WO2002038490A2 - Method for producing glass-silicon-glass sandwich structures - Google Patents

Abstract

The invention relates to a method for producing glass-silicon-glass sandwich structures which are connected irreversibly and in such a way that they are adjusted to correspond. Said structures consist of a bottom and a top glass substrate (2, 3) and a silicon substrate (1) in-between. At least one of the substrates (1; 2; 3) is provided with 3D depth structuring. The aim of the invention is to provide a low-cost production method, especially with a view to mass production of glass-silicon-glass sandwich structures. To this end, the silicon substrate (1) is irreversibly connected to one of the glass substrates (2; 3) before or after the 3D depth structuring. The bond is reduced to a predetermined end thickness from the glass and/or the silicon side by means of grinding, etching and polishing methods and the remaining silicon surface is then connected to a second glass substrate (3; 2) by anodic bonding.

Description

 Process for the production of glass-silicon-glass sandwich structures

The invention relates to a method for producing irreversibly and aligned interconnected glass-silicon-glass sandwich structures, consisting of a lower and an upper glass substrate, and an intermediate silicon substrate, at least one of the substrates being provided with a 3-D depth structuring ,

For the production of three-dimensional glass-silicon-glass sandwich structures, there are already a variety of technical solutions for a wide variety of applications.

For example, EP 0 633 468 A2 describes a process for the production of three-dimensional microcapillaries for the production of complex microsystems, which allows the integration of singular sensor elements using special fluidic, mechanical, electrical interface elements, the so-called channel stoppers. A disadvantage of this technology can be seen in the fact that the height of the microchannel cannot deviate from the specified thickness of the silicon substrate used, which is usually a few hundred micrometers, and therefore extremely small channel volumes of 150 ... 5 nl / cm can hardly be achieved are.

PCT / DE 00/00768 describes a manufacturing technology for manufacturing 3-D manifolds, which is based on the use of low-temperature cofiring ceramic (short: LTCC - ceramic) and names the possibility as a specific advantage Integrate intersecting fluidic and electrical functional levels in a compact module. Cons This technology means that channel systems with channel volumes below 2μl / cm cannot be produced in this way and that the surface quality of the ceramic material is significantly poorer because of the porosity of the materials silicon and glass. For extreme low-volume applications, this method is therefore [generally not suitable.

The technical article "A 3-D microelectrode system for handling and caging single cells and particles", Biosensors & Bioelectronics 14 (1999) pp-247-256 and the German patent application [No. 100 44 33.8] describe manufacturing techniques for three-dimensional microcapillary systems , which consist of the materials glass and photopolymer and can be used for extreme low-volume applications down to the range of 350pl / cm channel volume.

Disadvantages of these three-dimensional microcapillary systems are the limited chemical resistance of the polymers used to chemically aggressive media, the relatively low pressure resistance and high side wall roughness.

An SOI wafer material (SOI: silicon on insulator) is available for the manufacture of 3-D microcapillary systems for channel volumes of less than 150 ... 5 nl / cm. However, due to the complex and lengthy manufacturing technology, this material is 10 times more expensive than conventional silicon material. In order to be able to produce an SOI structure, a sacrificial substrate is required, which requires the use of the Si-Si fusion bond at 1000 ° C. for several hours.

The disadvantage of the high material costs and the large additional technological expenditure in the production should be countered with the introduction of the production technology according to the invention. The invention has for its object to provide an inexpensive manufacturing process, particularly with a view to the mass production of glass-silicon-glass sandwich structures, which is also suitable for applications in, for example, molecular biology or biotechnology. -.

The object on which the invention is based is achieved in that the silicon substrate is irreversibly connected to one of the glass substrates by anodic bonding before or after its 3-D deep structuring, the bond by means of grinding, etching and polishing methods of the glass and / or Silicon side is thinned to a predetermined final thickness and that the remaining silicon surface is subsequently connected to a second In glass substrate by anodic bonding.

