Wet Chemical Etching of InP for Cleaning Applications

Abstract

The wet chemical etching of InP and its native oxide has been studied in HCl and H 2 SO 4 solution to create oxide-free surfaces. The (100) InP surface is not etched in ≤2 M HCl and ≤6 M H 2 SO 4 . As the v etch <0.1 nm/min for these concentrations, the native oxide after OFOD treatment can be effectively removed without significantly etching the surface, as confirmed by contact angle measurements, ellipsometry and X-ray photoelectron spectroscopy. STM and AFM measurements showed that after OFOD treatment and subsequent oxide removal very smooth surfaces are achieved due to the creation of atomic terraces. The size of these terraces can be increased up to micron-size in 6 M H 2 SO 4 . Furthermore, it was shown that in presence of oxygen, n-type InP is photoetched/oxidized during wet processing. Last, the anisotropy in etching is discussed for InP in 2 M HCl and 2 M H 2 SO 4 .For the past and current technology node, transistors in integrated circuits are fabricated on silicon substrates, and in some cases, SiGe alloys are used. In order to meet the future requirements imposed by the scaling roadmap, the next generation of transistors (i.e. the 7 nm node and beyond) will be based on high mobility III-V compound semiconductors. 1,2 To be cost effective, the III-V materials will be integrated on Si substrates. In part A of this paper, we show a possible integration route for such a technology; a Quantum Well based III-V transistor using InP buffer and InGaAs channel layers. 3 The manufacture of transistors consists of many different processing steps, which involve multiple exposures to chemical solutions. The goal of these wet treatments is to obtain a well-defined surface, (i.e. free of contaminants and stoichiometric), essential for obtaining good interfacial properties and, consequently, device performance. 4 There are different ways of preparing III-V surfaces for subsequent processing steps: ion sputtering followed by high temperature annealing, atomic hydrogen cleaning, sulfur passivation, and wetchemical cleaning. 5 Wet-chemical cleaning offers an effective and practical cleaning method for semiconductor surfaces. 6 In the case of III-V compound semiconductors special care should be taken due to the possible formation of highly toxic hydrides during low pH processing. Additionally, anisotropy in etching may be expected, 7,8 which leads to significant surface roughening. In part A of this paper, we propose an oxide formation/oxide dissolution (OFOD) model that prevents hydride formation and allows for smooth etching. 3 In a first step the semiconductor is oxidized by a strong oxidizing agent in solution and, subsequently, the (hydr)oxides formed are dissolved by the acid. Due to the presence of a strong oxidizing agent in solution no dissolved hydrides are expected. This approach, was developed for cleaning of (100) oriented InP buffer layers after a chemo-mechanicalpolishing (CMP) step, and can, in principle, be used for other III-V semiconductors. After OFOD treatment a native oxide is present. In order to p...

Study of InP Surfaces after Wet Chemical Treatments

“…15 The measured indium cannot be explained by oxide removal only and is therefore attributed to the chemical etching of the semiconductor. By measuring the total amount of dissolved indium after immersion into the chemical solution, an approximate value for the etch rate could be determined.…”

Wet-Chemical Approaches for Atomic Layer Etching of Semiconductors: Surface Chemistry, Oxide Removal and Reoxidation of InAs (100)

“…Highly anisotropic etching behavior, as evidenced by the formation of distinct etching pits, induces significant surface roughening. 34 In addition, formation of highly toxic AsH 3 is of important concern. Recently we demonstrated that these issues can be circumvented by using an oxidizing agent in the chemical solution.…”

Epitaxial Defects in Nanoscale InP Fin Structures Revealed by Wet-Chemical Etching

“…The striking difference in pit morphology for the two acids possibly originates from an anisotropy in V s . In earlier work, we demonstrated that the morphology of atomic terraces on InP (100) was different for H 2 SO 4 and HCl solution, supporting such a crystal orientation dependence [38,39].…”

“…Although the pit depth has been correlated to the energy of dislocations (e.g., edge versus screw) [35,36], the chemical properties of the Cottrell atmosphere may also have an impact [37]. Based on inductively coupled plasma mass spectrometry measurements, we estimate that V n is 2-3× larger than the bulk etch rate (V b ) of the (100) surface for both HBr and HCl [38]. The striking difference in pit morphology for the two acids possibly originates from an anisotropy in V s .…”

“…The increase in planar defects with decreasing fin width may be attributed to a higher surface roughness of the STI walls for narrower trenches, causing additional defect nucleation during epitaxial growth. Some fin narrowing is observed after HCl immersion, attributed to anisotropy in etching-Vb (110) > (100) [27,38]. Apparently, HCl can penetrate the InP/SIO2 interface.…”