EP2318885A1

EP2318885A1 - Method for resist coating a recess in the surface of a substrate, in particular a wafer

Info

Publication number: EP2318885A1
Application number: EP09782047A
Authority: EP
Inventors: Katrin Weilermann
Original assignee: Suess Microtec Lithography GmbH
Current assignee: Suess Microtec Lithography GmbH
Priority date: 2008-08-29
Filing date: 2009-08-20
Publication date: 2011-05-11
Also published as: WO2010023156A1; EP3112935A1; EP3112935B1; TWI494701B; DE102008045068A1; TW201027264A

Abstract

The invention provides a method for resist coating a recess in the surface of a substrate, in particular a wafer. This involves filling the recess with a resist solution and heating the substrate, so that the solvent of the resist solution evaporates and the bottom of the recess and at least portions of the inner walls of the recess that adjoin the bottom are coated with the resist.

Description

Process for resist coating a depression in the surface of a substrate, in particular a wafer

The invention relates to a process for resist coating a depression, e.g. one

VIA ("vertical interconnect access") holes or a blind hole in the surface of a substrate, such as a wafer.

The coating with a resist, e.g. Varnish or dielectric layer, for example, is important for the wiring and coupling of MEMS ("micro-electro-mechanical system") devices.Contacts of these devices via wells such as VIA holes are advantageous to ever smaller encapsulations of MEMS devices (such as Sensors, memory, electronic or micromechanical devices).

Coatings of substrates are e.g. Known from Kutchoukov, V.G., Mollinger, J.R., Bossche, A .: "New Photoresist Coating Method for 3-D Structured Wafers" in Sensors and Actuators A, 2000, Vol. 85, pp. 377-383; Pham, Nga P., Burghartz, Joachim N., Sarro, Pasqualina M .: "Spray coating of photoresists for pattern transfer on high topography surfaces" in Journal of Micromechanics and Microengineering, 2005, Vol. 15, pp. 691-697; US-A-5,849,435; EP-A-1 840 940; and JP-A-2008-55268.

In order to obtain as accurate as possible contacts on the surface of a substrate, e.g. of a wafer, it is advantageous to have a uniform coating layer, e.g. from a photoresist, on the inner surface of the recess of the substrate. For wells having a large depth / width (or small diameter) ratio of the recess, it is particularly difficult, e.g. by spray coating to cover the walls of the recess over the entire surface.

One way to coat a well of a substrate is to apply a resist solution to both the surface of the substrate in one step and to fill in the well. Air trapped in the recess by the resist is then removed from the recess by means of, for example, ultrasound (see, for example, FIG. 1). With conventional methods, it is difficult to make a uniform resist layer over the entire area on the inner surface of a depression on a surface of a substrate.

It is therefore an object of the invention to provide an improved process for resist coating the inner surface of a depression on the surface of a substrate.

This object is achieved with the features of the claims.

In the method according to the invention, in a first process step (a) the depression on the surface of a substrate is filled with a resist solution and in a second process step (b) the substrate is heated such that the solvent of the resist solution evaporates and the bottom and at least portions of the interior walls of the recess adjacent to the bottom are coated with the resist. Preferably, the inner walls are partially or completely coated with the resist after the evaporation process.

A depression on the surface of a substrate may e.g. a VIA hole and has an inner surface of inner walls to be coated. These inner walls may be bottom and / or side walls of the recess. In a particular embodiment, the depression has a bottom wall ("bottom") which extends parallel to the surface of the substrate In a further embodiment, the depression has at least one side wall extending perpendicularly to it, parallel to the bottom The surface of such a depression is preferably an ellipse, in particular a circle, or a rectangle, in particular a square, or any polygon, and may be constant over the entire depth of the depression. opposite the surface of the substrate may be between 50 ° and 100 °, preferably at 90 °.

A resist solution essentially contains a resist and a solvent for the resist. A resist can e.g. a lacquer or photoresist, a positive novolak or a dielectric, e.g. BCB or SU-8, a photoresist from Microchem Corp., wherein mesitylene or PGMEA can be used as solvent.