The particular advantage of this method can be seen in the fact that the production of glass-silicon-glass sandwich structures is technically possible even with the smallest possible deep structuring and, moreover, can be carried out in a particularly cost-effective manner and in a mass process.

Another advantage can be seen in the fact that it is possible to make changes to the thickness of the substrates or the composite before its final completion by means of mechanical-chemical processes, without using a sacrificial substrate, as in the SOI technology described at the outset got to.

Further configurations emerge from the associated subclaims. In particular, subclaims 2 and 3 show two advantageous variants of the method according to the invention. In the associated drawing figures show:

1 shows the target structure of a glass-silicon-glass sandwich structure produced according to the invention;

2 shows the most important SOG process sequences for a variant I for producing a glass-silicon-glass sandwich structure; and

3 shows the most important SOG process sequences for a variant II for producing a glass-silicon-glass sandwich structure.

The glass-silicon-glass sandwich structures according to the invention can be used, for example, as a microreaction space in chemical analysis, the status of the chemical reaction taking place in the microcapillary 4 being able to be queried online and, due to the transparent structure, preferably by means of optical detection methods.

The special feature of the manufacturing process according to the invention (SOG process) is that the manufacture of glass-silicon-glass sandwich structures is technically possible even with the smallest channel geometries or the smallest 3-D depth structuring and can also be carried out particularly economically and in bulk. The SOG process is to be understood as a silicon-on-glass process, in which the silicon substrate 1 is either attached unstructured to a glass substrate 3 by anodic bonding and subsequently thinned (variant I), or the silicon substrate 1 is structured, then with the structured one Side is fixed on the glass substrate 2 by anodic bonding and subsequently thinned (variant II). Which variant can be used depends on the design and the required quality characteristics of the end product. the masking of the silicon substrate 1 by Coatings are carried out, which has been applied to the surface of the silicon substrate 1 by spin coating from Fotopolyme.ren or by a CVD coating.

For the structuring of the silicon substrate 1, the deep etching by wet chemical or dry chemical, anisotropically working deep etching processes is used. For this purpose, the masking of the silicon substrate 1 is necessary, which is done by means of structured photoresists, structured metal layers or also by structured inorganic insulator layers. The structured metal layers can consist of aluminum. Si0 ₂ or Si ₃ N ₄ can be used as the inorganic insulator layers.

Variant I of the process for producing a glass-silicon-glass sandwich structure comprises the following steps:

a) anodic bonding of the silicon substrate 1 with a thickness of significantly more than 15 μm on a first glass substrate 3,

b) thinning the silicon substrate 1 to a target value of X + 30 μm, and then finely polishing the silicon substrate 1 to the intended target value,

c) masking the silicon substrate 1 and photolithography in preparation for the subsequent deep etching,

d) anisotropic deep etching of the silicon substrate 1 to complete the structure provided in the silicon substrate, and

e) anodic bonding of a second glass substrate 2 on the silicon substrate 1. According to variant II, the process comprises the following steps:

a) masking the silicon substrate 1 in the unprocessed initial thickness in preparation for the deep etching,

b) subsequent anisotropic deep etching of the silicon substrate 1,

c) connecting the silicon substrate 1 to a glass substrate 2 by anodic bonding,

d) thinning the silicon substrate 1 to a target value of X + 30 μm and then finely polishing the silicon substrate to the predetermined target value,

e) attaching a second glass substrate 3 to the silicon substrate 1 by anodic bonding.

In both variants, the typical lateral dimensions of the microcapillary 4, ie the length, width and height of the microchannel, can be any value from a few 5 μm. The microcapillary can take any shape and can also be connected to a microreaction space or the like. In principle, there is also the possibility of simultaneously integrating electronic function modules or assemblies in the silicon substrate 1 using the usual means of microelectronics. In addition, with both variants it is also possible to provide the glass substrate 2 (top glass) and the glass substrate 3 (down or bottom glass) with suitable electrode systems before or after the anodic bonding, outside or inside the bond interface. Such electrode systems can be transparent or non-transparent, but in any case they can be extremely thin. For coupling the fluids into the microcapillary 4, holes 5 can be provided in one or both glass substrates 2, 3, which ensures access perpendicular to the course of the microchannel 4. However, it is also possible to couple fluids laterally into the composite, specifically via the channel on the silicon substrate 1 that is open at the end, so that access can be guaranteed parallel to the plane of the microchannel 4.

