摘要:

A three‐dimensional thermal model of generic multilevel interconnection systems in very large scale integrated (VLSI) circuits is presented. The temperature distributions are quantitatively studied using the transmission‐line matrix modeling method. The temperature increase of a triple‐level parallel and crossing interconnection‐line scheme is found to be several times higher than that of a single‐level parallel line structure if the same magnitude of current density in the 106A/cm2range is maintained. More than 50% of the temperature rise occurs across the Si substrate; the treatment of which as a perfect heat sink in many previous thermal analyses of metallization structures is, therefore, inadequate. The large thermal gradients within the SiO2insulators between different metallization levels can be eliminated and the temperature rise can be significantly reduced if the SiO2interlevel and passivation dielectrics are replaced by a material with much higher thermal conductivity. Lower temperatures would be beneficial for improving electromigration lifetime and reducing thermal stress voiding in high density VLSI multilevel interconnections.

ISSN:0734-211X    

DOI:10.1116/1.587108

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The effects of the grain size in the Al layer and the passivation structure on the electromigration performance in the two level Al interconnections, the bottom (M1) and the top (M2) interconnections, each of which had a TiW/Al/TiW multilayered structure, were studied regarding void and extrusion formation in the Al layers. In M2, the resistance increase of the interconnection having a larger grain size in the Al layer formed with a reflow treatment, was smaller than that without any reflow treatment. Larger numbers of Al extrusions were, however, observed in the M2 interconnection with the reflow treatment than without it. In M1 which was buried under a thick insulation layer, enlargement of the Al grains by the reflow treatment was more effective to suppress the resistance increase than in the M2 interconnections. This result meant that the combination effect occurred when both treatments, enlargement of the Al grains in the interconnection and strengthening the passivation layer surrounding it, were applied simultaneously.

ISSN:0734-211X    

DOI:10.1116/1.587109

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

It is proposed that the plasma enhanced chemical vapor deposited tungsten nitride (PECVD‐W–N) thin film is used as a diffusion barrier to prevent the interdiffusion between Al and Si during postannealing process. The atomic concentration of N in W–N film deposited with NH3/WF6partial pressure ratio of 0.5 is about 33 at. % and its resistivity is 90–110 μΩ cm. The Rutherford backscattering spectrometry, Auger electron depth profiles, x‐ray diffraction, and scanning electron micrographs show that 900 Å PECVD‐W67N33film interposed between Al and Si is more impermeable than PECVD‐W film due to N atoms and it also keeps its chemical integrity during the postfurnace annealing at 600 °C for 30 min in Ar ambient.

ISSN:0734-211X    

DOI:10.1116/1.587110

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Ion beam induced deposition is a novel method of thin film growth in which adsorbed, metal‐bearing molecules are decomposed by incident energetic ions thus leaving a deposit. In conjunction with finely focused ion beams this process is used in microelectronics for local repair, i.e., deposition of patches of metal film with better than 0.1 μm resolution. Each ion can decompose as many as 40–50 adsorbed molecules. The fundamental aspects of this process, namely how is the energy of the ion transferred to adsorbed molecules over a radius of up to 5 nm, have been studied. The decomposition yield (number of molecules decomposed/ion) was measured for Ne, Ar, Kr, and Xe ions at 50 and 100 keV. A model based ontrimcalculations was developed. The data correlate with this model confirming the view that collision cascades which can provide energy to surface atoms over a substantial area are responsible for ion beam induced deposition.