The heating of the substrate, for example, at temperatures of 30 to 90 ° C, preferably from 50 to 90 ⁰ C, take place. The temperature increases can, for example, by one or more Infrared radiation sources or an electric heater can be generated, for example, the underside of the substrate touched directly or at a distance of 1 - 20 cm away from the surface of the substrate.

Upon heating, the solvent evaporates in the resist solution. Preferably, due to adhesion forces, the resist deposits as a substantially continuous layer on the bottom and at least on the parts of the inner walls of the depression which adjoin the bottom. Preferably, all inner walls of the recess are completely coated with the resist after the heating of the substrate. In this case, there are no portions of inner walls that are not coated with resist.

In a preferred embodiment, after step (b), in a further method step (c), the surface of the substrate is coated with a resist in such a way that also portions of inner walls of the recess which adjoin the surface of the substrate and according to method steps (a) and (b) are not yet coated, also coated.

By this coating of the surface of the substrate can be achieved that even in the cases in which after the steps (a) and (b), the inner walls of the recess were not completely coated with resist (such as at sections furthest from the bottom are removed), these have a resist layer at least after step (c). In this case, a continuous resist layer may be present on the inner walls of the recess and on the surface of the substrate.

In a preferred embodiment of the present invention, the surface of the substrate is coated with the resist by applying a resist solution. This resist solution is preferably applied to the surface by spray coating. In a particular embodiment, the viscosity of this solution is equal to or higher than the viscosity of the resist solution for filling the recess. The viscosities of resist solutions can range from> 0 centipoise to 200 centipoise.

In a preferred embodiment, the filling of the recess takes place simultaneously with a coating of the surface of the substrate with the resist solution. In this way, it can be achieved that in a single process step, preferably with a single spray nozzle, the resist solution is applied both to the surface of the substrate and into the depression on the surface of the substrate. The subsequent heating of the substrate then causes the solvent to evaporate, leaving a continuous resist layer on the surface and in the recess.

In a preferred embodiment, heating the substrate is heating the recess and / or the surface. By heating portions near the deposited or filled resist solution, the solvent is heated and evaporated so that a resist layer remains on the inner walls of the recess and / or on the surface of the substrate.

In a preferred embodiment, after the steps (a), (b) and optionally (c), the resist forms a continuous layer on the inner walls of the recess.

A continuous layer on a surface has no portions where the surface is not coated. The continuous resist layer on the surface of the substrate and / or in the recess (on the inner walls of the recess) is advantageous for the subsequent further processing of the substrate, e.g. during exposure, development and etching for later contacting on these surfaces.

In a preferred embodiment, the filling of the recess of the substrate is done by a spray coating.

A spray-coating is particularly advantageous for these purposes because it allows a very uniform application of the resist solution, thereby substantially eliminating / compensating for unevenness in the surface of the substrate and on the interior walls of the recess ,

In a preferred method, the volume of the filled resist solution is equal to or less than the volume of the well.

In a preferred embodiment, the recess is a through-hole, preferably a VIA hole, through the substrate. The substrate also has on its underside, its Surface opposite, a carrier, which closes the through hole on this side as the bottom. It may be advantageous that the through-hole has at least one side wall perpendicular to the substrate surface. In a particular embodiment, at least one side wall can have an inclination of, for example, 70 ° with respect to the substrate surface.

In a particularly preferred embodiment, the process according to steps (a) and (b), if appropriate after steps (a), (b) and (c), comprises a step (d) in which the carrier is removed.

The carrier may be attached to the substrate, e.g. glued on. Possible adhesives for these purposes may e.g. Acrylates or epoxy adhesives. Preferably, the substrate is easy to detach from the support, e.g. by using UV light or a chemical solvent. In this way, coated through-holes can be produced in a substrate or wafer.

In a preferred embodiment, after step (d), the method comprises a step (e) in which the underside of the substrate is coated with a resist, preferably spray-coated, such that portions of inner walls of the through-hole located on the underside of the substrate at lie next to be coated.

