WO2018190780A1

WO2018190780A1 - Chemical mechanical planarization of gallium nitride

Info

Publication number: WO2018190780A1
Application number: PCT/TR2017/050138
Authority: WO
Inventors: Gul Bahar BASIM DOGAN
Original assignee: Ozyegin Universitesi
Priority date: 2017-04-12
Filing date: 2017-04-12
Publication date: 2018-10-18

Abstract

The present invention provides for the characterization of the surface chemical nature of GaN samples and optimization of the CMP process in terms of material removal rates and surface quality by slurry chemistry and tool design development. It was observed that GaN CMP is preliminarily driven by the chemical impact from the slurry chemical interactions based on the observation of increasing material removal rates and better surface quality when the mechanical components of the CMP process are kept less aggressive while the chemical components are promoted. The effect of the CMP process set-up variables such as applied downforce, pad type, and slurry flow rate and temperature are also evaluated to optimize the CMP performance.

Description

The present invention is related to chemical mechanical pianarization (CMP) of hard and difficult materials to polish such as gallium nitride (GaN) and alternative I07V, II/VI semiconductors, and in particular to chemical modification of CMP slurries, adaptation of processes, and tool setup to the particular design and chemistry requirements for these specific slurry modifications used in microelectronics and photonics semiconductor device manufacturing.

GaN has become a material of choice for semiconductor applications that require direct and wide band-gap energy and high power applications. It is highly utilized for light-emitting diodes (LEDs), and high-power, high-frequency field effect transistor (FET) devices. Particularly, the utilization of GaN in LED applications requires a very smooth and defect free surface finish, and hence CMP is needed after its deposition. Epitaxial layers of GaN are most commonly grown on sapphire substrates, although other substrates such as silicon substrates may be implemented as well. However, large lattice mismatch and difference in thermal expansion between the GaN layer or film and the substrate often results in defects in the epitaxial GaN film, thereby limiting the performance of the manufactured device. GaN is also known to be a difficult material to polish due to its hardness. Thus, introducing CMP on a film that is poorly grown due to epitaxial challenges, in addition to GaN being a very hard film, makes the use of GaN a challenging task.

The preliminary studies on CMP of GaN in the literature using colloidal silica based slurries focused on modulating the CMP performance mainly by increasing the applied downforce or pre-polishing the GaN surface by using a diamond-based abrasive slurry that enhanced the mechanical abrasions. Although the diamond-based slurries were able to remove GaN, the surface finish was very rough. The colloidal silica based slurries were able to improve surface quality by enabling polishing on the Ga reach face of GaN (Face-β), but the nitrogen reach face (Face-cc) showed an extremely low polishing rate due to chemical inertness. However, it served as important evidence that softer silica particles were able to remove the hard GaN material without inducing sub-surface damage. Prior research has also proposed a basic chemical interaction mechanism explaining the reaction on the -face of GaN in the colloidal silica based slurry. The mechanism suggests that along the [1 1 2 0] direction for N-polar Ga selective etching takes place through: (i) formation of a nitrogen terminated layer with one negatively- charged dangling bond on each nitrogen atom; (ii) adsorption of hydroxide ions; (iii) formation of oxides; and (iv) dissolution of the oxides. While there are conventional techniques available for the application of planarization on materials surfaces, such as sandblasting, nano-lithography, anodic oxidization, ion implantation, and the like, most of these techniques have some disadvantages such as: (i) the tendency of particles used in sandblasting to stick on the metal surfaces creating points of anodization; (ii) lithography techniques being very expensive; and furthermore the fact that neither of these techniques can help prevent corrosion,

GaN is a difficult material to polish and mechanical polishing techniques typically result in poor surface quality. It is therefore highly desirable to improve the post-CMP surface quality and removal rates of GaN in order to improve various applications, such as in the manufacture of LED and microelectronics devices, SUMMARY

Gallium Nitride (GaN) is a key electronic material for light emitting diode (LED) applications based on its direct band gap and high power adoptability. Manufacturing LEDs made of GaN requires enhanced smoothness and wafer planarity that necessitates the application of a chemical mechanical planarization (CMP) process. GaN is a difficult material to polish and planarize due to its hardness. Mechanical polishing applications result in limited removal rates and unacceptable surface quality and hence a chemical component is required to enable smooth surface finish and optimal material removal rates. The present invention provides for the characterization of the surface chemical nature of GaN samples and optimization of the CMP process in terms of material removal rates and surface quality by slurry chemistry and tool design development. It was observed that GaN CMP is preliminarily driven by the chemical impact from the slurry chemical interactions based on the observation of increasing material removal rates and better surface quality when the mechanical components of the CMP process are kept less aggressive while the chemical components are promoted. The effect of the CMP process set-up variables such as applied downforce, pad type, and slurry flow rate and temperature were also evaluated to optimize the CMP performance.

