METHOD FOR DOPING SEMICONDUCTOR SUBSTRATES BY MEANS OF A CO-DIFFUSION PROCESS AND DOPED SEMICONDUCTOR SUBSTRATE PRODUCED BY MEANS OF SAID METHOD

Abstract

The invention relates to a method for doping semiconductor substrates by means of a co-diffusion process. First, semiconductor substrates are coated at least on one side with a layer containing at least one first dopant. Two of said substrates in each case are arranged in a process chamber in such a way that two of the coated sides thereof are brought in direct contact.

Claims

1-21. (canceled)

22. A method for doping semiconductor substrates by means of a co-diffusion process, comprising a) coating semiconductor substrates, at least on one side, with a layer comprising at least one first dopant, b) disposing respectively two of the coated semiconductor substrates from a) in a process chamber such that two of their coated sides are in direct contact, c) introducing at least one second dopant, in the form of a gaseous dopant source, into the process chamber, and d) the introduction of the first dopant and of the second dopant into the semiconductor substrates is effected during which the first dopant and the second dopant diffuse into the semiconductor substrates, at the same time, at least partially.

23. The method according to claim 22, wherein, during step c), the particle concentration of the gaseous dopant source in an atmosphere within the process chamber is less than 0.5%.

24. The method according to claim 22, wherein, during step d), the atmosphere within the process chamber comprises oxygen at a concentration higher than 0.1% and lower than 5%.

25. The method according to claim 22, wherein, during step d), an oxygen content of the process atmosphere within the process chamber is increased such that the oxygen concentration at the beginning of step d) is lower than 5% and, at the end of step d), is higher than 10%.

26. The method according to claim 22, wherein, after step d), an oxygen content of the process atmosphere within the process chamber is increased during the cooling process, the oxygen concentration is higher than 10%.

27. The method according to claim 22, wherein the concentration of the first dopant in the layer produced in step a) is less than 10%.

28. The method according to claim 22, wherein the introduction of the first and second dopant, in step d), is effected at temperatures of 800 to 1,000 C. and/or over a period of time of 1 to 120 min.

29. The method according to claim 22, wherein step c) is effected before and/or at the beginning of step d).

30. The method according to claim 22, wherein, during step c), a temperature within the process chamber is not higher than 850 C.

31. The method according to claim 22, wherein, from step c) to step d), a temperature within the process chamber is increased by 50 to 250 C.

32. The method according to claim 22, wherein, between step b) and c), a temperature of several regions within the process chamber is adjusted such that the temperatures of these regions deviate from each other by less than 5 C. within the process chamber.

33. The method according to claim 32, wherein step c) is effected at the latest 60 seconds after concluding adjustment of a temperature in regions of the process chamber.

34. The method according to claim 22, wherein the first dopant is boron and the second dopant is phosphorus or the first dopant is phosphorus and the second dopant is boron.

35. The method according to claim 22, wherein: the second dopant is phosphorus and the gaseous dopant source is POCl.sub.3 and/or PH.sub.3, or the second dopant is boron and the gaseous dopant source is selected from the group consisting of BBr.sub.3, BCl.sub.3, B.sub.2H.sub.6 and mixtures thereof.

36. The method according to claim 22, wherein the gaseous dopant source in step c) is at a pressure less than 500 mbar.

37. The method according to claim 22, wherein the gaseous dopant source is POCl.sub.3, which is introduced through a bubbler into the process chamber, and the carrier gas flow through the POCl.sub.3 bubbler during step c) is less than 1.5 standard liters per minute.

38. The method according to claim 22, wherein the coating in step a) is effected by chemical vapour phase deposition at atmospheric pressure (APCVD), plasma-enhanced chemical vapour phase deposition (PECVD), inkjet printing, screen printing, or rotational coating.

39. The method according to claim 22, wherein the process chamber is a tube furnace or a continuous furnace.

40. The method according to claim 22, wherein, in step a), the semiconductor substrates are provided with the layer comprising the first dopant only on one side, the coating on the one side being effected over the entire area.

41. The method according to claim 22, wherein, in step a), a front-side of each semiconductor substrate is provided, over the entire area, with the layer comprising the first dopant and a rear-side, situated opposite the front-side, of each semiconductor substrate is provided, only partially, with the layer comprising the first dopant, in step c) an additional quantity of the second dopant is introduced into the process chamber which overcompensates for the part of the first dopant situated on the rear-side of the semiconductor substrates.

42. A doped semiconductor substrate produced according to claim 41, wherein the semiconductor substrate has a lateral gradient in the dopant profile on the rear-side thereof, the proportion of first dopant, on the rear-side of the semiconductor substrate, decreasing from the edge of the semiconductor substrate towards the centre of the semiconductor substrate.

Description

EMBODIMENT

[0060] Wafers are coated, on one side, with a borosilicate glass (BSG) layer with a dopant concentration of 2.Math.10.sup.22 cm.sup.3. Then respectively two wafers are introduced into a quartz boat with the coated sides towards each other. This quartz boat is then introduced into a quartz tube. After closing the tube door, the temperature in the individual heating zones is brought to (7505) C. Thereafter, POCl.sub.3 is introduced into the atmosphere, this being able to take place either before or during the heating process. The heating process leads to achieving a peak temperature of 950 C. During this heating process, the temperatures in the five heating zones of the quartz tube deviate from each other by less than 5 C. After conclusion of the high-temperature process, the wafers are then removed from the furnace.

[0061] Solar cells which were diffused according to the method described here achieve the following IV parameters: V.sub.OC=653 mV, J.sub.XC=38.6 mA/cm.sup.2, FF=79.6%, conversion efficiency=20.1%.

[0062] FIG. 1 shows doping profiles by way of example which were produced with the method according to the invention. It emerges clearly herefrom that, with the method according to the invention, a large number of different doping profiles can be produced.

[0063] FIG. 2 shows dark saturation flows of boron-doped regions for different dopant sources with single loading and backtoback loading. It emerges clearly from this Figure that, by using the backtoback method, recombination is reduced and hence the operation of the solar cell is improved.