Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Uniting two separate solid materials
Patent
1997-07-18
1999-08-17
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Uniting two separate solid materials
65 40, 65 43, 10628726, 10628734, 1562722, 1562731, 204164, 252309, 2523132, C03C 2900, C03B 802, C04B 3700, H01L 21316
Patent
active
059389117
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of producing connections between an alkali-containing glass and an electrically conductive material, for example a metal or a semiconductor. Such connections are in particular suitable for connecting the surfaces of two semiconductor elements, for example two silicon wafers with an intermediate alkali-containing glass coating. These methods are used above all in the semiconductor industry.
By anodic bonding is understood a method of producing a connection between alkali-containing glass and electrically conductive material. Anodic bonding is particularly suitable for connecting a semiconductor platelet with a glass layer. In this case, at a temperature of 300.degree. C. to 450.degree. C. an electrical voltage is applied between the ion-conductive alkali-containing glass and the semiconductor, for example silicon. This electrical voltage causes electrochemical reactions at the boundary layer between glass and semiconductor, by means of which the glass is securely connected to the semiconductor. A decisive factor for anodic bonding is substantially the alkali content of the glass coating. The result is a secure undetachable connection between the alkali-containing glass and the semiconductor material.
For anodic bonding of silicon wafers, particularly suitable are boron silicate glasses with a variable content of B.sub.2 O.sub.3, SiO.sub.2 and/or Al.sub.2 O.sub.3. They are characterised by high chemical strength and by a low coefficient of expansion.
The glass coatings required for anodic bonding are conventionally produced by molecular coating processes such for example as sputtering or vapour deposition or by coating with appropriate colloidal solutions. In the molecular coating processes however, at larger coating thicknesses such as for example required for connecting to silicon wafers, process times of some hours result. In addition the production of such coatings in sputtering or vapour deposition installations always involves the formation of such thick coatings inside the apparatus. These coatings must be removed from time to time, leading to frequent servicing and cleaning operations. Therefore the application of glass coatings by molecular coating processes such as sputtering or vapour deposition are expensive and unprofitable for anodic bonding with glass intermediate layers.
In contrast, glass coatings produced by spin-on deposition of or immersion in appropriate colloidal solutions, are characterised in that the coating process and the apparatus required therefor provide good value. For this purpose sol-gel-coatings on the basis of TEOS (tetraethyl orthosilicate) are normally used. When this coating method is used, however, at the required coating thicknesses for anodic bonding of two semiconductor panels, mechanical stresses occur within the layers which lead to the formation of cracks. Therefore the normally used sol-gel-coatings on the basis of TEOS cannot be used for the production of coating thicknesses which exceed 100 nm.
In summary it can be seen that in order to produce glass coatings for anodic bonding with a thickness between 0.1 and 10 .mu.m, as are required for example for anodic bonding of two semiconductor plates, molecular application methods such as sputtering or vapour deposition are extremely expensive and involve a high outlay on servicing and cleaning, while the more cost-effective methods in which appropriate colloidal solutions are applied for example by spin-on deposition or immersion, are not suitable for the production of such thick glass coatings. Thus until now there has been no suitable and at the same time cost-effective method of producing alkali-containing glass coatings with a thickness between about 0.1 and about 10 .mu.m.
It is therefore the object of the invention to make available a simple and cost-effective method for anodic bonding, in which alkali-containing glass coatings with a thickness exceeding 100 nm and can also extend as far as about 10 .mu.m, are used on an electrically conductive carrier material such for example
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Dell Carola
Quenzer Hans-Joachim
Fraunhofer-Gesellschaft zur Foerderund der Angewandten Forschung
Gorgos Kathryn
Leader William T.
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