Method for joining two substrates

Abstract

The present invention relates to a method for joining a first substrate (100) and a second substrate (200), the method comprising the steps of bringing the first substrate and the second substrate into contact and heating a peripheral portion of at least one of the first substrate and the second substrate, the heating starting before the substrates are brought into contact and continuing at least until the substrates are in contact in said portion, the method being characterized in that the heating is effected by means of an infrared lamp (2) configured to emit radiation having an outer boundary corresponding to the edge of the substrate.

Description

Technical Field

[0001] The present invention relates to a method of bonding a first substrate and a second substrate. Background Art

[0002] Bonding methods and specifically bonding by molecular adhesion are widely used in the production of semiconductor substrates.

[0003] Specifically, in order to manufacture a semiconductor-on-insulator substrate, especially a silicon-on-insulator (SOI) substrate, it is known practice to bond a first semiconductor substrate to a second substrate, which may or may not be a semiconductor substrate, wherein the surface of at least one of the substrates is covered with an oxide layer to create an oxide / semiconductor or oxide / oxide bond.

[0004] Bonding by molecular adhesion does not require the application of any adhesive; in the case where the surfaces to be bonded are perfectly smooth, the bonding typically starts by locally applying a slight pressure to the substrates, thereby generating a bonding wave that then propagates across the entire extent of the bonding interface.

[0005] However, it has been determined that the bonding method can be the cause of "edge void" defects in semiconductor-on-insulator substrates. These defects occur when a thin layer is transferred from the first substrate (also called the donor substrate) to the second substrate (also called the receptor substrate) after bonding (e.g., by separating the first substrate along a weakened zone previously formed in the substrate). This layer transfer method is called Smart Cut TM method.

[0006] Edge voids are holes that extend through the transferred thin layer and through the oxide layer located at the bonding interface. These holes typically have a diameter of 50 μm to 2 mm and are typically located at the periphery of the semiconductor-on-insulator substrate.

[0007] As shown in a view Figure 1 illustrating an observation from above the surface of the transferred thin layer 1 of an SOI substrate, when bonding starts at one edge (part A) of the substrates to be bonded, edge voids are typically generated at the opposite edge in part B, where the propagation of the bonding wave 11 ends.

[0008] Therefore, edge voids are serious and often disabling defects because electronic components formed in or on the area of the transferred thin layer including such edge voids will be defective.

[0009] Document WO2008 / 107029 describes a method of bonding a first substrate and a second substrate, wherein, in order to limit the formation of such edge voids, at least one of the substrates is heated before and while bringing the substrates into contact to control the propagation speed of the bonding wave.

[0010] This heating is limited to the outer part (zone) where the edge gaps are concentrated, and is achieved by means of halogen lamps arranged in a quartz housing facing said part.

[0011] However, during bonding, the heating tends to deteriorate the carrier (or "chuck") holding the substrate. Specifically, the carrier is formed of a metal substrate covered with a polymer coating, and the polymer coating separates from the substrate and deforms, thus forming bubbles under the action of overheating. However, such damage to the carrier is likely to generate other defects in the final substrate, and specifically non-bonded parts.

[0012] If an attempt is made to reduce the damage to the carrier by reducing the duration or intensity of heating, it may not be possible to sufficiently control the propagation speed of the bonding wave, resulting in the formation of edge gaps.

[0013] In addition, the method lacks stability over time and thus cannot be well reproduced. Summary of the Invention

[0014] Therefore, an object of the present invention is to define a method for bonding substrates, which enables minimizing the formation of edge gaps, while being more stable and more reproducible than existing methods and causing no damage to the substrate carrier.

[0015] To this end, the present invention provides a method for bonding a first substrate and a second substrate, the method comprising the steps of: bringing the first substrate and the second substrate into contact, and heating the peripheral part of at least one of the first substrate and the second substrate, the heating starting before the substrates are brought into contact and continuing at least until the substrates are in contact in said part, characterized in that the heating is achieved by means of infrared lamps configured to emit radiation having an outer boundary corresponding to the edge of the substrate.

[0016] Due to the type of radiation and the arrangement of the lamps relative to the substrate, it is possible to more effectively heat the water present at the bonding interface, which greatly affects the bonding kinetics, while reducing the heating of the substrate, and specifically the heating of the substrate carrier, with lower power.

