Corresponding author: Roman Yu. Kozlov ( rykozlov@giredmet.ru ) © 2020 Svetlana S. Kormilitsina, Elena V. Molodtsova, Stanislav N. Knyzev, Roman Yu. Kozlov, Dmitry A. Zavrazhin, Elena V. Zharikova, Yuri V. Syrov.
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Citation:
Kormilitsina SS, Molodtsova EV, Knyzev SN, Kozlov RYu, Zavrazhin DA, Zharikova EV, Syrov YuV (2020) Effect of mechanical treatment type on the strength of undoped single crystal indium antimonide wafers. Modern Electronic Materials 6(4): 147153. https://doi.org/10.3897/j.moem.6.4.64991

Thin (100) wafers of single crystal undoped InSb have been strength tested by plane transverse bending. The strength of the wafers (≤ 800 mm in thickness) has been shown to depend on their mechanical treatment type. If the full mechanical treatment cycle is used (grinding + chemical polishing) the strength of the InSb wafers increases twofold (from 3.0 to 6.4 kg/mm^{2}). We show that the strength dependence on mechanical treatment type for (100) wafers is similar to that for (111) wafers, the strength of (111) wafers being 2 times higher. The roughness of the thin wafers after the full mechanical treatment cycle has been measured using contact profilometry. After the full mechanical treatment cycle the roughness of the InSb wafers R_{a} decreases from 0.6 to 0.04 mm leading to general surface smoothening. We have compared the strength and roughness between (100) InSb and GaAs wafers. The roughness of InSb and GaAs wafers after the full mechanical treatment cycle decreases significantly: by 10 times for InSb due to the general surface smoothening and by 3 times for GaAs (R_{z} from 2.4 to 0.8 mm) due to a reduction of the peak roughness component. The full mechanical treatment cycle increases the strength of InSb wafers by removing damaged layers through the sequence of operations and reducing the risk of mechanical damage development.
indium antimonide, Czochralsky method, thin wafers, yield strength, mechanical treatment, chemical polishing, crystallographic orientation, wafer roughness
Single crystal indium antimonide is still among the main semiconductors used for the fabrication of electronic components in a broad application field of solid state electronics, i.e., optoelectronics. This material is used for the fabrication of linear and array photocells operated in the 3–5 mm wavelength range that are employed as photosensitive elements in heat vision systems [
Indium antimonide has a special position in the range of A^{III}B^{V} semiconductors. Its lowest crystallization temperature, narrow band gap, high carrier mobility, relatively simple technology of high purity single crystals with high structural perfection and good homogeneity of electrical parameters show good promise of this material for many potential applications. Currently indium antimonide is used in field effect transistors with fast response and low power consumption which is important for digital devices [
Analysis of advertizing announcements [
The epiready indium antimonide wafer technology is developed quite poorly in Russia and its implementation requires profound studies of individual mechanical properties of this semiconductor compound that differ significantly from those of other A^{III}B^{V} semiconductors. Single crystal calibration and dicing operations, mechanical and chemomechanical treatment of wafers are lowtemperature processes which still affect the final product quality (wafers) and hence influence the product yield [
The trend to increase single crystal diameter (and hence wafer diameter) is common for all the A^{III}B^{V} semiconductors due to the permanent growth of opto, micro and nanoelectronics markets. The structural perfection and geometry requirements to the wafer surface are increasingly stringent. Therefore improving the mechanical and chemomechanical treatment processes for largediameter wafers requires authentic data on the depth and structure of the damaged layer and the geometry of the wafers after each treatment step, as well as their dependence on the process parameters and intrinsic properties of specific materials.
An important specific feature of indium antimonide is its extreme brittleness which complicates any chemomechanical treatment of the crystals, causing cracks and eventual destruction. This problem is aggravated for large diameter crystals. It originates from thermal elastic stresses induced during crystal growth and subsequent cooling. In [100] InSb crystals the axial temperature gradient near the crystallization front is large, reaching 35–40 deg/cm [
The aim of this work is to study the effect of different mechanical treatment types (cutting, grinding and etch polishing) on the strength of undoped single crystal indium antimonide wafers.
