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GC–ICP–MS ANALYSIS OF IMPURITIES IN CONSCI GERMANE Consolidated Sciences 1416 E Southmore Ave William M. Geiger Pasadena, TX 77502 www.consci.com CONSCI LTD. 800-240-3693

Introduction 20 TIC: 13528.D 18 16 ) (Ge) is an important element in the produc- 5 14 tion devices. Germane (GeH4), the 12 of germanium, is used via metal organic vapor phase 10 8 (MOVPE) to produce single or polycrystalline thin  lms. Ef- 6 Abundance (x 10  ciencies of amorphous silicon (a-Si) photovoltaic cells can 4 be improved by producing multi-junction cells using amor- 2

phous silicon and germanium (a-Si, a-Ge) alloys. Feedstock 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 gases for this process include germane and germanium tetra- Time (min) Scan 447 (5.859 min): 13528.D (-457)(-)  uoride (GeF4). Atmospheric contaminants such as oxygen, 28 148 nitrogen, carbon dioxide, and water are contaminants that 24

can have extremely deleterious e ects on the deposited layer. ) 3 Technologies for measurement of these contaminants are well 20 established. In addition to atmospheric contaminants, other 16 such as phosphine and arsine, chlorogermanes, and 12

Abundance (x 10 8 germane homologs can have an extremely negative e ect on 142 75 154 the performance of a semiconductor device. 4 0 50 60 70 80 90 100 110 120 130 140 150 160 170 Mass to Charge Ratio (m/z) Analytical Strategy Figure 1b. GC/MS screen of a highly contaminated germane sample. Bulk germane product is usually screened using convention- al GC/MS to identify those impurities existing in substantial (ppm) amounts. Conditions for this screening are listed below: 20 TIC: 13528.D Column: 60 m x 0.32 mm x 5.0 µm DB–1 (J&W) 18 16

Carrier: Helium @ 22 psig ) 5 Initial temperature: 45°C 14 12 Initial time: 5 min 10 Ramp: 15°C/min 8 Perdeuterated germane ° 6 Final temperature: 230 C Abundance (x 10 Mass Range: 39–300 amu 4 2

3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 Time (min) Scan 610 (7.968 min): 13528.D (-621)(-) Example 1 156 30 77 25 )

An example of this screening on a highly contaminated ger- 3 mane sample is illustrated by Figures 1a, 1b, and 1c. 20

15

10 20 TIC: 13528.D Abundance (x 10 18 5 70 16 Chlorogermane 150 ) 5 14 0 12 60 70 80 90 100 110 120 130 140 150 160 170 Mass to Charge Ratio (m/z) 10 8 6 Abundance (x 10 Figure 1c. GC/MS screen of a highly contaminated germane sample. 4 2 Once the qualitative analysis is performed the quantitation is 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 Time (min) performed using similar conditions with ICP–MS detection Scan 430 (5.639 min): 13528.D (-408)(-) tabulated below: 76 14 Column: 100 m x 0.53 mm x 5.0 µm RTX–1 (Restek)

12 Carrier: Argon @ 20 psig ) 4 ° 10 72 Initial temperature: 35 C Initial time: 4 min 8 ° 109 Ramp: 15 C/min 6 Final temperature: 200°C Abundance (x 10 4 Masses used: 35, 70, 72, 73, 74, 76 2 105 113 Since the ICP has compound independent calibration (CIC) 0 capability the concentrations can be performed using a low 50 60 70 80 90 100 110 120 Mass to Charge Ratio (m/z) concentration standard of germane or surrogate cross calibra- tion.1 Figure 1a. GC/MS screen of a highly contaminated germane sample. 1 Geiger, W., Raynor, M. (Eds.). (2013). Trace Analysis of Specialty and Electronic Gases. Hoboken, New Jersey: John Wiley & Sons.  e interface of the GC to the ICP torch is illustrated by Fig- ure 2.  e torch has an extra leg so that GC column e uent Example 2 can be connected while simultaneously aspirating an through the nebulizer and spray chamber.  e make- A more typical distribution of germane impurities is described up gas at the tee has a  ow of approximately 120 mls/min. In by Figure 6 containing digermane, trigermane, and tetrager- order to avoid major contamination of the torch during the manes. Due to the relatively high concentrations, a 50 µl sam- elution of the bulk germane, a valve is automatically opened to ple was su cient. a vacuum pump diverting most of the germane away from the 2 torch. 16 1 2

14 Compound Concentration 1 Digermane 180 ppm )

Argon Makeup 6 12 2 Trigermane 13 ppm To Vacuum 3 iso-tetragermane 140 ppb Water In Argon 10 4 n-tetragermane 130 ppb Argon Makeup Preheater Argon 8 6

Intensity (cps x 10 4 Drain GSV 4 2 3

Torch 0 0 1 2 3 4 5 6 7 8 9 Transfer Line Time (ms x 105)

Figure 6. Chromatogram at m/z 72 (72Ge). GC Oven

Figure 2. GC–ICP torch interface. Arsine content was also measured on this sample. Generally a 200–300 m column is used to e ect a good separation since Figures 3-5 describe ion chromatograms and concentrations there is only modest separation and quite a bit of mass ‘splash of the impurities found in this product. Note that the GC– over.’ Figure 7 illustrates this analysis.  e arsine content was ICP–MS found an additional germanium component not de- 1.4 ppb with a detection limit of approximately 60 ppt. A larger tected by GC/MS. Since these concentrations were fairly high sample of 300 µl was required to achieve this detection limit. the sample size was limited to 50 µl.

5 Chlorogermane 4 ) 4 4 Arsine ) 6 3 3

2 2 Intensity (cps x 10 1 Intensity (cps x 10 1 0 3 4 5 6 7 8 9 10 11 Time (ms x 105) 0 1 2 3 4 5 Time (ms x 105) Figure 7. Chromatogram at m/z 75 (75As) of 1.4 ppb arsine on ‘tail’ of germane. Figure 3. Chromatogram at m/z 35 (35Cl) of 86 ppm chlorogermane.

Conclusion 8 1 Compound Concentration

) Gas chromatography coupled with ICP–MS detection is an

8 1 Chlorogermane 86 ppm 6 2 Digermane 5.5 ppm extremely e ective tool in determining metallic hydride con-

4 taminants in semiconductor grade germane. Detection limits of parts per trillion for these contaminants can be achieved,

Intensity (cps x 10 2 levels that in the near future may be required to achieve the fu- 2 ture quality of semi-conductor devices. Although chromatog- raphy does the ‘heavy li ing’ and the ICP–MS /torch is 0 1 2 3 4 5 Time (ms x 105) reasonably robust, it is still vital that a strategy be used to min- imize the bulk of the matrix from contaminating the torch. 76 Figure 4. Chromatogram at m/z 76 ( Ge). Since most germane contaminants elute a er the germane ma- trix, the vacuum diversion strategy employed here is key to a successful analysis.

William M. Geiger is a Senior Partner at CONSCI. 1 [email protected] 5 Compound Concentration ) 6 4 1 Deuterated digermane 180 ppb 2 Unknown germane compound 3 ppb

3

2 Intensity (cps x 10

1 2

4 5 6 7 8 9 10 Time (ms x 105)

Figure 5. Chromatogram at m/z 74 (74Ge).

2 Glindemann, D., Ilgen, G., Herrmann, R., & Gollan, T. (2002). Advanced GC/ICP-MS design for high-boiling analyte speciation and large volume injection. Journal of Analytical Atomic Spectrometry, 17 (10), 1386–1389.