The Chemical Mechanical Polishing For The GaN Assisted By The Electro-Fenton Reaction

As the third-generation semiconductor material,single-crystal gallium nitride（Ga N）has a broad prospect by virtue of high thermal conductivity,low energy consumption,high electron mobility and other characteristics.It is suitable for high temperature,high power and other extreme environmental conditions.The flatten and non-destructive wafer surface is a necessary condition for using Ga N as a substrate for semiconductor components.Due to the high mechanical hardness and chemical inertness,it is difficult to carry out efficient ultra-precision processing.Chemical mechanical polishing（CMP）is one of the processing methods that can achieve full-area flattening.At present,the low surface oxidation rate of Ga N wafer is an important factor limiting the improvement of its processing efficiency.In this paper,the Electro-chemical Fenton reaction（Electro-Fenton）was applied to the CMP process of Ga N by controlling the electro-chemical parameters to enhance the hydroxyl radical（·OH）concentration in the solution,which enhanced the oxidation effect of the solution on the wafer surface due to its strong oxidizing property.Finally,under the mechanical action of abrasive particles,a high material removal rate（MRR）and low surface roughness were obtained.In this paper,through single-factor experiments,the effects of p H,H₂O₂ concentration,voltage value,DC current value and catalyst type on generated·OH concentration in Fenton or Electro-Fenton solutions were studied and the enhancement mechanism of the Electro-Fenton reaction was investigated.The results showed that with the increase of p H value,H₂O₂concentration and constant voltage value,the·OH concentration and the peak·OH concentration generated in the solution showed an increasing trend followed by a decreasing trend.With the increase of the DC current value,the·OH concentration and the peak value of·OH concentration in the solution showed a gradual downward trend.Compared with the solid-phase catalyst,the use of the liquid-phase catalyst in the electro-Fenton solution effectively enhanced the ion conversion rate between Fe²⁺and Fe³⁺in the solution,and the peak·OH concentration in the solution was reached when Fe SO₄ was used as the catalyst.Through electrochemical experiments,the effects of p H,H₂O₂ concentration,voltage value,DC current value and catalyst type on the corrosion characteristics of Ga N wafer surface were investigated.The results demonstrated that the corrosion potential of Ga N wafer surface showed a decreasing and then increasing trend with the increase of p H and H₂O₂ concentration and voltage value.With the increase of current strength in the Electro-Fenton solution,the corrosion potential of Ga N showed a gradually increasing trend.Compared with the solid-phase catalyst,the corrosion potential of the wafer surface gradually decreased when the electro-Fenton solution with the liquid-phase catalyst was used to etch the wafer surface,and reacheed the lowest value under the condition of using Fe SO₄ as the catalyst.Through the CMP experiments,the effects of electrochemical parameters,catalyst types and polishing process parameters on the effect of CMP for Ga N were investigated.The results showed that applying the Electro-Fenton reaction into the CMP for Ga N effectively improved the MRR.The MRR increased by 20.86%and 47.37%when DC current and voltage were applied to the Electro-Fenton solution,respectively.Compared to the pure H₂O₂ solution with applied voltage,MRR increased by 30.35%when the solid phase catalyst（Fe₃O₄）was added to the solution,76.94%when the Fe₂（SO₄）₃ was added,and 150%when the Fe SO₄ was added.High MRR and low surface roughness of Ga N wafer were obtained with the processing parameters of pressure of 500 g/cm²,speed of 60 rpm and flow rate of 60 ml/min.Through Energy Dispersive Spectrometer（EDS）and X-ray photoelectron spectroscopy（XPS）,the effect of electrochemical parameters and catalyst types on the oxidation effect of Ga N wafer surface was investigated.The results showed that the O element concentration on the wafer surface increased by 123.39%when the wafer surface was oxidized by Electro-Fenton solution compared to Fenton solution.The Ga-O bond concentration and N-O bond concentration on the wafer surface peaked at 58.32%and 66.12%,respectively,with the solution parameters of p H value of 3.25,H₂O₂ concentration of 0.6 wt%,Fe SO₄ concentration of 1 m M,and voltage of 1.0 V.Compared with solid-phase catalysts,the oxidation effect of the solution was further improved when using liquid-phase catalysts.Based on the bidirectional diffusion theory and the Deal-Grove oxidation model,the oxidation mechanism of-OH on the surface of Ga N wafers was,and the parameters affecting the oxidation reaction rate were analyzed theoretically,According to the two-way diffusion theroy and the Deal-Grove oxidation model,the oxidation mechanism of the Ga N wafer surface oxidized by·OH was investigated.The parameters affecting the oxidation reaction rate were analyzed theoretically,and the oxidation model and material removal model of Ga N wafers under electric Fenton conditions were established.