Epitaxially coated silicon wafer and method for producing an epitaxially coated silicon wafer
View Patent ↗Epitaxially coated silicon wafers have a rounded and polished edge region and a region adjacent to the edge having a width of 3 mm on the front and rear sides, a surface roughness in edge region of 0.1-1.5 nm RMS relative to a spatial wavelength range of 10-80 μm, and a variation of surface roughness of 1-10%. The wafer edges, after polishing, are examined for defects and roughness at the edge and surrounding region. Silicon wafers having a surface roughness of less than 1 nm RMS are pretreated in single wafer epitaxy reactors, first in a hydrogen atmosphere at a flow rate of 1-100 slm and in a second step, an etching medium with a flow rate of 0.5-5 slm is conducted onto the edge region of the wafer by a gas distribution device. The wafer is then epitaxially coated.
1. An epitaxially coated silicon wafer having a front side, a rear side and an edge region comprising a rounded and polished edge of the silicon wafer and also a region adjacent to the edge and having a width of 3 mm on the front and rear sides, having a surface roughness in the edge region of 0.1-1.5 nm RMS relative to a spatial wavelength range of 10-80 μm, and a variation of the surface roughness of 1-10%.
2. A silicon wafer having a front side, a rear side and an edge region comprising a rounded and polished edge of the silicon wafer and also a region adjacent to the edge and having a width of 3 mm on the front and rear sides, having a surface roughness in that edge region of 0.1-0.8 nm RMS relative to a spatial wavelength range of 10-80 μm, and a variation of the surface roughness of 1-3%.
3. A method for producing an epitaxially coated silicon wafer, comprising the following sequential process steps: (a) providing a group of silicon wafers having rounded edges; (b) polishing the edges of the silicon wafers; (c) cleaning the silicon wafers; (d) examining the edge regions of the group of silicon wafers with regard to defects and edge roughness and selecting silicon wafers from the group of silicon wafers which have a surface roughness of less than 1 nm RMS relative to a spatial wavelength range of 10-80 μm; (e) individually pretreating the selected silicon wafers in a single wafer epitaxy reactor, wherein, in a first step, a treatment in a hydrogen atmosphere at a flow rate of 1-100 slm is effected and, in addition, in a second step, an etching medium with a flow rate of 0.5-5 slm is added to the hydrogen atmosphere and is distributed in the reactor chamber by means of a gas distribution device; and (f) epitaxially coating the silicon wafer.
4. The method of claim 3 , wherein providing a group of silicon wafers in accordance with step a) is effected by slicing the wafers from a silicon single crystal, rounding the edges of the silicon wafers and grinding or lapping the front and rear sides thereof.
5. The method of claim 3 , wherein the silicon wafer selected in step d) comprises a front side, a rear side and an edge region comprising a rounded and polished edge of the silicon wafer and also an extended region adjacent to the edge and having a width of in each case 3 mm on the front and rear sides, and also has a surface roughness in that edge region of 0.1-0.8 nm RMS relative to a spatial wavelength range of 10-80 μm and also a variation of the surface roughness of 1-3%.
6. The method of claim 5 , wherein the selected silicon wafers have in the edge region no defects having an extent of greater than 1 μm.
7. The method of claim 3 , wherein cleaning in step c) comprises cleaning with aqueous hydrofluoric acid (HF), cleaning with TMAH/H 2 O 2 (tetramethylammonium hydroxide/hydrogen peroxide), and rinsing with ultrapure water.
8. The method of claim 3 , wherein the silicon wafers are cleaned by means of a cleaning solution comprising ultrapure water, tetramethyl ammonium hydroxide (TMAH) and hydrogen peroxide (H 2 O 2 ).
9. The method of claim 8 , wherein the cleaning in step c) is effected by the wafer being moved relative to cleaning rollers while wafer and/or cleaning rollers are flushed with the cleaning solution.
10. The method of claim 9 , wherein the cleaning rollers are synthetic sponges.
11. The method of claim 3 , wherein during pretreatment in the epitaxial reactor, the gas flows introduced into the reactor chamber by injectors are distributed into an outer zone and an inner zone of the reactor chamber by means of valves, such that the gas flow in the inner zone acts on a region around the center of the silicon wafer and the gas flow in the outer zone acts on an edge region of the silicon wafer, wherein during the second pretreatment step with addition of an etching medium to the hydrogen atmosphere, the distribution of the etching medium in inner and outer zones is I/O=0-0.5.
12. The method of claim 3 , wherein the two pretreatment steps in accordance with step e) are in each case effected in a temperature range of 950 to 1200° C.
13. The method of claim 3 , wherein the etching medium added to the hydrogen atmosphere is hydrogen chloride.
14. The method of claim 3 , wherein during the first pretreatment step, the hydrogen flow rate is 40-60 slm.
15. The method of claim 3 , wherein during both pretreatment steps in step e), the duration of the pretreatment is 10-120 s.
16. The method of claim 15 , wherein during both pretreatment steps, the duration of the pretreatment is 20-60 s.
17. The method of claim 3 , wherein the flow rate of the etching medium in the second step of the pretreatment in step e) is 1.5-5 slm.
18. The method of claim 3 , wherein the flow rate of the etching medium in the second step of the pretreatment in step e) is 3-5 slm.
19. The method of claim 3 , wherein the hydrogen flow rate in the second step of the pretreatment in step e) is 1-10 slm.
20. The method of claim 3 , wherein the hydrogen flow rate in the second step of the pretreatment in step e) is 5-10 slm.