By means of this coating of the underside of the substrate, it can be achieved that even in the cases in which the inner walls of the through-hole are not completely coated with resist after removal of the carrier (eg caused by damage to the coating on ground-side side wall sections as a result of removal of the carrier). Soil), these at least after step (e) have a resist layer. In this case, e.g. a continuous resist layer on the inner walls of the through-hole and on the surface and the underside of the substrate. Preferably, after step (e), the substrate is heated so that any remaining solvents evaporate from the resist solution.

In a preferred embodiment, after steps (a), (b), (d) and (e), optionally after steps (a), (b), (c), (d) and (e), the resist forms in the through-hole and on the surface and the underside of the substrate, a continuous layer. This can For example, in the case of a through-hole as a depression, it is achieved that a resist solution, preferably by spray coating, is applied first to the upper side of the substrate and then to the lower side of the substrate, or vice versa. Alternatively, only the side walls of the through hole can be coated by, for example, a support is attached to the underside of the substrate such that it closes the through hole at this side liquid-tight. The resist solution is then filled in the through hole, the substrate is heated, and then the surface of the substrate is also coated with a resist (as another alternative, the inner walls may be simultaneously coated with the surface in one step). After removal of the carrier / bottom, the underside of the substrate is coated with the resist, preferably by spraying.

The e.g. The continuous resist layer produced in this manner at the surface, underside and the inner walls of the through-hole is advantageous for later contacting in the hole, since defects in this layer can thereby be avoided.

In a preferred embodiment, the substrate has on its surface and in the depression a dielectric layer on which the resist coating is carried out.

The dielectric layer may e.g. be an oxide layer.

A dielectric layer may e.g. serve as an insulator if a metal structure (for example of aluminum) is to be applied to the surface of the substrate in the event of a subsequent further processing of the substrate.

In a preferred embodiment, the ratio of the greatest depth of the depression, measured perpendicular to the substrate surface, to the greatest width or diameter of the depression, measured parallel to the substrate surface, is equal to 2: 1 or greater. The greatest depth of the depression, measured perpendicularly to the substrate surface, can be between 20 μm and 300 μm, preferably between 30 μm and 150 μm or between 40 μm and 70 μm, and the greatest width of the depression, measured parallel to the substrate surface, can be 10 μm 200 microns, preferably 10 microns to 100 microns or 20 microns to 50 microns, amount.

In a preferred embodiment, the thickness of the resist layer in the recess of the substrate and preferably also on the surface and / or the underside of the substrate at least 0.5 μm, preferably at least 0.8 μm or at least 1.0 μm. Such resist layer thicknesses may allow for further processes, such as exposure, development and etching, particularly accurate (sharp-edged) surface structures for subsequent contacting.

In a preferred embodiment, after step (a), a step (a1) is performed in which air trapped by the resist in the well is removed by application of ultrasound and / or nitrogen flow or vacuum.

As discussed above, the application of ultrasound (e.g., by placing an ultrasound source under the substrate) and / or vacuum removes trapped air from the filled resist from the well. As an alternative or in addition to the ultrasound source, it is also possible to use nitrogen which flows from a nozzle arranged at an angle to the surface of the substrate. By removing entrapped air, it is possible to produce a uniform resist layer over the entire surface of the inner surface of the depression.

In a preferred embodiment, ultrasound is used at a frequency of 100 kHz to 5 MHz, preferably more than 400 kHz, for example between 1 MHz and 3 MHz ("megasonic").

In a preferred embodiment, after step (a) and optionally after step (a1), a step (a2) is carried out in which the surface of the substrate is cleaned by centrifuging, in particular using the resist solution or a solvent.

