DIRECT BONDING METHOD

Abstract

The invention relates to a method for directly adhering a lower substrate to an upper substrate which includes the following steps: a) providing a mounting; b) positioning the lower substrate on the mounting, the mounting being configured such as to raise a portion of the lower substrate; c) positioning the upper substrate above the lower substrate; d) allowing the upper substrate to fall by gravity onto the lower substrate such as to form an initial contact point between the upper substrate and the lower substrate, located on the raised portion of the lower substrate; and e) completing the contact between the upper substrate and the lower substrate such as to adhere the upper substrate to the lower substrate by direct adhesion.

Claims

1. A direct bonding method between a lower substrate and an upper substrate comprising the following steps: a) providing a carrier, b) positioning the lower substrate on the carrier, the carrier being configured so as to raise a portion of the lower substrate, c) positioning the upper substrate above the lower substrate, d) allowing the falling by gravity of the upper substrate on the lower substrate so as to form an initial contact point between the upper substrate and the lower substrate, located on the raised portion of the lower substrate, and e) completing the contacting of the upper substrate and the lower substrate so as to bond the upper substrate and the lower substrate by direct bonding.

2. The direct bonding method according to claim 1, wherein step a) for providing a carrier comprises the provision of a plate and a raising member arranged on the plate, the plate and the raising member being configured to deform the lower substrate by gravity, so as to form said raised portion and an inflection zone in the lower substrate in step b).

3. The direct bonding method according to claim 2, wherein the raising member has a height comprised between 0.05 and 3 times the thickness of the lower substrate.

4. The direct bonding method according to claim 2, wherein the raising member is configured to be adjustable in height, and in which the method comprises prior to step d) a step m) consisting in adjusting the height of the raising member.

5. The direct bonding method according to claim 2, wherein the raising member extends through the thickness of the plate.

6. The direct bonding method according to claim 2, wherein the raising member is a removable spacer.

7. The direct bonding method according to claim 2, wherein the plate is integral with the raising member.

8. The direct bonding method according to claim 1, wherein the carrier provided in step a) comprises a receiving portion of the lower substrate, the receiving portion being flat, and in which step c) comprises the positioning of the upper substrate substantially parallel to the receiving portion of the carrier.

9. The direct bonding method according to claim 1, comprising a step i) carried out prior to step b) consisting in inclining the carrier relative to the horizontal at an angle of inclination ().

10. The direct bonding method according to claim 9, wherein the angle of inclination () is greater than 0 and lower than or equal to 85.

11. The direct bonding method according to claim 1, wherein the carrier comprises at least one stop configured so that at least one peripheral part of the upper substrate and at least one part of the lower substrate are aligned against the stop.

12. The direct bonding method according to claim 1, comprising a step k) for detecting the bonding wave between the lower substrate and the upper substrate.

13. The direct bonding method according to claim 12 comprising a step I) including the lowering of the raised portion of the lower substrate when the bonding wave is detected.

14. The direct bonding method according to claim 2, wherein step d) is carried out under an atmosphere greater than or equal to vacuum.

15. The direct bonding method according to claim 1, wherein step c) is carried out under a vacuum atmosphere.

Description

[0044] Other aspects, objects and advantages of the present invention will appear better on reading the following description of different embodiments thereof, given by way of non-limiting examples and made with reference to the appended drawings. The figures do not necessarily meet the scale of all shown members so as to improve the readability thereof. In the following description, for sake of simplification, identical, similar or equivalent members of the different embodiments bear the same numerical references.

[0045] FIGS. 1 and 2 illustrate a direct bonding according to a first embodiment of the invention.

[0046] FIG. 3 illustrates a direct bonding according to a variant of the first embodiment of the invention.

[0047] FIG. 4 illustrates a direct bonding according to another variant of the first embodiment of the invention.

[0048] FIG. 5 illustrates a direct bonding according to a second embodiment of the invention.

[0049] FIG. 6 illustrates a direct bonding according to a variant of the second embodiment of the invention.

[0050] FIG. 7 illustrates a direct bonding according to another variant of the second embodiment of the invention.

[0051] FIG. 8 illustrates a direct bonding according to yet another embodiment of the invention.

[0052] FIG. 9 illustrates a direct bonding according to a variant of the embodiment illustrated in FIG. 8.

[0053] FIG. 1 shows a carrier 1 on which is positioned a lower substrate 2, such as a silicon substrate with a diameter of 200 mm and a thickness of 725 micrometers prepared for the bonding (surface roughness lower than 0.2 nm RMS measured by AFM on a field of 55 micrometers and particulate contamination lower than 20 particles in a diameter range from 90 to 500 nm measured by a Surfscan SP2 type detector). The carrier 1 comprises a plate 10 and a raising member 3, such as a removable silicon spacer of a height of 200 micrometers and including a base having dimensions smaller than the dimensions of the lower substrate 2 (typically lower by 20% or even 10% or 5% than the surface of the lower substrate) and about 1010 mm. This spacer 3 is inserted between the plate 10 and the lower substrate 2 (steps a and b). The raising member 3 thus raises a portion 4 of the lower substrate 2 with respect to a second portion of the lower substrate 2 in contact with the plate 10. This raising leads to a deformation by the effect of gravity and to the formation of an inflection zone in the lower substrate 2 with respect to its initial shaping. Then, an upper substrate 5, identical to that of the lower substrate 2, is positioned in vertical alignment with the lower substrate 2 as illustrated in FIG. 1 (step c). The upper substrate 5 is then free from any restraint, such that it falls by gravity on the deformed lower substrate 2, under an atmosphere having a pressure typically comprised between 100 Pa and 1013 hPa. As illustrated in FIG. 2, the initial contact point 6 of the two substrates 2, 5 is located on the raised portion 4 of the lower substrate 2, in vertical alignment with the raising member 3 so as to enable a good flow of the air on either side of the initial contact point 6 (referring to the arrows in FIG. 1). An infrared camera enables detecting the initiation of the bonding wave (not illustrated). The bonding wave appears after a few tens of seconds and releases the air from the initial contact point 6. The shape of the air flow, due to the deformation of the lower substrate 2, prevents the occurrence of a secondary bonding wave. Once the bonding is initiated, the raising member 3 is removed (not shownstep I) so as to obtain the straightening up of the lower substrate 2 by lowering the raised portion 4, leading to a stack of the two substantially flat bonded substrates 2, 5.