The present disclosure provides optimized CMP setup procedures for GaN through characterization of the surface nature of GaN samples and then correlating the results to the surface energy, surface wettability, and CMP. The effect of the CMP process setup variables such as slurry/platen rotational speed, slurry temperature, pad conditioning, applied down-force and slurry flow rate are outlined to obtain optimal CMP results through increased material removal rate response, reduced surface roughness and defects for LED applications as well as integrated microelectronics device fabrication where GaN is used.

The CMP material removal rate of Ga depends on the crystallographic orientation of the GaN surface and hence it is beneficial to determine the specific crystallographic orientation of the GaN surface prior to CMP. A simple and accurate method of surface crystalline structure determination is desirable prior to CM]³ process setup. The type of surface crystalline structure can be determined by wettability (contact angle) measurements in accordance with embodiments of the present disclosure.

The system and process of the present disclosure each helps improve the GaN removal rate by 6 to 10 times as compared to the conventional CMP implementations. The system and process of the present disclosure al so improve surface roughness by 2 to 3 times. The process setup is optimized in terms of slurry flow rate, solids concentration, pH, temperature, and applied down force.

The present disclosure also introduces a procedure of adding an acid, such as hydrochloric acid (HC1), citric acid or similar acid, at the pad surface in conjunction with a high pH slurry formulation to neutralize the ammonia generated as a product of the GaN dissolution reaction. Hence, the present disclosure stimulates the reaction towards the products side, thereby- improving material removal rates.

The present disclosure also introduces a tool setup with a slurry pool designed on top of the platen and the polishing pad that helps minimize the slurry consumption in combination with the neutralization process of the ammonia (N¾) that is a product of the GaN dissolution reaction.

The present disclosure may be utilized with a two-dimensional (2D) CMP process and processing tool, a three-dimensional (3D) configured CMP processing tool with the integration of a robotic arm and a force/torque sensor sample holder, and the like, to enable improved CMP of GaN layers and also nano-structuring of multidimensional objects.

CMP is a process that is used to planarize the wafer surfaces in microelectronics manufacturing to enable multi-layer metallization. A CMP process employs slurries that involve an aggressive chemistry to alter the properties of the layer or film to be polished and this film is removed by the mechanical actions of the particulates in the suspension. In one example particularly applied to metallic layers the formation of a metal oxide film may be self-limiting and once formed, it can protect the underlying metal from further attack of the slurry chemicals. This allows the polishing of the higher level metal while protecting the lower levels; in other words, to achieve topographic selectivity and hence provide planarization. In another example, the polishing and material removal of the oxide type layers is achieved by formation of a hydrated gel-like layer on the surface of the material through mainly a pH adjustment.

It is possible to induce roughness on the surfaces of the metallic materials at variable root mean square (RMS) values by changing the polishing pads as well as slurry formulations (both chemicals and the sizes and solids loading of the slurry nano-particles) used during the CMP process, which affect the surface roughness both chemically and mechanically.

Through utilization of a CMP system and/or process in a controlled manner, it is plausible to induce improved material removal rates and also improved polished surface quality with nano- scale smoothness as well as nano-scale roughness for GaN layers in various applications, such as in materials science and engineering fields where processes are frequently required to improve the surfaces of the materials.

The present disclosure provides systems, tools, and methods that improve efficient smoothening or roughening of the materials surface, both mechanically and chemically, to provide highly efficient material removal rates and surface quality while providing efficient usage of slurry raw materials, and in some cases nano-structuring. Thus, another aspect of the present disclosure is to provide a process, which can perform nano-structuring by employing CMP techniques.

