Chemical Mechanical Polishing Treatment Research Articles

Micro-cones Cu fabricated by pulse electrodeposition for solderless Cu-Cu direct bonding

In the post-Moore’s era, Cu-Cu direct bonding has garnered significant attention as a promising alternative to solder joints for chip interconnection in advanced electronic packaging technology. Its advantages lie in reduced process restrictions and steps, as well as lower bonding temperature, which align with the demands for low cost and high compatibility. In this study, (110)-oriented micro-cones Cu was fabricated via template-free pulse electrodeposition, enabling solderless Cu-Cu direct bonding at 250 ℃ under three distinct bonding pressures without chemical mechanical polishing (CMP). The contact bonding area and shear strength gradually increased corresponding to the applied bonding pressure. Seamless bonding interface was achieved under high bonding pressure, leading to high shear strength of 116.4 MPa for Cu-Cu bonding joints. The obtuse polygon pyramid micro-cones, characterized by an enlarging cross-sectional area from apex to base, coupled with inherent mechanical properties, induce high applied stress at micro-cone’s tip and a low yield stress, facilitating the initiation and propagation of plastic deformation during the bonding process. This study has demonstrated the feasibility of utilizing the micro-cones Cu for low-temperature bonding without CMP treatment, offering valuable insights into the advanced interconnection technologies.

The effect of chemical-mechanical processing of silicon wafers on their surface morphology and strength

The mechanical strength of various silicon wafers with a thickness of 100 μm has been studied, depending on the methods of their preparation and the modes of their subsequent grinding or polishing, including chemical-mechanical (HMP). The plates were loaded using the ring-to-ring method, the magnitude of stresses and deflection under the small ring was determined by the finite element method. For all the samples studied, the profiles and roughness parameters of the plates were obtained by stylus profilometry and atomic force microscopy (AFM) when scanning the surface along the baseline and over the area. A direct correlation was found between the strength of the plates and the characteristic parameters of their surface profile (the average values of the magnitude and period of fluctuations in the height of the irregularities). Keywords: silicon wafer, strength, chemical-mechanical polishing treatment, surface morfology.

Oxygen partial pressure controlling epitaxy of CuGaO2 and CuGa2O4 films on β-Ga2O3 substrate by reactive deposition epitaxy

Single-oriented pure phase CuGaO2 and CuGa2O4 films have been successfully grown on β-Ga2O3 (2¯01) substrate by reactive deposition epitaxy at different oxygen partial pressures. Oxygen partial pressure-controlled mass-transport of Cu atoms is the dominant controlling parameter for CuGaO2 and CuGa2O4 growth. As the oxygen partial pressure increases, the amount of Cu atoms diffused in to the substrate surface under the control of mass-transport increases gradually and the Cu/Ga atomic ratio involved in the reaction progressively decreases, resulting in the product changing from CuO and CuGaO2 to CuGa2O4. After Chemical-mechanical Polishing (CMP) treatment, the CuGaO2 and CuGa2O4 films show pure phase with narrow full-width half-maximum (FWHM) according to high-resolution X-ray diffraction (HR-XRD). In addition, the transmission electron microscopy (TEM) results indicated better interface quality and epitaxial relationship between Cu-Ga-O films and β-Ga2O3 substrate. The smooth surface of Cu-Ga-O films can be obtained after CMP treatment which is confirmed by atomic force microscopy (AFM) results. It presents a feasible route to prepare β-Ga2O3-based heterojunction via reactive deposition epitaxy to expand the application of β-Ga2O3 in ultraviolet detection and power devices.

Effect of Surface Treatment by Chemical-Mechanical Polishing for Transparent Electrode of Perovskite Solar Cells

Perovskite solar cells (PSCs) are usually fabricated by using the spin coating method. During the fabrication process, the surface status is very important for energy conversion between layers coated in the substrate. PSCs have multilayer-stacked structures, such as the transparent electrode layer, the perovskite layer, and a metal electrode. The efficiency and uniformity of all layers depend on the surface status of the transparent electrode coated on the glass substrate. Until now, etching methods by chemical processes have been introduced to make the substrate surface smooth and uniform by decreasing surface roughness. However, highly reactive chemical treatments can be harmful to the environment. In this study, we employed an eco-friendly chemical-mechanical polishing (CMP) process to ensure the fluorine-doped tin oxide (FTO) substrate is treated with a smooth surface. Before the perovskite layer and electron transport layer (ETL) are applied, the TiO2 layer is coated with the FTO substrate, and the surface of the FTO substrate is polished using CMP. As a result, the CMP-treated surface of the FTO substrate showed a smooth surface, and the PSCs with CMP treatment did not require conventional TiCl4 treatment.

