摘要:

The discharge downstream from a 9 cm i.d. multipolar electron cyclotron resonant (ECR) plasma was characterized in terms of positive ion density, electron energy distribution functions (EEDFs), ion energies incident on a biased conducting substrate, and silicon etching performance. Ion density in the process chamber was found to decrease exponentially away from the plasma source with a peak density of 6×1011cm−3in 1 mTorr argon with 250 W of microwave power. While EEDFs are non‐Maxwellian, no evidence of high‐energy ECR electrons was observed in the process chamber. The ion flux to a conducting substrate diverges by approximately 15° from normal but the ion incidence energy is easily controllable with a dc bias to the substrate. Despite the divergent ion flux from the ECR source, anisotropic etching of silicon was possible with etch rates of 300 nm/min. Uniform etching of silicon over 7.6 cm (3 in.) diam wafers was attained 8 cm below the plasma source.

ISSN:0734-2101    

DOI:10.1116/1.576592

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Neutral gas density has been measured in both the source and sample regions of an axial electron cyclotron resonance (ECR) plasma device. The measurements involved sampling with a small tube to an external capacitance manometer. The gas density in the central ECR region was found to be strongly dependent on the applied power and to decrease approximately linearly with discharge power. At the maximum applied power of 1250 W, and at an Ar pressure of 0.7 mTorr, the gas density was reduced to 14% of its preplasma value, indicative of significant gas heating and rarefaction. This is equivalent to a gas temperature of 2500 K (0.2 eV), which is consistent with reported Doppler broadening optical emission measurements. At the sample region, approximately 35 cm from the ECR region, the gas density was reduced by gas heating to only 85% of its preplasma value. The electron density was measured in the ECR region by means of a commercial microwave interferometer device. Electron densities, integrated across the width of the chamber, reached ≂2×1012cm−3at 1250 W and 0.7 mTorr Ar. The ionization fraction at 0.7 mTorr and 1250 W of applied power was 0.31, assuming an average electron density across the chamber. Indications point towards a localization of the plasma in the center of the chamber, which would indicate an ionization fraction of more than 0.50. These results suggest a significant influence of gas temperature and rarefaction on the dynamics of plasma formation and ionization efficiency. In addition, an isotropic, chemical component to many reactive etching systems must be anticipated due to the potentially high gas temperatures in and near the ECR region.

ISSN:0734-2101    

DOI:10.1116/1.576593

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Using laser vaporization of cryogenic films of XeF2, a beam of F atoms is produced with most probable kinetic energy variable from 0.3 to 1.1 eV. Fluorine atoms are observed with energies up to 4.3 eV. Also present in the beam are F2, Xe, XeF, XeF2, and impurity H and HF. The beams are produced by vaporizing thin films of XeF2with 266 nm photons of a quadrupled Nd:YAG laser (∼0.5 J cm−2, 5 ns). The kinetic energy of the F atoms can be increased monotonically by decreasing the repetition rate of the vaporization laser from 1 to 0.1 Hz while the deposition rate of XeF2is constant. The relative velocities of the heavier species are always less than that of the F atoms, but their most probable energies are greater than the energy of the F beam. This result suggests that a hydrodynamic flow of the lighter species propels the heavier F2, Xe, XeF, and XeF2particles to higher velocities. Evidence is presented that complete desorption of the XeF2film occurs within the vaporization area during each laser pulse, from which a desorption yield can be estimated. Such a source may be suitable for novel studies of anisotropic etching of semiconductor substrates with energetic reactive species.

ISSN:0734-2101    

DOI:10.1116/1.576594

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Measurements of ion flux and energy at a radio frequency (rf) target are given here for Ar sputtering discharges at 7 and 27 MHz, and at pressures between 1–20 Pa. These measurements allow comparison with models of the rf discharge sheath. In turn, these models can be used to correlate external observables, such as sheath voltage and height, with microscopic quantities such as sputtering rate. A numerical model of the rf sheath based upon experimentally determined glow voltage waveforms is used to calculate sheath heights, which are compared with experimental measurements. The rf sheath is modeled as a monotonic structure, permitting a simple description of ion flow in the sheath. This is an approximation because the target ion energy distribution contains a series of discrete energy peaks, superimposed upon a background caused by ion‐neutral collisions. However, at high frequencies or at high pressures these peaks decrease in size relative to the background. The method used here accounts accurately for ion collision behavior in the normal sputtering regime, in between the ‘‘free‐space’’ and the ‘‘collisional’’ pressure extremes. Sheath voltage waveforms are determined from the observed discharge glow voltage, and yield close agreement between theoretical and experimental sheath heights. In addition, sheath voltages are close to being self‐consistent. Sine‐derived waveforms are shown to yield similar self‐consistency, and are appropriate at high‐target voltages. The rf sheath heights at low pressure are about 1.2 times larger than would be predicted from the free‐space dc sheath model, for a given ion current density and average sheath voltage. In summary, this paper shows that: (i) rf sheath voltage waveforms are distinctly nonsinusoidal, especially at low voltages; and (ii) the major features of the target ion flux can be deduced from knowledge of the discharge pressure, voltage, and sheath height.

