DEVICE AND METHOD FOR BONDING OF SUBSTRATES

Abstract

A method for bonding a first substrate with a second substrate at respective contact faces of the substrates with the following steps: holding the first substrate to a first sample holder surface of a first sample holder with a holding force F.sub.H1 and holding the second substrate to a second sample holder surface of a second sample holder with a holding force F.sub.H2; contacting the contact faces at a bond initiation point and heating at least the second sample holder surface to a heating temperature T.sub.H; bonding of the first substrate with the second substrate along a bonding wave running from the bond initiation point to the side edges of the substrates, wherein the heating temperature T.sub.H is reduced at the second sample holder surface during the bonding.

Claims

1. A method for bonding a first substrate with a second substrate at respective contact faces of the substrates, the method comprising: holding the first substrate to a first sample holder surface of a first sample holder with a holding force F.sub.H1 and holding the second substrate to a second sample holder surface of a second sample holder with a holding force F.sub.H2, contacting the respective contact faces of the substrates at a bond initiation point; bonding the first substrate with the second substrate along a bonding wave running from the bond initiation point to respective side edges of the substrates; and switching-on and switching-off fixing means of the second sample holder at least once, the switching-on and switching-off being location-resolved and/or time-resolved.

2. The method according to claim 1, wherein the contacting is performed using a nozzle.

3. The method according to claim 2, wherein the contacting comprises applying a force in a range of 100 mN to 5000 mN using the nozzle.

4. The method according to claim 1, wherein a distance between the first substrate and the second substrate before the bonding is less than 100 μm.

5. The method according to claim 1, wherein the holding force F.sub.H1 is reduced during the bonding at a time t.sub.1 to an extent such that the first substrate is released from the first sample holder.

6. The method according to claim 1, wherein the holding force F.sub.H2 is reduced during the bonding at a time t.sub.2, to an extent such that the second substrate on the second sample holder is able to be deformed along the contact face of the second substrate.

7. The method according to claim 1, wherein the second substrate is ventilated from the second sample holder surface at a time t.sub.3 with an overpressure.

8. The method according to claim 1, wherein the holding force F.sub.H2 is increased at a time t.sub.4 after the bonding.

9. The method according to claim 7, wherein the overpressure is in a range of 10 mbar to 500 mbar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0174] FIG. 1a shows a diagrammatic cross-sectional representation (not true to scale) of a first process step of a first embodiment of a method according to the invention,

[0175] FIG. 1b shows a diagrammatic cross-sectional representation (not true to scale) of a second process step,

[0176] FIG. 1c shows a diagrammatic cross-sectional representation (not true to scale) of a third process step,

[0177] FIG. 1d shows a diagrammatic cross-sectional representation (not true to scale) of a fourth process step,

[0178] FIG. 1e shows a diagrammatic cross-sectional representation (not true to scale) of a fifth process step,

[0179] FIG. 1f shows a diagrammatic cross-sectional representation (not true to scale) of a sixth process step,

[0180] FIG. 1g shows a diagrammatic cross-sectional representation (not true to scale) of a seventh process step,

[0181] FIG. 1h shows a diagrammatic cross-sectional representation (not true to scale) of an eighth process step,

[0182] FIG. 1i shows a diagrammatic cross-sectional representation (not true to scale) of a ninth process step,

[0183] FIG. 1j shows a diagrammatic cross-sectional representation (not true to scale) of a tenth process step,

[0184] FIG. 2 shows a diagrammatic cross-sectional representation (not true to scale) of an additional process step of a third embodiment of a method according to the invention,

[0185] FIG. 3 shows a diagrammatic cross-sectional representation (not true to scale) of an optional additional process step, and

[0186] FIG. 4 shows a diagrammatic cross-sectional representation (not true to scale) of two substrates.

DETAILED DESCRIPTION OF THE INVENTION

[0187] Identical components and components with the same function are denoted by the same reference numbers in the figures.

[0188] FIG. 1a shows a first process step, wherein a first, in particular upper, substrate 2 has been fixed to a sample holder surface 1o of a first, in particular upper, sample holder 1. The fixing takes place by means of fixing means 3 with a holding force F.sub.H1.