Chemical Mechanical Polishing Implementation for Corrosion Prevention of Titanium Bio-Implants

Corrosion and surface film dissolution are two mechanisms for titanium-based bioimplants to release ions into the human body and hence degrading the biocompatibility. Electrochemical methods are commonly practiced in testing metallic biomaterials in-vitro measurements[1] (Kuhn, Neufeld and Rae, 1988). In an attempt to prevent the in-vivo corrosion of the titanium implants, we have introduced a new approach by utilizing chemical mechanical polishing (CMP) as a synergistic approach to form a protective surface film and as a tool to control the surface nanostructure [2] to promote or demote cell attachment. In this paper, application of CMP on titanium implant surfaces is studied through electrochemical analyses in the absence and presence of an oxidizer. Corrosion rates are extrapolated from anodic polarization of the potentiodynamic curves (Figure 1) with and without CMP implementation to compare the affect of surface engineering. It was observed that the higher corrosion (Table 1) rates correlated to the higher material removal during polishing, which can be controlled through oxidizer concentration that affects the surface TiO2 film growth. Furthermore, potentiostatic measurements showed that the addition of oxidizer increased the rate of oxide growth and decreased the surface current density levels indicating that the surface self-passivation took place. Post CMP contact angle (wettability) and AFM measurements confirmed an improved surface topography and surface homogeneity by CMP treatment as better surface smoothness and wettability control was achieved. [1] Kuhn, A., Neufeld, P. and Rae, T. (n.d.). Synthetic Environments for the Testing of Metallic Biomaterials. The Use of Synthetic Environments for Corrosion Testing, 1988, pp.79-79-19. [2] Ozdemir, Z., Ozdemir, A. and Basim, G. (2016). Application of chemical mechanical polishing process on titanium based implants. Materials Science and Engineering: C, 68, pp.383-396. Figure 1

Chemical Mechanical Polishing and Direct Bonding of YAG

Current limitations in both single crystal and polycrystalline (ceramic) solid state laser technologies for high power applications stem from thermal effects that cause degradation in both lasing efficiency and beam quality. YAG and Y2O3 have favorable material properties for producing these high power lasers. We demonstrate chemical mechanical polishing (CMP) processes for YAG and Y2O3 resulting in smooth surfaces, (< 1 nm RMS roughness), defect free, and subsequently suitable for direct bonding. The CMP process has been used in conjunction with surface activation to form single crystal YAG-YAG and polycrystalline Y2O3-Y2O3 bonded elements showing a proof of concept for the fabrication of composite laser elements. YAG single crystals were successfully polished with a 70-nm colloidal silica solution containing NaOH (pH 9.9). X-ray photoelectron spectroscopy measurements provided insights to the chemical impact of the NaOH. After NaOH exposure, YAG showed complete removal of Al from tetrahedral sites and a change in the Y3/2 and Y5/2 peak area ratios, indicating that the surface of YAG was sufficiently modified to allow the silica particles to abrade the byproduct surface layer. The final surface roughness after polishing was measured at 0.1 nm RMS roughness with no scratches deeper than 0.3 nm. YAG single crystals were also polished with a 70-nm Al2O3 slurry containing NaOCl (pH 11.4), however AFM measurements showed that the surface produced, 0.5 nm RMS roughness with no scratches deeper than 6.0 nm, was not as good as polishing with the colloidal silica slurry which was attributed to the effect of the chemical action of NaOH with the YAG surface. Polishing polycrystalline Y2O3 required a slurry with less aggressive chemical reactions, so the NaOCl/Al2O3 slurry was used to successfully polish the substrates to RMS roughness values of 0.5 nm and scratches no deeper than 1.0 nm. Triple axis diffraction rocking curves and double crystal x-ray diffraction imaging were used to demonstrate that the CMP process also removed subsurface damage that was present in the as-supplied material. The triple axis technique was also successfully employed for the first time to demonstrate that the polycrystalline Y2O3 subsurface damage was also significant reduced after the CMP process. After CMP and surface treatment, YAG-YAG and Y2O3-Y2O3 were bonded together and annealed at 1425 °C with no applied pressure. Cross section and plan view high resolution transmission electron images of the YAG-YAG bonded interface revealed a defect free bonding interface. Light transmission measurements showed that 90% of the interface area was bonded at room temperature contact and was further strengthened with annealing at 1425 °C for 72 hours. These conditions possess a much lower thermal budget than those previously shown to be required to bond YAG without a CMP step. The CMP and surface treatment processes that have been developed are applicable towards the creation of solid state laser composite elements and enable further progress and development for high power laser applications.