[0017] In some embodiments, the first substrate and the second substrate are circular in shape, and the infrared lamps are arc-shaped, and the diameter of the infrared lamps is less than or equal to the diameter of the substrate.

[0018] In some embodiments, the first substrate and the second substrate are held by a carrier having a peripheral region extending around the edge of the substrate, and the infrared lamp is arranged in such a way as to heat the peripheral portions of the first substrate and / or the second substrate without heating the peripheral region of the carrier.

[0019] Advantageously, the heating ends at the latest at the end of the propagation of the bonding wave between the substrates.

[0020] According to a preferred embodiment, the infrared lamp emits the radiation in a wavelength range suitable for causing water present between the substrates to absorb the radiation.

[0021] Another subject of the present invention relates to a method for manufacturing a semiconductor-on-insulator substrate by transferring a semiconductor layer from a first semiconductor substrate as a donor substrate to a second substrate as a receptor substrate, the method comprising the following steps:

[0022] - forming a weakened region in the donor substrate to define the semiconductor layer to be transferred,

[0023] - providing a receptor substrate, at least one of the donor substrate and the receptor substrate being covered with an electrically insulating layer,

[0024] - using the above method to bond the first substrate and the receptor substrate, the electrically insulating layer being located at the bonding interface,

[0025] - separating the donor substrate along the weakened region to transfer the semiconductor layer to the receptor substrate.

[0026] Another subject of the present invention relates to a device allowing the implementation of this method.

[0027] The device comprises: a carrier configured to hold the first substrate and the second substrate when they are in contact, the carrier having a peripheral portion extending around the edge of the substrate; and a lamp arranged in such a way as to face the peripheral portion of at least one of the first substrate and the second substrate, the device being characterized in that the lamp is an infrared lamp configured to emit radiation having an outer boundary corresponding to the edge of the substrate so as not to expose the peripheral region of the carrier to the radiation.

[0028] According to one embodiment, the infrared lamp is designed to emit fast mid-waves. This means that the wavelength of the emitted radiation is greater than 1 μm.

[0029] In some embodiments, the infrared lamp comprises a filament designed to reach a temperature of approximately 1600 °C during operation of the lamp.

[0030] Advantageously, the infrared lamp has a power peak at a wavelength between 1.5 μm and 2 μm. Thus, compared to the absorption of radiation by the semiconductor material, the lamp promotes more the absorption of radiation by water, which makes it possible to reduce the heating of the carrier and prevent the formation of defects liable to result therefrom. Description of the Drawings

[0031] Additional features and advantages of the invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0032] - Figure 1 is a view of the surface of an SOI substrate, which schematically shows the propagation of the bonding wave and the formation of an edge void;

[0033] - Figure 2 is a view of the surface of an SOI substrate, in which a halogen lamp as described in document WO2008 / 107029 is schematically shown;

[0034] - Figure 3 is a view of the surface of an SOI substrate, in which an infrared lamp according to the invention is schematically shown;

[0035] - Figure 4 is a graph showing the emission spectra of a halogen lamp and an infrared lamp and the absorption spectrum of water as a function of wavelength;

[0036] - Figure 5 schematically illustrates a substrate held on a carrier for a bonding step;

[0037] - Figure 6 shows an image of the temperature map of a substrate carrier during heating by an infrared lamp according to the invention (left image) and by a halogen lamp (right image);

[0038] - Figure 7 is a view of the surface of an SOI substrate with an edge void formed in a portion not sufficiently heated by a halogen lamp in a known bonding method;

[0039] - Figure 8A is a cross-sectional view of a weakened zone formed in a donor substrate;

[0040] - Figure 8B is to Figure 8A a cross-sectional view of a donor substrate bonded to a receptor substrate;

[0041] - Figure 8C is a cross-sectional view of the donor substrate separated along the weakened zone to transfer the semiconductor layer from the donor substrate to the receptor substrate.

[0042] For the sake of readability of the drawings, the layers of the substrate and / or the components of the device do not have to be shown to scale. Detailed Description

[0043] The present invention proposes to change not only the heat source but also the shape of the source.

[0044] In the prior art, halogen lamps have a straight-line shape. However, since the substrate is usually circular in shape, the halogen lamp only irradiates a partial peripheral portion of the substrate.

