Method for bonding substrates

Abstract

This invention relates to a method for bonding of a first contact area of a first at least largely transparent substrate to a second contact area of a second at least largely transparent substrate, on at least one of the contact areas an oxide being used for bonding, from which an at least largely transparent interconnection layer is formed with an electrical conductivity of at least 10e1 S/cm.sup.2 (measurement: four point method, relative to temperature of 300K) and an optical transmittance greater than 0.8 (for a wavelength range from 400 nm to 1500 nm) on the first and second contact area.

Claims

1. A method for bonding a first contact area of a first transparent substrate to a second contact area of a second transparent substrate, on at least one of the contact areas an oxide being used for bonding to form a transparent interconnection layer on the first and second contact areas, said method comprising the following steps: applying a first oxide layer with an electrical conductivity of at least 10e.sup.1 S/cm (measurement: four point method, relative to temperature of 300K) and an optical transmittance greater than 0.8 (for a wavelength range from 400 nm to 1500 nm) to the first substrate, applying a second oxide layer to the second substrate, applying a third oxide layer to the second oxide layer, the third oxide layer having an oxygen volume S.sub.1 which is smaller than 70% of the maximum oxygen volume S.sub.max of the third oxide layer, applying a fourth oxide layer to the third oxide layer, plasma-activating the first substrate to produce a reservoir, bonding the first and second substrates, wherein a first educt intercalated in the reservoir diffuses through the fourth oxide layer (9) and oxidizes the third oxide layer.

2. The method as claimed in claim 1, wherein the oxide or one or more of the oxide layers contain at least one of the following components, as doping: indium, tin, aluminum, zinc, gallium, fluorine or antimony.

3. The method as claimed in claim 1 or 2, wherein the oxide or one or more of the oxide layers are applied by one of the following methods: metal organic chemical vapor deposition, metal organic molecular beam deposition, spray pyrolysis, pulsed laser deposition or sputtering.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic view of one embodiment of this invention briefly before the first substrate makes contact with the second substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(2) The same or equivalent features are identified with the same reference numbers.

(3) The situation in FIG. 1 shows only one cross sectional segment of a first contact area 3 of a first substrate 1 and a second contact area 4 of a second substrate 2. The surfaces of the contact areas 3, 4 are terminated with polar OH groups and are accordingly hydrophilic. The first substrate 1 and the second substrate 2 are held by the force of attraction of the hydrogen bridges between the OH groups which are present on the surface and the H.sub.2O molecules and also between the H.sub.2O molecules alone, among others by van der Waals forces and/or hydrogen bridges. The hydrophilicity of at least the first substrate 1 has been increased by plasma treatment in a preceding step.

(4) Plasma treatment takes place in a plasma chamber which can be exposed to plasma and a vacuum and/or a defined gas atmosphere and which can be provided in its own module of a corresponding apparatus. To be exposed to a vacuum and/or a defined gas atmosphere means that pressures below 1 mbar can be set and controlled. In the exemplary embodiment described here the gas is N.sub.2 at a pressure of 0.3 mbar.

(5) It is advantageous according to the alternative embodiment to subject the second substrate 2 or the second contact area 4 to plasma treatment in addition, simultaneously with the plasma treatment of the first substrate 1.

(6) A reservoir 5 in an oxide layer 6 consisting of the selected TCO has been formed as claimed in the invention by the plasma treatment. Under the oxide layer 6, a semiconductor 7 directly adjoins and can be used among others optionally also as a reaction layer which contains a second educt or a second group of educts. Plasma treatment with N.sub.2 ions with the aforementioned ion energy yields an average thickness R of the reservoir 5 of roughly 15 nm, the plasma ions forming channels or pores in the oxide layer 6. The reservoir is filled with a first educt which reacts with the second educt.

(7) The semiconductor 7 is temporarily supported by a carrier 8 in the illustrated embodiment.

(8) The second substrate 2 on the second contact area 4 is comprised of a fourth oxide layer 9, directly followed by a third oxide layer 10.

(9) The oxide layer 10 (precursor layer) is comprised of a TCO which contains incompletely oxidized components so that the layer has an oxygen volume S.sub.1 which is smaller than the maximum oxygen volume S.sub.max which would be contained in the layer if the entire volume were completely oxidized. In particular, the oxygen volume S.sub.1 is a maximum 70% of S.sub.max. Advantageously, this percentage is 55%, more advantageously 40% and most advantageously 25%.

(10) The second oxide layer 11 is joined tightly to a semiconductor 12 of the second substrate 2 which in turn is temporarily fixed on a carrier 13.

(11) The semiconductor 12 is used as a reaction layer which contains a second educt or a second group of educts.

(12) A growth layer is formed by the reaction of the first educt with the second educt between the oxide layers 6, 9, 10, 11 and optionally the reaction layers (semiconductor 7, 12).

(13) In one preferred embodiment, the first educt which has been intercalated in the reservoir 5 formed in the oxide layer 6 reacts with the precursor layer 10. This reaction results in an increase in volume since the reaction product of the first educt and the precursor layer has a higher molar volume.

(14) By increasing the molar volume and diffusion of the H.sub.2O molecules, especially on the interface between the oxide layers 9 and 10, a volume in the form of a growth layer grows, due to the objective of minimizing the free Gibb's enthalpy intensified growth, taking place in regions in which gaps are present between the contact areas 3, 4. The gaps are closed by the increase in the volume of the growth layers.

(15) The oxide layers 6, 9, 10, and 11 after bonding jointly form an interconnection layer 14.

(16) This interconnection layer in one preferred embodiment after the reaction is advantageously comprised of a homogenous material which corresponds essentially to the same TCO comprising the originally deposited oxide layers 9, 11 and 6.

REFERENCE NUMBER LIST

(17) 1 first substrate 2 second substrate 3 first contact area 4 second contact area 5 reservoir 6 first oxide layer 7 first semiconductor 8 first carrier 9 fourth oxide layer 10 third oxide layer 11 second oxide layer 12 second semiconductor 13 second carrier 14 interconnection layer