A blanket layer of silicon can be added to a silicon substrate by a CVD process to achieve changes in the properties, like resistivity, type and defect density. This CVD process is called epi (or epitaxial) deposition. The thickness monitoring of the epi layer is part of the production process of making the epi wafers. This monitoring is executed on a sample basis, or only to confirm that the epi reactor is set up properly.
Semilab can offer non-contact optical solution for Epi thickness monitoring, depending on infrared reflection techniques.
Figure 1. Resistivity measurement flow
The MCV systems allow the elimination of the need for costly metal and poly deposition processes by using a pneumatically controlled, non-damaging probe design and a topside mercury contact. The system features an extremely stable contact area and uses only a small quantity of mercury to make highly repeatable CV and IV measurements for process development and process monitoring applications. MCV is a superior technique for both bulk/epitaxial- and dielectric layer characterization.
Modern device structures require accurate and precise resistivity control and carrier density profile of epitaxial silicon. Semilab’s mercury (Hg) Schottky-CV technique is suitable for either production or R&D monitoring, offering speed, high repeatability and sensitivity.
The Hg Schottky-CV technique uses a high repeatability, non-scrubbing, vertical arm probe. The probe includes a 2 cm long capillary that holds a small volume of mercury and is electrostatically shielded to reduce stray capacitance and it’s positional dependence. The epitaxial wafer is placed on the stage, processed side up, either manually or with a robot. The Hg probe is then lowered from the topside in a controlled manner to form a high quality Schottky contact.
The Hg Schottky-CV technique can be used to measure n/n+, p/p+, n/p and p/n epitaxial structures. The carrier density profiles on other semiconductor materials, such as GaAs, GaP, InP and SiC can also be measured.
Examples of the carrier density profiles measured on thin p/p+ epitaxial structures are shown on Figure 3-4. Valuable information about epitaxial resistivity, autodoping effects and epitaxial layer thickness can be obtained with great repeatability, see Figure 5.
Figure 3. Carrier density profiles on thin p/p+ epitaxial structures
Figure 4. Carrier density profiles on thin p/p+ epitaxial structures
Figure 5. Resistivity, autodoping and layer thickness information
Application and specs
Epitaxial resistivity monitoring
Depth and doping ranges limited by zero-bias depletion width, breakdown voltage.
Resistivity range for silicon: according to ASTM 1392
Alternate semiconductor materials
All Semilab's MCV tools are equipped with automated, full hand-off, mercury handling system to increase safety and reliability. The user friendly software environment controls the measurements and also offers a great flexibility for detailed analysis of the measured structures. Full map capability up to 12"/300 mm. All features listed, including optional ones, are compatible with both the manual MCV-530(L) and the automatic MCV-2200/2500 tools.
On top of the standard CV measurements and standard electronic units, a number of advanced metrology options are available to extend measurement capabilities:
The MCV-530 system is designed for the fast and reliable testing of dielectric and epitaxial layers by mercury probe, and it is ideal for R&D or small volume production.
MCV-530/530L tools are manual loading systems, however they have the same measurement abilities like the automatic MCV-2200/2500 products.
Manual wafer handling:
The MCV automatic mapping systems provide a mercury C-V measurement for non-patterned wafers used in epitaxial silicon production and front-end semiconductor processing.
In MCV-2200 and MCV-2500, the wafers are robotically loaded onto the mapping stage from a cassette or opened FOUP. The test wafer moves to each site specified in a pre-programmed map as electrical characterization tests are made. The system stores test data and reports them in a variety of formats.