[0045] As Figure 2 shown, the lamp 2' is arranged tangentially to the edge of the substrate on the side opposite to the part A, where the bonding wave is initiated. Due to the width of the lamp 2', this lamp 2' irradiates a strip extending from the edge of the substrate towards the center of the substrate. This strip corresponds to a part of a chord of the circle, which intersects the edge of the substrate at two parts, the intersecting parts being spaced apart at an angle of approximately 60°.

[0046] However, the edge gap usually extends over a 120° angular sector opposite to the initiation zone of the bonding wave.

[0047] As a result, as Figure 2 schematically shown, edge gaps 10 remain on either side of the peripheral portion irradiated by the lamp 2'.

[0048] These remaining edge gaps are highlighted in Figure 7 .

[0049] Referring to Figure 3 , a lamp 2 is proposed, which is configured to emit radiation having an outer boundary corresponding to the edge of the substrate.

[0050] In other words, in the case of a circular substrate, the lamp 2 takes the shape of an arc, the diameter of which is less than or equal to the diameter of the substrate. The length of the lamp is chosen to occupy an angular sector of the order of 120° with respect to the periphery of the substrate.

[0051] Thus, the lamp 2 irradiates all or at least most of the part where edge gaps are likely to occur. In addition, the lamp only irradiates the part to be processed, without irradiating the other parts of the substrate and the carrier holding the substrate, thereby avoiding or minimizing damage to the other parts caused by the heat generated.

[0052] Furthermore, the lamp 2 is not a halogen lamp but an infrared lamp.

[0053] In a manner known per se, an infrared lamp includes a conductive filament, usually made of tungsten, arranged in a tube (e.g., a quartz tube) transparent to infrared radiation. When an electric current flows through the filament, the filament reaches a high temperature and emits infrared radiation. Advantageously, the lamp includes a reflector arranged along the filament to direct the radiation in a preferred direction.

[0054] Preferably, the infrared lamp is selected from lamps that emit fast medium waves. In such lamps, the filament reaches a temperature of approximately 1600 °C.

[0055] Compared with halogen lamps, infrared lamps have two significant advantages.

[0056] On the one hand, infrared lamps allow for greater stability of heating over time, which provides higher repeatability and better reliability of the bonding method.

[0057] On the other hand, compared with halogen lamps, infrared lamps emit radiation in a wider wavelength range, which is more conducive to controlling the speed of the bonding wave and is less erosive to the substrate and the underlying carrier.

[0058] Figure 4 is a graph showing the emission spectrum of a halogen lamp (curve a) used in a known bonding method, the emission spectrum of an infrared lamp (curve b) used in the bonding method according to the present invention, and the absorption spectrum of water (curve c) as a function of wavelength λ. The left vertical axis represents the power P of the radiation emitted by the two lamps (in relative units u.r), and the right vertical axis represents the absorption coefficient A of water (in %).

[0059] The absorption of the radiation in water is of concern because water significantly affects the bonding kinetics of the substrate. Specifically, a small amount of water (on the order of a few monolayers) needs to be adsorbed on the substrate surface to ensure the adhesion of the substrate by van der Waals forces. However, too much water will reduce the bonding energy. Therefore, the heating provided by the lamp must be strong enough to remove the excess water while maintaining sufficient water adsorption on the substrate surface.

[0060] It is observed that the power peak of the infrared lamp is at a wavelength (between 1.5 μm and 2 μm) higher than the power peak of the halogen lamp (which is on the order of 1 μm), which makes the degree of water absorption of the radiation emitted by the infrared lamp greater than the degree of water absorption of the radiation emitted by the halogen lamp (water exhibits significant absorption in the range between 2.5 μm and 3.7 μm).

[0061] Conversely, the radiation from the halogen lamp is more absorbed by the silicon of the substrate, which is less useful in controlling the bonding energy on the one hand and promotes heating by conduction of the carrier holding the substrate on the other hand.

[0062] In addition, the power of the infrared lamp is lower than the power of the halogen lamp.

[0063] It should be noted that although the halogen lamp emits in the near-infrared range in addition to emitting in the visible range, it should not be considered similar to the infrared lamp according to the present invention. In fact, the radiation from the infrared lamp in the visible range is negligible; in other words, the infrared lamp mainly emits thermal radiation.

