JPS6155267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a solar cell using a magnetic field scanning high current ion implantation device having a microwave ion source.

Conventionally, solar cells have been produced by an impurity diffusion method. That is, for an n ⁺ p type solar cell,
An n ⁺ -type layer with a depth of 0.3 to 0.4 μm was formed on a semiconductor substrate such as p-type Si using POCl ₃ at 850° C. for a diffusion time of 30 to 60 minutes. In this method, the wafer processing speed is limited to 150 to 200 wafers/hr due to the relationship between the soaking length of the electric furnace and the wafer spacing, even if the uniformity of the diffusion layer is sacrificed a little.

On the other hand, in the solar cell manufacturing method using the ion implantation method, if a conventional high-current ion implantation device with a P ⁺ ion current of 5 mA or more is used, the P ⁺ implantation amount is 5 ×
At 10 ¹⁵ cm ^-2 , it is possible to process 110 to 230 3″φ wafers/hr. However, with conventional equipment, the implantation method mainly relies on mechanical scanning, and when changing wafers, it is possible to process 3″φ wafers at atmospheric pressure. It is necessary to replace the entire return disk, the process is not fully automatic, and the number of disks that can be processed is limited to the above value.

In order to solve this problem, the present invention has a microwave ion source 1 from which a large current ion beam can be easily taken out and a simple deflector magnet 2, as shown in FIG. Then, a solar cell is manufactured using a simple magnetic field scanning type high current ion implantation device that scans the ion beam using a magnetic field scanning method. This device is
The beam diameter is large, several centimeters, and the beam is scanned, so the separation of ion species is not good.
When PH ₃ is used as a source gas, the P ⁺ ion group (P ⁺ , PH ⁺ , PH ⁺ ₂ , PH ⁺ ₃ ) and the H ⁺ ion group (H ⁺ , PH ⁺ ₂ ) are simply separated. However, by implanting only a group of P ⁺ ions into the Si surface, it is possible to produce an n ⁺ p type solar cell with characteristics equivalent to those produced by conventional equipment.

Furthermore, in the present invention, by uniaxially scanning the wafer 4 in a direction perpendicular to the scanning direction of the ion beam 3, a laser annealing method or an electron beam annealing method can be used as an annealing method after ion implantation. Continuous high speed can be automated. Processing speed is 500 4″φ wafers/hr or more.

FIG. 2 shows the ion beam spectrum obtained using PH ₃ as the source gas in the above ion implantation apparatus. The ions that are actually irradiated are P ⁺ ions.PH visible at the tail of the P ⁺ ion spectrum.
⁺ , PH ⁺ ₂ and PH ⁺ ₃ ions. After implanting P ⁺ ions into a p-type Si wafer, the sheet resistance distribution of a sample is annealed in an electric furnace at 850°C for 30 minutes in dry nitrogen, for example, based on the beam scanning width,
That is, it depends on the ratio of the AC modulated magnetic field amplitude to the DC magnetic field strength. In Figure 3, the ratio is 5%.
Figure 4 shows the results at 12.5%. The standard deviation values of the sheet resistance value distribution are 1.8% and 1.0%, respectively. These values are approximately comparable to 0.7-1.5% when using conventional ion implantation equipment.
In addition, the diffusion method has a processing speed of 200 sheets/hr.
The standard deviation of the sheet resistance value distribution when an n ⁺ layer is formed is 3.5%.

Example Using the above ion implantation apparatus configured to scan the beam by superimposing an alternating magnetic field on the mass separator and move the wafer in a direction perpendicular to the direction of the beam scan, the implantation energy was 5 to 30 keV and the implantation amount was 1. After implanting the above P ⁺ ion group into _a p-type Si wafer at ×10 ¹⁵ to 5 × 10 ¹⁵ cm ^-2 ,
Electric furnace annealing was performed at 850°C for 30 minutes. After this, mask the peripheral part on the back side and make a film with a thickness of about 1 μm.
Al was deposited and alloyed at 750°C for 30 minutes. After that, a metal mask was used on the front side to form a fishbone pattern, and a ring-shaped metal mask was used on the back side to form Ti (0.1 μm)/Ag (5 μm) on the entire surface except for the periphery.
was deposited. This solar cell showed a conversion efficiency of over 10% without an anti-reflection coating at 28°C and under irradiation with an AM1 solar simulator. This value is comparable to that using a conventional ion implanter and a diffused solar cell.

In addition, after performing ion implantation under the same implantation conditions as above, using a Q Switch Chilby laser,
Annealing was performed. Laser pulse width is 20-40
nanosecond, and the irradiation energy density is 2.0~
It was set to 2.5J/ ^cm2 . Electrode formation after annealing was performed in the same manner as above to produce a solar cell. However, in order to take advantage of the characteristic of laser annealing that the substrate is not heated, alloying of the backside Al was performed at a relatively low temperature of 400 to 600°C. This solar cell showed a conversion efficiency of close to 11% at 28°C and under irradiation from an AM1 solar simulator without an antireflection coating.

In the above, an example was shown in which a Si wafer was used as the substrate and a group of P ⁺ ions were used as the ions, but it is clear that the present invention can be applied to other semiconductor wafers and other ion groups, and solar cells can be manufactured. It is.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a magnetic field scanning type high current ion implantation device having a microwave ion source, Figure 2
The figure shows an ion beam spectrum obtained using the apparatus of Figure 1 using _PH3 gas as a source gas. Figures 3 and 4 are sheets of n ⁺ p type Si wafers manufactured by the manufacturing method of the present invention. FIG. 3 is a diagram showing resistance distribution. 1...Ion source, 2...Deflector magnet, 3...Ion beam, 4...Wafer.

Claims (1)

[Claims] 1. A second conductivity type semiconductor substrate is provided in a surface region of a first conductivity type semiconductor substrate.
In the manufacturing method of solar cells, which is manufactured by implanting conductive impurity ions to form a pn junction, an ion beam from a microwave ion source is scanned using a magnetic field scan method in which an alternating current magnetic field is superimposed on a separator direct current magnetic field. A method for manufacturing a solar cell, comprising implanting an ion group containing multiple types of ions. 2. The method of manufacturing a solar cell according to claim 1, wherein the semiconductor substrate is moved in a direction perpendicular to the scanning direction of the ion beam. 3. The method for manufacturing a solar cell according to claim 1 or 2, wherein the ion implantation includes laser annealing or electron beam annealing following the ion implantation. 4. The method of manufacturing a solar cell according to claim 1, wherein a p-type Si wafer is used as the semiconductor substrate, and a p ⁺ ion group is used as the ion group.