Development of a novel non-contact inspection technique to detect micro cracks under the surface of a glass substrate by thermal stress-induced light scattering method

Fine polishing techniques, such as a chemical mechanical polishing treatment, are important techniques in glass substrate manufacturing. However, these techniques may cause micro cracks under the surface of glass substrates because they used mechanical friction. A stress-induced light scattering method (SILSM), which was combined with light scattering method and mechanical stress effects, was proposed for inspecting surfaces to detect polishing-induced micro cracks. However, in the conventional SILSM, samples need to be loaded with physical contact, and the loading point is invisible in transparent materials. Here, we introduced a novel non-contact SILSM using a heating device. A glass substrate was heated first, and then the light scattering intensity of micro cracks was detected by a cooled charge-couple device camera during the natural cooling process. Results clearly showed during the decreasing surface temperature of a glass substrate, appropriate thermal stress is generated for detecting micro cracks by using the SILSM and light scattering intensity from micro cracks changes. We confirmed that non-contact thermal SILSM (T-SILSM) can detect micro cracks under the surface of transparent materials.

The Novel Way to Inspection Technique for SiC Substrate by Applying Stress Effects

Silicon carbide (SiC) has attracted much attention as an important material for high temperature, high power and high frequency devices, because it has advantages compared to silicon (Si) devices. However, SiC substrates are made the same way with Si substrates in production manufacturing. In production site, fine polishing techniques, such as a chemical mechanical polishing treatment (CMP), are some of the most important base techniques used for the semiconductor manufacturing. Mechanical interaction in the form of friction occurs between the abrasive and the substrate surface during polishing, which may cause formation of latent flaws on the silicon carbide (SiC) substrate surface. Fine polishing-induced latent flaws may become obvious during a subsequent cleaning process if SiC substrates are corroded away by chemical interaction with the cleaning liquid. Latent flaws thus reduce product yield. Recently, many nondestructive inspection systems that use light scattering from foreign matter particles for their detection have been made commercially available for use in production sites. These systems use laser incident light and a photo-detector (e.g. a photomultiplier tube) for detecting light scattering from foreign particles with high sensitivity. Inspection systems based on Rayleigh scattering and Mie scattering can detect particles smaller than the laser wavelength. However, these systems detect all light scattering as foreign matter particles on the surface. Therefore, these system cannot discriminate between latent flaws and particles. In addition, these inspection techniques cannot detect defects under the surface of substrates. We propose a novel inspection technique for fine polishing-induced latent flaws by combining the light scattering method with stress effects, referred to as the stress-induced light scattering method (SILSM, Y. Sakata, et al, Review of Scientific Instruments, Vol. 85, No. 8, p. 083303-1 (2014)). In this method, samples are deformed by an actuator and stress effects are induced around the tips of latent flaws. Due to the photo elastic effect, the refractive index of the material around the tip of a latent flaw is changed. This changed refractive index is in turn detected by a cooled CCD camera as variations in the light scattering intensity. In this report, latent flaws under the surface of SiC substrate are detected non-destructively by applying SILSM, and the utility of SILSM will be evaluated as a novel inspection technique for the substrate. In addition, the results detected by SILSM is compared with the results of conventional laser raman spectrometry and photo-luminescence results, respectively. And latent flaws under SiC substrate surface is evaluated from various directions. This research was partially supported by AIST-AMRI budget for Exploratory Research and we gratefully acknowledged this budget with deepest appreciation.

