The best quality control can be achieved by inline process monitoring to check every wafer in the manufacturing process. However, in some cases the short cycle time (usually less than 1 second) does not allow to realize detailed analysis of the wafer, which may include full wafer mapping and techniques requires mechanical contacts.
The measurement tools were designed to include non-destructive techniques and favor non-contact methods where possible.
The applications include the followings:
The combination of the ion implant process and the process to anneal implants is usually monitored by measuring the sheet resistance of the implanted layer. The sheet resistance varies with dose, energy, and the amount of implanted species that has become electrically active. It is the sheet resistance that ultimately determines the device performance. Thus, measuring sheet resistance is an excellent way to monitor everything associated with an implant process.
The basic idea of the JPV method is the light excitation of the np or pn layer structure, and the pick-up of the resulting junction photovoltage by a capacitive probe. The detected potential is determined by the sheet resistance of the implanted layer, capacitance of junction and resistance through over the diode.
Figure 2. Sheet resistance measurement (lower range)
Figure 3. Sheet resistance measurement (higher range)
Semilab offers JPV technology to make non-contact, high resolution fast maps of sheet resistance.
The sample is illuminated by chopped LED light, which generates electrons and holes in the substrate layer. The generated charge carriers diffuse to the junction and the electric field located in the junction separates them. The result of the separation is the change in the junction voltage. This voltage change spread laterally in the implanted layer and the attenuation depends on the sheet resistance, junction capacitance, resistance of the junction and chopping frequency of the LED.
The potential change is detected by a capacitive sensor in order to evaluate the JPV signal, as a function of the frequency of the emitted light.
Based on the evaluation, the sheet resistance (Rs), capacitance of junction (Cd) and the resistance of the diode (Rd) can be calculated.
The junction leakage current is directly connected to the Rd by the following equation:
Figure 5. The detected potential is determined by Rs, Cd, Rd and frequency
Light sources: monochromatic LED, wavelength can be 470 nm, 520 nm, 740 nm and 970 nm (depending on junction depth)
Lateral resolution: 1 mm
Resolution in X-Y mapping: 1, 2, 4, 8 and 16 mm spatial resolution, or single point measurements at predefined points (up to 50)
Samples: np or pn structure (diffused or implanted USJ)
SHR-1000 is a fast, non-contact and reliable alternative of four point probe in the characterization of emitter layers. Emitter sheet resistance is a primary quality control parameter for silicon cells in PV applications.
Features and System specifications:
Features and System specifications:
It is a new integrated platform with the following capabilities:
Other testing capabilities:
The WT-2000PVN is a table top measurement system, capable of performing a variety of measurements on PV cells, wafers, and blocks. The base system includes the overhead functions, and you configure the measurement capabilities to match your specific needs, by selecting from the options below.
The WT-2000PVN can measure blocks and ingots, as well as wafers and cells. For measuring wafers and cells, people typically produce maps. When measuring blocks or ingots, people often produce only line scans, to save time, WT-2000PVN can do both.
Most producers of PV cells own a WT-2000PVN. It is extremely useful for:
Measurement techniques that can be integrated in WT-2000PVN: