Wear of single crystal silicon as a function of surface roughness

With increasing activities on micro electro-mechanical systems (MEMS) type microactuators, there is a growing need in understanding the tribological properties of silicon, the most commonly used wafer material for those devices. In particular, it is of interest if single crystal silicon used in microactuators exposed to rather low vertical loads is subject to wear. Therefore, wear tests using monocrystalline silicon on both sides of the tribological interface were conducted.A classic way to measure wear on sliders in contact with a tape or a rotating disk is to create an imprint using a Berkovich diamond tip mounted on a picoindenter. However, in our case we used a different approach. We created three studs on a slider’s surface by recessing the material outside the studs through an ion milling process. During the wear tests, the studs wore off. By measuring the remaining stud height, the wear volume could be determined at any point in time. The tests were performed on a pin on disk tester with a gimbaled slider to realize a flat on flat contact and a rather low normal force of 30 mN.     

Lowering friction coefficient under low loads by minimizing effects of adhesion force and viscous resistance

Conditions (normal load, sliding speed, ambient conditions, and material) to obtain the lower friction coefficient were studied by measuring the friction and pull-off forces between a metal pin (copper or gold) and a plate (steel or single crystal silicon). First, a pin was rubbed against a plate under a normal load between −12 and 870 μN at a sliding speed between 0.012 and 9.6 μm/s. The friction force was measured during reciprocating sliding motion. The pull-off force was measured before and after each friction force measurement. All the force measurements were taken in high vacuum at 10⁻⁵ Pa, dry argon at 1 atm, and ambient humid air of 38 and 60% relative humidity. Then, the friction coefficient was calculated by dividing friction force by the sum of normal load and pull-off force. In high vacuum, when a copper pin was rubbed against either a silicon or steel plate, the friction coefficient decreased to less than 0.05 with decreasing sliding speed. The effect of sliding speed on the friction coefficient suggests that under a low normal load the viscous resistance of liquid contributed to the friction force. When a gold pin was rubbed against a silicon plate, the friction coefficient was not affected by sliding speed.     

Research on the fretting wear behavior of silicon wafers before and after carbon ions implantation

Carbon ions with different doses of 2×10¹⁵ and 2×10¹⁶ ions/cm² were implanted into single crystal silicon wafers under an energy level of 80 keV. The nanohardness and elastic modulus of silicon wafers were studied on the nano-mechanical testing system. The fretting wear tests were performed on the UMT-2 Micro-tribometer to evaluate the fretting wear resistance of C⁺ implanted silicon wafer and to investigate its micro-tribological properties. The results demonstrate that the nanohardness and elastic modulus of silicon wafer with dose of 2×10¹⁵ ions/cm² decreased and those of 2×10¹⁶ ions/cm² changed little. Implanted silicon wafer with dose of 2×10¹⁶ ions/cm² had much lower coefficient of friction and wear volume under low loads, which suggests a significant effect of friction-reducing and anti-wear. The results also indicate that abrasive wear was the main wear mechanism for both virgin silicon and C⁺ implanted silicon with dose of 2×10¹⁵ ions/cm². However, adhesive wear played a significant role in the wear mechanism of the C⁺ implanted silicon with dose of 2×10¹⁶ ions/cm² under the low loads, while the abrasive wear dominated the wear mechanism under high loads.     

Fretting on the cubic face of a single-crystal Ni-base superalloy at room temperature

Fretting experiments were conducted on the (1 0 0) crystal (cubic) face of a single crystal Ni-base superalloy in two directions, 〈1 0 0〉 and 〈1 1 0〉, to study the effect of crystallographic orientation on the fretting response in both partial slip and gross slip regimes. The study involved point contacts using a tungsten carbide (WC) ball with radius 10 mm tested at room temperature. Ball indentation was used to determine secondary crystallographic orientations. Under sufficiently high normal force, the friction on the cubic face in the 〈1 1 0〉 direction was larger than in the 〈1 0 0〉 direction. This difference can be explained by the extent of plastic deformation in the surface layer and associated microstructure changes, both of which depend on the coupling between the crystallographic orientation and the cyclic deformation field.     

High load AFM friction and wear experiments on V2O5 thin films

High load friction and wear experiments by means of atomic force microscopy were carried out at the surface of highly (0 0 1) oriented vanadium oxide V₂O₅ thin films deposited on silicon by reactive magnetron sputtering. Microscopic friction coefficient was estimated for wide range of loads. The nature of surface wear due to multiple, high load scanning is presented and discussed.     

