ECI Technology | We Keep Your Chemistry Right
Leading Provider of Chemical Management Systems for Semiconductor, PV, and PCB Industries
ECI Technology will be exhibiting at Semicon China 2020, June 27-29 in Shanghai. Come visit us at the WESI/ECI booth #E2263, where we will be happy to discuss our line of products enabling your next-generation manufacturing with world-leading chemical process control.
June 22, 2020 – June 24, 2020
CPCA – The 29th International Electronics Circuit Exhibition (Shanghai)
ECI Technology will feature its new proprietary QualiLab Elite® plating-bench chemical analyzer and ECI’s Chempack® computer software/parameters for chemical analysis. ECI experts will be on hand in WKK PCB Trading Ltd. booth to discuss advanced cleaning and etch analyzers as well as customized control solutions for new and established processes.
At WKK PCB Trading Ltd. Booth #7R46, Hall 7.1
National Exhibition and Convention Center, Shanghai, China
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Optimize Electroplating and Electroless-Plating bath solutions with the all-new QualiLab Elite system that combines Cyclic Voltammetric Stripping and the largest library of analytical recipes for metal deposition to determine additives in electroplating baths.
TOTOWA, NEW JERSEY, December 3, 2019 – ECI Technology, a leading manufacturer of chemical analytical equipment for Semiconductor and Printed Circuit Board (PCB) manufacturing and WKK PCB Trading Ltd., a leading distribution company supplying capital equipment, materials and services to the PCB industry throughout Asia, today announced that they will be showcasing the new QualiLab Elite® Benchtop Plating Bath Analyzer at this year’s International Electronics Circuit Exhibition at Shenzhen Convention & Exhibition Center, China from December 4th to December 6th.
“The new QualiLab Elite Analyzer combined with our extensive ChemPack® library of analytical metrology further demonstrates ECI Technology’s industry leadership in metal deposition, and our ongoing commitment to technology innovation through further advanced research and development,” said ECI Technology’s CEO Marianna Rabinovitch.
“We are seeing significant interest from our customers for QualiLab Elite Benchtop Plating Bath Analyzer with ChemPack analytical recipes and are pleased to be showcasing this system at HKPCA,” said Randy Lui, Director and General Manager, WKK PCB Trading Limited.
The QualiLab Elite analyzer supports multi-language operations and provides accurate analyses in an ergonomic design. Its modular design configurations range from a simplified, compact single-sample manual analyzer to a fully automated closed-cell system that can measure up to 42 samples without operator intervention. All models offer high-precision selectivity and analyses combined with easy-to-use software, advanced reporting and data handling features along with ECI Technology’s proprietary Chempacks® analytical recipes. Visit ECI Technology at WWK Booth #1Q01, Hall 1 during the exhibition for a demonstration.
July 21, 2020 – July 23, 2020
Virtual SEMICON West
ECI Technology will be exhibiting at the 50th Anniversary Semicon West. ECI Technology is supplying fully qualified chemical metrology for sub-10nm nodes to leading foundry, IDM, and equipment suppliers in the semiconductor industry. ECI will display its Process Chemical Monitoring Systems that interface with advanced cleaning and etch tools as well as customized control solutions for new and established processes.
ECI will feature its new proprietary QualiLab Elite® plating-bench chemical analyzer and ECI’s Chempack® computer software/parameters for chemical analysis.
ECI Technology Booth
Visit the show website
In the process of fabricating 3D NAND devices, the complex deposition and etch have been proven to be challenging. Two etch processes: silicon nitride sacrificial removal and W etch-back in the 3D NAND word-line formation have been identified as the two critical steps that significantly impact the 3D NAND product yields. In this paper, we present the results of an automated on-line chemical management system that were specifically developed to enable real-time monitoring and control of both the sacrificial silicon nitride removal and W etch-back processes.
Keywords—Silicon Nitride Etch, Tungsten Etch, 3D NAND, Phosphoric-Acetic-Nitric Acid, PAN
One of the key challenges of 3D NAND is scaling stack height for higher bit density. Unlike 2D planar NAND that is constrained by lithography, the bit density of 3D NAND is limited by the complex deposition and etch process steps while stacking the NAND structures in the vertical direction. The process of fabricating 3D NAND begins with multilayered silicon nitride and oxide deposition, followed by high aspect-ratio hole etch for the channel and word-line. The silicon nitride in the word-line is a sacrificial layer that is removed by immersion wet-etch, followed by dielectric (ONO) and tungsten metal gate, deposition and etch-back [1]. In this process flow, the silicon nitride sacrificial removal and W etch-back have been identified as the two critical steps that require accurate real-time metrology and process control.
