Silicon wafer thickness monitor SIT-200 Alnair Labs Corporation 2016.04.20
Principle of Measurement Silicon wafer Optical fiber Sensor head Wavelength tunable laser PD PD Interference signal Power monitor Optical power Wavelength The cycle of the interfered waveform depends on the thickness of the measured wafer. 1 2 3 The interference waveform (light-intensity periodical change) is generated by the reflected lights from the silicon wafer, of which cycle depends on the wafer s thickness under test. The thickness is computed by using the interference waveform s cycle calculated from FFT and the refractive index of the wafer. Real time measurement is achieved within the wafer process time of <0.1 sec, which is typical in Silicon wet etching.
Specifications General Specifications Remarks Operating temperature +15 to +30 The Max. sensor head temperature is 110 o C Storage temperature 0 to +40 Humidity 20%R.H. to 80%R.H. No condensation permitted. Power Dimensions Weight Characteristics Specifications Remarks Measured object Measurable thickness range Measurement light source Silicon wafer 10 mm - 500 mm Wavelength tunable laser TWFL-200 AC 100-240 V, 48-66Hz, 60 VA max AC 100-240 V, 48 66 Hz, 80 VA max 364 mm x 147 mm x 391 mm 165 mm x 100 mm x 300 mm 9.0 kg 1.6 kg 5.0 kg Wavelength range: 1515 nm~1585 nm (typ.) Bandwidth >70 nm Specific details refer to the specification sheet of TWFL-200 Optical output power >-2 dbm Class 1 Guiding light source 660-nm laser Class 1M Measurement time >20 msec Measurement accuracy <±2 % In thickness of 300-mm and 200-mm silicon wafer Measurement repeatability <0.1 mm 3σ of 30-times measured in 30-mm wafer Sensor focused beam diameter 50 mm ±10 mm Max. movable range of sensor ±5 x ±5 x 4 mm (horizontal, x) x (horizontal, y) x (height, z) Sensor position accuracy <10 mm Max. angular movement of sensor ±10 Manual control Sensor fiber length 700 mm±50 mm Fiber is protected by metal tube, SMF, FC/SPC Extension fiber length 4.8 m±0.5 m Fiber is protected by metal tube, SMF, FC/SPC Monitor output Interference signal Analogue output Indications Wafer thickness (mm), Signal power, Error code, Lifetime ratio (%) External interface Ethernet Main functions Wafer thickness, search measuring points, focusing, turn on/off visible light, others Controller Stage controller Controller Stage controller Controller Sensor Stage Alnair controller Laboratories
Panel display Thickness Signal power Error code Life time ratio Thickness Signal power Error code Lifetime ratio Thickness of measured silicon wafer is displayed. The unit is in mm. Signal power for measurement is displayed. When flat silicon wafer is measured, 1000 or higher value is shown. If any problem occurs, an error cord regarding the problem is shown. The lifetime of the tunable laser inside is shown. 100 % is shown in initial state. Please make a contact with the manufacturer, when it is near 0 %.
Example of measuring 3σ = 0.012 mm 3σ = 0.007 mm Thickness (mm) 296.8 296.7 296.6 296.5 296.4 Thickness (mm) 13.7 13.6 13.5 13.4 13.3 296.3 0 50 100 150 200 Time (sec) 13.2 0 100 200 300 Time (sec) High measurement repeatability and high measurement accuracy below 0.1 mm.
Applications Thickness monitor for the wafer In-situ monitoring of the thickness Etchant Optical sensor Wafer Wet-etched wafer Optical sensor Our thickness monitor adapts a wavelength-tunable laser. The characteristic of this method is the high sensitivity against low reflection from the wafer, such as rough wafer surface. So this high-sensitive thickness monitor can be applicable for in-situ wet etching thickness monitor.