Growth of a uniformly doped silicon ingot by doping only the initial charge
The present invention relates to a method of growing a silicon ingot comprising a dopant material having a segregation coefficient of k, wherein the concentration of the dopant is axially substantially uniform throughout the ingot. The method comprises the steps of providing a crucible having an inner growth zone in fluid communication with an outer feed zone, and the inner growth zone and the outer feed zone have cross-sectional areas that are can be used to determine conditions for maintaining dopant uniformity for the specific dopant material used. A crystalline growth system for growing at least one uniformly doped silicon ingot is also disclosed.
1. A continuous Czochralski growth method for growing a silicon ingot comprising a dopant material having a segregation coefficient of k, the method comprising the steps of:
i) providing a crucible having an inner growth zone in fluid communication with an outer feed zone, wherein the inner growth zone and the outer feed zone have cross-sectional areas that are preselected based on the segregation coefficient k of the dopant material;
ii) providing an initial charge in the inner growth zone and the outer feed zone prior to initiating growth, the initial charge in the inner growth zone comprising silicon and the dopant material and the initial charge in the outer feed zone comprising silicon and no dopant material;
iii) once the initial charge to the inner growth zone and the outer feed zone has been provided, melting the silicon and dopant material in the inner growth zone to form a melted mixture and the silicon in the outer feed zone to form a silicon melt, the melted mixture and the silicon melt having upper melt surfaces at substantially similar heights, wherein the inner growth zone has a cross-sectional surface area As at the upper melt surface of the melted mixture and the crucible has a total cross-sectional surface area A t at the upper melt surface area of the melted mixture and the silicon melt;
iv) growing the silicon ingot to an amount M x from the inner growth zone, wherein during the growing, a feed comprising silicon and no dopant material in an amount M F is delivered at a feed rate into the silicon melt in the outer feed zone,
wherein the feed rate at which the feed is delivered is based on a) the cross-sectional areas of the inner growth zone and the outer feed zone and b) the segregation coefficient k of the dopant material in the initial charge,
wherein a ratio of the feed rate to an ingot growth rate of the silicon ingot is equal to 1−k(A t /A s ), and
wherein no additional dopant is supplied to the inner growth zone and the outer feed zone after providing the initial charge until the silicon ingot is grown to the amount M x ; and
v) removing the grown silicon ingot comprising the dopant material in an axially substantially constant concentration.
2. The method of claim 1 , wherein the crucible is substantially circular in cross-sectional shape.
3. The method of claim 1 , wherein the inner growth zone is in fluid communication with the outer feed zone through at least one apertured wall.