摘要:

Contamination associated with ion implantation is reviewed with an emphasis on secondary ion mass spectrometry (SIMS) characterization. Specific examples are provided using SIMS as a tool to detect and resolve contaminant problems. This study of contamination is organized according to the path of the ion beam through an ion implanter, starting with the source and continuing to the end station. The source material, ion source components, and vacuum system can produce contaminant mass interferences that may not be eliminated by mass filtration in the implanter. A table of possible mass interferences is provided. The mass resolution of the implanter may be insufficient to remove adjacent masses and therefore may permit additional contaminants in the mass‐analyzed ion beam. Charge exchange and molecular ion dissociation due to poor vacuum can occur at several locations in the implanter, especially after mass separation but before final acceleration. Detailed examples of BF2dissociation are presented. Collisions of the ion beam with end station components result in low energy deposition of contaminants that can be driven into the target by the ion implanting beam. The fluence of the species of interest can be in error. Examples of multiple contaminant sources are also provided.

ISSN:1071-1023    

DOI:10.1116/1.587753

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Ion bombardment damage on GaAs surface has been studied with Ar ion implantation, followed by controlled removal of the damaged GaAs surface layer by anodic oxidation/stripping prior to Schottky metallization. The electrical characteristics of subsequently fabricated Au/n‐GaAs Schottky barriers display progressive recovery towards those of undamaged control samples as a function of implanted Ar dose. The recovery depth for different material/device parameters are well in excess of the projected range for 10‐keV Ar ions (10.5 nm) in GaAs. Deep level transient spectroscopy measurements of the Ar‐implanted samples show both suppression and enhancement of deep levels in the GaAs surface region. A Ga‐rich surface region introduced by low‐energy Ar implantation appears to be responsible for the modification of deep level traps. The recovery in Schottky barrier height with a postimplantation rapid thermal anneal process is very poor at temperatures below 600 °C and significant degradation occurs at a higher temperature of 700 °C. Carrier compensation and suppression of donorlike antisite defects AsGahave been found in a Ga‐rich region resulting from either ion bombardment or high‐temperature annealing.

ISSN:1071-1023    

DOI:10.1116/1.587754

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Optical characterization has been performed on the InAs/InP surface layer in order to study the arsenic (As) stabilization process of InP. The InAs layers are formed by the simple exchange of phosphorus (P) from the InP surface substrate by arsenic. Samples prepared under arsenic overpressure in the temperature range 450–600 °C have been examined. Luminescence from the InAs layer which acts as a surface quantum well has been detected. We have compared this emission with theoretical calculations and reasonable agreement was observed. Moreover, we have determined that when the arsenic stabilization temperature increases the InAs thickness increases as a consequence of P–As exchange and that after the replacement of the five first top monolayers this exchange seems to stop. We explain this result in terms of the shield effect of the InAs overlayers which efficiently cap the InP substrate against further P evaporation and the restoration of surface structural order which limits any other phosphorus exodiffusion. Comparing our results with those of x‐ray photoelectron spectroscopy measurements we have concluded that on samples treated at high temperatures, three‐dimensional InAs islands are formed.  

ISSN:1071-1023    

DOI:10.1116/1.587756

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Fe‐doped InP was grown by hydride‐vapor phase epitaxy. Doping levels up to 8×1018cm−3were determined by secondary ion mass spectrometry. Additionally performed photoluminescence measurements revealed a homogeneous distribution of electrically active Fe atoms. From microstructural investigations by analytical transmission electron microscopy, spherical‐shaped precipitates were detected in plan‐view samples. These precipitates with diameters up to 13 nm are homogeneously arranged in the epilayer. For conglomerates of precipitates a distinct enrichment with Fe and P was measured by a comparative energy dispersive x‐ray analysis. The lattice plane distances of the precipitates were deduced from the electron diffraction patterns and from high‐resolution electron micrographs. A comparison with calculated values for different Fe–P alloys indicates that the precipitates consist mainly of orthorhombic FeP.

ISSN:1071-1023    

DOI:10.1116/1.587757

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We have studied the etching performance of two commercially available low pressure, high density plasma sources and their application for the etching of 0.35 μm features in polysilicon films. The two sources are a rf‐inductively coupled helicon made by Lucas Labs of Sunnyvale, CA and a multipole electron cyclotron resonance (ECR) source made by Wavemat of Plymouth, MI. The sources are mounted on a dual chamber etching platform to remove platform dependent effects. Performance metrics consist of measuring the polysilicon etching rate, etching rate uniformity, and profile control in HBr gas‐phase chemistry. The effect of applied source power, applied rf‐bias power, and reactor pressure on the etching rate and uniformity is examined using a response surface experiment. Profile control is determined by examining nested and isolated lines and trenches using oxide mask/polysilicon/oxide structures. In both sources, high uniformity and vertical profiles are obtained at low reactor pressure, high applied source power, and applied rf‐bias powers between 50 and 60 W. To decrease the lateral etching rate and increase the anisotropy of the etching process, approximately 3% of O2is added to the feed‐gas. For the helicon, the operating point for best uniformity is at 2.0 mTorr, 2500 W applied source power, and 57 W applied rf‐bias power resulting in a measured etching rate of 2340 Å/min and uniformity of ±3.3%(2σ). For the ECR, the operating point for best uniformity is at 2.8 mTorr, 1370 W applied source power, and 60 W applied rf‐bias power resulting in a measured etching rate of 2580 Å/min and uniformity of ±1.4%(2σ). Since both sources exhibit remarkably similar performance for the etching of polysilicon films, other factors such as ease of operation, plasma stability, and plasma ignition sequence become relatively more important when deciding which source to use for a particular application.  