In order to avoid contamination on the surface, even for later contact, it may be useful to clean the surface during the coating. This is preferably done with the resist solution itself or using a solvent which does not damage the surface. Vorteilhafiterweise the cleaning is done so that the substrate is rotated so that the appropriate cleaning solution can be applied to the surface and can be thrown off of this together with any impurities. In a particularly preferred embodiment, a solution of AZ 4620 and acetone (1-5 centipoise) is used as the resist solution. After filling the well, the solvent acetone is evaporated from the resist solution at a temperature of 30 to 90 ° C by means of a hot plate, which is located directly under the substrate over a period of 10 min. The resist layer remaining in the recess is at least about 2 μm thick in this case.

The invention will be explained in more detail below with reference to the figures, which schematically show the method of resist coating recesses.

Fig. 1 is a side view of a substrate having a recess for explaining a conventional coating method;

Figure 2 shows a side view of a substrate having a recess which has been coated by the method according to the invention;

FIG. 3 shows a side view of a substrate with a through hole which has been coated on a dielectric layer by the method according to the invention;

FIG. 4 shows a side view of the substrate from FIG. 3 after a further treatment, in which the resist coating has been removed and a metal layer has been applied.

Figure 1 shows by way of example a conventional method, such as a substrate 10, e.g. a wafer, with a recess 11 can be coated. For this purpose, a resist layer 13 is applied to the surface 12 of the substrate 10 and thereby also filled in the recess 11. Any air bubbles 14 trapped in the resist solution being applied may then e.g. With ultrasound 16 (and / or nitrogen flow from a nozzle or vacuum) are removed from the recess 11 through the resist layer 13 (upward).

An inventive method for coating a depression 110 on the surface 120 of a substrate 100 will be described by way of example with reference to FIG.

A resist solution is filled in the recess 110. Before, simultaneously or after filling, the substrate 100 is heated (via a heat source 160), so that the Solvent in the resist solution can evaporate. What remains is a resist layer 131 in the recess 110 covering the inner walls 112, 114, that is, the side walls 112 and the bottom 114. The side walls 112 are thereby covered at least at the portions which adjoin the bottom 114. It may be possible that the entire sidewalls 112 are not covered by the resist layer 131. In this case, by subsequently applying a resist solution to the surface 120 of the substrate 100, it is also possible to obtain sections of the side walls 112 of the recess 110 which are closest to the surface 120 (such as, for example, sections above the horizontal line 115 in FIG Figure 2) covered with the resist solution (eg, by overflowing the resist solution from the surface 120 of the substrate into the well 110, at least along the upper sidewalls 112). Reheating the substrate 100 causes the solvent to evaporate out of the resist solution, leaving a resist layer 130 behind.

In this way, a depression in a substrate can be coated with a resist throughout and evenly (i.e., substantially flat except for corner or edge regions).

Alternatively, it is also possible that a resist solution is applied to the surface 120 of the substrate 100 and simultaneously filled into the recess 110. After heating the substrate 100 by a heat source 160, the bottom 114 of the recess 110 and the surface 120 of the substrate 100 and at least portions of the sidewalls 112 adjoining the bottom 114 are then covered with a resist layer 130, 131. If sections of the side walls 112 of the depression 110 are not covered with a resist layer, this can be done by applying (for example by spray coating) a resist solution to the surface of the substrate 100 again. In this case (possibly after renewed heating of the substrate), the previously uncovered upper portions of the side walls 112 can be coated with resist.

Even with this alternative, a depression in a substrate can be continuously and evenly coated with a resist.

In a further alternative, a resist solution is applied to the surface 120 of the substrate 100 and simultaneously filled into the recess 110. Heating the Substrate 100 may be provided by a heat source 160 and, finally, the bottom 114 of the recess 110, the surface 120 of the substrate 100, and the sidewalls 114 are completely covered by a continuous, uniform resist layer 130, 131.

FIG. 3 shows by way of example a side view of a substrate 200 with a through-hole 210. The substrate and the through-hole have a dielectric layer 240 to which a resist layer 230 has been applied by one of the methods described above. In this case, a contact structure 250 functions as the bottom. On this substrate, a lithographic process is subsequently carried out in order to enable contacting through the through-hole 210. To this end, the resist layer 230 is exposed and developed so that the portion 232 of the resist layer 230 can be removed. Subsequently, the portion 242 of the dielectric layer is released from the layer by etching. The residual resist layer 230 is then removed with a solvent.

