Semiconductor structure and forming method thereof

Abstract

The invention relates to a semiconductor structure and a forming method thereof. The forming method of the semiconductor structure comprises the following steps of providing a first substrate, wherein the first substrate comprises a front surface and a back surface which are oppositely distributed; a second substrate is bonded to the front face of the first substrate, a semiconductor substrate comprising the first substrate and the second substrate is formed, and the resistance value of the second substrate is higher than that of the first substrate; and forming a device structure on the surface, deviating from the first substrate, of the second substrate. According to the invention, the influence of the self-doping effect in the epitaxial process on the distribution uniformity of the doped ions in the second substrate is fundamentally avoided, the distribution uniformity of the resistance value of the second substrate is ensured, and the performance of the semiconductor structure is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and in particular to a semiconductor structure and a forming method thereof. Background Art

[0002] Epitaxial growth technology began to develop in the 1960s. At that time, the collector of high-frequency, high-power devices was required to have a high breakdown voltage, that is, the collector resistivity was required to be high; at the same time, the collector series resistance was required to be small, that is, the collector resistivity was required to be low, and the two were contradictory. A high-resistance epitaxial layer is grown on a low-resistance substrate through an epitaxial process, and the device is made on top of the high-resistance epitaxial layer. The high-resistance epitaxial layer and the low-resistance substrate together constitute a semiconductor substrate. The high resistivity of the high-resistance epitaxial layer ensures that the device has a high breakdown voltage, and the low resistivity of the low-resistance substrate reduces the series resistance of the device, thereby effectively solving the demand for high-frequency, high-power devices. High-resistance products generally require epitaxial resistance values ​​between hundreds of ohms and thousands of ohms, which is significantly different from conventional epitaxial products with tens of ohms.

[0003] However, in the process of forming a high-resistance epitaxial layer on the surface of a low-resistance substrate using an epitaxial process, there will be a relatively serious self-doping effect. The self-doping effect refers to the phenomenon that during the high-temperature epitaxy process, impurities such as doped particles in the highly doped low-resistance substrate diffuse from the low-resistance substrate into the gas phase boundary layer, and then diffuse from the gas phase boundary layer into the high-resistance epitaxial layer. The self-doping effect will cause the resistance distribution uniformity and measurement stability of the high-resistance epitaxial layer to be poor, thereby limiting the improvement of semiconductor structure performance.

[0004] Therefore, how to reduce the influence of the self-doping effect and thus improve the uniformity of the resistance distribution of the semiconductor substrate to achieve improvement in the performance of the semiconductor structure is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present invention provides a semiconductor structure and a method for forming the same, which are used to reduce the influence of the self-doping effect, thereby improving the uniformity of the resistance distribution of the semiconductor substrate, so as to improve the performance of the semiconductor structure.

[0006] According to some embodiments, the present invention provides a method for forming a semiconductor structure, comprising the following steps:

[0007] Providing a first substrate, wherein the first substrate comprises a front side and a back side that are oppositely distributed;

[0008] Bonding a second substrate to the front surface of the first substrate to form a semiconductor substrate including the first substrate and the second substrate, wherein the resistance value of the second substrate is higher than the resistance value of the first substrate;

[0009] A device structure is formed on the surface of the second substrate facing away from the first substrate.

[0010] In some embodiments, the second substrate includes a first surface and a second surface that are relatively distributed; the specific steps of bonding the second substrate to the front surface of the first substrate include:

[0011] Bond the second substrate and the first substrate in a direction such that the second surface of the second substrate faces the front surface of the first substrate, so that the second surface of the second substrate is directly in contact and connected to the front surface of the first substrate.

[0012] In some embodiments, before bonding the second substrate and the first substrate in a direction such that the second surface of the second substrate faces the front surface of the first substrate, the following steps are further included:

[0013] Clean the front surface of the first substrate and the second surface of the second substrate.

[0014] In some embodiments, before bonding the second substrate and the first substrate in a direction such that the second surface of the second substrate faces the front surface of the first substrate, the following steps are further included:

[0015] Activation treatment is performed on the second surface of the second substrate to form hydrophilic bonding groups or hydrophobic bonding groups on the second surface of the second substrate; and / or

[0016] Activation treatment is performed on the front surface of the first substrate to form hydrophilic bonding groups or hydrophobic bonding groups on the front surface of the first substrate.

