Intra-cavity gettering of nitrogen in SiC crystal growth
View Patent ↗In method of crystal growth, an interior of a crystal growth chamber ( 2 ) is heated to a first temperature in the presence of a first vacuum pressure whereupon at least one gas absorbed in a material ( 4 ) disposed inside the chamber is degassed therefrom. The interior of the chamber is then exposed to an inert gas at a second, higher temperature in the presence of a second vacuum pressure that is at a higher pressure than the first vacuum pressure. The inert gas pressure in the chamber is then reduced to a third vacuum pressure that is between the first and second vacuum pressures and the temperature inside the chamber is lowered to a third temperature that is between the first and second temperatures, whereupon source material ( 10 ) inside the chamber vaporizes and deposits on a seed crystal ( 12 ) inside the chamber.
1. A method of growing a crystal inside a crystal growth chamber, said method comprising:
(a) providing a crystal growth chamber having therein at least one component formed of a material that absorbs at least one gas that is a donor impurity in the growth of crystals in the chamber, said chamber further including therein a source material and a seed crystal;
(b) heating the interior of the chamber to a first, elevated temperature in the presence of a first pressure whereupon the combination of the first temperature and the first pressure is sufficient to degas the at least one gas from the component;
(c) exposing the interior of the chamber to an inert gas at a second, elevated temperature in the presence of a second pressure, wherein the second temperature is higher than the first temperature and higher than a third, desired crystal growth temperature which is also higher than the first temperature, and the second pressure is greater than the first pressure;
(d) reducing the inert gas pressure in the chamber to a third pressure that is between the first pressure and the second pressure; and
(e) lowering the temperature inside the chamber to the third, desired crystal growth temperature whereupon the source material sublimates (changes from a solid into a vapor) and the vapor from said sublimation deposits on the seed crystal, wherein each of the first, second and third temperatures is established by controlled heating of the interior of the chamber.
2. The method of claim 1 , wherein steps (b)-(e) occur in the listed order.
3. The method of claim 1 , wherein steps (b)-(e) occur absent exposing the interior of the chamber to the ambient atmosphere and/or absent exposing the interior of the chamber to temperature less than the first temperature.
4. The method of claim 1 , wherein:
step (b) is performed for a period between 12 and 18 hours; and/or
step (c) is performed for a period of between 18 and 30 hours.
5. The method of claim 1 , wherein:
the first temperature is about 1200° C.;
the second temperature is 50 to 150° C. above the third temperature; and/or
the third temperature is between 2000 and 2400° C.
6. The method of claim 1 , wherein:
the first pressure is between 10 −5 and 10 −7 Torr;
the second pressure is between 200 and 600 Torr; and/or
the third pressure is between 1 and 100 Torr.
7. The method of claim 1 , wherein the seed crystal and the crystal being grown are made from SiC.
8. A crystal produced according to the method of claim 1 .