Effects of Anisotropy and Substrate Shape on Atomic Friction Force in Two-Dimensional Model

Understanding the effects of anisotropy and substrate shape on atomic friction force is critically needed for the designed development of nanoscale friction devices. The simulation of atomic force microscope on various substrate shapes using the 2D Prandtl–Tomlinson model is investigated in the framework of three representative surface lattices: \({\hbox {MoS}}_2\), NaCl and highly oriented pyrolytic graphite surfaces. The results show that the lateral force map reveals a significant contrast between different surface lattice shapes yielding lattice rows which differ from their neighboring ones. Careful analysis of the friction force during the individual friction scanning revealed that the friction forces over the narrow maxima domains were lower than those over the narrow wells domains. Depending on crystal orientation and the potential shape, variations in the frictional force can also be seen in the simulations. It has been numerically observed that frictional force depends on the crystal orientation as well as on the shape of the substrate potential. Velocity dependence of the kinetic friction force has the form of a power law \(F_{k}-F_{k0}={\hbox {cst}} \, v_{\mathrm{s}}^{2/3}\), for small scanning velocities. The effects of the shape parameter r on this law have been shown.     

Dry wear and friction properties of an A356/SiC foam interpenetrating phase composite

The dry sliding wear and friction behaviors of A356 aluminum alloy and a hybrid composite of A356 aluminum alloy and silicon carbide foam in the form of an interpenetrating phase composite were evaluated using a ball-on-disk apparatus at ambient conditions. The stationary 6.35 mm alumina ball produced a wear track (scar) diameter of 7 mm on the rotating specimen surface. Three different loads; 5 N, 10 N and 20 N were applied at a constant sliding speed of 33 mm/s for both materials. Wear tracks were characterized with a scanning electron microscope and measured with an optical surface profilometer. In general, this novel A356/SiC foam composite reduced the friction coefficient and wear rate from that of the base alloy for all loading conditions. In addition, as the load increased, the friction coefficient and wear rate decreased for both materials. The results indicate the composite could be used in light-weight applications where moderate strength and wear properties are needed.     

干摩擦和水润滑条件下单晶硅的摩擦磨损性能研究

在UMT-2微摩擦试验机上,对单晶硅片进行了干摩擦和水润滑两种状态下的摩擦磨损试验,分析讨论了载荷和滑动速度对单晶硅片的摩擦因数和磨损率的影响规律;运用扫描电子显微镜,观察和分析了其磨损表面形貌。结果表明:干摩擦条件下的磨损机理主要表现为黏着磨损,水润滑条件下的磨损机理主要表现为机械控制化学作用下的原子/分子去除过程;水润滑条件下的摩擦因数和磨损量均较小,最小磨损率仅为10μm3/s;在水润滑条件下,载荷和滑动速度达到一定值时,硅片表面将发生摩擦化学反应,生成具有润滑作用的Si(OH)4膜,即机械作用在一定条件下对化学反应具有促进作用。     

A three-point-probe method for measuring resistivity and the Hall coefficient using Hall devices with minimal design complexity

A novel empirical method for express measurement of resistivity and the Hall coefficient, i.e. the sign, the concentration and the bulk mobility of the majority carriers in semiconductor (silicon) wafers is presented and tested. This approach is based on the parallel-field Hall devices with minimal design complexity containing only three contacts–two input and one (Hall) output. The unique simplicity of this three-point-probe method, the lack of numerical coefficients’ calculation and particular requirements for the geometrical dimensions, probe spacing, wafer form, etc. allows to obtain the necessary information following experimentally clear and technically reproducible steps. The data obtained from non-structured n- and p-type silicon wafers at carrier’s concentration of 10¹⁵ ? n; p ? 10¹⁶ cm⁻³ by appropriate probe arrangements corroborate very well with the results from wafers’ certificates and the results obtained using common measurement techniques. The error does not exceed 5–6% which is about the same as the accuracy of other approaches used for this purpose. The results are especially promising in IC fabrication and complementing the classical Van der Pauw method.     

Effects of support method and mechanical property of 300 mm silicon wafer on sori measurement

This paper describes the effects of support methods and mechanical properties of 300 mm silicon wafer on sori measurement. A new supporting method, named three-point-support method, used in the sori measurement of a large diameter silicon wafer was proposed in this study to obtain a more stable measuring process. The wafer was supported horizontally by three steel balls on the vertexes of a regular triangle at the wafer edge. The measuring repeatability and anti-disturbance ability were compared between the proposed method and the conventional one-point-support method, in which the wafer is supported with a small-area chuck at the wafer center. The effects of friction between the supports and wafer surface for the three-point-support were also estimated. Finally, the influences of different mechanical characteristics at the front and back surfaces and the crystal orientation on sori measurement were investigated.     