Investigation on the surface treatments of CdMnTe single crystals

The surface quality of CdMnTe crystal plays an important role in the performance of CdMnTe nuclear radiation detectors. In this paper, the surfaces of CdMnTe samples treated by Mechanical Polishing (MP), Chemical Polishing (CP), Chemical–Mechanical Polishing (CMP), and CMP followed by CP treatment (CMP+CP) were investigated. The structural properties of CdMnTe surfaces were characterized by a High Resolution Scanning Electron Microscope (HRSEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The Circular Transmission Line Model (CTLM) was adopted to reveal the specific contact resistivity (ρc) of Au/CdMnTe contacts after various surface treatments. The AFM measurements shown an ultra-smooth surface was achieved after the CMP+CP treatment with the roughness value of 0.84nm, and the surfaces by MP, CP and CMP were with the roughness of 8.2nm, 5.1nm and 1.4nm, respectively. The XPS analysis indicated that the (Te+Te4+)/(Cd+Mn) ratios of the CdMnTe samples after the CMP+CP and MP treatment were 1.1 and 1.07 which are close to stoichiometric composition, while after the CP and CMP treatment were 2.00 and 1.40 which are enriched with Te. The CMP+CP treatment decreased the Te4+/(Te+Te4+) ratio from 7% in CMP to 1%, which reveals the surface with few Te oxides. The specific contact resistivity (ρc) was used to determine the ohmic characteristic of Au/CdMnTe contacts by the CTLM. The calculated ρc values of Au/CdMnTe contacts on the CP, CMP and CMP+CP treated surfaces are 383, 112 and 15Ωcm2, respectively.

Suppression of 3C-Inclusion Formation during Growth of 4H-SiC Si-Face Homoepitaxial Layers with a 1° Off-Angle.

We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed to decrease residual nitrogen incorporation. 3C inclusions were generated both at the interface between the substrate and epitaxial layer, and during epitaxial growth. 3C-SiC nucleation is proposed to trigger the formation of 3C inclusions. We suppressed 3C-inclusion formation by performing deep in situ etching and using a high C/Si ratio, which removed substrate surface damage and improved the 4H-SiC stability, respectively. The as-grown epitaxial layers had rough surfaces because of step bunching due to the deep in situ etching, but the rough surface became smooth after chemical mechanical polishing treatment. These techniques allow the growth of epitaxial layers with 1° off-angles for a wide range of doping concentrations.

Stress-induced light scattering method for the detection of latent flaws on fine polished glass substrates.

Fine polishing techniques, such as the chemical mechanical polishing treatment, are one of the most important technique to glass substrate manufacturing. Mechanical interaction in the form of friction occurs between the abrasive and the substrate surface during polishing, which may cause formation of latent flaws on the glass substrate surface. Fine polishing-induced latent flaws may become obvious during a subsequent cleaning process if glass surfaces are corroded away by chemical interaction with the cleaning liquid. Latent flaws thus reduce product yield. In general, non-destructive inspection techniques, such as the light-scattering methods, used to detect foreign matters on the glass substrate surface. However, it is difficult to detect latent flaws by these methods because the flaws remain closed. Authors propose a novel inspection technique for fine polishing-induced latent flaws by combining the light scattering method with stress effects, referred to as the stress-induced light scattering method (SILSM). SILSM is able to distinguish between latent flaws and particles on the surface. In this method, samples are deformed by an actuator and stress effects are induced around the tips of latent flaws. Due to the photoelastic effect, the refractive index of the material around the tip of a latent flaw is changed. This changed refractive index is in turn detected by a cooled charge-coupled device camera as variations in light scattering intensity. In this report, surface latent flaws are detected non-destructively by applying SILSM to glass substrates, and the utility of SILSM evaluated as a novel inspection technique.

Note: Detection of micro-cracks in the interlayer dielectric film by the stress based light scattering method

A phenomenon was discovered wherein light scattering strength from cracks increases when tensile stress is applied to micro-cracks produced in the interlayer dielectric film by chemical mechanical polishing treatment. It is likely that the change in light scattering intensity occurs because a region of high stress concentration (region with high variation in index of refraction) is produced near the crack tip due to stress, thus forming a type of scatterer. With this method, it is possible to detect only scatterers which respond to stress, and thus, it is possible to classify and separately detect cracks and particles.

Using Chemical-Mechanical Polishing for Planarizing a High-&lt;I&gt;κ&lt;/I&gt; Nanocomposite Polyimide Insulator for Organic Thin Film Transistors Application

To solve the large leakage current of the heavily blended nanocomposite (Polyimide and nano-TiO2 particles) gate dielectric film exhibiting a high-kappa, the chemical-mechanical polishing (CMP) was adopted to flatten the surface of the PI-TiO2 nanocomposite film. An extremely high dielectric constant (is congruent to 13) of the nanocomposite with CMP treatment is obtained and its leakage current is comparable to that of the neat polyimide in our studies. An OTFT based on the nanocomposite gate dielectric exhibiting high capacitance and a smooth surface after CMP treatment shows very promising performance. Compared with the OTFT based on the neat polyimide gate dielectric, the threshold voltage is improved from -22 to -5 (V), the sub-threshold voltage is decreased from 3.44 to 0.50 (V/dec), the current on/off ratio is increased from 1.6 x 10(6) to 3.53 x 10(8), and the mobility is increased from 0.416 to 0.624 (cm2V(-1)s(-1)). Moreover, it is worth noting that the hysteresis effect of OTFT based the nanocomposite can be significantly reduced due to the few charge trapped in the interface when the nanocomposite dielectric surface was further polished by CMP treatment.

