PAM-XIAMEN offers 10*10mm2 undoped Freestanding GaN Substrate:
1. Specification of Undoped Freestanding GaN Wafer
|Dimension||10 x 10.5 mm2|
|Orientation||C plane (0001) off angle toward M-axis 0.35 ±0.15°|
|Conduction Type||N-type / Undoped|
|Resistivity (300K)||< 0.1 Ω·cm|
|TTV||≤ 10 µm|
|BOW||BOW ≤ 10 µm|
|Surface Roughness:||Front side: Ra<0.2nm, epi-ready;
Back side: Fine Ground or polished.
|Dislocation Density||≤ 5x 106 cm-2 (calculated by CL)*|
|Macro Defect Density||0 cm-2|
|Useable Area||> 90% (edge exclusion)|
|each in single wafer container, under nitrogen atmosphere, packed in class 100 clean room|
2. Standard Method for Testing Surface Roughness of Undoped Gallium Nitride Single Crystal Substrate
The standard in semiconductor material industry specifies the method for testing the surface roughness of gallium nitride single crystal substrates with an atomic force microscope, which applies to GaN single crystal substrates grown by chemical vapor deposition and other methods with a surface roughness of less than 10nm.
2.1 Test Principle for Freestanding GaN Substrate
This standard uses an atomic force microscope to test the three-dimensional surface morphology of a certain area of the sample, and then evaluates the roughness based on a set of surface contour values contained in the surface morphology. Because of the refractive index of the atomic force microscope in the height direction (that is, the longitudinal splitting rate) usually does not exceed 0.1 nm, and the lateral resolution can usually reach 10nm, so it can clearly distinguish the atomic steps on the single crystal GaN substrate (step height is usually <1nm), which is an effective means to evaluate the roughness of the undoped GaN freestanding substrate.
2.2 Evaluation method for Undoped GaN Bulk Substrate Roughness
This standard uses the mid-line system (profile method) to assess surface roughness.
The surface profile in this standard is obtained by the atomic force microscope method; the surface profile of a given sampling length is obtained by scanning the probe in a certain direction, and the probe is moved at equal intervals in the scanning direction to obtain a group of surface contours. The surface profile describes the surface topography of a district.
The center line of the surface profile is obtained by fitting the least squares method of the n-th order (1≤n≤3) polynomial. The contour formed after subtracting the center line from the surface contour is the basis for evaluating the surface roughness.
The surface roughness value is expressed by the arithmetic mean deviation Ra of the contour after subtracting the center line.
2.3 Test Environment for Undoped Gallium Nitride Single Crystal Film
Unless otherwise specified, the test should be carried out in the following environment:
a) The temperature is 18℃~28℃;
b) Humidity <90%;
c) Vibration noise should be ≤0.1 nm.
2.4 Repeatability of Undoped Freestanding GaN Substrate Roughness Tests
Using 3 pieces of GaN single crystal substrate samples S245., S246. S255 with different roughness, the roughness Ra is in the three typical ranges of Ra≤0.3 nm, 0.3 nm<Ra≤3 nm and 3 nm<Ra. According to the method specified in this standard, the same atomic force microscope is used to perform 6 independent measurements on each sample. The average roughness and relative standard deviation are shown in the Table. The relative standard deviation of the surface roughness test results of the samples is less than 6 %.
Average roughness and relative standard deviation of multiple tests for GaN free standing substrate without dopant on the same instrument:
|Relative Standard Deviation||5.9%||4.0%||4.4%|