GB2146566A - Electrostatic bonding - Google Patents

Abstract

A silicon body, e.g. a transducer 11 is provided with a surface coating 12 of a glass. The glass is ground and polished to a thickness of 5 to 100 microns and the assembly is then electrostatically bonded to a silicon substrate 13. <IMAGE>

Description

SPECIFICATION Electrostatic bonding This invention relates to electrostatic bonding processes, and in particular to a process for bond ing a silicon body to a substrate.

Silicon transducers such as those described in our published specifications No. 2115551 (J.C.

Greenwood 44) and No. 2095911 (J.C. Greenwood 40) are finding increasing use in a variety of applications. For many of these applications it is necessary to mount the transducer in a housing and this in turn entails bonding the transducer to a substrate. Conventionally this is done with an adhesive such as an epoxy resin but problems have been encountered in the form of thermal mismatch between the adhesive and the transducer.

According to the invention there is provided a process for bonding a silicon body to a silicon substrate, the method including applying a glass to at least a portion of the body, grinding and polishing the glass to a thickness between 5 and 100 microns and electrostatically bonding the glass coated body to the substrate.

As the bond is effectively silicon to silicon the problem of thermal mismatch is overcome.

Embodiments of the invention will now be described with reference to the accompanying drawings in which the single figure is a cross sectional view of a transducer prior to bonding to a substrate.

Referring to the drawing, a silicon transducer 11 is coated on a surface with a layer 12 of a glass composition, typically a borosilicate glass. This glass layer is ground and polished and the assembly is then placed in contact with a silicon substrate 13.

The transducer and substrate are heated to a temperature below the softening point of the glass.

For a borosilicate glass a temperature of 400 to 5000C is suitable. An electric potential of 800 to 1200 volts is applied between the transducer and substrate, the substrate being negative, relative to the transducer. After a short time a permanent electrostatic bond is effected.

The glass may be applied to the transducer either by electrostatic bonding or by firing of a glass frit. Where electrostatic bonding is used the glass is ground and polished to a thickness of 5 to 100 microns prior to bonding to the substrate. If however the glass is applied as a glaze it is ground and polished to a thickness not less than 5 microns, typically 10 to 15 microns before bonding to the substrate is effected.

1. A process for bonding a silicon body to a silicon substrate, the method including applying a glass to at least a portion of the body, grinding and polishing the glass to a thickness between 5 and 100 microns and electrostatically bonding the glass coated body to the substrate.

2. A process as claimed in claim 1, wherein the glass is electrostatically bonded to the silicon body.

3. A process as claimed in claim 2, wherein the glass is ground and polished to a thickness of 10 to 15 microns prior to bonding to the substrate.

4. A process as claimed in any one of claims 1 to 3, wherein the glass is a borosilicate glass.

5. A process as claimed in claim 4, wherein the glass is heated to a temperature of 400 to 500'C during the bonding process.

6. A process as claimed in any one of claims 1 to 5, wherein a potential of 800 to 1200 volts is applied across the glass layer to effect bonding, the substrate being negative relative to the silicon body.

7. A process for bonding a silicon body to a silicon substrate substantially as described herein with reference to the accompanying drawings.

8. A transducer assembly prepared by a process as claimed in any one of claims 1 to 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrostatic bonding This invention relates to electrostatic bonding processes, and in particular to a process for bond ing a silicon body to a substrate. Silicon transducers such as those described in our published specifications No. 2115551 (J.C. Greenwood 44) and No. 2095911 (J.C. Greenwood 40) are finding increasing use in a variety of applications. For many of these applications it is necessary to mount the transducer in a housing and this in turn entails bonding the transducer to a substrate. Conventionally this is done with an adhesive such as an epoxy resin but problems have been encountered in the form of thermal mismatch between the adhesive and the transducer. According to the invention there is provided a process for bonding a silicon body to a silicon substrate, the method including applying a glass to at least a portion of the body, grinding and polishing the glass to a thickness between 5 and 100 microns and electrostatically bonding the glass coated body to the substrate. As the bond is effectively silicon to silicon the problem of thermal mismatch is overcome. Embodiments of the invention will now be described with reference to the accompanying drawings in which the single figure is a cross sectional view of a transducer prior to bonding to a substrate. Referring to the drawing, a silicon transducer 11 is coated on a surface with a layer 12 of a glass composition, typically a borosilicate glass. This glass layer is ground and polished and the assembly is then placed in contact with a silicon substrate 13. The transducer and substrate are heated to a temperature below the softening point of the glass. For a borosilicate glass a temperature of 400 to 5000C is suitable. An electric potential of 800 to 1200 volts is applied between the transducer and substrate, the substrate being negative, relative to the transducer. After a short time a permanent electrostatic bond is effected. The glass may be applied to the transducer either by electrostatic bonding or by firing of a glass frit. Where electrostatic bonding is used the glass is ground and polished to a thickness of 5 to 100 microns prior to bonding to the substrate. If however the glass is applied as a glaze it is ground and polished to a thickness not less than 5 microns, typically 10 to 15 microns before bonding to the substrate is effected. CLAIMS

1. A process for bonding a silicon body to a silicon substrate, the method including applying a glass to at least a portion of the body, grinding and polishing the glass to a thickness between 5 and 100 microns and electrostatically bonding the glass coated body to the substrate.

2. A process as claimed in claim 1, wherein the glass is electrostatically bonded to the silicon body.

3. A process as claimed in claim 2, wherein the glass is ground and polished to a thickness of 10 to 15 microns prior to bonding to the substrate.

4. A process as claimed in any one of claims 1 to 3, wherein the glass is a borosilicate glass.

5. A process as claimed in claim 4, wherein the glass is heated to a temperature of 400 to 500'C during the bonding process.

6. A process as claimed in any one of claims 1 to 5, wherein a potential of 800 to 1200 volts is applied across the glass layer to effect bonding, the substrate being negative relative to the silicon body.

7. A process for bonding a silicon body to a silicon substrate substantially as described herein with reference to the accompanying drawings.

8. A transducer assembly prepared by a process as claimed in any one of claims 1 to 7.