Sample mounting

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Silicon wafers


silicon wafers Silicon wafers may be clamped between the annealing contacts and heated by current passing directly through the sample.

It requires self-supporting sample of rectangular shape approximately 10 mm long and 3-10 mm wide. The best width is 5-7 mm. The suggested thickness is about 0.5 mm.

The electrical resistance should be in the range 0.1-1000 Ω depending on required temperature (in the case of silicon it means that it must be sufficiently doped). If the resistance is too high it is impossible to anneal the sample.
silicon wafers For annealing we usually use the 70 V×24 A power supply.

The centre of the sample is theoretically at half of the annealing voltage so it is difficult to acquire spectra during annealing.

The temperatures up to about 1100 °C/1400 K can be reached. Maximum annealing current is 10 A.

Thermocouple is optional. Some users prefer to estimate the temperature during high-temperature annealing by eye or use a pyrometer. They claim that at high temperatures nickel from the thermocouple alloys migrates on the sample and contaminates it. So if you want to use the thermocouple place a thin tantalum spacer to avoid the direct contact of the thermocouple with the sample.
silicon wafers Example of Si sample 10×6×0.5 mm³ mounted.
silicon wafers

Assembly:

item count name material notes
S 1 sample doped silicon 10×(3-10)×0.5 mm³
1 1 baseplate molybdenum 1 mm thickness
2A 1 thermocouple
pins		 alumel (magnetic) must stick out 3.8-4 mm below the baseplate bottom surface
2B 1 chromel (non magnetic)
3a 6 ceramic
spacers		 alumina thinner
3b 2 thicker
4 8 nut molybdenum M1.2 thread
5 1 thermocouple chromel
(non magnetic)
alumel
(magnetic)		 0.1-0.25 mm diameter wires, spot-welded together
and touching the spacer 8 below the sample
6 4 rod molybdenum M1.2 thread
7a 1 annealing
contacts		 tungsten brushed on the left side, see surfaces highlighted in yellow;
must be 3.6-3.8 mm above the baseplate top surface
7b 1
8 1 spacer tantalum 0.05-0.1 mm thickness
9 2 clamp tantalum 0.1-0.25 mm thickness
silicon wafers For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface.
silicon wafers For the correct connection the annealing contacts must be 3.6-3.8 mm above the baseplate top surface. This distance (if 3.5 mm or lower) can be increased by placing tiny spacers made of properly thick wire below the bottom ceramic spacers (3a) or swapping the thin ceramic spacers (3a) with the thicker ones (3b)



Last Updated on Thursday, 09 March 2023 10:32