .     

Activation of nitrogen implants in 6H-SiC

We have studied the effect of anneal time and temperature on activation of high-dose nitrogen implants into 6H-SiC. At a fixed anneal temperature, a strong dependence on anneal time is seen. For short anneals, the resistivity initially decreases with anneal time. After a minimum resistivity is reached, resistivity increases with further anneal. The optimum anneal time for minimum resistiv-ity increases as anneal temperature is reduced. Successful activation has been achieved at temperatures as low as 900°C.     

p型Al/6H-SiC肖特基二极管特性研究

研究了 p型 Al/6H- Si C肖特基二极管的基本制作工艺及其电学参数。采用电流 -电压法 ( I-V)测试了肖特基二极管的理想因子 n和肖特基势垒高度b。对其基本电学参数 n和b 的温度特性进行了研究 ,并分析了串联电阻对 I- V特性的影响。     

中子辐照下的6H-SiCpn结电特性分析

用中子辐照在６Ｈ－ＳｉＣｐｎ结中引入的复合中心和深能级陷阱解释了ＳｉＣｐｎ结辐照后电特性退化的现象,并推导了辐照后ＳｉＣｐｎ结理想因子与外加电压的关系,给出了ＳｉＣｐｎ结中子辐照电特性退化的模型,模拟结果和实验数据的对比说明关于ＳｉＣｐｎ结电特性退化的理论解释是正确的。     

电子和中子辐照n型6H-SiC的光致发光谱

对用电子能量为1.7, 0.5和0.4MeV的电子辐照和中子辐照后的n型6H-SiC样品进行低温光致发光研究. 对于Ee≥0.5MeV电子辐照和中子辐照后的样品,首次发现了位于478.6/483.3/486.1nm的S1/S2/S3谱线.对样品进行热退火研究表明S1/S2/S3谱线在500℃下消失,而退火温度高于700℃时D1中心出现.考虑到产生C空位和Si空位所需的位移阈能以及热退火行为,说明S1/S2/S3为初级Si空位初级缺陷,而D1中心为二次缺陷.     

Identification of a Three-Site Defect in Semi-Insulating 4H-SiC

Using electron paramagnetic resonance (EPR), we observe a defect that increases significantly with annealing temperature. This spin S = 1 defect is characterized by g _x ≈ g _y ≈ g _z = 2.0056 and a fine structure splitting D ∼ 100 G whose principal axis lies in a plane perpendicular to the c-axis. Also resolved are several hyperfine interactions with the low abundance ²⁹Si and ¹³C neighboring nuclei. A careful analysis of the intensity of these hyperfine lines allows a precise determination of the identity and the quantity of interacting nuclei. This center is diamagnetic in the ground state but can be excited into a paramagnetic triplet state by sub-bandgap light. We identify this new defect as a three-site vacancy involving V _C-V _Si-V _C. The angular dependence of the ¹³C hyperfine interaction supports the proposed model. These may be the simplest of a family of more complex and extended defects that play a role in the semi-insulating (SI) character of SiC.     

6H-SiC高反压台面pn结二极管

在可商业获得的单晶 6 H- Si C晶片上 ,通过化学气相淀积 ,进行同质外延生长 ;并在此 6 H - Si C结构材料上 ,利用反应离子刻蚀和接触合金化技术 ,制作台面 pn结二极管 .详细测量并分析了器件的电学特性 ,测量结果表明此 6 H - Si C二极管在室温、空气介质中 ,- 10 V时 ,漏电流密度为 2 .4× 10 - 8A/cm2 ,在反向电压低于 6 0 0 V及接近30 0℃高温下都具有良好的整流特性 .