[0054] Of course, this direct bonding may also be carried out alternatively under a vacuum pressure, in particular under a pressure lower than 100 Pa without generating secondary bonding wave (not illustrated).

[0055] FIG. 3 illustrates a variant of the method which differs from the preceding embodiment in that the raising member 3 is integral with the plate 10. The lower substrate 2 positioned on the carrier 1 is therefore deformed by gravity following the shaping of the carrier 1. During the fall of the upper substrate 5, the air is discharged in a privileged manner above the raised portion 4 then upstream of the propagation of the bonding wave.

[0056] According to another variant illustrated in FIG. 4, the raising member 3 extends through the thickness of the plate 10. The raising member 3 is in particular configured to be adjustable in height, typically between 1/5 and 2 times the thickness of the lower substrate 2 so as to select a deformation amplitude adapted for the direct bonding without creating a secondary bonding wave. This adjustment possibility may be provided for example by the existence of a threading provided on a finger-shaped raising member 3 and complementary threading in an orifice arranged in the plate 10 enabling the screwing or the unscrewing of the finger in the plate 10 (not illustrated).

[0057] FIG. 5 illustrates a second embodiment of the method in which the plate 10 is inclined relative to the horizontal at an angle of about 10 by the presence of a pad 8 (FIG. 5step i). Moreover, a raising member 3 identical to the raising member described with reference to FIG. 4 ensures obtaining the deformation and the inflection zone in the lower substrate 2. In this second embodiment, the direct bonding is carried out under vacuum from the lower 2 and upper 5 substrates, prepared to the bonding in the same way as the bonding described for the preceding embodiment. The upper substrate 5 is positioned in vertical alignment with the deformed lower substrate 2 (step c). It is maintained substantially parallel to a flat receiving portion of the carrier 1 by wedge members (not shown) such that the location of the initial contact point 6 takes place on the raised portion 4 of the lower substrate 2. As illustrated in FIG. 5 the carrier 1 further comprises a stop 9 enabling aligning the peripheral edges of the substrates 2,5 to be bonded. Once the vacuum produced, the wedge members holding the upper substrate 5 in place are removed to enable a fall by gravity. The initial contact point 6 actually takes place on the raised portion 4 of the lower substrate 2 and the bonding takes place without the occurrence of secondary bonding wave.

[0058] Alternatively, the angle of inclination of the carrier 1 relative to the horizontal is selected between a value greater than 0 and lower than or equal to 85 and preferably between a value greater than 0 and lower than or equal to 45 so as to obtain the optimum raising of the portion 4 of the lower substrate 2.

[0059] The inclination of the carrier 1 may be alternatively obtained by a device 11 for adjusting the inclination located for example in the extension of the rising member 3, as illustrated in FIG. 6.

[0060] This embodiment generating a deformation and an inflection zone 5 in the lower substrate 2, it can also be executed under a pressure greater than the prssure of vacuum, without causing the formation of a secondary bonding wave.

[0061] According to another variant illustrated in FIG. 7, the inclination is obtained by the shaping itself of the carrier 1 which comprises a portion for receiving the lower substrate 2 generally inclined relative to the horizontal at the angle .

[0062] FIG. 8 illustrates another embodiment which differs from the preceding ones in that the carrier 1 is not configured to generate a deformation and an inflection zone in the lower substrate 2. Indeed, the carrier 1 is inclined at the angle of inclination as defined hereinabove, leading to form the raised zone 4 in the lower substrate 2. It is therefore possible to proceed with the direct bonding by falling by gravity the upper substrate 5 under a vacuum atmosphere, typically lower than 100 Pa, while avoiding the generation of a secondary bonding wave.

[0063] As illustrated in FIGS. 8 and 9, such a carrier 1 having a surface for receiving the inclined lower substrate 2 may be obtained in different ways such as by providing a carrier 1 intrinsically having the angle of inclination or by providing a carrier 1 under which a pad 8 is positioned.

[0064] Thus, the method of the invention provides a direct bonding method enabling initiating a single bonding wave at a predetermined position. This method allows obtaining a direct bonding under ambient atmosphere or under vacuum, without requiring a dedicated device for applying a local pressure, by using only gravity to operate the contact between the two substrates. Moreover, the method of the invention also enables controlling the location of the initiation of the bonding on the raised portion of the lower substrate 2 and preventing a secondary bonding wave at low pressure in particular thanks to the adjustment of the parallelism between the upper substrate 5 and that of the carrier 1. The invention thus subtracts from the problematic related to the synchronization of the fall of the upper substrate 5 and the application of the local pressure determining the starting point of the bonding of the known techniques.

[0065] It goes without saying that the invention is not limited to the embodiments described hereinabove by way of examples but that it encompasses all technical equivalents and variants of the described means as well as the combinations thereof.