As seen from Figure 4, after the resist layer 230 has been removed, a metal layer 260 (e.g., of aluminum) may be applied to the dielectric layer 240. This metal layer 260 may then cause a contact 262 to the contact structure 250, since the dielectric layer has been interrupted at the section 244 by the etching process described above.

In this way, coatings for through holes or other depressions in substrates, such as silicon wafers, for further processing to e.g. microelectromechanical systems are realized.

Claims

claims

A method of resist-coating the inner surface of a depression in the surface of a substrate, comprising the steps of:

(a) filling the well with a resist solution,

(al) removing trapped air in the well by using

Ultrasound and / or nitrogen flow or of ultrasound and vacuum,

(b) heating the substrate so that the solvent of the resist solution evaporates and the bottom and at least portions of the inner wall of the recess adjacent to the bottom are coated with the resist,

wherein the width of the recess is 10 to 100 microns.

2. The method of claim 1, wherein after step (b) the following step is performed:

(c) coating the surface of the substrate with a resist such that also portions of inner walls of the recess adjacent to the surface of the substrate are coated.

3. The method of claim 2, wherein the coating of the surface of the substrate with the resist by applying a resist solution, preferably by spray coating occurs.

4. The method of claim 3, wherein the viscosity of this solution is equal to or higher than the viscosity of the resist solution for filling the recess.

5. The method of claim 1, 2, 3 or 4, wherein the filling of the recess occurs simultaneously with the coating of the surface of the substrate with the resist solution.

6. A method according to any one of the preceding claims, wherein heating the substrate causes heating of the recess and optionally of the surface.

7. The method according to any one of the preceding claims, wherein after the steps (a), (b) and optionally (c), the resist forms a continuous layer on the inner wall of the recess.

8. The method according to any one of the preceding claims, wherein the filling of the recess of the substrate is carried out by spray coating.

9. The method according to any one of the preceding claims, wherein the volume of the filled solution is smaller than the volume of the recess or equal.

10. The method according to any one of the preceding claims, wherein the recess is a through hole through the substrate and the substrate has on its underside, which is opposite to its surface, a support which closes the through hole at this side as a bottom.

11. The method of claim 10, wherein after steps (a) and (b), optionally after the steps (a), (b) and (c), the following step is provided:

(d) removing the carrier.

12. The method according to claim 11, comprising the following step (e) after step (d):

(E) coating, preferably spray coating, the underside of the substrate with a resist such that also portions of inner walls of the through hole, which are closest to the underside of the substrate, are coated.

13. The method of claim 12, wherein after steps (a), (b), (d) and (e), optionally after steps (a), (b), (c), (d) and (e) that forms resist in the through-hole and at the surface and the bottom of the substrate a continuous layer.

14. The method according to any one of the preceding claims, wherein the substrate has on its surface and in the recess a dielectric layer on which the resist coating is performed.

15. The method according to any one of the preceding claims, wherein the ratio of the greatest depth of the recess measured perpendicular to the substrate surface, measured to the greatest width of the recess, parallel to the substrate surface, equal to 2: 1 or greater.

16. The method according to any one of the preceding claims, wherein the greatest depth of the recess, measured perpendicular to the substrate surface, is between 20 microns and 300 microns.

17. The method according to any one of the preceding claims, wherein the thickness of the resist layer in the recess of the substrate is at least 0.5 .mu.m, preferably at least 0.8 .mu.m.

18. The method according to any one of the preceding claims, wherein after step (al) the following step is carried out:

(a2) cleaning the surface of the substrate by centrifuging, especially using the resist solution or a solvent.

19 substrate having at least one recess in its surface, preferably with a blind hole or a through hole, wherein the inner surface of the recess a

Resist layer produced by a method according to any one of claims 1 to 18.