A. Sacrificial Silicon Nitride Etch using Hot Phosphoric Acid
The method of using hot phosphoric (Hot Phos) acid to etch silicon nitride is well understood and has been used in semiconductor manufacturing for many years. The control of temperatures and water content in H3PO4 was found critical in controlling the nitride and oxide etch rates. It was also found that seasoning the Hot Phos etching bath with silicate can further reduce the etching rate of SiO2 and improve the etch selectivity. Theoretically, a critically high etch selectivity can be achieved by seasoning the H3PO4 with high concentration of silica. Nevertheless, maintaining a stable etch process with such a high etch selectivity over time has been proven difficult to achieve without real-time monitoring and control, due to the dynamic bath loading behavior and etch by-products. A reliable real-time monitoring and control of Si is also important to prevent process induced defects due to Si precipitation.
At ECI, we have developed a suite of methods [2,3] designed to accurately analyze the components of the Hot Phos etch bath for stable and reliable monitoring and control of the etch process. These methods not only enable a reliable and stable etch process in the life time of the etching solution, but also the feed and bleed and cost savings that extend the lifetime of the etching baths. We have demonstrated that real-time results can be obtained using the methods implemented in our automated on-line system QualiSurf QSF-500 (see figure 1). To ensure the real-time results are accurate, we measured and compared the results with off-line Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) (see Figure 2).
In the experiments of seasoning and etch, we demonstrated the capability of accurate monitoring and control of the Hot Phos silicon nitride etch process. The results are shown in Figure 2 and Figure 3.
For a well-controlled selective etch of aluminum over Si or SiO2, PAN (Phosphoric-Acetic-Nitric acid) is commonly used. PAN is also considered for the W etch-back in the 3D NAND process. Similar to Aluminum etch, W oxidizes in the nitric acid forming a by-product W(NO3)x, which dissolves in the phosphoric acid. Acting as a wetting agent, the acetic acid in PAN facilitates the etch process by removing the H2 by-product.
Over the lifetime of the PAN solution, the concentration of H3PO4 increases due to the evaporation loss of the Nitric/Acetic/H20. To maintain a stable and consistent etch rate of W, the H3PO4 concentration must be controlled. Figure 5 illustrates the consequences of inconsistent etch of W where 3D NAND devices will short when W under-etches. At ECI, we have developed an on-line automated chemical management system that accurately monitors and controls the components of PAN. In a spiking experiment, different concentrations of H3PO4 were added into the bath. The system accurately measured the H3PO4 component concentrations as shown in Figure 6.
The demand for a higher bit density in 3D NAND will continue to push the limits of the fabrication process and stack height. The monitoring and control of the process becomes critically important as the number of stacking layers increases. In this paper, we presented the results of real-time on-line automated solutions in accurately monitoring and control Si3N4 and W etch.
Nickel electroplating is widely used in semiconductor manufacturing, primarily during the packaging stage. It is not used as a final coating, but instead as a barrier layer to prevent formation of copper–tin intermetallic compounds that affect the reliability of solder joints. The nickel is deposited from baths containing nickel salt (in relatively high concentrations), boric acid, and other ions.
The quality of the deposited nickel is highly dependent on the composition of the plating bath. Metallic contaminants are acceptable when their concentrations are below approximately 30 ppm. Copper, lead, zinc, and cadmium, even in relatively small quantities (higher than 30 ppm) produce a dull, black, or skip plate condition in the low-current-density areas. These metals may be removed from the plating solution by low-current-density dummyplating, but a sensitive and accurate analytical method must be used to determine when to treat the bath. Copper is considered a main contaminant due to its higher concentrations in the bath and its most detrimental effect on the nickel deposit. To prevent plating defects, the bath contaminants must be monitored.