ISSN:0734-211X    

DOI:10.1116/1.587111

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Ultraclean wet chemical preparationinairand a fast new load‐locking technique opens up a way to characterizerealSi(111) surfaces after processing for microelectronic device fabrication with the proven surface‐analytical tools available in an ultrahigh vacuum. For the first time thermodesorption spectroscopy can be utilized, without interference from typical artefacts like contamination introduced by theexsitupreparation, to investigate the chemical termination and molecular composition of silicon surfaces after initial wet chemical key processes in semiconductor technology (chemical and UV/ozone‐enhanced cleaning, liquid and gaseous phase etching, rinsing with de‐ionized water). By multiplexing a mass spectrometer and analyzing thermally desorbed molecules over a wide range of masses simultaneously, we can separate quantitatively between the major surface‐terminating molecules that are inherently responsible for the different chemical surface properties (hydrophilicdue to –OH groups after wet chemical or UV/ozone‐enhanced oxidation;hydrophobicdue to termination with hydrides after etching with hydrofluoric acid/ammonium fluoride, HF/NH4F) and minor species characteristic for details of the preparation process (physisorbed residues upon omission of a final rinsing step; contributions from residual carbon–hydride contamination). Furthermore, distinct desorption channels of hydrogen molecules from mono‐, di‐, and trihydride surface states allow a characterization of thepH‐dependent etching by H2O:HF:NH4F [concentrated HF: selective removal of surface oxides; dilute HF: additional slow isotropic attack of bulk silicon; HF/NH4F: anisotropic attack by fast removal of higher hydride defect sites on Si(111)] and a determination of the resulting microroughness of the silicon surface. Slow regrowth of an ultrathin oxide on HF‐treated surfaces during final rinsing with water can be monitored by a separation between H2O desorption at high temperature from surface silanol groups and low‐temperature desorption of physisorbed water.

ISSN:0734-211X    

DOI:10.1116/1.587112

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

As design rules shrink to conform with ultra‐large‐scale integration device dimensions, gate dielectrics for metal–oxide–semiconductor field effect transistor structures are required to be scaled to below ∼60 Å, where some properties of the device, such as interface roughness, that are negligible for thicker films become critical. Microroughness at the interface of ultrathin MOS capacitors has been shown to degrade these devices. The present study focuses on the interfacial region of ∼50 Å SiO2on Si, using the quantum oscillations in Fowler–Nordheim tunneling currents as a probe. The oscillations are sensitive to the electron potential and abruptness of the film and interfaces. In particular, inelastic scattering of the electrons will reduce the amplitude of the oscillations. The amplitude of the oscillations is used to examine the degree of microroughness at the interface that results from a preoxidation high temperature anneal in an inert ambient containing various amounts of H2O. Atomic force microscopy imaging has shown correlations supporting a microroughness induced change in the quantum oscillation amplitudes.

ISSN:0734-211X    

DOI:10.1116/1.587113

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The etching of poly‐Si (n+and undoped) in a radio‐frequency‐biased electron cyclotron resonance plasma of HBr was studied. Etch rates of Si, oxide, and photoresist were obtained by ellipsometry as a function of the bias voltage and two substrate temperatures (15 and 50 °C) at 5 mTorr pressure. The etch rate of poly‐Si depends on the doping level, withn+Si etching faster than intrinsic Si. High selectivities of Si over both oxide and photoresist can be achieved at low bias voltages. Using angle‐resolved x‐ray photoelectron spectroscopy, it is shown that a carbon and bromine containing layer is deposited on the sidewall of the poly‐Si during the etching process when a photoresist patterned wafer is used. The thickness of the sidewall film decreases with increasing substrate temperature and increases at the bias voltage is raised. The thickness of this sidewall film influences the anisotropy of the process, with some undercutting occurring at high temperature and low bias voltage.