Furthermore, the present disclosure may be easily adoptable to the other fields of materials processing with adjustments and process configurations. Hence, it will be possible to apply the innovation on three dimensional materials in a number of sectors where surface structure (roughness or smoothness) is important besides the semiconductor and photonics industries, such as in automotives, biomateriais, aircrafts, resistors, implants, and the like.

In accordance with embodiments of the present disclosure, a slurry composition for chemical mechanical polishing of a gallium nitride layer is comprised of: a silica particle based slurry; wherein the slurry has a particle size between 0,04 μη - 0.2 μηι; wherein the slurry has a temperature between 2 °C - 25 °C; wherein the slurry has a pH between 3 - 12; a pH adjusting agent, and an aqueous medium, wherein the slurry composition is comprised of 5 - 25 wt% solids, and wherein the slurry composition is combined with an acid prior to chemical mechanical poll shing. In accordance with other embodiments, a method for chemical mechanical polishing of a gallium nitride layer is provided. The method comprises providing a slurry composition as described above. The method further includes applying an acid to a polishing pad; and applying the slurry composition onto the substrate with the polishing pad.

In accordance with yet other embodiments, a system for chemical mechanical polishing (CMP) of a gallium nitride layer is comprised of: a carrier/chuck for holding a gallium nitride wafer to be polished; a CMP device (B) including: a rotatable pad (D) for CMP including a a slurry retainer, the slurry retainer having a base coupled to the pad (D), a retaining cylinder coupled to the base, and a cover coupled to the retaining cylinder; and a slurry pump system for providing a slurry composition as described above to the pad (D), the slurry composition pooled within the slurry retainer, and an acid applied to the pad (D) prior to CMP. DESCRIPTION OF THE FIGURES

Systems and methods according to the invention and some particular embodiments thereof will be described with reference to the following figures. These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings. Some embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings. Unless noted, the drawings may not be drawn to scale.

Figures 1 A and I B illustrate a top view and a sectional view, respectively, of a 2D CMP system in accordance with embodiments of the present disclosure. Figures 2A, 2B, and 2C illustrate a perspective view, a side view, and a top view, respectively, of an assembly of the slurry retainer parts in accordance with embodiments of the present disclosure.

Figures 3 A-3E illustrate different views of a cover component of a slurry retainer for a rotatable CMP pad in accordance with embodiments of the present disclosure, Figures 4 A-4E illustrate different views of a retaining cylinder component of slurry retainer for a rotatable CMP pad in accordance with embodiments of the present disclosure. Figures 5A-5E illustrate different views of a base component of a slurry retainer for a rotatable CMP pad in accordance with embodiments of the present disclosure.

Figure 6 shows a configuration of a CMP device and a robotic arm that is used to hold the work piece against the CMP device for 3D CMP in accordance with embodiments of the present disclosure.

Figure 7 is an enlarged view of the CMP device and the distal end of the robotic arm of Figure 6 in accordance with embodiments of the present disclosure.

Figure 8 illustrates an assembly perspective view of the robotic arm configuration employed in the method used for 3D CMP configuration in accordance with embodiments of the present disclosure.

Description of Part References

A. Robotic arm configuration

1. Industrial robotic arm

2. Flange

3. Connection plate

5, Force-torque sensor

9. Retainer base

10. Retainer head

1 1. Fastener

B. CMP device

1 10. Slurry retainer

1 12. Cover

1 14. Retaining cylinder

1 16. Base

120. Slurry pump system

130. C arri er/chu ck

140. Wafer

150. Pad conditioner

160. Platen

C. Work piece

D. Pad DETAILED DESCRIPTION

A systematic experimental approach was followed to determine the conditions to promote material removal rate while controlling surface defects for GaN CMP. Initially, surface characterization of a 2" GaN wafer was conducted through FTIR and the results were compared to the surface energy and wettability responses enabling an easy approach to predict the material removal rates of GaN. Furthermore, CMP tests were performed as a function of applied downforce, slurry flow rate, slurry pH, and temperature adjustment, as well as with and without conditioning by using a mono-sized commercial silica slurry. The optimal polishing conditions were implemented to screen for the polishing pad selection that can enable high removal rates while protecting the surface quality in terms of minimum surface roughness.

Materials

2" diameter n-type GaN wafers with 350±25 micrometer of GaN deposited on a silicon substrate or bulk GaN coupons with a and β sides exposed at the front and backside, respectively.