Nickel, electroplating, copper, contamination
Traditionally, low concentrations of metals in plating solutions can be monitored using highly sensitive polarography methods or spectral methods such as AAS or ICP [1]. These methods can detect parts per trillion of copper and other metals. However, utilization of mercury electrodes makes this method less desirable due to safety and environmental concerns. In nickel-plating solutions, concentrations of copper are high enough that it would be more appropriate to measure copper with a solid electrode. Mercury electrodes are more sensitive than solid electrodes, but in the case of nickel-plating baths, such sensitivity is not required.
Prior publications describe methods for the determination of low copper concentrations using solid electrodes [2]. These methods work well when copper is present in low (ppm) concentrations and other compounds are present in low amounts or absent.In the nickel-plating bath, the main challenge is that concentrations of nickel and other components (boric acid, chloride, or bromide ions) are very high, while the concentrations of copper are much lower [3,4]. For that reason, a new analytical method was carefully verified for possible interference with other bath components. In addition, nickel plating baths are utilized at high temperatures (40-50°C) to prevent precipitation of boric acid. This required additional precautions during analysis as boric acid can precipitate and distort the results. Results showed that if highly concentrated and hot nickel solutions are pre-treated (diluted and cooled) prior to analyses, the results of copper analysis can be accurate and reproducible.
Chemicals and Materials- Solutions were prepared with boric acid (Fisher), nickel (II) chloride hexahydrate (Sigma-Aldrich), sodium chloride (Fisher), 50% aqueous nickel (II) sulfamate (Palm), Nikal BP wetting agent (Dow), and sodium bromide (Spectrum). For dilution tests pH 4.00 reference standard buffer from Ricca was used.
Instrumentation- Analyses were performed using an ECI QualiLab QL-10 bench top plating bath analyzer. A 4 mm Platinum Rotating Disk Electrode, an Ag/AgCL electrode with 0.1 M KCL junction solution, and a stainless steel rod counter electrode comprised the three-electrode system.
Procedures- Samples were prepared by dissolving properly measured quantities in de-ionized water. The analyzer performed modified pulse voltammetric stripping analysis (MPVS) on the samples. During the electrochemical scan, the platinum electrode surface was polarized with negative voltage to accumulate copper as per equation (1) and then subsequently polarized with positive voltage to dissolve accumulated metal.
Cu2 + 2e <=> Cu0
The reaction of copper deposition and dissolution is quite reversible, allowing collection of multiple electrochemical cycles. The dissolution peak area was selected as a main analytical signal. Electrochemical parameters such as scan rate and deposition potential were tested and optimized. The ranges are 10 to 50 mV/sec and -0.25 to -0.35 V (vs. Ag/AgCl reference electrode) respectively. The rotation speed of the platinum disk electrode was also validated in the range between 100 and 6000 rpm. Data was then processed using a proprietary algorithm where Cu peak areas were determined and compared.
A. Parameter optimization
To establish a suitable electrochemical signal, initial parameter screening was performed. It was observed that the electrochemical outputs (voltammogram peaks) were sensitive to the changes in deposition voltage, scan rate, and rotation speed of the platinum disc electrode. The shape of the copper dissolution peak affects the subsequent data processing. The analysis parameters were optimized to provide the highest and most reproducible dissolution peak.
Fig. 1 shows optimization results of platinum electrode rotation rate.
As this graph shows, the most suitable peak shape is achieved at the highest possible rotation rate. This is because the copper concentration in solution is quite low and can be easily depleted in the layer near the electrode. Further increase in rotation rate was not beneficial due to high turbulence in the electrochemical cell that caused solution disturbance and splashing. 6000 rpm was found to be the optimum rotation rate and provides reproducible and suitable data for peak processing. In all subsequent electrochemical experiments, the rotation rate of the platinum electrodes was set at 6000 rpm.
The concentration of copper can potentially be as high as 30 ppm. However, as previously mentioned, the nickel plating baths contain high concentrations of boric acid and are kept hot to allow boric acid to remain in solution. When the bath is taken for analysis, the temperature can drop, causing precipitation of boric acid. This makes further analysis complicated. The solubility of boric acid at room temperature is about 47 g/l, but the presence of other ions in the solution will reduce its solubility [5]. We determined that for analytical purposes, boric acid concentration should be maintained below 30 g/l.
When rotation rate and dilution factor were optimized, copper calibration experiments were conducted (Fig. 2). These tests were performed in a copper concentration range from 0 to 10 ppm. The responses are linear through a wide range of rotation rates. However, at the highest rpm, the response is strongest, but not as linear as at lower rpm.
