GC–ICP–MS ANALYSIS OF IMPURITIES IN GERMANE

GC–ICP–MS ANALYSIS OF IMPURITIES IN
GERMANE
CONSCI
Consolidated Sciences
1416 E Southmore Ave
Pasadena, TX 77502
www.consci.com
800-240-3693
William M. Geiger
CONSCI LTD.
Introduction
20
TIC: 13528.D
18
Abundance (x 105)
14
12
10
8
6
Digermane
4
2
3.00
3.50
4.00
4.50
5.00
5.50 6.00 6.50 7.00
Time (min)
7.50
8.00
8.50 9.00
9.50
Scan 447 (5.859 min): 13528.D (-457)(-)
148
28
24
Abundance (x 103)
Germanium (Ge) is an important element in the production semiconductor devices. Germane (GeH4), the hydride
of germanium, is used via metal organic vapor phase epitaxy
(MOVPE) to produce single or polycrystalline thin films. Efficiencies of amorphous silicon (a-Si) photovoltaic cells can
be improved by producing multi-junction cells using amorphous silicon and germanium (a-Si, a-Ge) alloys. Feedstock
gases for this process include germane and germanium tetrafluoride (GeF4). Atmospheric contaminants such as oxygen,
nitrogen, carbon dioxide, and water are contaminants that
can have extremely deleterious effects on the deposited layer.
Technologies for measurement of these contaminants are well
established. In addition to atmospheric contaminants, other
hydrides such as phosphine and arsine, chlorogermanes, and
germane homologs can have an extremely negative effect on
the performance of a semiconductor device.
16
20
16
12
8
142
75
4
154
0
50
60
70
80
90
Analytical Strategy
100 110
130
120
Mass to Charge Ratio (m/z)
150
140
160
170
Figure 1b. GC/MS screen of a highly contaminated germane sample.
Bulk germane product is usually screened using conventional GC/MS to identify those impurities existing in substantial
(ppm) amounts. Conditions for this screening are listed below:
Column: 60 m x 0.32 mm x 5.0 µm DB–1 (J&W)
Carrier: Helium @ 22 psig
Initial temperature: 45°C
Initial time: 5 min
Ramp: 15°C/min
Final temperature: 230°C
Mass Range: 39–300 amu
20
TIC: 13528.D
18
Abundance (x 105)
16
14
12
10
8
Perdeuterated germane
6
4
2
3.00
3.50
4.00
4.50
Example 1
5.00
5.50 6.00 6.50 7.00
Time (min)
7.50
8.00
8.50 9.00
Scan 610 (7.968 min): 13528.D (-621)(-)
156
30
TIC: 13528.D
18
Abundance (x 105)
15
10
70
150
0
14
60
12
10
70
80
90
100
110
120
130
Mass to Charge Ratio (m/z)
140
150
160
170
8
6
Figure 1c. GC/MS screen of a highly contaminated germane sample.
4
2
3.00
3.50
4.00
4.50
5.00
5.50 6.00 6.50 7.00
Time (min)
7.50
8.00
8.50 9.00
Scan 430 (5.639 min): 13528.D (-408)(-)
76
12
72
10
8
109
6
4
2
105
113
0
50
60
70
80
90
100
Mass to Charge Ratio (m/z)
Figure 1a. GC/MS screen of a highly contaminated germane sample.
110
9.50
Once the qualitative analysis is performed the quantitation is
performed using similar conditions with ICP–MS detection
tabulated below:
Column: 100 m x 0.53 mm x 5.0 µm RTX–1 (Restek)
Carrier: Argon @ 20 psig
Initial temperature: 35°C
Initial time: 4 min
Ramp: 15°C/min
Final temperature: 200°C
Masses used: 35, 70, 72, 73, 74, 76
14
Abundance (x 104)
20
5
Chlorogermane
16
77
25
Abundance (x 103)
An example of this screening on a highly contaminated germane sample is illustrated by Figures 1a, 1b, and 1c.
20
9.50
120
Since the ICP has compound independent calibration (CIC)
capability the concentrations can be performed using a low
concentration standard of germane or surrogate cross calibration.1
1
Geiger, W., Raynor, M. (Eds.). (2013). Trace Analysis of Specialty and Electronic Gases. Hoboken, New Jersey: John
Wiley & Sons.
The interface of the GC to the ICP torch is illustrated by Figure 2. The torch has an extra leg so that GC column effluent
can be connected while simultaneously aspirating an aqueous
solution through the nebulizer and spray chamber. The makeup gas at the tee has a flow of approximately 120 mls/min. In
order to avoid major contamination of the torch during the
elution of the bulk germane, a valve is automatically opened to
a vacuum pump diverting most of the germane away from the
torch.2
Example 2
A more typical distribution of germane impurities is described
by Figure 6 containing digermane, trigermane, and tetragermanes. Due to the relatively high concentrations, a 50 µl sample was sufficient.
2
1
16
Compound
Concentration
1 Digermane
180 ppm
2 Trigermane
13 ppm
3 iso-tetragermane
140 ppb
4 n-tetragermane
130 ppb
14
Argon
To Vacuum
Intensity (cps x 106)
Water In
Argon
Argon Makeup
Makeup Preheater
Argon
GSV
Drain
12
10
8
6
4
4
3
2
0
Torch
0
Transfer Line
1
2
3
4
5
Time (ms x 105)
7
6
8
9
Figure 6. Chromatogram at m/z 72 (72Ge).
GC Oven
Figure 2. GC–ICP torch interface.
Figures 3-5 describe ion chromatograms and concentrations
of the impurities found in this product. Note that the GC–
ICP–MS found an additional germanium component not detected by GC/MS. Since these concentrations were fairly high
the sample size was limited to 50 µl.
Arsine content was also measured on this sample. Generally
a 200–300 m column is used to effect a good separation since
there is only modest separation and quite a bit of mass ‘splash
over.’ Figure 7 illustrates this analysis. The arsine content was
1.4 ppb with a detection limit of approximately 60 ppt. A larger
sample of 300 µl was required to achieve this detection limit.
5
Chlorogermane
Intensity (cps x 104)
Intensity (cps x 106)
4
3
2
4
Arsine
3
2
1
1
0
3
0
1
2
3
4
4
5
5
Time (ms x 105)
6
7
Time (ms x 105)
8
9
10
11
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
Intensity (cps x 108)
8
1
Compound
Concentration
1 Chlorogermane
86 ppm
2 Digermane
5.5 ppm
6
4
2
2
0
1
2
3
4
5
Time (ms x 105)
Figure 4. Chromatogram at m/z 76 (76Ge).
Intensity (cps x 106)
William M. Geiger is a Senior Partner at CONSCI.
[email protected]
1
5
Compound
Concentration
1 Deuterated digermane
180 ppb
2 Unknown germane compound
3 ppb
4
3
2
1
2
4
5
6
Gas chromatography coupled with ICP–MS detection is an
extremely effective tool in determining metallic hydride contaminants in semiconductor grade germane. Detection limits
of parts per trillion for these contaminants can be achieved,
levels that in the near future may be required to achieve the future quality of semi-conductor devices. Although chromatography does the ‘heavy lifting’ and the ICP–MS plasma/torch is
reasonably robust, it is still vital that a strategy be used to minimize the bulk of the matrix from contaminating the torch.
Since most germane contaminants elute after the germane matrix, the vacuum diversion strategy employed here is key to a
successful analysis.
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 solvent injection. Journal of Analytical Atomic Spectrometry, 17 (10), 1386–1389.

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