Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Utility Patent
1994-04-08
2001-01-02
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S359000, C156S362000, C156S556000, C156S583100
Utility Patent
active
06168678
ABSTRACT:
The subject of the invention is used in particular when fabricating sensors built up in laminar construction. Thus for instance pressure- or acceleration-sensors can be manufactured in a particularly advantageous manner by means of stacked substrates, wherein the substrates or substrata have previously been processed in a suitable manner, meaning they have been provided with specific delicate structures.
In order to now connect the substrates to one another, various technologies have already been developed. At this time we will only mention the following methods known to the specialized community without any more precise explanations:
anodic bonding
silicon fusion bonding
eutectic bonding
low temperature glass bonding
All these bonding methods require that the surface of the substrates must be polished and thoroughly cleaned, that the substrates to be bonded to one another therefore must be manipulated in as particle-free an environment as possible, that they must meet very tight specifications as far as the evenness or flatness of the contact faces of the individual substrates is concerned and that the interconnection of the substrates must occur so that they remain free of mechanical stresses, in order to prevent void-like free spaces in between the substrates. The non-observance of these basic requirements considerably reduces the quality of the surfaces to be joined to one another. It can even put into question the intended function of the product to be fabricated.
The present invention will be described in the following for better understanding by way of an example of the method of anodic bonding. Although it is naturally not limited to this specific method, it can rather be used with other bonding methods.
Anodic bonding serves for establishment of a hermetic and mechanically solid connection between glass- and metal-substrates or a connection between glass- and semiconductor-substrates. For this purpose the stacked one-upon-the-other substrates must be heated to a temperature of several hundred ° C. and a DC voltage of about 1000 Volts must be applied to them. Electrostatic forces and the migration of ions lead finally to an irreversible chemical bond at the boundary layer between the individual substrates.
This fabrication method is for instance used in the fabrication of acceleration sensors or accelerometers. Structures in the range of micrometers can be placed in a semiconductor substrate or substratum by anisotropic etching. Herein in many application cases the substrates are not etched through their entire thickness, so that the substrate remains “non-transparent”. A semiconductor structured in such a way is covered on both sides by glass substrates for obtaining a functional sensor, wherein the glass substrate also mostly has delicate structures on the side facing the semiconductor substrate, wherein for instance conductor parts and contact strips for the sensor produced by metallizing or etched channels, which on their part must be oriented with respect to the active structures of the semiconductor substrate participating in the change of the measured magnitude.
In the fabrication of such multilayer substrate packages a problem occurs, if one or several of the substrates which have to be aligned with high precision to one another is or are not transparent.
Methods and devices are known which perform the construction of a substrata package consisting of several substrates in a layered manner, by to begin with aligning a glass layer with the semiconductor substrate and connect same by bonding and thereupon turn the thus constituted two layer package, in order to subsequently apply the second glass layer to the other surface of the semiconductor substrate.
However this method has several disadvantages. On the one hand glass and semiconductor materials have different coefficients of thermal expansion, so that in the course of the initial bonding of the intermediate layered packets same bends in accordance with the bimetallic spring principle. The unevenness caused by the arching must be compensated by a compressive force during the alignment of the second glass substrate. In this method it is thus unavoidable, that the thus fabricated multilayer package warps in an unsymmetrical manner.
Devices for performing the described method have often a heating arrangement, which is designed in such a way, that the substrate package to be bonded is heated only from one side. During the first bonding process the semiconductor substrate is for instance placed upon a heating plate, during the second bonding process the glass substrate is then placed upon the heating plate. The glass substrate however has a considerably lower heat conductivity than the semiconductor substrate. Thus the temperature of the boundary layers to be bonded are in both cases different. A temperature regulation at the bonding surface does not result in any improvement, since the differing temperatures of the heating device again cause warping of the substrate package in a disadvantageous manner.
Another disadvantage in the described known device for performing the fabrication method consists in that in the course of the second bonding process the first substrate package is subjected to an electric pole reversal, since the heating plate is usually connected solidly to the cathode potential due to the construction of this apparatus. The anode contacts should however always be applied to the semiconductor substrate. An impairment of the mechanical properties of the first bond connection cannot be completely excluded by the chemical process at the boundary surface triggered by reversal of the poles.
The present invention is now based upon the task of creating a method and an appropriate device, in order to bond substrates, which have approximately the same surface area and of which at least one is not transparent, with one another while observing a very high adjustment or alignment accuracy to one another in accordance with their structure, wherein cycle times must be achieved, which are suitable for a series fabrication of the substrate packages to be bonded.
As a marginal condition the solution must take account, that the device must meet all those requirements which apparatus used in a clean room must satisfy. Freedom from particles is especially one of those, meaning it has to be assured that none of the components of the device produces particles. Thus for instance no guides causing abrasion wear can be used in the transportation means and if pneumatic drives are used the waste air must be directed below the working surface.
The discovered solution solves the problem as defined in an advantageous manner and completely avoids the disadvantages of the known methods and devices. The separation in space of the adjustment- and heating-units is particularly expedient. The adjustment unit, which aligns the position of the substrate with an accuracy of a few micrometers, is thus not exposed to the high temperatures required for bonding. The length- and volumetric-expansion of the means for receiving and retaining the substrate as well as that of the substrates themselves would, at the required temperatures, be of the same order of magnitude as the adjustment accuracy required due to the width of the structures or it would even exceed these. Therefore, in the invention the extremely accurate alignment of the substrates to one another corresponding to their structure is performed in a first working region of a handling device. Thereupon the substrates are then conveyed to another working region of the handling device by a transport arrangement and are there deposited one upon the other in the defined manner, prior to all the substrates being fed together to a heating device in the form of a substrate package containing them in an aligned manner.
All the superimposed substrates are simultaneously bonded in only one work step, wherein the disadvantages of the thermal warping by stepwise bonding are completely eliminated and the fabrication period is considerably shortened. The bonding is a fabrication step requiring
Lindner Thomas
Plankenhorn Horst
Brown & Wood LLP
Mannesmann Kienzle GmbH
Mayes Curtis
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