Malvern Panalytical

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Malvern Panalytical - We're BIG on Small

The advancements in materials research and semiconductor technology have brought great changes to the way we live. They have driven developments in almost every aspect of our daily life. Growth technologies now allow the deposition of multilayered structures with individual layers exhibiting film thickness from microns down to monolayers. 

Typical materials involved in advanced thin film devices are semiconductors, metal alloys, dielectrics, oxides, and polymers. This mandates accurate monitoring and control of the device parameters using multiple investigation techniques. Equally important is the fine control over the process materials, like CMP slurry, which is an indispensable part of any thin-film device manufacturing. 

X-ray fluorescence (XRF) and X-ray diffraction (XRD)  are an integral part of any manufacturing process to monitor and control critical thin film parameters at every step.  Electronic displays employ various technologies such as liquid crystals, pigment dispersions, quantum dots, and OLEDs. In most of these, the particle size and shape play an important role and need reliable characterization.

 Press Releases

• Analysis of Giant Magneto Resistance GMR film stacks using X-ray fluorescence spectrometry (20211109)

  2830 ZT

  Introduction

  The manufacturing of devices based upon giant magneto- resistance (GMR) effect will require an unprecedented level of film thickness control. The spin valve, the most common GMR device, has seven ultra thin layers comprised of five distinct materials as depicted in Figure 1.

  Figure 1. Typical spin valve film stack

  

  The thinnest layers in a spin valve film stack are a mere 5 to 10 Å thick. Moreover, some performance characteristics of a spin valve can display a nonlinear dependence upon layer thickness over the range of a few Ångströms. These factors highlight the importance of a film thickness metrology instrument capable of measuring multilayer thicknesses in a spin valve. Wavelength dispersive X-ray fluorescence spectrometry, utilized by the 2830 ZT Wafer Analyzer, represents such a technique.

  Instrumentation

  A Malvern Panalytical 2830 ZT XRF Wafer Analyzer equipped with a fixed channel for Cu. Details of the measurement conditions are presented in Table 1.

  Table 1. Measurement conditions

  Tube	Tube setting	Channels	Measuring time	Spot size	Software package
  4 kW Rh anode, SST-mAX50	32 kV 125 mA	Fixed channels:  Cu-Kα	100s	40 mm diameter	SuperQ, FP Multi

  Measurements and results

  Sensitivity and repeatability are two critical properties of any capable measuring technique. In this section, we present data demonstrating both of these properties for the 2830 ZT Wafer Analyzer.

  All data (except where noted) were acquired upon NiMn top spin valve stacks (see Figure 1) deposited upon thermally oxidized silicon wafers. Although data were acquired for all layers of the spin valve stacks, we focus on the critical copper layer only for this application note.

  Figure 2 represents a plot of measured copper thickness versus deposition time for a copper film. Note the linearity of the plot (R squared > 0.99) over 2 orders of magnitude variation in deposition time. This is a verification of the linearity of the measurement technique and of the stability of the deposition system. This means that calibration standards, thick enough to be measured by other techniques, such as profilometry and AFM, may be produced. The 2830 ZT Wafer Analyzer may be calibrated utilizing the thicker standards and a zero point (blank wafer). This calibration is valid for films too thin to measure accurately by traditional methods.

  Figure 3 shows a plot of measured copper thickness versus the deposition time for the copper layer in the center of a spin valve stack. This plot demonstrates that the 2830 ZT Wafer Analyzer very easily can resolve sub-Ångström variations in the copper thickness. Once again note the linearity of the plot except for the flat spot around 20  seconds of deposition time. The flat spot indicates either a loss of stability in the deposition system or an error in programming the deposition system.

  Figure 4 is a plot of measured copper thickness in the same spin valve stack taken at intervals over a two-week period. The standard deviation of the measured thickness was 0.04 angstrom, or less than 0.2% relative. The plots at the right demonstrate that X-ray fluorescence spectrometry is a powerful technique for monitoring the deposition of metal films in GMR fabrication process.