Process for the production of glass-silicon-glass sandwich structures

LIST OF REFERENCE NUMBERS

Silicon substrate glass substrate (top glass) glass substrate (bottom glass) microcapillary bore

Claims

Process for the manufacture of glass-silicon-glass sandwich structures 1. Method for producing irreversibly and aligned interconnected glass-silicon-glass sandwich structures, consisting of a lower and an upper glass substrate (2, 3), and an intermediate silicon substrate (1), at least one of the substrates (1; 2, 3) being provided with a 3-D depth structuring, characterized in that the silicon substrate (1) is in front of or after its 3-D depth structuring is irreversibly connected to one of the glass substrates (2; 3) by anodic bonding, the composite is thinned from the glass and / or silicon side to a predetermined final thickness by means of grinding, etching and polishing processes, and subsequently the remaining silicon surface is connected to a second glass substrate (3; 2) by anodic bonding. 2. The method according to claim 1, characterized in that the final thickness of the silicon substrate (1) is at least 15 microns. 3. The method according to claim 1 and 2, characterized in that the glass-silicon-glass sandwich structure is produced by the following process steps: a) anodic bonding of the silicon substrate (1) with a 'thickness of well over 15 μm on a first glass substrate (3), b) thinning the silicon substrate (1) to a target value of X + 30 μm, and then finely polishing the silicon substrate (1) to the intended target value, c) masking the silicon substrate (1) and photolithography in preparation for the subsequent deep etching, d) anisotropic deep etching of the silicon substrate (1) for! Completion of those provided in the silicon substrate Structure, e) anodic bonding of a second glass substrate (2) on the silicon substrate (1). 4. The method according to claim 1 and 2, characterized in that the glass-silicon-glass sandwich structure is produced by the following process steps: a) masking the silicon substrate (1) in the unprocessed initial thickness in preparation for deep etching, b) subsequent anisotropic deep etching of the silicon i substrate (1), c) connecting the silicon substrate (1) to a glass substrate (2) by anodic bonding, d) Thinning of the silicon substrate (1) to a target value of X + 30 μm and subsequent fine polishing of the silicon substrate (1) to the specified target value. e) attaching a second glass substrate (3) to the silicon substrate (1) by anodic bonding. 5. The method according to any one of claims 1 to 4, characterized in that the initial thickness of the silicon substrate (1) is between 300 and 1000 microns. 6. The method according to any one of claims 1 to 5, characterized in that the thickness of the first and the second glass substrate (2, 3) is between 200 ... 1000 microns. I. Method according to one of claims 1 to 6, characterized in that the silicon substrate (1) is thinned out by means of rough machining by mechanical or etching material removal. 8. The method according to claim 7, characterized in that the material removal is carried out after the rough machining by a fine polishing step. 9. The method according to claim 8, characterized in that the fine polishing step is carried out by chemical-mechanical polishing. 10. The method according to any one of claims 1 to 9, characterized in that the masking of the silicon substrate (1) is carried out by coatings which have been applied to the surface of the silicon substrate (1) by spin coating of photopolymers or by a CVD coating , II. Method according to one of claims 1 to 10, characterized in that the deep etching of the silicon substrate (1) is carried out by wet chemical or dry chemical, anisotropic deep etching processes. 12. The method according to any one of claims 1 to 9, characterized in that the masking of the silicon substrate (1) by structured photoresists, structured metal layers or by structured inorganic insulator layers. 13. The method according to claim 12, characterized in that the structured metal layers consist of aluminum. 14. The method according to claim 12, characterized in that the inorganic insulator layers consist of Si0 ₂ or Si ₃ N ₄ .