Atomically controlled surfaces with step and terrace of β-Ga 2O 3 single crystal substrates for thin film growth

The surface of β-Ga 2O 3 (1 0 0) single crystal grown with floating zone method was treated by chemical–mechanical-polishing (CMP) for 30–120 min followed by annealing in oxygen atmosphere at temperature 600–1100 °C for 3–6 h. The evolution of the step arrangement was investigated with reflection high energy electron diffraction and atomic force microscopy. Atomically smooth surfaces with atomic step and terrace structure of β-Ga 2O 3 substrates were successfully obtained after just CMP treatment as well as CMP treatment and post annealing at 1100 °C for 3 h. The uniform step height was 0.57 nm, and smooth terrace width was 100 nm, where the misorientation angle was about 0.36°. The obtained atomically smooth surface provides a potential application for the high-quality epitaxial film growth.

Evaluation of Etch Behavior of Doped Silicon Wafer in Wet Cleaning Process

Determination of the silicon etch rate of a number of n- and p-type doped epitaxial silicon wafers with different crystal orientations, dopant types, and dopant levels have been made. Oxidation behavior of the silicon in solution is found to be affected by the doping level of the arsenic doped wafer. Observed variation in the removal rate of the chemical mechanical polishing (CMP) process for these doped silicon wafers is correlated with the etch rates. The surface quality of these wafers following CMP and standard clean chemical treatment is found to impact the defect level and cleanliness of the post-CMP cleaning process. Resistance to oxidation and chemical dissolution of silicon is explained by the generation of surface charge, charge transfer mechanism, etching anisotropy, and activation energy for surface reaction caused by the dopant and crystal orientation. Information obtained thereof is useful to develop the wafer-manufacturing process, starting from silicon crystal to the final clean substrate or epi wafer with low surface defects.

Evaluation of Etch Behavior of Doped Silicon in Wet Cleaning of Silicon Wafer

Recent increases in the demand for advanced discrete and power devices produced from low-resistivity heavily-doped wafer demand better understanding of the surface preparation for this type of silicon wafer. Production of these doped wafers with low surface defects require, among other things, etch behavior of the materials by the standard clean (SC1) solution of the wet cleaning process. Determination of the silicon etch rate of a number of N-type and P-type doped epitaxial silicon wafers with different crystal orientations, dopant types and dopant levels have been made. Furthermore, observed variation in the removal rate of the chemical mechanical polishing (CMP) process for these doped silicon wafers is correlated with the etch rates. The surface quality of these wafers following CMP and SC1 chemical treatment is found to impact the defect level and cleanliness of the post-CMP cleaning process. Information obtained thereof is useful to develop wafer manufacturing process starting from silicon crystal to the final clean substrate or epi wafer with low surface defect.

Gap-filling property of Cu film by chemical vapor deposition

The gap-filling property of Cu deposited by chemical vapor deposition was investigated in 1/4-μm-wide trenches and 1/4-μm-diam holes. Attention was paid to the influences on the gap-filling property of both substrate temperature and partial pressure of the source gas. At a low deposition temperature of 180 °C, Cu could completely fill a hole with an aspect ratio of 7. A high deposition rate could be obtained at the high substrate temperature and high partial pressure of the source gas. However the coverage probably deteriorated because of the increase in sticking coefficient due to an increase in the reaction rate at high temperature. As the source gas pressure increased, the deposition rate increased and saturated in the high source pressure region. The good gap-filling property at high source pressures was attributed to the Langmuir–Hinshelwood reaction where almost the same deposition rate is realized from the top to the bottom of the trench. At a high temperature of 215 °C, voids were observed at both the center and along the wall of the trench. The voids along the wall were assumed to be formed at the initial stage of deposition. They disappeared with an increase in source gas flow rate. Therefore, the formation of voids could be due to an insufficient supply of source gas. By annealing the Cu film, its properties of increase in grain size and the reduction in the amount of C, O, and F contaminants were improved. After annealing and chemical mechanical polishing treatment, scanning electron microscopy observation showed Cu interconnecting lines with grains larger than the wire width.