The increase in currents at higher rotation rates is expected due to an increase in the supply of reactants to the electrode surface. This should agree with the Levich equation (2), where mass transport limited currents are proportional to the square root of the rotation rate.
IL = (0.620)*n*F*A*D2/3*w1/2*v-1/6* C,
where ILis the Levich current (A), n is the number of moles of electrons transferred in a half reaction, F is the Faraday constant (C/mol), A is the electrode area (cm2), D is the diffusion coefficient (cm2/s), w is the angular rotation rate of the electrode (rad/s), v is the kinematic viscosity (cm2/s), and C is the concentration (mol/cm3).
Fig. 3 shows a linear relationship between the square root of the rotation rate and currents obtained during copper deposition experiments
Similar results were observed when scan rate was varied. Increased scan rate caused shorter deposition time and reduction of copper deposited on the electrode. This was undesirable as the decrease in the copper deposition reduces the sensitivity of the analysis. A linear relationship was observed for the entire range of scan rates tested.
B.Verification of method accuracy
The effects of all components in the bath were validated prior to the final testing of the analytical procedure.
The effects of all components in the bath were validated prior to the final testing of the analytical procedure.
Concentration changes in boric acid and nickel sulfamate have been shown to slightly distort the copper peak, affecting final analytical results. Table I summarizes the data collected in this study. It must be noted that pH changes could negatively affect the final result as well. This effect was observed when the plating solution was diluted by 50% with DI water. The result did not improve when higher dilutions were used.
| Solution | Signal, % |
| Target Nickel bath | 100 |
| Target Ni bath with 20% lower Boric Acid | 74 |
| Target Ni bath with 10% lower Ni Sulfamate | 84 |
This interference could not be reduced by altering electrochemical parameters. Generally, the interference significantly increased when any of the main electrochemical settings were altered.
Because the bath must be diluted to avoid crystallization of boric acid, several different diluents were tested. We observed that dilution with pH 4 buffer (close to pH of the plating bath) aids in the elimination of the possible effects of boric acid and sulfamate. Essentially, both of these materials can affect pH values and buffer use or dilution simply cancels those effects.
During our testing, pH 4 buffer was used for bath dilution. The previously noted commercial buffer solution has enough buffering capacity to maintain the pH within ±0.1 units after dilution. Changes in the concentrations of multiple components in the bath had no effect (or only a negligible effect that was within analysis accuracy) on the analytical signal. A desirable dilution of the bath was achieved and boric acid did not precipitate.
Fig. 4 shows voltammograms obtained from the same nickel target bath with boric acid concentrations that are varied by dilution with DI water and with pH 4 buffer. Dilution with pH 4 buffer shows a clear advantage. The data are shown in Table II.
| Solution | Diluent | Signal, % |
| Target Nickel bath | pH Buffer | 100 |
| Target Ni bath with 20% lower Boric Acid | pH Buffer | 99.5 |
| Target Ni bath with 10% lower Ni Sulfamate | pH Buffer | 99.8 |
| Target Ni bath with 20% lower Boric Acid | DI Water | 74 |
Scans obtained from baths with varying boric acid concentrations looked very similar and subsequently led to the same integrated peak area. When all work on interferences was completed, we validated its precision by performing multiple analyses of three solutions with different Cu concentrations and target concentrations of other components. As shown in Table III, the results were highly repeatable, producing a Relative Standard Deviation (RSD) below 2%.
Table III Reproducibility of Analysis
| Solution tested (5x each) | Relative Standard Deviation, % |
| Cu 5 ppm | 1.2 |
| Cu 10 ppm | 1.4 |
| Cu 20 ppm | 1.1 |
A newly developed electrochemical method provides reproducible results of analysis for copper in nickel plating baths. This method has advantages in comparison to polarographic methods as it does not use a mercury working electrode. During this study, it was demonstrated that the matrix effects of other bath components can be eliminated by dilution with commercial buffer solution. This new analytical method can be easily automated to provide fast online (within 10 minutes) analysis results for copper in nickel electroplating baths.
Michael Pavlov, Mitchell Coffin, Danni Lin, and Eugene Shalyt
ECI Technology
60 Gordon Drive
Totowa, NJ 07512 USA
Ph: 973-773-8686; Fax: 973-773-8797
Email: mpavlov@ecitechnology.com