[0064] The temperature of the filament of the halogen lamp (on the order of 2600 °C) is higher than that of the filament of the infrared lamp, which, as mentioned above, is on the order of 1600 °C.

[0065] By using an elongated curved tube having the same radius of curvature of the filament as that of the substrate, or by juxtaposing a plurality of tubes along a curve having the same radius of curvature as that of the substrate, the shape of the lamp can match the shape of the substrate.

[0066] Therefore, the changes in technology and lamp shape make it possible to reduce thermal damage to the carrier.

[0067] In Figure 5 the carrier that holds the substrate to be joined is schematically shown in a view from above. The carrier 3 includes a central portion covered by the substrate and a peripheral portion 30 that extends around the substrate, and optionally includes means (not shown) for fixing the substrate. It should be understood that for a linear halogen lamp of the prior art, this peripheral portion is directly heated by the radiation from the lamp. In contrast, the infrared lamp according to the present invention does not extend over this peripheral portion 30, so the infrared radiation does not directly heat the portion 30.

[0068] A more favorable effect on the carrier is visible in Figure 6 which shows an image of the temperature map of the substrate carrier during heating of the substrate by an infrared lamp according to the present invention (left-hand image) and by a halogen lamp according to the prior art (right-hand image). This map was obtained using a thermocouple (schematically represented by a black dot) arranged in the central portion of the carrier below the substrate. Figure 6 When using a halogen lamp, the temperature reached on the carrier (about 50 °C to 55 °C) is higher than that when using an infrared lamp (about 35 °C to 40 °C). This temperature difference is sufficient to improve the life of the carrier.

[0069]

[0070] Figure 7 Figure 6 is an image of the surface of an SOI substrate having edge voids formed in a portion not sufficiently heated by a halogen lamp in a known bonding method. The temperature map shown below this image is the temperature map of the right-hand portion of . It is observed that the region B1, which has been effectively heated by the halogen lamp and is the hottest part, has no edge voids. However, in the surrounding regions B2 and B3 that extend on either side of the region B1 and are not directly arranged below the halogen lamp, edge voids are retained.

[0071] In practice, an industrial apparatus for bonding substrates may include a structure for supporting the substrate carrier and the infrared lamp.

[0072] Advantageously, the carrier is arranged in a horizontal plane and the infrared lamp extends above the carrier in a plane parallel to the plane of the carrier.

[0073] The distance between the lamp and the carrier is large enough to allow the substrate to be processed without disturbing the laminar flow applied within the device, thereby preventing the presence of contaminants. In practice, the distance between the lamp and the carrier can be on the order of 20 cm.

[0074] The shape of the lamp matches the shape of the substrate to be bonded. For example, when the substrate to be bonded has a diameter of 300 mm, the lamp has a radius of curvature of at most 150 mm, preferably on the order of 145 mm or less.

[0075] The reflector of the lamp is arranged to direct the infrared radiation towards the substrate.

[0076] Due to the shape and arrangement of the lamp, the infrared radiation has an outer boundary corresponding to the edge of the substrate, such that the peripheral region of the carrier that radially extends beyond the edge of the substrate is not exposed to the radiation.

[0077] Figures 8A to 8C Illustrated is the Smart Cut TM steps of the layer transfer method for implementing the above bonding method.

[0078] Reference Figure 8A , a donor substrate 100 including at least one semiconductor layer is provided. The substrate can be a bulk substrate or take the form of a stack of layers of different materials.

[0079] The substrate 100 can be covered with a dielectric layer 102, for example, a silicon oxide layer.

[0080] Atomic species such as hydrogen and / or helium are implanted into the donor substrate 100 through the dielectric layer 102. Thus, a weakened region 101 that defines the semiconductor layer 1 to be transferred is formed in the donor substrate.

[0081] Reference Figure 8B , the so-weakened donor substrate 100 is bonded to the receptor substrate 200. The bonding is carried out via the dielectric layer 102, and the receptor substrate may also be covered with a dielectric layer (for oxide-oxide bonding) or not (for oxide-semiconductor bonding). Alternatively, the dielectric layer can only be present on the receptor substrate (for semiconductor-oxide bonding).

[0082] To achieve such bonding, the substrates are held on a carrier (not shown), and the infrared lamp is arranged opposite the carrier with respect to the substrate, facing the peripheral part where the propagation of the bonding wave should end. By locally applying a slight pressure to the substrate at the edge opposite the position of the lamp, a bonding wave is initiated between the substrates.