改进微静电马达的摩擦与磨损

在微观结构中,摩擦及磨损严重地影响着部件的力学性能和可能性不同材料的摩擦系数相差很大,多晶硅和多晶硅之间的静摩擦系数约４．９,多晶硅和单晶硅之间的静摩擦系数约０．４８￣０．２８,动摩擦系数约０．３５￣０．２０,材料表面的粗糙度对摩擦系数影响也很大。鉴于此,提出了一种单晶硅台面结构晃动微马达,取代多同机械工艺制作的多晶硅法兰盘。它具有机械强度高、摩擦系数、抗磨损、不塌陷等优点,马达的轴也加工成实心轴     

Atomic-scale anisotropy of nanoscratch behavior of single crystal iron

In this paper a parallel molecular dynamics (MD) model has been developed to investigate the nanoscratch process of single crystal iron. The simulations were performed for two cases with different crystallographic orientations and scratch directions. In Case I the scratch plane is (1 0 0) and the scratch direction is [0 0 1]. In Case II the scratch plane and the scratch direction are (1,−1,2) and [1 1 1], respectively. To validate the MD simulation the nanoscratch testing was conducted using the TriboIndenter. The simulation results reveal that the vertical force and the lateral force tend to increase with the scratch displacement for both cases. Case I has smaller forces than Case II. However, the coefficient of friction for both cases is similar, which is in good agreement with the experimental value. The crystallographic orientation also affects the scratch hardness. The scratch hardness of Case I is smaller than that of Case II.     

On the surface and tribological characteristics of burnished cylindrical Al-6061

Surface treatment is an important aspect of all manufacturing processes to impart specific physical, mechanical and tribological properties. Burnishing process is a post-machining operation in which the surface irregularities of the workpiece are compressed by the application of a ball or roller. In the present study, simple and inexpensive burnishing tools, with interchangeable adapter for ball and roller were designed and fabricated. Ball burnishing processes were carried out on aluminium 6061 under different parameters and different burnishing orientations to investigate the role of burnishing speed, burnishing force and burnishing tool dimension on the surface qualities and tribological properties. The results showed that burnishing speed of 330 rpm and burnishing force of 160 N produce optimum results. Meanwhile, a decrease in the burnishing ball diameter leads to a considerable improvement in the surface roughness up to 75%. On the other hand, parallel burnishing orientation exhibits lower friction coefficient compared to cross-burnishing orientation. Furthermore, ball burnishing process is capable of improving friction coefficient by 48% reduction and weight loss by 60-80% reduction of burnished surface of aluminium 6061. These findings are further supplemented by the surface features as seen in SEM photomicrographs.     

The influence of phase transformations and oxidation on the galling resistance and low friction behaviour of a laser processed Co-based alloy

The effect of oxide formation on the tribological properties of a CO₂-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions in air and in an oxygen free environment. The tests were carried out by sliding two identical specimens against each other in a load-scanning test. A friction coefficient at a level of about 0.20 was observed for both test environments. However, the wear of the Co base material is accelerated when the sliding is performed in an oxygen free environment. The friction level appears to be controlled by the shearing of hcp {0 0 0 1} planes rather than by the presence of an oxide layer.     

掩模偏转方向对硅尖形状影响的研究

为制备高纵横比的纳米硅尖,研究了掩模的偏转方向对硅尖形状的影响。设计了硅尖制备的工艺流程,采用KOH溶液湿法各向异性腐蚀制备硅尖,将实验和{411}晶面模型相结合,分析了硅尖的成型机理,讨论了掩模偏转方向对硅尖形状的影响,得到制备高纵横比纳米硅尖的工艺参数。实验结果表明：硅尖侧壁是由与(100)面夹角为76.37°的{411}晶面组成;利用正方形掩模的偏转,可以制备出八面体和四面体的硅尖。当正方形掩模边缘沿<110>晶向时,在78℃、浓度40%的KOH溶液中腐蚀的硅尖,经980℃氧化削尖,可以得纵横比大于2的八面体纳米硅尖阵列。     

Frictional Properties of a Mesoscopic Contact with Engineered Surface Roughness

Friction between titanium spheres and an artificially structured silicon surface was measured with a friction force microscope. Two spheres with radii of 2.3 μm and 7.9 μm were firmly glued to the tip of the microscope cantilever. A periodic stripe pattern with a groove depth of 26 nm and systematically increasing groove width from 500 nm to 3500 nm was fabricated from a silicon wafer with a focused ion beam. The sphere substrate friction coefficient shows a strong enhancement at a certain groove periodicity, which is related to geometrical interlocking of the two surfaces. This shows that careful modification of the surface roughness can help to control the tribological behavior of mesoscale contacts.     