We grew indium antimonide single crystals using a twostage Czochralsky process in static vacuum [
To measure the electrical parameters and the dislocation density of the crystals we cut out (100) wafers perpendicular to the growth axis from the top and bottom parts of the crystals.
For dislocation pit etching we ground the wafers sequentially with M14 and M7 powders and chemically etched first in CP4 polishing etchant and then in HCl_{conc.} : H_{2}O_{2} = 2 : 1 selective etchant for 5 min [
We monitored the dislocation density distribution under an optical microscope and counted etch pits following the dislocation density measurement method for InSb crystals, i.e., by taking nine fields located within two diameters arranged at a 90 arc deg angle relative to each other [
We measured the electrical parameters of the undoped indium antomonide single crystals using the Van der Pau method [
The 77 K carrier concentration in the asgrown crystals was 2∙10^{14}–3∙10^{15} cm^{3}, the electron mobility being at least 2∙10^{5} cm^{2}/(V∙s). These figures agree with those for undoped indium antimonide.
We calibrated the cylindrical part of the crystal on an OD grinding machine to ∅ 50.8 mm and then oriented it on an Xray diffractometer to exactly locate the (100) planes. Then we placed the crystal into a wire cutting machine and cut it into ~830 mm thick wafers. After cutting we rinsed the wafers in a water solution of washing agents, dried and took samples for mechanical strength tests and control of damaged layer parameters.
For the mechanical strength tests we used the plane transverse bending method [
Figure
For the threepoint loading pattern (Fig.
${\sigma}_{\mathrm{max}}=\frac{1,5pl}{b{h}^{2}}$, (1)
where p is the load in kg, and l, b and h are the linear dimensions (length, width and thickness) of the specimen, respectively, in mm.
For the fourpoint loading pattern (Fig.
$\mid {\sigma}_{\mathrm{max}}=\frac{pl}{b{h}^{2}}$, (2)
To measure the mechanical strength with the plane transverse bending method we cut the wafers into rectangular specimens 3–14 mm in length, 1–6 mm in width and 0.5–0.8 mm in thickness. Then we ground the specimens with M7 powder and treated with CP4 polishing etchant. Thus we made 4 specimen batches ~25 specimens in each which differed by surface treatment type (ascut, asground, aspolished and asground + polished) and mechanically tested each batch with the plane transverse bending method. The specimen load was from 0.25 to 2 kg. The yield strength (brittle fracture stress) formula used was as follows:
${\stackrel{~}{\sigma}}_{\mathrm{av}}=\frac{1}{n}\sum _{i=1}^{i=n}{{\sigma}_{\mathrm{max}}}_{i}$, (3)
where n is the number of specimens.
The RMS measurement error was calculated as follows:
$\Delta {\stackrel{~}{\sigma}}_{\mathrm{av}}=\sqrt{\frac{{\sum}_{i=1}^{n}{\left({\sigma}_{{\mathrm{max}}_{i}}{\stackrel{~}{\sigma}}_{\mathrm{av}}\right)}^{2}}{n1}}$. (4)
Along with the strength we measured the surface roughness parameters R_{a} and R_{z} for differently treated surfaces of the remaining parts of the wafers using contact profilometry [
Surface roughness is defined as the total unevenness of the surface measured with relatively small steps. In order to differentiate between surface roughness and other unevenness having a relatively large scale (shape deviation and waviness), roughness is measured within a relatively small area the length of which is referred to as the base length. Surface roughness is evaluated from unevenness profiles obtained by specimen surface sectioning with a plane. Example of a surface roughness profile is shown in Fig.
– R_{а}: arithmetical mean of absolute values of profile deviation within the base length, mm;
– R_{z}: sum of average absolute values of heights for five highest profile peaks and depths for five deepest profile valleys within the base length, mm;
– R_{max}: highest profile unevenness within the base length, mm [
Specimen loading patterns ((a) threepoint and (b) fourpoint) and bending moment curves for plane transverse bending method.
