摘要:

The reactive ion etching behavior of GaAs in Cl2and SiCl4gases is investigated with regard to the suitability of this process for etching through wafer via holes using a photoresist mask. The criteria used are etch rate, profile (wall angle), selectivity, undercut, and smoothness of the etch. The experimental points were chosen using aD‐optimal statistical design. The experimental results have been evaluated by multiple stepwise regression, eliminating insignificant terms from a quadratic model of the controlled parameters (mask bake time, power, pressure, chlorine flow, and etch time). Empirical models of the dc bias and each etch criterion are obtained. The highest etch rates, at over 3 μm/min, are obtained in high chlorine concentrations at high dc bias values (high power and low pressure) for short etch times. This method yielded an optimized process for etching metallizable via holes.

ISSN:1071-1023    

DOI:10.1116/1.587539

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

GaInAs was etched in a Cl2plasma generated with an electron cyclotron resonance source. The effects of changing etch parameters on etch rate, morphology, and surface damage were analyzed. Increased microwave power, rf power, and Cl2percentage in Ar caused the etch rate to increase monotonically. The etch rate decreased with increasing distance and reached a maximum for a pressure of 1.0 mTorr. The etch conditions were chosen to maintain smooth morphology, which requires a balance between ion energy, ion flux, concentration of reactive species, and pressure. Ohmic contacts for transmission lines and Schottky contacts for diodes were deposited directly on the etched GaInAs surface for the evaluation of etch induced damage. It was found that the transmission line measurements were more sensitive to surface damage than the diode characteristics and the specific contact resistivity (ρc) was a more sensitive measure of the damage than sheet resistivity. Defects generated by dry etching typically caused a reduction in ρc. The contact resistivity decreased with increasing rf power and source distance. More damage was introduced when only rf power was applied, as indicated by the lower ρccompared to when both microwave and rf power were applied. Addition of 10% Cl2in Ar dramatically reduced the damage when compared to etching only with Ar. Increasing the pressure from 0.5 to 5.0 mTorr caused an increase in ρcbut a degradation in surface morphology. The damage depth was estimated to be ∼6 nm at 50 W rf power and increased to ∼18 nm at 200 W rf power. Minimal surface damage was obtained when low rf power was used. For a self‐induced dc bias of −68 V (25 W rf power), ρcwas 8.3×10−5Ω cm2, similar to the control sample.

ISSN:1071-1023    

DOI:10.1116/1.587540

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We report on a dry etch process for backside through‐wafer via hole fabrication in InP‐based transistors which addresses many manufacturing issues including wafer mounting schemes, degradation of the frontside ohmic metal pads, yield across two‐inch wafers, and reliability issues. Low pressure electron cyclotron resonance plasma etching using a CH4/H2/Ar/Cl2gas chemistry is investigated and compared to other InP via etching techniques. A photoresist mask was used to define 54 μm×54 μm backside vias in substrates thinned to ∼50 μm. Post‐baking the resist served both to strengthen the mask against the plasma, and to control the profile of the through‐via. The etching was performed at a temperature of 130 °C to enhance etch product volatility while allowing a reliable wax‐mounting scheme for the thinned wafers. Etch rates of ∼1 μm/min were obtained for 950 W microwave power and 250 W rf power (−260 V). After ∼95% of the etched depth was achieved, the rf bias was reduced to minimize sputtering of the frontside metal pad on which the etch terminates. After the residual resist mask was removed, the samples were metalized, de‐mounted, and tested for electrical connection, resulting in high yield via etching across the wafer.

ISSN:1071-1023    

DOI:10.1116/1.587541

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

This article describes an investigation of the etching of polysilicon in a CF4/O2plasma. The ‘‘undercut’’ observed in etch profiles is related to the surface transport of reaction precursors. The possible mechanisms for this transport include surface re‐emission and surface diffusion of the precursors. Simulations of profile evolution, conducted with both mechanisms, are compared with experimental results. The surface reemission simulations are found to predict experimental profile evolution accurately, whereas surface diffusion simulations require unphysical values for the surface diffusion length. Novel test structures have been fabricated and etched under the same conditions as used for trench etching. Surface re‐emission simulations accurately predict the etch rate deep inside the shadowed cavity of different structures. On the other hand, simulations assuming surface diffusion to be dominant do not capture even the qualitative trends in test structure etching. This is strong evidence that surface re‐emission is the dominant mechanism for transport of etch precursors in CF4/O2plasmas.

