Method for producing silicon wafers, and silicon solar cell
In order to produce silicon wafers, liquid ultra-pure silicon is solidified on a silicon monocrystalline seed arranged in the bottom area of a crucible and having a seed surface comprising a {110}-crystal orientation and an edge surface having a {100}-crystal orientation starting from the bottom of the crucible, thus forming a silicon block on the seed surface of the silicon monocrystalline seed which largely takes over the {110}-crystal orientation. Subsequently, the silicon block is divided into wafers with a wafer surface having a {100}-crystal orientation.
1. A method for producing silicon wafers, comprising the steps of:
providing a silicon monocrystalline seed in the bottom area of a crucible, the silicon monocrystalline seed having a seed surface with a <110>-crystal orientation, the <110>-crystal orientation being perpendicular to the bottom area of the crucible, and an edge surface with a <100>-crystal orientation, the <100>-crystal orientation being perpendicular to a side face of the crucible;
surface-melting silicon and providing it in the crucible;
solidifying the liquid silicon starting from the bottom area of the crucible on the seed surface of the silicon monocrystalline seed to form a silicon block, whereby the silicon block takes over the <110>-crystal orientation and as a structure which is more than 70% monocrystalline; and
dividing the silicon block into wafers in such a way that a main wafer surface comprises a <100>-crystal orientation, the main wafer surface being delimited by four wafer edges, wherein two respectively opposite wafer edges of the four wafer edges run parallel to the [110]-crystal direction.
2. The method of claim 1 , wherein the silicon monocrystalline seed is produced from a monocrystalline silicon ingot, the ingot axis having a [100]-spatial orientation, whereby the monocrystalline silicon ingot for forming the seed surface of the silicon monocrystalline seed having the <110>-crystal orientation and the edge surface of the silicon monocrystalline seed having the <100>-crystal orientation is cut open.
3. The method of claim 1 , wherein the silicon monocrystalline seed consists of several parts covering the bottom area of the crucible with the same crystal orientation.
4. The method of claim 1 , wherein prior to cutting into wafers the silicon block is divided into rectangular silicon ingots in such a way that an ingot axis runs in parallel to the seed surface of the silicon monocrystalline seed.
5. The method of claim 1 , wherein the wafer surface having the <100>-crystal orientation is subjected to texture etching by means of an alkaline etching solution.
6. The method of claim 2 , wherein the silicon monocrystalline seed consists of several parts covering the bottom area of the crucible with the same crystal orientation.
7. The method of claim 2 , wherein prior to cutting into wafers the silicon block is divided into rectangular silicon ingots in such a way that the ingot axis runs in parallel to the seed surface of the silicon monocrystalline seed.
8. The method of claim 3 , wherein prior to cutting into wafers the silicon block is divided into rectangular silicon ingots in such a way that an ingot axis runs in parallel to the seed surface of the silicon monocrystalline seed.
9. The method of claim 2 , wherein the wafer surface having the <100>-crystal orientation is subjected to texture etching by means of an alkaline etching solution.
10. The method of claim 3 , wherein the wafer surface having the <100>-crystal orientation is subjected to texture etching by means of an alkaline etching solution.
11. The method of claim 4 , wherein the wafer surface having the <100>-crystal orientation is subjected to texture etching by means of an alkaline etching solution.
12. The method of claim 1 , wherein the edge face with the <100>-crystal orientation is perpendicular to a bottom surface of the crucible, wherein the bottom surface is perpendicular to the side face of the crucible.
13. The method of claim 1 , wherein the seed surface with the <110>-crystal orientation is parallel with a bottom surface of the crucible, wherein the bottom surface is perpendicular to the side face of the crucible.