GaN 表面的清洁

The work described in this paper is part ofa systematic study of surface cleaningand ohmic contact strategies for GaN. The goal of this investigation was todetermine the most effective methods of wet chemical and thermal desorptioncleaning for the removal of oxygen (0) and carbon (C) prior to metallization.Hydrochloric(HCl) and hydrofluoric (HF) acid-based cleaning treatments werecompared, and thermal desorption as a function of temperature was character-ized by sequential heating under ultra high vacuum (UHV) conditions. Augerelectron spectroscopy(AES)analysis was used to monitor the presence ofsurfaceO and C throughout the study. For the removal of surface oxide, HCl-basedsolutions were found to be most effective: under as-cleaned, air-exposed condi-tions,HCI:DI HO(1:1) solution resulted in the lowest levels of residual O andC.However,HF-based solutions resultedin more effective thermal desorption ofC from the surfaces.In contrast to the results typically observed in the thermaldesorption cleaning of GaAs, complete removal of oxygen and carbon from air-exposed GaN surfaces was not seen using vacuum heating alone, even totemperatures where GaN decomposition occurs (>800-900°C)The results ofthis study indicate that the presence of oxygen and carbon on the GaN surfaceis persistent even to high temperatures, and that further in-situ cleaningmethods must be added to obtain spectroscopically clean GaN surfaces.

INTRODUCTION

The surfaces and interfaces between the variouslayers of semiconductor device structures are funda-mental components of solid state architecture. Asdevice size has diminished and the scale of integra-tion has increased,the quality ofthese interfaces hasbecome an increasingly important concern.In addition,the presence ofparasitic resistances and capaci.tances, such as those existing at contact interfacesbecomes more detrimental at higher operating pow-ers and higher oscillation frequencies. For many de-vices, the losses that occur at the contact interfacesaccount for a large fraction of the total losses, and assuch are responsible for significant impact on device performance. Over the course of the development ofsemiconductor device technology, surface cleaningprocedures have been devised to 

·degrease and remove gross contamination,remove particulates and metalatom contamination,and

·remove surface oxides to provide surfaces asatomically clean as possible.

In practice, surface cleaning is as much ofan art formor craft as itis a science;understanding ofthe surfacecomposition and structure often lags well behind thesuccessfulapplication ofprocessing steps.Proceduresare frequently derived empirically with little detailedinvestigation of the chemistry or physics involvedOften, the meaning ofthe word“clean”varies depend-ing on the surface conditions requiredfor success withdifferent processing steps, though surface impurity concentrations may vary by orders of magnitude.  Given that the sensitivity of surface analytical techniques for detection of submonolayer coverage is limited, there are inherent limits on the ability to show  conclusively that a surface is truly atomically clean.