ISSN:1071-1023    

DOI:10.1116/1.587542

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Etch rate, etch rate uniformity, linewidth uniformity, and microloading in tungsten, molybdenum, and niobium plasma etching have been studied. Electrical linewidth data with typically 100–300 measured lines/wafer have been used. Relation between linewidth uniformity and etched depth uniformity (as measured by profilometer) has been explored. Effects of tungsten film deposition processes (oxygen contamination) have been studied. Tungsten etch rate maximum in SF6/O2is at 85/15 ratio for the oxygen contaminated films, but higher oxygen percentage in SF6/O2is required for maximum etch rate of pure films. Oxygen impurities in the tungsten film affect the etch rate but neither linewidth nor linewidth uniformity. In molybdenum etching in Cl2/O2plasma the etched depth uniformity gives an overly pessimistic uniformity value even though linewidth uniformity is acceptable 12% (3σ). Addition of 3%–6% of CHF3to Cl2/O2is shown to change microloading characteristics and to improve linewidth uniformity. On 100 mm wafers, 6%–12% (3σ) linewidth uniformities were obtained for the different metals. Linewidth differences between isolated and array lines were 4%–8%.

ISSN:1071-1023    

DOI:10.1116/1.587543

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Tungsten etching in pulsed plasmas has been investigated in a helicon plasma source reactor. The time dependence of the fluorine atom concentration has been measured using the time‐resolved actinometry technique and related to the etch rate. According to our observations, it appears that fluorine adsorption on the tungsten substrate surface continues in the post‐discharge period until the surface saturates. Moreover, it appears that two etching regimes exist. For short discharge off periods, the etching is limited by the fluorine adsorption ability of the surface, whereas for long periods, the etching is limited by the desorption rate of the etch products. Experiments were performed at different substrate temperatures and plasma gas pressures. An empirical model has been developed, in good agreement with the experimental data.

ISSN:1071-1023    

DOI:10.1116/1.587544

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Tungsten films were deposited by decomposing films of frozen tungsten hexafluoride (WF6) with an electron beam and then warming the substrate to remove unreacted WF6. Deposition rates increase with increasing beam intensity.

ISSN:1071-1023    

DOI:10.1116/1.587545

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

To test for re‐emission of titanium and/or tungsten during sputter deposition (PVD) of Ti and Ti–W, films were deposited on wafers with test structures which have large interior areas which are not in line of sight to the source volume. Auger electron spectroscopy (AES), scanning electron microscopy, and transmission electron microscopy results show that very little Ti is re‐emitted during Ti PVD, but a significant fraction of incoming Ti is re‐emitted during Ti–W PVD. AES spectra along the perimeter of a cross section show that Ti–W films become Ti rich in areas of the test structures without line of sight to the source volume. We also considered Ti–W deposited into trench structures. Physically based, three dimensional deposition process simulations, assuming either diffuse or specular re‐emission of Ti, qualitatively explain the experimental results for these trenches. The available information is not sufficient to decide whether the Ti sticking factor is lower on Ti–W films or if Ti is resputtered by incoming W.

ISSN:1071-1023    

DOI:10.1116/1.587546

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Reliability of Ti–Pt–Au and Ti–Mo–Au systems has been investigated for GaAs integrated circuit first‐level metallizations on semi‐insulating GaAs substrates and second‐level metallizations on interlayer SiO2films using Auger depth profile analysis, residual resistance examination and temperature storage step‐stress testing. Auger analysis and residual resistance examination showed significant reaction between first‐level Ti–Pt–Au and GaAs substrates during metallization processes, while Ti–Mo–Au system with the electron‐beam evaporated Mo film showed higher thermal stability because the Mo film acted as a good diffusion barrier between GaAs and Au. The second‐level Ti–Pt–Au on SiO2was found to be free from the reaction with GaAs substrates, and its degradation was ascribed to interdiffusion of composite metals. The resistance increase in step‐stress testing for the second Ti–Pt–Au was analyzed on the basis of a new diffusion‐controlled model, and long‐term reliability was estimated. A mean time to failure value of 3×105h at 150 °C was obtained for a failure defined as 10% increase in resistance. Much higher reliability was estimated for Ti–Mo–Au, because the resistance continued to decrease as long as 3000 h at 250 °C. The decrease in resistance clearly indicates defect annealing with reduced defect scattering in Au layers. This also shows that foreign metal diffusion into Au, acting as impurity scattering centers, is perfectly eliminated by Mo diffusion barriers.

ISSN:1071-1023    

DOI:10.1116/1.587547

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

AlSiCu/Ti(TiN)//TiN/Ti interconnect structures, which have been fabricated by depositing a Ti or TiN additional layer on the TiN/Ti barrier exposed in atmospheric ambient and then by depositing AlSiCu on the additional layer without breaking vacuum, have shown improved electromigration lifetimes. These were 1.9 and 6.5 times longer than that of the conventional AlSiCu//TiN/Ti structure, for the TiN and Ti additional layer, respectively. From an analysis of these results, it has been assumed that elongated lifetimes were caused by an enhancement of the Al(111) crystallographic orientation in the AlSiCu/TiN//TiN/Ti structure, and caused by both a reduction of the Si nodule concentration in AlSiCu due to Al–Si–Ti ternary alloy formation and Al(111) texture further enhanced by the additional Ti underlayer in the AlSiCu/Ti//TiN/Ti structure.

ISSN:1071-1023    

DOI:10.1116/1.587548

出版商:American Vacuum Society    

年代:1994

数据来源: AIP