ISSN:1071-1023    

DOI:10.1116/1.587758

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Radial profiles of electron temperature, electron density, and ion current density near the wafer surface are presented for a rf‐inductively coupled helicon and a multipole electron cyclotron resonance source as a function of applied source power, applied rf‐bias power, and reactor pressure. Both sources show similar trends with respect to changing process conditions, with electron densities in the mid 1011cm−3range and electron temperatures between 5.5 and 6.5 eV. An increase in applied source power results in an increase in both electron density and ion current density as expected. An increase in applied rf‐bias power results in a 10% change in the measured electron density and ion current density; however, the electron temperature shows a much stronger dependence, indicating that ion flux and ion energy are not completely independent. Radial uniformity is similar in both sources, with the helicon exhibiting better uniformity at the conditions explored. Neither applied source power nor rf‐bias power significantly affect radial plasma uniformity above the wafer in both sources, but higher reactor pressure does degrade uniformity in the helicon. We attribute this to the 2:1 geometric expansion between the upper antenna section and the lower plasma confinement section where the measurements are taken. The conditions resulting in optimum radial uniformity of electron temperature, electron density, and ion current density are similar to those for the optimum etching rate uniformity measured in previous studies; yet the uniformity obtained from the Langmuir probe diagnostic is not affected by changing process conditions to the degree that etching uniformity is affected. This can be a result of the difference in chemistry between the two studies since hydrogen bromide was used for etching and argon was used for Langmuir probe measurements. It may also indicate that the correlation between plasma uniformity and etching uniformity is relatively weak or second order compared to other variables affecting uniformity such as rf bias of the wafer.

ISSN:1071-1023    

DOI:10.1116/1.587759

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

As part of our research effort in evaluating the etching performance of high density plasma sources, we measured ion energy distribution functions near the wafer surface for a helicon and a multipole electron cyclotron resonance source (ECR). The following two salient results stand out: first is the remarkable similarity in behavior of the two sources which was also observed in previous studies comparing etching rates, profile control, and Langmuir probe diagnostics; and second is the surprising level of coupling between the applied rf bias and the bulk plasma. For both sources, the ion flux increases strongly with source power, decreases by 20%–40% as the reactor pressure increases from 2.0 to 5.0 mTorr, and is weakly modified by the applied rf bias. The mean ion energy is strongly influenced by the applied rf‐bias and is relatively insensitive to source power and pressure. The ion flux exhibits high uniformity for both sources, with the helicon exhibiting slightly better uniformity. However, we note that instabilities in the ECR discharge from mode jumps caused by different operating conditions and changing reactor wall conditions, such as temperature, result in poorer uniformity. The behavior of ions with respect to applied source and rf‐bias powers follows roughly the trends expected of quiescent, high density plasmas in contact with a rf‐biased electrode (i.e., independent control of ion flux and mean ion energy). However, there exist subtle effects upon the ion flux, such as bimodal energy distributions, brought about by the coupling of the rf‐bias power into the bulk plasma. This coupling may be an essential parameter in wafer platen design that must be addressed in order to obtain high etching rate uniformity.

ISSN:1071-1023    

DOI:10.1116/1.587760

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Si masked by patterned SiO2was etched using an electron cyclotron resonance hydrogen plasma. The dependence of the etch rate and the etched profile on substrate temperature and dc bias potential has been investigated, and an etch mechanism has been considered. The substrate temperature was varied between room temperature and 400 °C, and a bias potential between −100 and +100 V was applied. The etch rate of Si had the highest value at the lowest substrate temperature and decreased with increasing temperature. For the bias potential, the etch rate of Si had its peak value at 0 V. It decreased with increase of the potential which was either positive or negative. Si was also etched laterally when the substrate temperature was low. For the negative bias potential, the etched Si had a terrace on the border of a SiO2mask. It is considered that the temperature dependence of the etch rate and the etched profile is caused by the action of hydrogen atoms, and the bias potential dependence is caused by the action of hydrogen ions. Thus, we conclude that both hydrogen ions with moderate energy and hydrogen atoms play an important role in Si surface etching.

ISSN:1071-1023    

DOI:10.1116/1.587761

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The etching of semiconductor wafers is modeled for etching by radicals (isotropic etching) and etching by both radicals and vertically incident cold ions (anisotropic etching) in a glow‐discharge plasma. Explicit analytical expressions for evolving two‐dimensional etched surfaces are found by the method of characteristics. These parametric relations are expressed in terms of the position along the initial exposed wafer surface. Exact surface equations are given for the radical etching with two different ansatz for the evolution equation. The superposition of radical etching and etching due to vertically incident, bombarding ions is solved by approximate analytical expressions for the etched surface. Two‐dimensional etched surfaces are displayed graphically for various times.

ISSN:1071-1023    

DOI:10.1116/1.587762

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Ta36Si14N50amorphous layers were reactive ion etched in CF4+O2plasmas. The etch depth was determined as a function of gas composition, pressure, and cathode power. Adding small amounts of O2to CF4increased the etch rates up to approximately 15% O2concentration, with etch rates then decreasing with further addition of O2. Etch rates increased with both pressure and power. Etching proceeded only after an initial delay time which depended upon gas composition and power. The delay is probably caused by a surface native oxide which must be removed before etching can commence. The presence of a surface oxide was observed from Auger electron spectroscopy intensity depth profile measurements and is estimated to be 2 nm thick. Under optimal conditions, the etch rate of Ta36Si14N50is about seven times higher than for SiO2, thus providing a high degree of selectivity for integrated circuit processing.

ISSN:1071-1023    

DOI:10.1116/1.587763

出版商:American Vacuum Society    

年代:1994

数据来源: AIP