[0017] In some embodiments, before forming a device structure on the surface of the second substrate facing away from the first substrate, the following steps are further included:

[0018] Thin the second substrate.

[0019] In some embodiments, the specific steps of thinning the second substrate include:

[0020] Adopt a grinding process to thin the second substrate starting from the first surface of the second substrate.

[0021] In some embodiments, the specific steps of forming a device structure on the surface of the second substrate facing away from the first substrate include:

[0022] Adopt an epitaxial growth process to form an epitaxial layer on the thinned second substrate, and the resistance value of the epitaxial layer is lower than the resistance value of the second substrate;

[0023] The device structure is formed inside or above the epitaxial layer.

[0024] In some embodiments, the specific steps of bonding the second substrate to the front surface of the first substrate include:

[0025] Providing the second substrate;

[0026] Thinning the second substrate;

[0027] Bonding the thinned second substrate to the front surface of the first substrate.

[0028] According to some other embodiments, the present invention further provides a semiconductor structure formed by using the formation method of the semiconductor structure as described above; the semiconductor structure includes:

[0029] A semiconductor substrate including a first substrate and a second substrate, the first substrate includes a front surface and a back surface distributed relatively, the second substrate is bonded to the front surface of the first substrate, and the resistance value of the second substrate is higher than the resistance value of the first substrate;

[0030] A device structure located on the surface of the second substrate facing away from the first substrate.

[0031] For the semiconductor structure and its formation method provided by the present invention, the second substrate is bonded to the front surface of the first substrate through a bonding process, and the resistance value of the second substrate is higher than the resistance value of the first substrate to form a semiconductor substrate including the first substrate and the second substrate. Since the process of forming the second substrate above the first substrate is a bonding process rather than an epitaxial process, the influence of the self-doping effect in the epitaxial process on the uniformity of the distribution of doped ions in the second substrate can be avoided from the root, ensuring the uniformity of the resistance value distribution of the second substrate and realizing the improvement of the performance of the semiconductor structure. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0033] Figure 1 It is a flowchart of the formation method of the semiconductor structure in the specific embodiment of the present invention;

[0034] Figure 2 It is a schematic structural diagram of the first substrate in the specific embodiment of the present invention;

[0035] Figure 3It is a schematic structural diagram of the second substrate in the specific embodiment of the present invention;

[0036] Figure 4 It is a schematic structural diagram after bonding and connecting the first substrate and the second substrate in the specific embodiment of the present invention;

[0037] Figure 5 It is a schematic structural diagram after thinning the second substrate in the specific embodiment of the present invention;

[0038] Figure 6 It is a schematic structural diagram after forming an epitaxial layer on the second substrate in the specific embodiment of the present invention. Specific Embodiment

[0039] The following will describe in detail the specific embodiments of the semiconductor structure and its forming method provided by the present invention with reference to the accompanying drawings.

[0040] The present specific embodiment provides a method for forming a semiconductor structure, Figure 1 It is a flowchart of the method for forming a semiconductor structure in the specific embodiment of the present invention. As Figure 1 shown, the method for forming the semiconductor structure includes the following steps:

[0041] Step S11: Provide a first substrate, and the first substrate includes a front surface and a back surface that are oppositely distributed;

[0042] Step S12: Bond a second substrate to the front surface of the first substrate to form a semiconductor substrate including the first substrate and the second substrate, and the resistance value of the second substrate is higher than that of the first substrate;

[0043] Step S13: Form a device structure on the surface of the second substrate facing away from the first substrate.

[0044] Figure 2 It is a schematic structural diagram of the first substrate in the specific embodiment of the present invention, Figure 3 It is a schematic structural diagram of the second substrate in the specific embodiment of the present invention, Figure 4 It is a schematic structural diagram after bonding and connecting the first substrate and the second substrate in the specific embodiment of the present invention. In some embodiments, as Figure 2 , Figure 3 and Figure 4 shown, the second substrate 30 includes a first surface 301 and a second surface 302 that are oppositely distributed; The specific steps of bonding the second substrate 30 to the front surface 201 of the first substrate 20 include:

[0045] Bond the second substrate 30 and the first substrate 20 in a direction with the second surface 302 of the second substrate 30 facing the front surface 201 of the first substrate 20, such that the second surface 302 of the second substrate 30 is in direct contact connection with the front surface 201 of the first substrate 20.