The plane transverse bending strength test method is destructive and does not allow reusing the specimens. Each test specimen batch included 25 rectangular specimens with 10×5×0.8 mm dimensions. The first batch specimens were ascut, those of the second batch were asground, the third batch consisted of aspolished specimens and the fourth one consisted of asground + polished specimens. All the four rectangular specimen batches were plane transverse bent, with the fracture stress increasing as we changed from rough treated specimens to finer treated ones.
Figure
As can be seen from Fig.
Figure
By way of comparison we measured the mechanical strength of ascut and asground + polished specimens of lowdoped GaAs (n = 2∙10^{16} cm^{3}) with the (100) orientation using the threepoint loading pattern. The polishing etchant composition for the GaAs specimens was H_{2}O : H_{2}O_{2} : H_{2}SO_{4} = 1 : 1 : 3. Figure
The data illustrated in Fig.
The strength of GaAs does not depend on mechanical treatment so critically but sequential removal of damaged layers is still a necessary condition for the production of undamaged surfaces and hence highquality device structures. This is confirmed by our wafer surface roughness data (see below).
Figure
As follows from Figs
We also measured the surface roughness of the (100) InSb wafers ascut, asground and after the full mechanical treatment cycle. For comparison we also measured the roughness of GaAs wafers. The Table
The data summarized in the Table
Yield strength of (100) single crystal indium antimonide specimens after different types of mechanical treatment: (a) threepoint loading pattern; (b) fourpoint loading pattern
Wafer treatment type  

Ascut  Asground  Asground + polished  
R _{a}, mm  R _{z}, mm  R _{a}, mm  R _{z}, mm  R _{a}, mm  R _{z}, mm 
InSb  
0.6  3  0.4  2.6  0.04  0.17 
0.7  3.2  0.4  2.3  0.03  0.13 
0.6  3.1  0.4  2.4  0.03  0.12 
0.6  3  –  –  0.04  0.15 
0.6  3.5  –  –  0.05  0.18 
GaAs  
0.3  2.4  0.4  1.8  0.16  0.8 
0.4  2.3  0.4  1.8  0.14  0.7 
0.4  2.4  0.4  1.9  0.19  0.8 
0.5  2.4  0.4  1.7  0.19  0.9 
Yield strength of (111) single crystal indium antimonide specimens after different types of mechanical treatment for threepoint loading pattern [21]
The strength of thin (100) single crystal undoped indium anitmonide wafers was studied using the plane transverse bending method. The strength of the wafers (≤ 800 mm in thickness) proved to depend on their treatment. Separate grinding and etching increase the strength of the wafers but slightly. The full mechanical treatment cycle with etching in CP4 fast polishing etchant that etches microcracks and surface defects faster than the crystal matrix increases the strength of the InSb wafers twofold (from 3.0 to 6.4 kg/mm^{2}). The dependence of wafer strength on mechanical treatment type for the (100) wafers is similar to the respective dependence for the (111) wafers but the strength of the (111) wafers is twice as high as that of the (100) wafers (6.2 kg/mm^{2}).
The roughness of the wafers after different mechanical treatment stages was studied using contact profilometry. After the full mechanical treatment cycle the roughness of the InSb wafers decreased substantially (R_{a} from 0.6 to 0.04 mm) causing general surface smoothening.
The strength and roughness of the InSb wafers were compared with those of GaAs wafers. The strength of the ascut GaAs wafers (6 kg/mm^{2}) is twice as high as that of the ascut InSb wafers (3 kg/mm^{2}) and increases but slightly as a result of the full mechanical treatment cycle. The roughness of the GaAs and InSb wafers after the full mechanical treatment cycle decreases substantially: by 10 times for InSb due to general surface smoothening and by 3 times for GaAs (R_{z} from 2.4 to 0.8 mm) due to a reduction of the peak roughness component.
Thus the full mechanical treatment cycle of InSb wafers increases their strength and reduces their surface roughness by removing the damaged layers through the sequence of operations and reducing the risk of mechanical damage development.