Polishing slurry was chosen as a baseline silica slurry. Slurry pH was consistently kept at pH 9 for all the experiments other than the study conducted on evaluating the effect of pH on material removal rate (MRR). The polishing slurry was detected to be 0.109 micrometer based on differential volume percent. A standard IC 1000/Suba IV stacked polishing pad with K-grove was used for the preliminary experiments conducted to study the effects of applied downforce, slurry pH, flow rate and pad conditioning. The effect of pad aging by extensive conditioning (up to 100 wafers) and pad type were also evaluated on the MRR response of the GaN wafers.

Methods

Wettability and surface energy analyses: The wettability and surface energy calculations of the GaN wafer was based on the contact angle measurements performed by sessile-drop contact angle measurement technique by KSV ATTENSION Theta Lite Optic Contact Angle Goniometer, Three bubbles were measured on each sample and the results were averaged. The bubble image stored by a camera and an image analysis system was used to calculate the contact angle (Θ) based on the shape of the bubble. In order to measure the surface energy and determine the work of adhesion of the GaN surfaces as a function of the temperature, an acid-base technique was adopted. Polar and apolar probe liquids were selected following standard procedures including ethylene glycol, formamide, glycerol, and deionized water. CMP experiments: CMP experiments were conducted on a desktop Tegrapol-31 polisher by using a standard IC 1000/Suba IV pad for the preliminary screening analyses. The down force was set to 100 N after optimization on the 2" diameter wafer coupons with 100 rpm rotational velocity and 25 mi/min slurry flow rate. Ail the CMP tests were performed for at least 5 minutes. CMP responses were obtained in terms of M R (A/min) and surface roughness measurements. The material removal rates were determined from the difference in the weights of the wafers before and after polishing measured by using a PRECISA 360 ES scientific balance with 0.01 mg accuracy.

Surface topography analyses: Surface roughness measurements were conducted by Nanomagnetics Instruments Atomic Force Microscope (AFM) on 2.5-μηι by 2.5-μιη scans using contact mode. The averages of minimum measurements were reported including the standard deviations to verify the statistical significance of the observed values.

Table 1 below includes ranges for various CMP settings or variables used for analysis.

Table 1

Optimization of operational CMP variables and consumables to maximize MRR response:

CMP tests were conducted on a desktop Tegrapol-31 polisher by using a standard SUBAIV- IC1000 stacked K-grove polishing pad. 2" GaN wafers were polished with an aged IC 1000/Suba IV stacked polishing pad (with in-situ conditioning) at room temperature (~23°C) and 30 N downforce. The MRR value of -10 A/min was obtained. When a fresh set of consumables were adopted, the new IC 1000/Suba IV stacked pad was only able to remove ~6 A/min of GaN. Hence, for the preliminary screening, the aged IC 1000 pad was used. In order to improve the MRR responses of the GaN wafers, experimental evaluations were started by screening the operational variables of the CMP process, namely the applied downforce and slurry flow rate. The effect of downforce was studied first by varying the values between 30 N to 200 N and retaining the platen and head rotational speeds at 100 rpm and the slurry flow rate at 20-25 ml/min. All polishing experiments were conducted for 5 minutes. Material removal rates as a function of the applied downforce using the standard colloidal silica slurry were determined. It was observed that the MRR values increased with increasing downforce up to 100 N (7, 15 psi) but decreased above the 100 N setting. Although not limited to this theory, it is suspected the decrease in the MRR can be explained by the limited slurry flow between the pad surface and the wafer surface at this high pressure setting. Furthermore, the very high pressure settings also resulted in elevated friction and heating of the pad at the 200 N downforce. Therefore, the optimal downforce was set to 100 N for the following experiments. In order to verify the impact of efficient slurry flow, the CMP tests were also conducted at 100 N with and without using in-situ conditioning and it was observed that the MRR values decreased from 40 A/min (with conditioning) to 36 A/min. These results also verified the tendency of increasing removal rates with more efficient slurry feeding between the pad and the wafer surface by use of conditioning. As another standard CMP setup variable, the effect of slurry flow rate on MRR responses was evaluated under the same experimental conditions by setting the downforce to 100N. MRR values were observed to tend to increase with increasing slurry flow up to 25 ml/min and then reach a plateau. Hence, as the second process variable the slurry flow rates were set to 25 ml/min.