[0046] For example, both the first substrate 20 and the second substrate 30 are silicon substrates, and the first substrate is a heavily doped low-resistance substrate, while the second substrate is a lightly doped high-resistance substrate, that is, the resistance value of the second substrate 30 is higher than that of the first substrate 20. The first substrate 20 includes the front surface 201 and the back surface 202 which are relatively separate, and the second substrate 30 includes the first surface 301 and the second surface 302 which are relatively distributed. During the bonding process, bond the second substrate 30 to the front surface 201 of the first substrate 20 in a direction with the second surface 302 of the second substrate 30 facing the front surface 201 of the first substrate 20, such that the second surface 302 of the second substrate 30 is in direct contact connection with the front surface 201 of the first substrate 20. During the process of connecting the low-resistance substrate (i.e., the first substrate 20) and the high-resistance substrate (i.e., the second substrate 30), there is no need to use the epitaxial process, thereby being able to avoid the influence of the self-doping effect in the epitaxial process on the uniformity of the distribution of doped ions in the second substrate 30 from the root, ensuring the uniformity of the resistance value distribution of the second substrate 30, and achieving the improvement of the performance of the semiconductor structure. By making the second surface 302 of the second substrate 30 in direct contact connection with the front surface 201 of the first substrate 20, that is, the second substrate 30 is in direct contact connection with the first substrate 20, it not only simplifies the process of forming the semiconductor substrate, but also helps to reduce the size of the semiconductor substrate, laying a foundation for the further miniaturization of the semiconductor structure size.

[0047] In some embodiments, before bonding the second substrate 30 and the first substrate 20 in a direction with the second surface 302 of the second substrate 30 facing the front surface 201 of the first substrate 20, the following steps are further included:

[0048] Clean the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30.

[0049] Specifically, an acidic cleaning agent or an alkaline cleaning agent can be used to clean the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30, removing particulate impurities such as dust and metal on the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30, thereby improving the cleanliness of the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30. This can not only improve the bonding strength between the first substrate 20 and the second substrate 30, but also ensure the performance uniformity of the semiconductor substrate, thus further contributing to improving the performance of the semiconductor structure.

[0050] In one example, after cleaning the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30, the first substrate 20 and the second substrate 30 are placed in a processing chamber, and a reducing gas (such as hydrogen) is introduced into the processing chamber, so that the first substrate 20 and the second substrate 30 are heat-treated (such as baked) in a reducing atmosphere for a preset time to remove the native oxide layer on the front surface 201 of the first substrate 20 and the native oxide layer on the second surface 302 of the second substrate 30, so as to avoid the influence of the presence of the native oxide layer on the performance of the subsequently formed semiconductor structure. Wherein, the preset time can be 60 seconds. The processing chamber can be an epitaxial chamber (i.e., an EPI machine chamber). After removing the native oxide layer, the first substrate 20 and the second substrate 30 are quickly bonded to avoid the re-formation of the native oxide layer during the transfer process.

[0051] In some embodiments, before bonding the second substrate 30 to the first substrate 20 in the direction that the second surface 302 of the second substrate 30 faces the front surface 201 of the first substrate 20, the following steps are further included:

[0052] Activating and processing the second surface 302 of the second substrate 30 to form hydrophilic bonding groups or hydrophobic bonding groups on the second surface 302 of the second substrate 30; and / or

[0053] Activating and processing the front surface 201 of the first substrate 20 to form hydrophilic bonding groups or hydrophobic bonding groups on the front surface 201 of the first substrate 20.