ISSN:0734-211X    

DOI:10.1116/1.587115

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The effects of polysilicon etch plasma conditions on metal–oxide–semiconductor (MOS) capacitor breakdown andn‐channel MOS transistor (NMOS) performance have been investigated. A high density electron cyclotron resonance (ECR) plasma source with multipolar magnetic confinement was integrated into a full NMOS process flow. The polysilicon etch plasma process parameters for designed experiments were microwave power, overetch time, rf bias, and plasma radial uniformity. MOS capacitor leakage currents increase with longer polysilicon edge lengths on gate oxide, higher ion density, and higher ion energy during the polysilicon overetch step. Lower NMOS transistor transconductance and higher threshold voltages correlate with longer overetch times and high microwave power and rf bias during the overetch step. Device performance degradation increases with decreasing channel length, and the exposure of the source and drain oxide edges to a high density flux is thought to be the main cause for observed degradation. A high rate, selective, and low damage polysilicon etch process can be obtained using a high density (≳1011cm−3) and moderate ion energy (<30 eV) ECR discharge, with moderate power and zero applied rf bias during the overetch step.

ISSN:0734-211X    

DOI:10.1116/1.587165

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Ultra‐large‐scale integration patterning with less than 0.25‐μm precision requires the optimization of electron cyclotron resonance (ECR) plasma discharge. This is because ion motion and etching results are affected by magnetohydrodynamic plasma instability and charge accumulation on the substrate in nonuniform plasma. Microloading and unusual notching at the boundary pattern between dense patterns and open spaces are both caused duringn+poly‐Si etching in nonuniform plasma. To prevent these problems, optimally uniform ECR plasma generation is necessary. This is accomplished by optimizing both the magnetic field profile and the introduction of microwaves.

ISSN:0734-211X    

DOI:10.1116/1.587166

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Knowledge of the lateral or spatial distribution of doping impurities is important for accurate process and device simulations of submicrometer silicon devices, since the edge effects of the electric fields can no longer be neglected. A newly developed technique, which utilizes the high sensitivity and high depth resolution of secondary ion mass spectrometry (SIMS), is capable of measuring two‐dimensional (2D, i.e., in the depth and the lateral direction) doping distributions. The technique is based on a series of one‐dimensional (1D) SIMS depth profiles obtained at different directions through a sample. The individual SIMS depth profiles are then recombined to generate a 2D doping profile using the expectation maximization algorithm, which was originally used in human body computer‐aided tomography. The SIMS tomography technique gives a doping distribution as a function of position. The positional accuracy or spatial resolution of the technique needs to be fully understood in order to properly use the technique. During a reconstruction process, the area of interest is divided into small volume elements or voxels, and the doping concentration for each voxel is estimated. Therefore, the size of the voxels determines the spatial resolution of the reconstructed profiles. The smaller the voxels are, the better the spatial resolution is. However, the size of the reconstructed area cannot be made infinitely small, due to the limited number of SIMS measurements.Since each SIMS measurement provides only one linear independent equation, the total number of equations (or the total number of the SIMS measurements) should be equal to the number of voxels (or unknowns). Thus, the size of the voxels, or equivalently, the number of SIMS measurements available imposes a practical limit on the spatial resolution. In addition, since the 1D SIMS depth profiles are used as the input for the profile reconstruction, the depth resolution of the 1D SIMS measurements dictates the spatial resolution of the reconstructed profiles. Furthermore, the depth resolution of the 1D SIMS measurements is also affected by the sample skew, which is the measure of the lack of parallelism of the dopant line with respect to the beveled surface. And finally, the alignment of the 1D SIMS depth profiles relative to each other contributes to the positional uncertainty of the reconstructed distributions. A 20 keV boron implant through a 1.2 μm wide window into germanium preamorphized silicon has been reconstructed recently. The spatial resolution of the reconstructed dopant profile is evaluated to be 40 nm. It is found that the spatial resolution is predominantly determined by the depth resolution of 1D SIMS profiles, and the microtopography of the SIMS craters is the major cause of the poor depth resolution. It is expected that the spatial resolution of the 2D doping tomography can be greatly improved through the use of a simplified sample structure, which will reduce the SIMS profiling depth and provide better depth resolution for the 1D SIMS measurements.

ISSN:0734-211X    

DOI:10.1116/1.587167

出版商:American Vacuum Society    

年代:1994

数据来源: AIP