DD281054A1 - PROCESS FOR PASSIVATING SI COMPONENTS - Google Patents

Abstract

The invention relates to a method for passivation of Si devices by anodic oxidation. It is the object of the invention to reduce the lateral fluctuations of the breakdown field strengths of thin oxide layers (d20 nm) and to achieve the highest possible average breakdown field strength without impairing the electrophysical interfacial properties of such layers compared to those of relatively thick oxide layers (d100 nm). The invention has for its object to provide a method for anodic passivation of semiconductor devices, can be made with the thin insulator layers (d20 nm) high quality and with slight lateral fluctuation of the electrophysical properties. According to the invention, the object is achieved by incorporating fluoride in a concentration of 11017 to 51018 F atoms cm 3 into the surface of the insulator layer during or after the anodization in such a way that the fluoride concentration decreases by an order of magnitude from the oxide surface to the oxide center. In order to avoid hysteresis in the CV measurement and high oxide charge densities (1013 cm 2) and high Grenzflaechenzustandsdichten (1013 eV 1 cm 2), the oxide layer must also be tempered.

Description

Field of application of the invention The invention relates to a method for the passivation of Si-Rauelementen by anodic oxidation. Characteristic of the known state of the art Semiconductor devices are passivated in the HL technique by various methods. Dai best known of these Method is that the semiconductor surface is coated with a layer of thermal SiO ₂ (eg.

DE-OS 2649078).

This thermal SiO 2 layer can be produced with very good interfacial properties with very good oxide quality. However, the thermal oxidation is a high-temperature process (T = 1000-1100 ⁰ C), the Minority carrier lifetime is reduced by more than half (G. Monde et al., Proceedings, Physics of the HL-Oberflüche, 12th Workshop, Binz 1981). With decreasing layer thickness, however, the defect density increases, so that for thin oxide layers (<20 nm) a lower

average breakdown field strength (A. Bhattacharyya, C. Vorst, and A. H. Carim, J. Electrochem Soc., 132 [1985] 1900). When

The reason for the lower average breakdown field strength is also the formation of uneven layer thicknesses, since

premature breakthrough can occur especially in thin spots (R. Singh, Proceedings of the 1984 International Symposium on Microelectronics, Loews Anatale Dallas, Texas, page 386).

By nitriding the thin SiO ₂ layers, the breakdown behavior can be significantly improved, however

thereby deteriorate the electrophysical interface properties (R.Singh, see above).

Furthermore, it is known that by NF ₃ -ZuSaU of O ₂ in the thermal oxidation, the reaction rate so strong

is accelerated that the reaction temperature can be lowered to 600-800 ⁹ C. By subsequent annealing of the layers in pure O ₂ at the same temperatures, the incorporated fluorine is forced through O ₂ . The oxide has a lower interface state layer (2 χ 10 ¹⁰ BV * ¹ cm ^"2), a relatively large Oxidlaaungsdichte (2.2 x 10" cm ^"2) and at a

Layer thickness of 30nm a Durchbruchsfeidstärke of about 12MVcm ~ ', although also early breakthroughs in the range

of 1-eMVcm- ¹ (M.Morita, S.Aritome, M.Tsukude.T.Murakawa and M.Hirose, Appl. Phys. Lett. 47 [1985] 253).

Furthermore, it is known to passivate semiconductor surfaces by anodic oxidation. Since it is a Low-temperature method is maintained, the life of the minority carrier is substantially preserved (M. Croset

and D.Dieumegard, J. Electrochem Soc. 120 (1973) 526).