[0083] The infrared lamp is turned on at the latest when the substrates come into contact and turned off at the latest when the interface between the substrates is completely closed. Advantageously, the turning on of the lamp is controlled by the movement feedback of the device that applies the pressure required to initiate the bonding of the substrates. The turning off of the lamp can be controlled to occur at the end of a predefined time period after it is turned on. This duration is pre-calibrated for each set of substrates to be bonded by measuring the speed of the bonding wave between the substrates.

[0084] Finally, referring to Figure 8C , the donor substrate 100 is separated along the weakening zone 101, thereby causing the layer 1 to be transferred to the receptor substrate. By the implemented bonding method, the transferred layer 1 has substantially no edge voids. In addition, since the carrier is not damaged by heating, the transferred layer 1 also has no carrier-related defects, such as non-bonded portions.

Claims

1. A method for bonding a first substrate (100) and a second substrate (200), the method comprising the following steps: Bring the first substrate and the second substrate into contact, and heat at least one peripheral portion of the first substrate and the second substrate, in which the propagation of the bonding wave between the first substrate and the second substrate ends. The heating starts before bringing the first substrate and the second substrate into contact and continues at least until the first substrate and the second substrate come into contact in the peripheral portion. The method is characterized in that the heating is achieved by means of an infrared lamp (2), the infrared lamp (2) is configured to face the peripheral portion, and the shape of the infrared lamp (2) matches the shapes of the first substrate and the second substrate to be bonded, so as to emit radiation having an outer boundary corresponding to the edges of the first substrate and the second substrate.

2. The method according to claim 1, wherein, The first substrate and the second substrate are circular in shape, and the infrared lamp is arc-shaped, and the diameter of the infrared lamp is less than or equal to the diameters of the first substrate and the second substrate.

3. The method according to claim 1 or 2, wherein, The first substrate and the second substrate are held by a carrier (3), the carrier having a peripheral region (30) extending around the edges of the first substrate and the second substrate, and the infrared lamp (2) is arranged in such a way as to heat the peripheral portions of the first substrate and / or the second substrate without heating the peripheral region (30) of the carrier.

4. The method according to claim 1 or 2, wherein, The heating ends at the latest when the propagation of the bonding wave between the first substrate and the second substrate ends.

5. The method according to claim 1 or 2, wherein, The infrared lamp (2) emits the radiation in a wavelength range suitable for water present between the first substrate (100) and the second substrate (200) to absorb the radiation.

6. A method for transferring a semiconductor layer from a first semiconductor substrate as a donor substrate (100) to a second substrate as a receptor substrate (200), the method comprising the following steps: - Form a weakened region (101) in the donor substrate (100) to define the semiconductor layer (1) to be transferred. - Provide the receptor substrate (200), at least one of the donor substrate and the receptor substrate being covered with an electrically insulating layer (102). - Use the method according to any one of claims 1 to 5 to bond the first substrate (100) and the receptor substrate (200), the electrically insulating layer (102) being located at the bonding interface. - Separate the donor substrate (100) along the weakened region (101) to transfer the semiconductor layer (1) to the receptor substrate (200).

7. An apparatus for bonding a first substrate and a second substrate, the apparatus comprising: A carrier (3), the carrier being configured to hold the first substrate and the second substrate when the first substrate and the second substrate are in contact, the carrier having a peripheral region (30) extending around the edges of the first substrate and the second substrate; and a lamp arranged to face at least one peripheral portion of the first substrate and the second substrate, in which the propagation of the bonding wave between the first substrate and the second substrate ends, the device being characterized in that the lamp is an infrared lamp (2), and the shape of the infrared lamp matches the shape of the first substrate and the second substrate to be bonded to emit radiation having an outer boundary corresponding to the edges of the first substrate and the second substrate so as not to expose the peripheral region (30) of the carrier (3) to the radiation.

8. The apparatus according to claim 7, wherein, The infrared lamp is designed to emit fast medium waves.

9. The apparatus according to claim 7 or 8, wherein, The infrared lamp includes a filament designed to reach a temperature of 1600 °C during the operation of the infrared lamp.

10. The apparatus according to claim 7 or 8, wherein, The infrared lamp has a power peak at a wavelength between 1.5 μm and 2 μm.

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