[0189] First sample holder 1 has an, in particular central, through-opening, in particular bore 4. The through-opening is used to pass through a deformation means 4 for deforming first substrate 2.

[0190] In an advantageous embodiment shown here, first sample holder 1 comprises holes 5, through which an observation of the bonding progress can take place by measuring means. Hole 5 is preferably an elongated milled-out portion.

[0191] A second substrate 2′ is loaded and fixed on a second, in particular lower sample holder 1′. The fixing takes place by means of fixing means 3′ with a holding force F.sub.H2.

[0192] Fixing means 3, 3′ are preferably vacuum fixing means.

[0193] Sample holders 1, 1′ in particular comprise heating 11 (heating means). For the sake of clearer illustration, heating 11 is represented diagrammatically only in second, lower sample holder 1′ in the figures.

[0194] All the stated parameters or forces, which describe or influence the properties of substrates 2, 2′, are generally functions of location and/or time.

[0195] Temperatures T1 and T2 of the two substrates 2, 2′ are mentioned as an example of a parameter. Temperatures T1 and respectively T2 can generally be location-dependent, for which reason temperature gradients exist. In this case, it is expedient to indicate the temperatures as explicit functions of location and/or time.

[0196] The two gravitational forces G1 and G2 are mentioned as an example of a force. In the figures, they represent the total gravitational forces acting on substrates 2, 2′. It is however perfectly clear to the person skilled in the art that the two substrates 2, 2′ can be split up into infinitesimal (dimensional) parts dm and that the influence of gravitation can be related to each of these dimensional parts dm. The gravitational force should therefore generally be indicated as a function of location and/or time.

[0197] Similar considerations apply to all the other parameters and/or forces.

[0198] FIG. 1b shows a second process step according to the invention, wherein deformation means 4, in particular a pin, exerts a pressure on a rear side 2i of first substrate 2 in order to bring about a deformation of first substrate 2. The deformation of first substrate 2 takes place with a first force F.sub.1.

[0199] In a process step according to FIG. 1c, a relative approach of the two sample holders 1, 1′ and therefore of the two substrates 2, 2′ towards one another takes place up to a defined spacing. The approach can also take place during or before the second process step.

[0200] In a process step according to FIG. 1d, the initiation of the bond, in particular a pre-bond, takes place with a second force F.sub.2. Second force F.sub.2 provides for a further, in particular infinitesimally small deflection and a further approach of the two substrates 2, 2′ and finally contacting at a contact point 7.

[0201] A bonding wave, more precisely a bonding wave front 8, starts to propagate in particular in a radially symmetrical manner, preferably concentrically, from contact point 7 at a bonding wave speed v. In the course of the further process steps, bonding wave speed v can change, so that bonding wave speed v can be defined as a function of location (or of time). Bonding wave speed v can be influenced by various measures.

[0202] In a further process step according to FIG. 1e, heating 11 of first and/or second sample holder 1, 1′ is switched off and further heating of first and/or second substrate 2, 2′ is thus interrupted. In a further process step according to figure if, monitoring of bonding wave front 8 takes place with the aid of measuring means 9, in particular at least one optical system, preferably an infrared optical system. Through the (at least one—the number preferably corresponds to the number of optical systems) hole 5, measuring means 9 can detect substrate rear side 2i of first substrate 2, more preferably the bond interface between the two substrates 2, 2′, and thus bonding wave front 8. The detection of the bond interface takes place in particular at measuring means 9 which are sensitive to electromagnetic radiation, which can penetrate the two substrates 2, 2′ without significant weakening. A light source 12 is preferably positioned above and/or below and/or inside sample holder 1′, the electromagnetic radiation whereof illuminates and/or shines through sample holder 1′ and/or substrates 2, 2′ and can be detected by measuring means 9. The images thus taken are preferably black-and-white images. The brightness differences permit an unequivocal identification of the bonded regions from the non-bonded regions. The transition region between the two regions is the bonding wave. By means of such a measurement, it is possible in particular to determine the position of bonding wave front 8 and therefore, especially for a plurality of such positions, also bonding wave speed v.