After the mechanical factors of the CMP process were set, the impact of slurry chemistry on removal rates was studied. The correlation between pH and MRR response was observed to be a direct correlation and the MRR values increased with increasing pH. Based on the through screening of the process settings, slurry properties and surface characterization, Table 2 below summarizes the optimal CMP conditions for GaN planarization in accordance with embodiments of the present disclosure. Although the removal rates are still limited, they can be modulated by setting the pressure values to -7-15 psi with 20-25 ml/min slurry flow rates and 100 rpm of platen and head rotational velocity at slurry pH of 9 for 2" GaN wafers.

Material Removal Rate Analyses with 0.1 M Nth as a Function of HC1 Addition during CMP:

GaN has two crystallographic faces, alpha and beta. Between these faces, the Alpha phase is typically harder to polish yet preferred for LED applications.

The differences in etch characteristics of the Ga-reach beta-face and the N-reach alpha-face have been examined in a number of studies. As an example, Palacois et al . demonstrated that the nitrogen polar GaN epiiayers (alpha-face) were etched in aqueous KOH between 26 and 80°C. The hydroxide ions (OFF) are first adsorbed on the GaN sample surface and subsequently react with Ga atoms following reaction [1] below:

KOH

2GaN + 3H₂0 + Ga₂0₃ + 2NH₃ [1]

According to this reaction, in a basic environment (after adding the KOFI), the reaction shifts to the right side resulting in more effective removal of N as NH₃. Hence, in order to promote the removal of the N layer, the reaction needs to be shifted to the products side. This action can be accomplished through (i) increasing the GaN as a reactant or (ii) removal of the NH₃ that forms as a reaction product. Since the GaN surface area cannot be changed on a given wafer size, the more practical method is to promote the formation of H₃ by removing it from the reaction products through addition of an acidic component. Therefore, HQ addition to the CMP pad surface was analyzed during the polishing application. Experiments and observations were carried out to increase MRR values of GaN in a silica based polishing slurry with 0.1 M NH₃ as a function of HCl concentration at pH 9-1 1 at room temperature. The maximum MRR was observed with the same concentration of NH₃ and HCl usage by using a SUBAIV-IC1000 stacked polishing pad. It was observed that the additional flow of HCl into the polishing environment at the same molar concentration as the NH₃ promoted removal rates (increased MRR value). If the HCl concentration was higher than the NH₃ concentration, the removal rates tended to decrease, which is expected due to the shift of the reaction towards the reactants side. Likewise, if an acidic slurry is used and an NH based flow is supplied to the pad surface, removal rates are negligible. In addition, the same process application on the pure silicon wafer also resulted in no material removal rate change. Hence, the addition of the same concentration of HCl or a weak acid to a H₃ based slurry during the polishing operation promoted material removal, particularly at low temperatures. Hence, an aspect of the present invention promotes GaN removal by adding the same molarity of HCl or similar acidic media during the CMP process.

Adaptation of the proposed process on a new too! setup A new tool set up is introduced in combination with the proposed process improvements in which the slurry is deposited on the polishing platen where a modification is made to collect the slurry in a pool. Since the reaction continuously produces ammonia during the polishing process the introduction of a small amount of HCl or similar acid would help push the reaction towards the products side and hence enable material removal on the GaN sample. This confi guration helps prevent excessive slurry consumption during the polishing of bulk GaN films while enabling faster material removal rates. A following buffing step can be introduced on a secondary polishing platen to further control the surface quality of the GaN wafers.

Example robotic arm configurations with a new tool set up are now explained in further detail.

