Process for producing doped semiconductor wafers from silicon, and the wafers produced thereby
View Patent ↗A process for producing doped semiconductor wafers from silicon, which contain an electrically active dopant, such as boron, phosphorus, arsenic or antimony, optionally are additionally doped with germanium and have a defined thermal conductivity, involves producing a single crystal from silicon and processing further to form semiconductor wafers, the thermal conductivity being established by selecting a concentration of the electrically active dopant and optionally a concentration of germanium. Semiconductor wafers produced from silicon by the process have specific properties with regard to thermal conductivity and resistivity.
1. A process for producing doped semiconductor wafers with a thermal conductivity k from silicon, which contain an electrically active dopant, and are further doped with germanium in a concentration of up to 2×10 20 atoms/cm 3 , comprising producing a single crystal from silicon and further processing said single crystal to form seimconductor wafers, and setting the thermal conductivity k in accordance with the formula
k =(1−5.6×10 −21 x c (Ge)+1.4×10 −41 x c (Ge) 2 )/6.8×10 −3 +alpha x c (Dop))
by selecting the concentrations of germanium and of the electrically active dopant, in which formula k is the thermal conductivity at 22° C. in W/mK, c(Ge) and c(Dop) are the selected concentrations of germanium and of the electrically active dopant, respectively, in atoms/cm 3 , and alpha is a coefficient which has the following values depending on the electrically active dopant:
Dopant:
Boron
Phosphorus
Arsenic
Antimony
alpha:
9.57 · 10 −23
6.42 · 10 −23
2.11 · 10 −22
1.30 · 10 −21 .
2. The process of claim 1 , wherein the single crystal is pulled from a silicon melt which contains the electrically active dopant and optionally germanium, using the Czochralski method, and the electrically active dopant concentration c(Dop), and germanium concentration c(Ge) in the single crystal are measured.
3. The process of claim 1 , wherein the single crystal is pulled from a silicon melt which contains germanium using the Czochralski method, the germanium concentration c(Ge) is measured, the single crystal is processed into batch wafers, wafers are doped with the electrically active dopant by diffusion or ion implantation, and the concentration c(Dop) is measured on a sufficient number of wafers to verify the concentration of electrically active dopant in the batch of wafers.
4. The process of claim 1 , wherein boron is an electrically active dopant and the boron concentration is selected in such a manner that one of the following combinations of properties results with regard to thermal conductivity (TC) and resistivity (R) of the semiconductor wafers:
a) TC<105 W/mK; R>5 mOhmcm,
b) TC=90 W/mK−30 W/mK; R=5−3 mOhmcm,
c) TC=80 W/mK−20 W/mK; R=3−2 mOhmcm,
d) TC=70 W/mK−20 W/mK; R=2−1.5 mOhmcm, and
e) TC<50 W/mK; R<1.5 mOhmcm.
5. The process of claim 4 , wherein the radial variation in the resistivity is less than 8%.
6. The process of claim 1 , wherein the semiconductor wafers are doped with phosphorus as an electrically active dopant, and the phosphorus concentration is selected in such a manner that one of the following combinations of properties results with regard to thermal conductivity (TC) and resistivity (R) of the semiconductor wafers:
a) TC=90 W/mK−50 W/mK; R=1.5−1.2 mOhmcm,
b) TC=80 W/mK−40 W/mK; R=1.2−0.9 mOhmcm, and
c) TC=75 W/mK−30 W/mK; R<0.9 mOhmcm.
7. The process of claim 6 , wherein the radial variation in the resistivity is less than 10%.
8. The process of claim 1 , wherein the semiconductor wafers are used as substrates for electronic power semiconductor components.
9. The process of claim 1 , wherein an epitaxial layer is deposited on the semiconductor wafers.
10. The process of claim 1 , wherein the single crystal is additionally doped with at least one further dopant.
11. The process of claim 1 , wherein the single crystal is additionally doped with nitrogen, carbon or a combination of nitrogen and carbon.
12. A semiconductor wafer formed from silicon, optionally with a deposited epitaxial coating, the wafer being doped with germanium in a concentration of up to 2·10 20 atoms/cm 3 , and with boron, and having one of the following combinations of properties with regard to thermal conductivity (TC) and resistivity (R):
a) TC<105 W/mK; R>5 mOhmcm,
b) TC=90 W/mK−30 W/mK; R=5−3 mOhmcm,
c) TC=80 W/mK−20 W/mK; R=3−2 mOhmcm,
d) TC=70 W/mK−20 W/mK; R=2−1.5 mOhmcm, and
e) TC<50 W/mK; R>1.5 mOhmcm.
13. A semiconductor wafer formed from silicon, optionally with a deposited epitaxial coating, the semiconductor wafer being doped with germanium in a concentration of up to 2·10 20 atoms/cm3, and with phosphorus, and having one of the following combinations of properties with regard to thermal conductivity (TC) and resistivity (R):
a) TC=90 W/mK−50 W/mK; R=1.5−1.2 mOhmcm,
b) TC=80 W/mK−40 W/mK; R=1.2−0.9 mOhmcm, and
c) TC=75 W/mK−30 W/mK; R>0.9 mOhmcm.