Physics / 2. Solid State Physics.

Fedin I.V., Skubo V.V.

Scientific supervisor Erofeev E.V., PhD.

Tomsk State University of Control Systems and Radioelectronics, 634050, Russia, C. Tomsk, Lenina 40str.

Influence of atomic hydrogen on the electrical and physical properties of epitaxial layers GaAs

Introduction

Atomic hydrogen can solve big number of problems in the electronics industry associated with cleaning and metallizing surface of semiconductor. It is known that hydrogenation of the semiconductor surface before deposition of the ohmic contacts reduces the contact resistance of the cuprum-germanium (Ge/Cu) ohmic contacts on the 40% [1].

Furthermore, atomic hydrogen can be used for cleaning nanoscale integrated circuit elements from the remnants of the resist [1].

However, there are a number of difficulties that arise due to the high electro-chemical activity of atomic hydrogen. So, if hydrogen enters into the channel, conductivity of it is decreasing, which is extremely undesirable effect. Furthermore, after processing remains thin layer chemisorbed hydrogen atoms on the surface of the semiconductor (As-H, Ga-H), which must be cleaned. [2]. This thin layer results in the future to degradation of the electrical parameters of devices. Thus, processing of the transistor in the hydrogen stream often results in failure of the device, this severely limits the application of such processing. The purpose of this work is studying effects of treatment in a stream of atomic hydrogen on the electrical conductivity of GaAs epitaxial layers.

Experimental technique

In our experiments we use epitaxial structures such GaAs/AlGaAs, which was grown on GaAs. Thickness of the top layer is 50 nm, with doping level (Si) 5·10¹⁸ cm^-18.

For processing in the flow of atomic hydrogen camera installation evacuated to a residual pressure of 5·10^-4 Pa. Discharge current is 2 A and discharge voltage is 230 V. Hydrogen flow is maintained at a level (7-8) • 10-2 liter per min, wherein the hydrogen pressure in the vacuum chamber was (2–4)·10^-2 Pa, and flux density of hydrogen atoms was 10¹⁵ at.·cm^-2·с^-1. Processing was carried out at room temperature.

The surface of the samples was studied by scanning electron microscope (SEM) Zeiss Supra 55 at the same brightness and contrast settings before and after treatment in atomic hydrogen (AH).

The results

At Fig. 1 you can see dependence of surface resistance of epitaxial layers of gallium arsenide on the processing time in the AH stream.

Fig. 1 - Dependence of surface resistance of GaAs epitaxial layers on the processing time in the AH stream

As you can see from Fig. 1, processing the AV stream leads to a significant increase in the surface resistivity GaAs (more then 2,5 times). Moreover, the main growth is observed within the first minute treatment (increasing the surface resistance by 150%).

Then, the growth rate of the surface resistance is significantly reduced: in the next two minutes resistance increased only ≈ 5%. This suggests that the surface layers of the semiconductor very quickly saturated with atomic hydrogen. Thus, it is possible to ensure the processing of the surface in AH, avoiding the ingress of significant quantities of hydrogen deep into the semiconductor.

Now let’s look at physical properties of GaAs surface. At Fig. 2 is a photomicrograph of the surface of GaAs before and after treatment in AH.

Рисунок 2 – A photomicrograph of the surface of GaAs before (a) and after (b) treatment in AH

As you can see from the picture, atomic hydrogen is definitely influence on the GaAs surface. Firstly AH made surface more smoother. Secondly the number of reflected electrons is increased (brightness of picture is increased – setting in both cases a and b are identical). As you know, some of the electrons are reflected from the surface into the SEM sensor (R_┴), some of them dissipates away from the sensor (R_─) and part of them penetrate deeper into the semiconductor (T). The brightness is increased because the number of reflected electrons (R_┴) is increased (R_┴). Considering the polishing properties of the processing in the flow of atomic hydrogen [1] increasing of R_┴ may be due to decreased dissipations (R_─) on the GaAs surface roughness. Thus, the possibility is further supported by cleaning the semiconductor surface in the AH stream claimed in [1].

References

1. Федин И.В., Ерофеев Е.В. / Способ очистки наноразмерных элементов интегральных схем // Доклады Томского государственного университета систем управления и радиоэлектроники. Томск. 2012. С 182 – 185.

2. Friedel P., Gourrier S. / Interactions Between H₂ and N₂ Plasmas and a GaAs (100) Surface: Chemical and Electronic Properties // Appl. Phys. Lett. – 1983. – Vol. 42. – No. 6. – P. 509 – 511.