[0203] FIG. 1g shows a further, seventh process step, wherein fixing means 3 of first sample holder 1 is released by the fact that holding force F.sub.H1 is at least reduced. If fixing means 3 is a vacuum fixing means, more preferably a vacuum fixing means with a plurality of separately controllable vacuum segments (with a plurality of holding forces F.sub.H1), the release takes place in particular from the inside outwards by means of a targeted switching-off of the vacuum segments (or reduction of holding force/holding forces F.sub.H1) from the inside outwards.

[0204] FIG. 1h shows a further process step, wherein bonding wave front 8 is monitored by measuring means 9 after the release from first substrate holder 1.

[0205] FIG. 1i shows a further process step, wherein the action of deformation means 6 on first substrate 2 is interrupted. If deformation means 6 is a mechanical deformation means, in particular a pin, the interruption takes place by a withdrawal. When nozzles are used, the interruption takes place by switching off the fluid flow. In the case of electrical and/or magnetic fields, the interruption takes place by switching off the fields.

[0206] FIG. 1j shows a further process step, after which the two substrates 2, 2′ are completely bonded together. In particular, further monitoring of bonding wave front 8 (no longer depicted, since the bond has already been completed in this process state) takes place in this process step with the aid of measuring means 9 up to the end of the bond, at which a substrate stack 10 formed from first and second substrates 2, 2′ is completed.

[0207] FIG. 2 shows an optional process step, wherein, in particular after the process step according to FIG. 1g, a reduction of holding force F.sub.H2 of second, lower fixing means 3′ of second, lower sample holder 1′ takes place. In particular, holding force F.sub.H2 is reduced to 0, i.e. the fixing is deactivated. The effect of this, in particular, is that second substrate 2′ can move unhindered, in particular in the lateral direction along lower sample holder surface 1o′.

[0208] In a further, advantageous embodiment, second substrate 2′ is raised along bonding wave front 8 to an extent such that it is raised, in particular locally, from second, lower sample holder 2′. This is brought about, in particular, by applying pressure to second substrate 2′ from second sample holder 1′.

[0209] Gravitational force G2 counteracts the lifting of second substrate 2′ throughout the bonding process and thus also influences the contacting of the two substrates 2, 2′ and therefore the “run-out”.

[0210] FIG. 3 shows an optional process step according to the invention, wherein the chamber in which the process according to the invention proceeds is ventilated before the production of the completely bonded substrate stack 10. The ventilation serves in particular to control advancing bonding wave front 8. A precise description of the possible ways of exerting an influence is disclosed in publication WO2014/191033A1, to which reference is made in this regard. The ventilation takes place with a gas or gas mixture. In particular, the ventilation takes place by opening a valve to the surrounding atmosphere, so that the chamber is ventilated with the surrounding gas (mixture). Subjecting the chamber to an over-pressure with a gas or gas mixture is also conceivable, instead of ventilation to the surrounding atmosphere.

[0211] FIG. 4 shows a diagrammatic representation (not to scale) of two substrates 2, 2′, which are defined by a plurality of parameters. Substrate surfaces 2o, 2o′ correspond to the bending lines of first upper substrate 2 and respectively second, lower substrate 2′ at a defined point in time. They are defined decisively by the aforementioned parameters. Their shape changes as a function of time during the bonding process according to the invention.

LIST OF REFERENCE NUMBERS

[0212] 1o, 1o′ sample holder surfaces [0213] 2, 2′ substrates [0214] 2o, 2o′ substrate surfaces [0215] 2i substrate rear side [0216] 3, 3′ fixing means [0217] 4 bore [0218] 5 holes [0219] 6 deformation means [0220] 7 contact point [0221] 8 bonding wave front [0222] 9 measuring means [0223] 10 substrate stack [0224] 11 heating [0225] 12 light source [0226] F.sub.1, F.sub.2 force [0227] F.sub.H1, F.sub.H2 holding force [0228] v bonding wave speed [0229] T.sub.H heating temperature [0230] T1, T2 substrate temperatures [0231] E1, E2 substrate moduli of elasticity [0232] d1, d2 substrate thicknesses [0233] V1, V2 substrate volumes [0234] m1, m2 substrate masses [0235] p1, p2 substrate densities [0236] G1, G2 substrate gravitational forces [0237] r1, r2 substrate curvature radii [0238] r10, r20 initial substrate curvature radii [0239] D substrate edge spacing