  Figure 2. Thickness versus deposition time for a copper film 

  

  Figure 3. Measured thickness versus deposition time for the copper layer in the center of a spin valve stack 

  

  Figure 4. Copper thickness versus deposition time in the the same spin valve stack measured at intervals of a two-week period 

  

  Conclusion

  It has been demonstrated that the X-ray fluorescence technique used by the 2830 ZT Wafer Analyzer has excellent sensitivity and repeatability for use as a GMR thickness metrology technique. The method is non-destructive and results are operator-independent.

  Acknowledgement

  We thank for their collaboration:
  • John W. Dykes, Physics and Materials Consultant, Bloomington, MN, USA
  • Leroy Longworth, Semiconductor Engineering Consultant, Louisville, CO, USA

• Analysis of BPSG films (20211109)

  2830 ZT

  Introduction

  In the semiconductor industry the monitoring of the deposition process of dielectrics such as BPSG is a demanding analytical application, requiring both high measurement accuracy and excellent precision. Wavelength dispersive X-ray fluorescence (WDXRF) has long been proven to meet these criteria. Films between 100 and 1250 nm are routinely analyzed for boron and phosphorus concentration. In addition to measuring these dopant concentrations, XRF allows simultaneous determination of the BPSG film thickness.

  In this report, the reproducibility and long-term stability is shown of the Malvern Panalytical 2830 ZT Wafer Analyzer in determining the boron and phosphorus concentration and film thickness of BPSG films. For the determination of the boron concentration, the gauge capability will be shown as a function of process tolerance.

  Instrumentation

  A Malvern Panalytical 2830 ZT equipped with fixed Si Kα and P Kα channels is used. In addition, a new generation extreme high performance B Kα channel is used to obtain the ultimate sensitivity for boron. Details of the measurement conditions are presented in Table 1. 

  Table 1. Measurement conditions

  Tube	Tube setting	Channels	Measurement time	Spot size	Software package
  4 kW Rh anode,  SST-mAX50	32 kV 125 mA	Fixed channels: Si Kα, P Kα, Fixed extreme high performance channel: B Kα	30s, 60s, 100s

  Procedure

  The Si Kα signal from the wafer is partially absorbed by the BPSG film, which results in reduction of the signal strength with increasing film thickness. The inverse relationship between thickness and intensity forms the basis for thickness measurement.

  The information depth of the P Kα radiation is larger than the typical BPSG film thickness. Therefore, the intensity of the P Kα depends both on concentration and thickness. By taking the product of thickness and concentration as calibration unit these two effects can be combined. The resulting unit mu% (μm × wt%) therefore includes both parameters. In the actual analysis, the phosphorus weight concentration can be determined by dividing the obtained P (mu%) value with the thickness obtained via the Si Kα calibration.

  The information depth of B Kα in BPSG is around 250 nm. For thinner films, the same calibration procedure must be applied as the one described for P Kα. For thicker films, the B Kα intensity is independent of film thickness and can be related directly to the boron concentration.

  In the Figures 1, 2 and 3 the thickness, P(mu%) and B(wt%) calibrations are shown, respectively.

  

  Results

  Short-term reproducibility

  The short-term reproducibility is determined by measuring a BPSG film 20 times at the center spot, while unloading the wafer after each measurement. Three counting times were used: 30, 60 and 100 seconds. The results obtained for 100 s are shown are shown in Table 2 and the Figures 4 and 5. 

  Figure 6 shows the influence of the counting time on the relative root mean square (RMS rel.) of the boron analysis.