Study on solid lubricant properties of carbon onions produced by heat treatment of diamond clusters or particles

Tribological properties of carbon onions prepared by heat treatment of diamond clusters or particles are presented. Diamond clusters used as the source material are heated with an infrared radiation furnace to 1730 °C in argon at atmospheric pressure. As a result of heating at 1730 °C for 1 min, diamond clusters are transformed into carbon onions. High resolution TEM observation is employed to confirm the formation of carbon onions that have near-spherical and multi-layered concentric structure. The particle size of these carbon onions ranges from 5 to 10 nm that corresponds to the original size of the diamond clusters. This preparation technique is also applied to diamond particles less than 0.5 μm in diameter to produce larger carbon onions. Tribological properties of the carbon onions are examined by ball-on-disc type friction testing using a silicon wafer and a steel ball. Carbon onions, which are spread on the silicon wafer without adhesive, exhibit stable friction coefficients lower than 0.1 both in air and in vacuum at room temperature. The wear rates of steel balls sliding on the silicon wafer on which carbon onions are distributed are much lower than wear rates for sliding on a wafer over which graphite powder is spread. Moreover, it is found that the larger carbon onions prepared from diamond particles show low friction property on the rough surface of silicon discs.     

Studies of chipping mechanisms for dicing silicon wafers

The purpose of this study was to investigate the chipping modes produced in the die edges of dicing silicon wafer using the thin diamond blades. The effects of dicing directions and different wafer types on the chipping size were studied. Furthermore, scratching tests were also used to assist the analysis of studying chipping conditions of the silicon wafer. The experimental results showed that the trace behaviors produced by the diamond indenter in the scratching test of silicon wafer can be divided into the three stages: rubbing, plastic deformation, cracking. The plastic pile up and crack of the scratching traces on the wafer mainly propagate along the development of the easiest slip direction family <110>. The chipping modes produced in dicing silicon wafer can be broadly classified as four types: (1) 30° chipping; (2) 60° chipping; (3) 90° chipping; (4) irregular chipping, which causes these mechanisms of chipping modes due to the meeting between the radial cracks of 30°, 60°, and 90° along the easiest slip direction family <110> and the lateral cracks along the easiest cleavage plane family {111}. When using the thin diamond blade diced on the (111) silicon wafer along the $ {\left[ {\overline{1} 10} \right]} $ direction, the size of top chipping produced was smaller than that of along the $ {\left[ {11\overline{2} } \right]} $ direction. Besides, for the (100) plane of silicon wafer, the size and the distribution of the chipping modes produced along the $ {\left[ {\overline{1} 10} \right]} $ and $ {\left[ {\overline{1} \overline{1} 0} \right]} $ directions were similar.     

On dry sliding friction and wear behaviour of PEEK and PEEK/SiC-composite coatings

In this work, polyetheretherketone (PEEK) and PEEK/SiC-composite coatings were deposited on Al substrates using a printing technique to improve their surfaces performance. The objective of this work was to investigate coatings friction and wear behaviour. Especially, the effect of sliding velocity and applied load on coatings friction coefficient and wear rate was evaluated in range of 0.2-1.4 m/s and 1-9 N, respectively. Compared to Al substrate, the coated samples exhibit excellent friction coefficient and wear rate. For PEEK coating, under an applied load of 1 N, the increase in sliding velocity can result in decreasing of friction coefficient at a cost of wear resistance. Under a load of 9 N, however, PEEK coating exhibits the highest friction coefficient and wear rate at an intermediate velocity. These influences appear to be mainly ascribed to the influence of contact temperature of the two relative sliding parts. In most test conditions, the composite coating exhibits better wear resistance and a little higher friction coefficient. SiC reinforcement in composite coating plays a combined role. First of all, it might lead to energy dissipation for activation of fracture occurred on the interface of PEEK and the powders. Moreover, it can reduce coating ploughs and the adhesion between the two relative sliding parts.     

Friction and Wear Characteristics of Single Crystal Ni-Based Superalloys at Elevated Temperatures

The purpose of this study was to investigate the friction and wear behavior of single crystal superalloys at elevated temperatures. Pin-on-plate experiments were conducted using a custom-built high-temperature fretting/wear apparatus. Measurements were performed on two single crystal Ni-based alloys and Waspaloy^® (used as a baseline material). The coefficient of friction for the single crystal materials (i.e., during running-in and steady state) was lower compared to the Waspaloy^®. In addition, the experiments showed that the friction coefficient of the single crystal is dependent on the crystallographic plane; the friction coefficient was lower for the tests on the {100} plane compared to the {111} plane. The wear behavior was aligned with the friction behavior, where the single crystal Ni-based alloys showed slightly higher wear resistance compared to the Waspaloy^®. Ex situ analysis by means of FIB/SEM and XPS analysis revealed the formation of Co-base metal oxide layer on the surface of the single crystal alloy. Similarly, a Co-base oxide layer is observed on the counterface providing a self-mated oxide-on-oxide contact and thus lower friction and wear compared to the Waspaloy^®.