First Alternative Configuration Referring now to Figures 1A and IB, a top view and a sectional view of a 2D CMP system 100 are respectively illustrated in accordance with embodiments of the present disclosure. System 100, for 2D chemical mechanical polishing (CMP), includes a rotatable pad D on a platen 160, a slurry retainer 110, a slurry pump system 120 for providing a slurry composition to the pad D, and a carrier/chuck 130 for holding a wafer 140 to be polished. System 100 may further include a conditioner 150 for conditioning pad D. In one example, the slurry composition may comprise a silica particle based slurry; wherein the slum' has a particle size between 0,04 μτη - 0,2 μτη; wherein the slurry has a temperature between 2 °C - 25 °C; wherein the slurry has a pH between 3 - 12; a pH adjusting agent; an aqueous medium, wherein the slurry composition is comprised of 5 - 25 wt% solids; and an acid applied to the pad (D) prior to CMP. Pad D and wafer 140 are pressed together by dynamic carrier/chuck 130, which may be rotated with different axes of rotation (e.g., non-concentric). This removes material and tends to even out any irregular topography, making the wafer flat or planar. For example, CMP can bring the entire surface within the depth of field of a photolithography system, or selectively remove material based on its position, As noted above, slurry retainer 1 10 provides for collecting the slurry in a pool, which then allows for the introduction of a small amount of HC1 or similar acid to push the reaction towards the products side and hence enables improved material removal on the GaN wafer. This configuration helps prevent excessive slurry consumption during the polishing of bulk GaN films while enabling faster material removal rates. Figures 2A-2C illustrate a perspective view, a side view, and a top view, respectively, of an assembly of components of the slurry retainer 1 10 in accordance with embodiments of the present disclosure. Slurry retainer 110 includes a base 116 for mounting to pad D and/or platen 160, a retaining cylinder 114 mounted on base 116 and/or pad D along an outer lip region 1 4a, and a cover 112 mounted on retaining cylinder 1 14 along the outer lip region 114a. In other words, pad D is positioned between retaining cylinder 14 and base 1 16.

Figures 3A-3E illustrate different views of cover 1 12 of slurry retainer 1 0 for a rotatable CMP pad in accordance with embodiments of the present disclosure. Figure 3B is a sectional view of cover 1 12 along line B-B in Figure 3A. Figure 3C is a top view and Figure 3E is a bottom perspective view of cover 1 12. Figure 3D is an upright side view of cover 1 12. Figures A-4E illustrate different views of retaining cylinder 114 of slurry retainer 110 for a rotatable CMP pad in accordance with embodiments of the present disclosure. Figure 4B is a sectional view of retaining cylinder 114 along line C-C in Figure 4A. Figure 4C is a top view and Figure 4E is a top perspective view of retaining cylinder 1 14. Figure 4D is an upright side view of retaining cylinder 1 14. Retaining cylinder 114 includes outer lip region 114a used for mounting to the base and the cover, and a retaining wall 1 14b for pooling the slurry.

Figures 5A-5E illustrate different views of base 116 of slurry retainer 1 10 for a rotatable CMP pad in accordance with embodiments of the present disclosure. Figure 5B is a sectional view of base 116 along line D-D in Figure 5 A. Figure 5C is a top view and Figure 5E is a top perspective view of base 16. Figure 5D is an upright side view of base 1 16.

When slurry retainer 110 is mounted onto pad D and/or platen 160, the slurry composition from slurry pumping system 150 may be collected within retaining wall 114b to pool the slurry for addition of acid and CMP processing. Advantageously, this configuration helps prevent excessive slurry consumption during the polishing process (e.g., of bulk GaN films) while enabling faster material removal rates.

Second Alternative Configuration

Referring now to Figure 6, a system 200 is illustrated including a CM³ device and a robotic arm that is used to hold the work piece against the CMP device for 3D CMP in accordance with embodiments of the present disclosure.

Referring now to Figures 6-8, a robotic arm configuration (A) is comprised of an industrial robot arm (1), a flange (2), connection plates (3), a force-torque sensor (5), a retainer base (9), a retainer head (10), and a fastener (1 1). In the robotic arm configuration (A), industrial robot arm (1) has industrial serial kinematics configuration with 6 degrees of freedom. The aforementioned industrial robot arm (1 ) ensures access to any point from any angle in 3 dimensional space, based on these features. Flange (2) connects the connection plates (3) and industrial robotic arm (1) together. Robotic arm configuration (A) contains two connection plates (3). The function of connection plates (3) is to connect force-torque sensor (5) to the flange (2). Function of force-torque sensor (5) is to measure the force between the surface of the work piece (C) and the pad (D ), Retainer base (9) is the part where retainer head (10) is placed inside. Retainer head (10) is the component, which retains the work piece (C). Fastener (11) is preferably a nut and used as an apparatus for tightening the retainer head ( 10) to the retainer base (9), Retainer is composed of retainer base (9), retainer head (10) and fastener (11). A configuration, which is similar to a claw, can be used as a retainer instead of these components.