  Table 2: Short-term reproducibility

  Cycle	B (wt%)	P (wt%)	Thickness (nm)
  1	3.971	3.776	482.15
  2	3.973	3.770	482.52
  3	3.968	3.780	481.56
  4	3.977	3.777	481.50
  5	3.967	3.774	482.67
  6	3.969	3.773	482.51
  7	3.965	3.773	482.55
  8	3.955	3.772	482.47
  9	3.975	3.775	481.55
  10	3.969	3.774	481.82
  11	3.972	3.780	481.24
  12	3.965	3.760	483.44
  13	3.965	3.773	481.80
  14	3.976	3.766	483.34
  15	3.961	3.775	481.61
  16	3.970	3.970	483.37
  17	3.971	3.774	482.54
  18	3.973	3.774	482.23
  19	3.962	3.770	3.770
  20	3.975	3.772	483.39
  Average	3.969	3.773	482.34
  Minimum	3.955	3.760	481.24
  Maximum	3.977	3.780	483.44
  RMS	0.006	0.005	0.69
  RMS rel. (%)	0.14	0.12	0.14

  

  Gauge capability for boron

  As the determination of the boron concentration is the most demanding step in the XRF analysis of BPSG films, the gauge repeatability and reproducibility (Gauge R&R) is determined for the boron analysis.

  Data was acquired by measuring a  BPSG film with 3.7 wt% boron, 3.3 wt% phosphorus and a thickness of 250 nm. The wafer was measured using a five- spot pattern according to Figure 7. The

  five–spot measurement was repeated 10 times, with the wafer being unloaded after each measurement.

  Two counting times were used in this gauge study: 60 s and 100 s per spot. For each measurement spot the standard deviation was calculated. These standard deviations were averaged over all spots. From this average standard deviation S , the measurement variation σm was calculated according to:

            S
  σm = ___ 

           C4

  in which c4 is a statistical unbiasing constant that equals 0.973 for the number of degrees of freedom used in this gauge study. 

  Consequently, the Gauge R&R is calculated according to: 

  Gauge R & R =5.15 σm   x 100%

                        Tolerance 

  The tolerance is defined as the difference between the upper specification level (USL) and lower specification level (LSL). In Figure 7, the gauge capability of the 2830 ZT is plotted as a function of process limits for boron concentration in wt%. Generally the gauge is accepted for Gauge R&R values smaller than 10%.

  

  Long-term reproducibility

  The long-term stability of the determination of the boron phosphorus concentration and film thickness was determined by measuring the center spot of a BPSG film with 3.3 wt% boron, 3.6 wt% phosphorus two times per day for five days. The results are shown in Table 3.

  Table 3: Long-term reproducibility

  Day/cycle	B (wt%)	P (wt %)	Thickness (nm)
  1/1	3.281	3.596	225.03
  1/2	3.275	3.598	224.71
  2/1	3.284	3.596	224.83
  2/2	3.265	3.601	224.55
  3/1	3.27	3.615	223.60
  3/2	3.266	3.605	224.13
  4/1	3.259	3.603	224.14
  4/2	3.271	3.599	224.73
  5/1	3.272	3.596	224.60
  5/2	3.281	3.598	224.50
  MEAN	3.2	3.601	224.48
  RMS	0.008	0.006	0.42
  RMS rel. (%)	0.231	0.164	0.19

  Conclusion

  The Malvern Panalytical 2830 ZT XRF Wafer Analyzer can analyze BPSG films with excellent precision.
  The high sensitivity and system stability allows the 2830 ZT to easily meet gauge capability requirements for measurement times well below 100 s.

• FP Multi analysis of TiNx thin films on Si substrates (20211109)

  2830 ZT

  Introduction

  Titanium nitride (TiNx) layers have been found very useful in the manufacture of integrated circuits. TiNx acts as an excellent barrier material against dopant diffusion between semiconductor layers and also been forms a good ohmic contact with other conductive layers. Determination of thickness and stoichiometric ratio (x) of TiNx layers is important because these parameters determine the electrical and microstructural properties of the layer. The typical thickness of TiNx layers used in semiconductor manufacturing is roughly 50 to 1000 Å with the stoichiometric value x varying from 1.0-1.2.