ISSN:0734-2101    

DOI:10.1116/1.576595

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

An approximate analytic description of radio frequency (rf) discharge sheaths is given here. This description employs simple power‐law equations, obtaining results for a family of sheath voltage waveforms. Both low‐pressure (‘‘free space’’) and high‐pressure (‘‘collisional’’) regimes are analyzed, yielding power‐law dependences of voltages, fields, and charges on distance into the sheath. The resulting sheath model yields asymmetric discharge sheath heights 1.1–1.3 times the corresponding dc sheath model. This family of sheath voltage waveforms is shown to be consistent with experimental sheath voltage waveforms, through experimental measurements of particle arrival times at rf sputtering targets with various electrode area ratios and chamber pressures. The imposition of a nonsinusoidal waveform on the sheath has interesting implications for voltages and ion flows in the remaining regions of the discharge. Ions may be accelerated from the ‘‘presheath’’ region both toward and away from the sheath around a negatively biased target. This is in contrast with dc sheaths, where ions are accelerated only toward the more negative electrode. Thus, ion bombardment of both the target and the counterelectrode is indicated by this model of asymmetric rf discharges. Final sections of this paper consider the velocity of the glow electron wavefront in the sheath, and the close correspondence between these power‐law solutions and sine waveforms.

ISSN:0734-2101    

DOI:10.1116/1.576596

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A simplified method of data analysis for time of flight measurements of the velocity of molecular beams sources is described. This method does not require the complex data fitting previously used in such studies. The method is applied to the study of Pb molecular beams from a true Knudsen source and has been used to show that a VG Quadrupoles SXP300H mass spectrometer, when fitted with an open cross‐beam ionizer, acts as an ideal density detector over a wide range of operating conditions.

ISSN:0734-2101    

DOI:10.1116/1.576597

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Plasma source ion implantation (PSII) is a non‐line‐of‐sight technique which is being developed as an alternative to beamline accelerator technology for ion implantation. The initial development phase of PSII concentrated on implantation of ion species which are gaseous at room temperature (primarily nitrogen ions) and employed a cylindrical vacuum chamber 16 in. high and 14 in. in diameter. A second generation PSII system is being constructed to extend the PSII process to ion beam mixing and ion beam assisted coating modes of operation. The new, larger system (with dimensions 36×36×36 in.) will feature multiple‐array sources for sputter deposition concurrent with ion bombardment.

ISSN:0734-2101    

DOI:10.1116/1.576598

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Sputtering of excited‐state potassium atoms from electron‐bombarded KBr crystals has been investigated at 300 and 443 K by measuring simultaneously the optical emission, Auger, and mass spectra. The beam current dependences of the intensities of the ground‐state and excited‐state potassium atoms at 443 K are nearly linear and quadratic, respectively, indicating that excited‐state potassium atoms are produced by gas‐phase collisions of potassium atoms desorbed from the surface. On the other hand, the room‐temperature data show complicated dependences, which can be divided into three current regions. In the low‐current region (25 μA), effects due to sample decomposition, nonstoichiometry, and gas‐phase collisions play important roles in the production of excited‐state potassium atoms. The nonlinear sputtering yield of excited‐state potassium atoms in the intermediate‐current region may be due to secondary effects including the formation of defects and cluster ions.

ISSN:0734-2101    

DOI:10.1116/1.576599

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Magnetron sputtering of graphite targets is frequently marred by the formation of topographic defects. The defects are either soft with a furry appearance or hard with a stalagmite appearance. The soft defects are often found on top of the hard ones, implying a close connection in formation sequence between the two types of defects. The formation mechanism of the hard defects is related to the presence on the surface of low sputtering‐yield impurities or other types of lattice imperfections, which suppress the erosion induced locally by sputtering, and to porosity‐induced asperities. The emergence of the soft defects is ascribed to a growth phenomenon involving redeposition of carbon from debris and possibly generated in a chemical vapor deposition (CVD) process. The gradual coverage of the target surface by defects causes a steady decrease of the sputtering rate of carbon. Also, the breakup of the soft defects promotes nodular defects in the subsequent growth of the carbon film, thus severely degrading the film quality. Remedial measures are devised for limiting the onset of defect formation.

ISSN:0734-2101    

DOI:10.1116/1.576600

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Chromium thin films were deposited by ion plating. The influence of argon gas pressure and substrate bias voltage on the morphology and crystal orientation of the films was investigated by using scanning electron micrography (SEM) and x‐ray diffraction. The preferred orientation of the films changed from (110) to (200) with the increase of argon gas pressure. Most of chromium films exhibited columnar structure and the width of the column became smaller at higher argon gas pressure. The chromium film which was deposited at higher argon pressure exhibited a finer granular structure. The microhardness of the films increased with the increase of bias voltage and argon gas pressure.

ISSN:0734-2101    

DOI:10.1116/1.576601

出版商:American Vacuum Society    

年代:1990

数据来源: AIP