Installation of the robotic arm configuration may be realized as follows. Firstly, the work piece (C) which is preferably a dental implant is placed inside the retainer head (10). Then, by tightening the fastener (1 1) work piece (C) as an example an implant, is tightened inside the retainer head (10). In a configuration where a claw is used as retainer, this installation steps can be omitted and the work-piece can be retained by the help of a claw. Force-torque sensor (5) is located between retainer and industrial robotic arm (1). Two connection plates (3) are used to fix the force-torque sensor (5) to the industrial robotic arm (1). One of the connection plates (3) is screwed to connect force-torque sensor (5) and the second one to the flange (2). Two connection plates (3) are screwed together to fix force-torque sensor (5) to the industrial robot arm (1). Pad (D) is contacted to the surface of the work piece (C) to ensure structuring or smoothing the aforementioned surface. Different types of pads (D) can be used in the robotic arm configuration

(A) . A slurry retainer (110) as described above is again mounted to pad (D) to enable pooling of the slurry for receiving acid, improving slurry consumption efficiency, and improving material removal rates. A robotic arm configuration may function as follows. First of all, the work piece (C) is held by the retainer and the pad (D), which will be used in the process is positioned inside the CMP device (B) according to the shape of the surface and location of the work piece by the help of the industrial robotic arm (1). The work piece (C) is pressed against the pad (D) by the help of the industrial robotic arm (!) and a contact surface is established between the pad (D) and the work piece (C). The force created on the aforementioned contact surface is measured by a force-torque sensor (5), retainer is positioned again to the force values determined beforehand and it is ensured that the work piece (e.g., a dental implant) is kept still by the industrial robotic arm (1). With the pad (D) installed, the pad table of the CMP device (B) originates rotation at a predefined speed to ensure mechanical abrasion on the contact surface. Meanwhile, chemical is fed to the work piece (C) at the required quantity by the slurry pump system of the CMP device

(B) throughout the predefined process and mechanical removal is performed on the surface of the work piece as a result of the friction occurring on the contact surface between the pad (D) and the work piece. Also, by the help of the slurry chemicals, a non-porous and protective oxide layer may be formed on the surface of the work piece and the hence the processed surface is protected. The retainer is positioned at different positions by the industrial robotic arm (1) to ensure that the overall surface of the work piece (C) is exposed during polishing uniformly. Upon performing positioning, aforementioned processes, which are listed below, are performed in a cycle until the entire surface of the work piece (C) is treated:

- measurement of the force created on the contact surface by force-torque sensor (5),

- repositioning of the retainer to the predefined force values;

- rotation of the pad table of CMP device (B) which is installed with the pad (D) at a defined speed; slurry flow on the work piece (C);

- positioning of the retainer at different positions during polishing process by the industrial robotic arm (1).

Chemical agents administered by the pump system of the CMP device (B) may vary dependent on the work piece (C) and may contain nano-particles of varying structures, water-based chemicals, surfactants etc.

The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been disclosed with reference to embodiments, the words used herein are intended to be words of description and illustration, rather than words of limitation, W e the present invention has been described with reference to particular materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein. Rather, the present invention extends to all functionally equivalent structures, materials, and uses, such as are within the scope of the appended claims. Changes may be made, within the purview of the appended claims, as presently stated and as may be amended, without departing from the scope and spirit of the present invention. All terms used in this disclosure should be interpreted in the broadest possible manner consistent with the context.

Claims

1. A slurry composition for chemical mechanical polishing of a gallium nitride layer, the slurry composition comprising:

a silica particle based slurry;

wherein the slurry has a particle size between 0,04 μηι - 0.2 μη ; wherein the slurry has a temperature between 2 °C - 25 °C;

wherein the slurry has a pH between 3 - 12;

a pH adjusting agent; and

an aqueous medium,

wherein the slurry composition is comprised of 5 - 25 wt% solids, and

wherein the slurry composition is combined with an acid prior to chemical mechanical polishing, 2. The slurry composition according to claim 1, wherein the particle size of the slurry is between 0.04 μιη - 0,08 μηι.