[0054] For example, the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30 are cleaned with ammonia water to activate the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30, so that a large number of hydrophilic hydroxyl groups are formed on the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30. Thus, in the process of bonding the first substrate 20 and the second substrate 30 with the second surface 302 of the second substrate facing the front surface 201 of the first substrate 20, a tight bond between the first substrate 20 and the second substrate 30 can be achieved through intermolecular forces, thereby increasing the bonding force between the first substrate 20 and the second substrate 30 and improving the bonding strength between the first substrate 20 and the second substrate 30. The step of activating the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30 can be carried out simultaneously with the step of cleaning the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30 to further improve the manufacturing efficiency of the semiconductor structure.

[0055] For another example, the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30 are cleaned with hydrofluoric acid to activate the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30, so that a large number of hydrophobic silicon-hydrogen bonds are formed on the front surface 201 of the first substrate 20 and the second surface 302 of the second substrate 30. Thus, in the process of bonding the first substrate 20 and the second substrate 30 with the second surface 302 of the second substrate facing the front surface 201 of the first substrate 20, a tight bond between the first substrate 20 and the second substrate 30 can be achieved through intermolecular forces, thereby increasing the bonding force between the first substrate 20 and the second substrate 30 and improving the bonding strength between the first substrate 20 and the second substrate 30.

[0056] Figure 5 It is a schematic structural diagram after thinning the second substrate in the specific embodiment of the present invention. In some embodiments, before forming a device structure on the surface of the second substrate 30 facing away from the first substrate 20, the following steps are further included:

[0057] Thin the second substrate 30, as Figure 5 shown.

[0058] In some embodiments, the specific steps of thinning the second substrate 30 include:

[0059] Thin the second substrate 30 starting from the first surface 301 of the second substrate 30 by using a grinding process.

[0060] Specifically, during the process of thinning the second substrate 30 by using a grinding process, since the first substrate 20 supports the second substrate 30, problems such as warping and fragmentation of the second substrate 20 during the thinning process can be avoided.

[0061] Figure 6 It is a schematic structural diagram after forming an epitaxial layer on the second substrate in a specific embodiment of the present invention. In some embodiments, the specific steps of forming a device structure on the surface of the second substrate 30 facing away from the first substrate 20 include:

[0062] Form an epitaxial layer 40 on the thinned second substrate 30 by using an epitaxial growth process, and the resistance value of the epitaxial layer 40 is lower than the resistance value of the second substrate 30, as Figure 4 shown;

[0063] Form the device structure inside the epitaxial layer 40 or above the epitaxial layer 40.

[0064] In other embodiments, the specific steps of bonding the second substrate 30 to the front surface 201 of the first substrate 20 include:

[0065] Provide the second substrate 30;

[0066] Thin the second substrate 30;

[0067] Bond the thinned second substrate 30 to the front surface 201 of the first substrate 20.

[0068] Specifically, before bonding the second substrate 30 to the first substrate 20, hydrogen ions or the like can be injected into the second substrate 30 first to form a peeling layer in the second substrate 30. Then, peel off a part of the second substrate 30 along the peeling layer to realize the thinning process of the second substrate 30. After that, bond the thinned second substrate 30 to the front surface 201 of the first substrate 20. The part of the second substrate 20 peeled off along the peeling layer has a complete morphology and can be recycled, for example, used for bonding with another first substrate 20, which helps to further reduce the manufacturing cost of the semiconductor structure.

[0069] This specific embodiment also provides a semiconductor structure formed by using the method for forming a semiconductor structure as described above, see Figures 1-6 . The schematic diagram of the semiconductor structure can be seen in Figure 6 . As Figures 1-6 shown, the semiconductor structure includes:

[0070] A semiconductor substrate, comprising a first substrate 20 and a second substrate 30, wherein the first substrate 20 includes a front surface 201 and a back surface 202 which are oppositely distributed, the second substrate 30 is bonded to the front surface 201 of the first substrate 20, and the resistance value of the second substrate 30 is higher than that of the first substrate 20;

[0071] A device structure is located on the surface of the second substrate 30 facing away from the first substrate 20.

[0072] The semiconductor structure and its forming method provided by this specific embodiment bond the second substrate to the front surface of the first substrate through a bonding process, and the resistance value of the second substrate is higher than that of the first substrate, so as to form a semiconductor substrate including the first substrate and the second substrate. Since the process of forming the second substrate above the first substrate is a bonding process rather than an epitaxial process, the influence of the self-doping effect in the epitaxial process on the uniformity of the distribution of doped ions in the second substrate can be avoided from the root, ensuring the uniformity of the resistance value distribution of the second substrate and realizing the improvement of the performance of the semiconductor structure.

