摘要:

The nucleation and defect structure of GaAs films grown on Ge(001) by molecular‐beam epitaxy (MBE) and ion‐assisted MBE (IAMBE) were studied using reflection high‐energy electron diffraction and transmission electron microscopy. Three‐dimensional (3D) islands nucleated during the initial stages of MBE growth at 580 °C, and continued growth led to nonplanar surfaces and a high density of stacking faults and twins in the films. Irradiation by 33 eV Ar ions during IAMBE growth at 580 °C suppressed 3D island nucleation, yielding relatively flat surfaces throughout growth. Antiphase domains were the only defects observed in the IAMBE films.

ISSN:0734-211X    

DOI:10.1116/1.586719

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

NpnAlGaAs/GaAs heterojunction bipolar transistors (HBTs) are fabricated to examine the critical passivation ledge thickness needed to prevent current gain degradation due to extrinsic base surface recombination current. The current gains of these molecular‐beam epitaxially grown HBTs with Be‐doped base layers are measured as the passivation ledge is gradually etched away. Experimental results indicate that partial passivation is achieved with a ledge thickness of 300 Å and a maximum current gain is measured with a ledge thickness of 900 Å. The ideality factor values of the base currents at various etch depths are also examined and compared with published results.

ISSN:0734-211X    

DOI:10.1116/1.586729

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

A phenomenological model is proposed to describe sulfide passivation of the surfaces of III–V semiconductors as a process of charge transfer between a semiconductor and a passivation solution. The model assumes that formation of the passivation sulfide coat occurs as a result of oxidation of the semiconductor in a photoelectrochemical reaction. The growth rate of the passivating coat is determined by the rate at which electrons are transferred from the semiconductor into the solution, as well as by the energy which binds atoms in the surface layer of the semiconductor and the heat evolving in the process. It is found that the growth rate of the coat is dependent upon conductivity type and doping level of the semiconductor, hydrogen ion exponent, and concentration of the solution and, as well, the intensity of light incident upon the electrolyte/semiconductor interface. In terms of the model, passivation of different III–V semiconductors is considered.

ISSN:0734-211X    

DOI:10.1116/1.586710

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Smooth anisotropic dry etching of ZnS, ZnSe, CdS, and CdTe in electron cyclotron resonance CH4/H2/Ar discharges at low pressure (1–25 mTorr) and low direct‐current (dc) bias (−100 to −250 V dc) is reported. The presence of CH4at low flow rates is necessary to obtain the best morphologies and to retain the stoichiometry of the surfaces, although H2/Ar discharges readily etch all four materials. Increasing the microwave power into the discharge at fixed dc bias produces significant increases in the resulting etch rates, while retaining the highly anisotropic nature of the pattern transfer.

ISSN:0734-211X    

DOI:10.1116/1.586718

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Surface conductance measurements, using the transmission line model (TLM) technique, have been used to assess surface electrical damage in GaAs resulting from dry etching. Reactive ion etching (RIE) in CH4/H2and SiCl4, ion beam etching in Ne and Ar and electron cyclotron resonance etching (ECR‐RIE) in CCl2F2/He have been investigated. A phenomenological model is proposed for determining the extent of the surface etching damage. It is found that the use of slow etch rates, high bias/accelerating voltage and light ions in etching increases the electrical damage in GaAs. Possible causes for the creation of deep damage are discussed, and the criteria for low damage etching are suggested. The TLM method is a powerful technique for assessing etching processes used for semiconductors.

ISSN:0734-211X    

DOI:10.1116/1.586720

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The parameters relevant to dry development of silylated polymers have been studied, in particular ion energy and atomic oxygen concentration. Critical dimension loss is demonstrated to depend upon silylation angle, sputtering rate of the silylated polymer, and development time. Anisotropic etch profiles are argued to be due to a compromise between critical dimension loss and isotropic etching of the unsilylated polymer.

ISSN:0734-211X    

DOI:10.1116/1.586721

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We have formed ultrathin metal films with nanometer‐scale features by metal shadowing of two‐dimensional protein crystals followed by fast atom beam milling. In this process, the metal overlayer is formed into a screen consisting of hexagonal arrays of 10 nm size holes with a 22 nm periodicity. Thin films of Ti, Ta, Pt, Pt/C, Pt/Ir, Pt/Ir/C, Va, Cr, Ni, Ag, Zr, and Nb show dramatic differences in their response to this method of nanotexturing. Evaluation of film morphology by transmission electron microscopy before and after milling reveals a correlation between microstructural characteristics and the features of the nanostructures formed by different metals. The dominant factor for determining the uniformity and quality of the formed nanostructure is a thin film which is amorphous or very fine grained after milling. Overall pattern uniformity and individual hole boundaries which are smooth and round are necessary for optimal patterning. Crystallization and grain growth seem to negatively affect patterning quality, resulting specifically in extensive bridging between holes which generally have irregular boundaries.

ISSN:0734-211X    

DOI:10.1116/1.586722

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Electron cyclotron resonance ion stream etching of Ta film was investigated for preparing x‐ray mask absorber patterns. Ta is etched by the system at a high rate and with high selectivity. Using Cl2as etching gas, the etch rate decreases rapidly with decreasing pattern width below 0.5 μm and large undercutting is observed. The problems are reduced by adding Ar or O2gas to the Cl2. Etching with a mixture of Cl2and O2produces highly accurate Ta absorber patterns for x‐ray masks. The pattern width dependence of the etch rate and the undercutting were simulated with a model that takes account of the angular distribution of active species incident on the sample. The experimental results agree well with those calculated assuming that the incidence angles are distributed between −36° and 36°. The addition of O2or Ar enhances ion assisted etching.  

ISSN:0734-211X    

DOI:10.1116/1.586723

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Conventional transmission electron microscopy and high‐resolution electron microscopy were used to study the cross sections of Au/Zn/Au ohmic contacts to a [001]‐orientedp‐type GaAs substrate. The metal contacts fabricated by sequential vapor deposition were capped with an Al2O3thin film to form a closed system when subjected to a 420 °C anneal for 3 min. For an as‐deposited specimen, the Zn layer was found to react with the two adjacent Au layers and the reaction products were three room‐temperature phases of Au3Zn. One of these phases is identified for the first time and its structure is characterized. Upon annealing, these phases remained stable and no interfacial reaction between the metal contact and GaAs was observed, as opposed to an uncapped contact. The interface between the annealed contact and GaAs exhibited the same degree of uniformity and planarity as that of the as‐deposited specimen. This study demonstrates that the formation of metallic protrusions into GaAs, as commonly found in an uncapped contact, is not necessary for the transition from rectifying to ohmic behavior of the contact.

ISSN:0734-211X    

DOI:10.1116/1.586724

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Laser induced deposition of tungsten from WF6on GaAs using a focused continuous wave scanning argon‐ion laser was investigated. Deposits were prepared with H2as a reducing agent, as well as without it. Deposition of tungsten is found to occur in a narrow process window, suggesting the existence of a competing etching reaction. Film composition and structure were analyzed by scanning electron microscopy and Auger electron microscopy. Surface reactions were studied by x‐ray photoelectron spectroscopy. The data suggest that the GaAs surface participates in the reaction with WF6, leading to the formation of GaF3which may poison the initiation of the deposition process.

ISSN:0734-211X    

DOI:10.1116/1.586725

出版商:American Vacuum Society    

年代:1993

数据来源: AIP