3. The slurry composition according to claim 1, wherein the temperature of the slurry is between about 2 °C and 4 °C.

4. The slurry composition according to claim 1 , wherein the pH of the slurry is about 9.

5. The slurry composition according to claim 1, wherein the pH adjusting agent is potassium hydroxide or ammonia,

6. A method for chemical mechanical polishing of a gallium nitride layer, the method comprising:

providing a slurry composition comprising:

a silica particle based slum';

wherein the slurry has a particle size between 0.04 μιη - 0.2 μηι;

wherein the slurry has a temperature between 2 °C - 25 °C;

wherein the slurry has a pH between 3 - 12;

a pH adjusting agent; and

an aqueous medium,

wherein the slurry composition is comprised of 5 - 25 wt% solids; applying an acid to a polishing pad; and

applying the slurry composition onto the substrate with the polishing pad. 7. The method according to claim 6, wherein the particle size of the slurry is between 0.04 μτη - 0.08 μιη.

8. The method according to claim 6, wherein the temperature of the slurry is between about 2 °C and about 4 °C.

9. The method according to claim 6, wherein the pH of the slurry is about 9,

10. The method according to claim 6, wherein the slurry composition is applied onto the substrate with the polishing pad at a force between 3 psi and 15 psi and at a rotational speed between 100 rpm and 150 rpm.

1 1. The method according to claim 6, wherein the slurry composition is applied onto the substrate with the polishing pad at a force between 7 psi and 8 psi and at a rotational speed between 100 rpm and 150 rpm.

12. The method according to claim 6, wherein the slurry composition is supplied to the polishing pad at a flowrate between 10 ml/minute and 200 ml/minute.

13. The method according to claim 6, wherein the slurry composition is supplied to the polishing pad at a flowrate between about 50 ml/minute and about 70 ml/minute.

14. The method according to claim 6, wherein the acid applied to the polishing pad is selected from the group consisting of acetic acid, citric acid, maleic acid, oxalic acid, lauric acid, hydrochloric acid, and a combination thereof. 5. The method according to claim 6,

wherein the slurry has a particle size between 0.04 μηι - 0.08 μηι;

wherein the slurry has a temperature between 3 °C - 4 °C;

wherein the slurry has a pH of about 9; and

further comprising:

supplying the slurry composition to the polishing pad at a flow rate of about 20-25 ml/minute; and

applying the slurry composition onto the substrate with the polishing pad at a force of about 7-15 psi and at a rotational speed of about 100 rpm.

16. A system, for chemical mechanical polishing (CMP) of a gallium nitride layer, the system comprising:

a carrier/chuck for holding a gallium nitride wafer to be polished;

a CMP device (B) including:

a rotatable pad (D) for CMP including a a slurry retainer, the slurry retainer having a base coupled to the pad (D), a retaining cylinder coupled to the base, and a cover coupled to the retaining cylinder;

a slurry pump system for providing a slurry composition to the pad (D), the slurry composition comprising:

a silica particle based slurry;

wherein the slurry has a particle size between 0.04 μηι - 0.2 μηι;

wherein the slurry has a temperature between 2 °C - 25 °C;

wherein the slurry has a pH between 3 - 12;

a pH adjusting agent; and

an aqueous medium,

wherein the slurry composition is comprised of 5 - 25 wt% solids; and an acid applied to the pad (D) prior to CMP. 17, The system according to claim 16, further comprising a robotic arm configuration (A) including:

a robotic arm (1) having serial kinematics configuration with 6 degrees of freedom,

a force-torque sensor (5) operably coupled to a distal end of the robotic arm (1), and

a work piece retainer operably coupled to a distal end of the force-torque sensor (5), the work piece retainer for holding a work piece (C) including a gallium nitride layer,

18, The system according to claim 16, wherein the carrier/chuck applies a force between 3 psi and 15 psi to the wafer and wherein the pad provides a rotational speed between 100 rpm and 150 rpm.

19, The system according to claim 16, wherein the slurry pump system supplies the slurry composition to the polishing pad at a fiowrate between 10 ml/minute and 200 ml/minute.

20, The system according to claim 16, wherein the retaining cylinder includes an outer lip for mounting and an interior retaining wall for pooling the slurry.