[0073] It should be noted that the terms "including" and "having" and their variants involved in the documents of the present invention are intended to cover non-exclusive inclusion. The terms "first", "second", etc. are used to distinguish similar objects and do not have to be used to describe a specific order or sequence, unless clearly indicated in the context. It should be understood that the data used in this way can be interchanged under appropriate circumstances. The term "one or more" depends at least in part on the context and can be used to describe a feature, structure or property in a singular sense, or can be used to describe a combination of features, structures or features in a plural sense. The term "based on" can be understood as not necessarily intended to express a set of exclusive factors, but alternatively, at least in part depending on the context, allowing the existence of other factors that are not necessarily clearly described. In addition, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. Furthermore, in the above description, the description of well-known components and technologies is omitted to avoid unnecessarily confusing the concepts of the present invention. In each of the above embodiments, the key point of each embodiment is to illustrate the differences from other embodiments. For the same / similar parts among the embodiments, reference can be made to each other.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for forming a semiconductor structure, characterized in that: The steps include: Providing a first substrate, wherein the first substrate comprises a front side and a back side that are oppositely distributed; Bonding a second substrate to the front surface of the first substrate to form a semiconductor substrate including the first substrate and the second substrate, wherein the resistance value of the second substrate is higher than the resistance value of the first substrate; A device structure is formed on a surface of the second substrate facing away from the first substrate.

2. The method for forming a semiconductor structure according to claim 1, wherein: The second substrate includes a first surface and a second surface that are oppositely distributed; The specific steps of bonding the second substrate to the front side of the first substrate include: The second substrate and the first substrate are bonded in a direction in which the second surface of the second substrate faces the front surface of the first substrate, so that the second surface of the second substrate is directly contacted and connected with the front surface of the first substrate.

3. The method for forming a semiconductor structure according to claim 2, wherein: Before bonding the second substrate to the first substrate in a direction in which the second surface of the second substrate faces the front surface of the first substrate, the following steps are also included: The front surface of the first substrate and the second surface of the second substrate are cleaned.

4. The method for forming a semiconductor structure according to claim 2, wherein: Before bonding the second substrate to the first substrate in a direction in which the second surface of the second substrate faces the front surface of the first substrate, the following steps are also included: Activating the second surface of the second substrate to form a hydrophilic bonding group or a hydrophobic bonding group on the second surface of the second substrate; and / or The front side of the first substrate is activated to form a hydrophilic bonding group or a hydrophobic bonding group on the front side of the first substrate.

5. The method for forming a semiconductor structure according to claim 2, wherein: Before forming a device structure on a surface of the second substrate facing away from the first substrate, the method further includes the following steps: The second substrate is thinned.

6. The method for forming a semiconductor structure according to claim 5, characterized in that: The specific steps of thinning the second substrate include: The second substrate is thinned starting from the first surface of the second substrate by using a grinding process.

7. The method for forming a semiconductor structure according to claim 5, characterized in that: The specific steps of forming a device structure on a surface of the second substrate facing away from the first substrate include: forming an epitaxial layer on the thinned second substrate by an epitaxial growth process, wherein the resistance value of the epitaxial layer is lower than the resistance value of the second substrate; The device structure is formed inside the epitaxial layer or above the epitaxial layer.

8. The method for forming a semiconductor structure according to claim 1, wherein: The specific steps of bonding the second substrate to the front side of the first substrate include: providing the second substrate; thinning the second substrate; The thinned second substrate is bonded to the front side of the first substrate.

9. A semiconductor structure, characterized in that: The semiconductor structure is formed by the method for forming a semiconductor structure according to claim 1; the semiconductor structure comprises: A semiconductor substrate, comprising a first substrate and a second substrate, wherein the first substrate comprises a front side and a back side which are oppositely distributed, the second substrate is bonded to the front side of the first substrate, and a resistance value of the second substrate is higher than a resistance value of the first substrate; The device structure is located on a surface of the second substrate facing away from the first substrate.

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