  X-ray fluorescence spectrometry provides a non-destructive, highly reproducible and robust method of analyzing thin films on wafers. These attributes make XRF analysis a highly cost-effective method for the analysis of a large variety of films used in the semiconductor manufacturing process.

  The 2830 ZT XRF Wafer Analyzer combined with FP Multi offers an excellent solution for simultaneous analysis of thickness and composition of single layers and stacks. FP Multi uses Fundamental Parameter analysis of thin films and stacks which minimizes the required amount of calibration samples and offers flexibility in selecting calibration materials. This constitutes a great advantage for thin film analysis as in-type calibration standards are often not readily available.

  In this report X-ray fluorescence and FP Multi are used to determine thickness and stoichiometry of TiNx thin films.

  Instrumentation

  The Malvern Panalytical 2830 ZT Wafer Analyzer used in the analysis of the TiNx samples was equipped with a 4 kW SST-maX50 X-ray tube and fixed channels for titanium and nitrogen.

  Details of the measurement conditions are presented in Table 1.

  Table 1. Measurement conditions 

  

  Methodology

  Calibration and analysis

  FP Multi was used for calibration and analysis of the TiNx thin film samples. In the calibration process, FP Multi models the X-ray generation process, taking into account the layer sequence, density, thickness, and composition of the calibration standards. In this way theoretical intensities are derived from the stack description of the sample for the characteristic X-ray lines of interest. The theoretical intensities obtained from the X ray characteristic lines are then related to the actual measured intensities, yielding the instrument factor, which is defined by the slope and intercept of the calibration line.

  For the analysis of unknown samples the calculated intensities are matched to the measured intensity through an iterative process in which the thickness and composition of the film is varied, and the instrument factor is taken into account. Twelve calibration samples were used with thickness ranging from 0 to 200 Å and stoichimetry values between 0 and 1. The calibration samples were referenced using X-ray reflectometry. Using the reference values acquired by XRR, linearly correlated calibration lines were obtained, shown in Figures 1 and 2.

  Measurement protocol

  A dynamic reproducibility test was performed by consequently measuring the center spot of a wafer with a TiNx film, incorporating unload and reload after each measurement. Thirty measurement cycles were performed and a measurement time of 100 s was used. In addition, a 41-spot wafer pattern analysis was performed to verify the homogeneity of thickness and composition throughout the whole wafer.

  Figure 1. Calibration line for N Kα

  

  Figure 2. Calibration line for Ti Kα

  

  Results

  Results of the repeated measurements are shown in Figures 3 and 4. Reproducibility results show excellent sensitivity and reproducibility as exhibited by the RMS values of stoichiometry and thickness.

  Figures 5 and 6 show the results of the 41-spot wafer mapping analyses. Wafer mapping results indicate a 0.623 Å thickness deviation and a 0.031 deviation in stoichiometry throughout the whole wafer. Results show the thickness and composition profiles throughout the whole wafer that resulted from the sample deposition process.

  Figure 3. Reproducibility obtained for thickness measurements

  

  Figure 4. Reproducibility obtained for stoichiometry measurements

  

  Figure 5. Thickness mapping of the wafer

  

  Figure 6. Stoichiometry mapping of the wafer

  

  Summary and conclusion

  The PANalytical 2830 ZT XRF Wafer Analyzer, together with the fundamental parameter software package FP Multi, was used to analyze thickness and stoichiometry of TiNx layers. Results showed excellent reproducibility and sensitivity, indicating that 2830 ZT is well capable of measuring the thickness and composition of TiNx films. The typical thickness reproducibility is well below 0.2% relative RMS at 100 seconds measurement time.

  The flexibility and reproducibility of 2830 ZT combined with FP Multi prove that this combination is an excellent metrology solution for monitoring the TiNx film deposition process.

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