Using appropriate technologies, anodic silicon oxide layers and gate oxide gate layers are related

solid oxide charge density, interface state density, mobile ion charge density, and breakdown field strength are virtually identical (G. Mende and F. Fonske, DD 236556A1). However, thin anodic oxide layers (d S 20 nm) have a laterally very fluctuating breakdown field strength with early breakthroughs in the range of 3-4MVcm ~ to a low average

Breakdown field strength leads (6.4 ± 0,95MVcm ~ \ ^h addition ei occur CV measurements on MOS Strukturon hysteresis and Instabilities on individual dots on. Furthermore, it is known that a fluoride addition to the electrolvtan (0.04 normal solution of KNO ₃ in NMA saturated with NaF),

in the case of the initial oxidation leads to a strong increase in the interface state density of anodic oxide layers

(AG Revesz, J. Electrochem Soc. 114 [1967] 629). The Oxidladungsdichte is about 10 ¹ 'cm ^"1, and the breakdown field strength is inversely proportional to the fluoride content of the oxide layer (M. D. and Croset Dieumegard, see above) in the range of 1.7 x 10" -6.5 x 10 "F- Atomscm " ³ , wherein the fluoride concentration of the oxide surface in the direction of the interface Si / SiO ₂ increases continuously.

Object of the invention

It is the object of the invention to reduce the lateral variations of the breakdown field strength of thin oxide layers (d 20nm) and to achieve the highest possible average breakdown field strength without deteriorating the electrophysical surface properties of such layers over those of relatively thick oxide layers (d £ 100nm) ,

Explanation of the essence of the invention

The invention has for its object to provide a method for anodic passivation of Si semiconductor devices can be made with the thin insulator layers (d S 20 nm) high quality and with slight lateral variation of the electrophysical properties.

According to the invention the object is achieved in that during or after the anodization fluoride in a concentration of 1 x 10 ¹⁷ -5 x 10 ¹ * F atoms cm " ³ is incorporated into the surface of the insulator layer, that the fluoride concentration of the oxide surface to Thus, the reduction in breakdown field strength observed by Croset and Dieumegard at high fluoride concentrations (from 1.7 χ 10 "cm ~ ³ ) is avoided, which leads to hysteresis in the CV measurement and high oxide charge densities (10 ¹³ cm '). ¹ ) and high interface state densities (10 ¹³ OV ^-1 Cm * ¹ ), the oxide layer must also be annealed.

embodiment

The Si samples are cleaned in a boiling mixture of H ₂ O ₂ and H ₂ SO ₄ (1: 1) and anodically preoxidized in a galvanic cell at a current density of 7 mAcm "*, using as electrolytes a 0.04 molar solution of KNO ₃ in ethylene glycol, which contains 0.35% by volume of H ₂ O. The 50 nm thick oxide film is then removed by etching with 1 nHF, the etching time being a maximum of 2 minutes immersed in 1 nHF, rinsed again with deionized water and spun dry, followed by anodic oxidation under the conditions already mentioned up to a layer thickness of 20 nm, whereby fluoride ions originally sorbed on the Si surface reach the oxide surface sample gespüh deionisieitem with water and tempered for ₂ stream at 800 ⁰ C in N Thereafter, there are the following electro-physical properties.:

Oxide charge density N ^ _n , = 1.25XiO ¹¹ Cm " ²

Density of states N _{rt> M9} = (3,3 ± 1,3) χ 10 ¹⁰ OV " ¹ cm" ² Density of the moving

ionic charges N _n = (1.8 ± 0.1) x 10 ¹⁰ cm ^"2

Breakdown field strength E ₈ = 8.45 ± 0.03 MVcm " ¹

Claims (2)

1. A method for the passivation of Si devices by anodic oxidation, characterized in that in the surface of the thin insulator layer during or after the anodization fluoride in a concentration of 1 x 10 ¹⁷ to5x 10 ¹⁸ F-atoms x cm " ^{3 is} incorporated, wherein the fluoride content in the center of the insulator layer does not exceed 10% of the surface concentration, and that the oxide layer is annealed before or after fluoride incorporation. 2. The method according to claim 1, characterized in that the Fluorideinbau carried out by pretreatment of the substrate in HF and subsequent anodization.