Methods of fabricating bottom thick oxide (BTO) in trenches of semiconductor material, and field oxide (FOX) on top of semiconductor material, and related semiconductor devices

Abstract

A method of fabricating a bottom thick oxide (BTO) in a trench of a semiconductor material, and a field oxide (FOX) on top of the semiconductor material, the method comprising the steps of providing a trench in the semiconductor material such that the trench penetrates from a surface of the semiconductor material into the semiconductor material, providing a first material on the surface of the semiconductor material, and in the provided trench, providing a mask on top of the first material at a location above the surface of the semiconductor material, the location directly related to a location of the FOX, and forming a mask on top of the first material using the mask provided on top of the first material. The first material on top of the surface of the semiconductor material is etched such that the first material remaining in the trench is the BTO, or results in the BTO.

Description

Technical Field

[0001] This disclosure generally relates to the field of manufacturing semiconductor devices, and more specifically, to an improved method for manufacturing trenches in said semiconductor devices. Background Technology

[0002] Metal-oxide-semiconductor field-effect transistors (MOSFETs) are components in modern electronic products, used as switches or amplifiers in various devices. In semiconductor devices, especially in power electronics, MOSFETs with gate trench structures are commonly used due to their performance characteristics. Gate trench MOSFETs are characterized by vertical trenches etched into a silicon substrate, extending downwards from the surface into the substrate, and filled with a gate material, typically polycrystalline silicon, insulated from the surrounding silicon by a layer of silicon dioxide, such as SiO2. This vertical design contrasts with conventional planar MOSFETs, where the gate electrode is located on the surface of the silicon wafer.

[0003] Gate trench MOSFETs offer several advantages. The vertical structure allows for improved electrostatic control of the channel, reducing leakage current and enhancing on-state performance. It also enables higher density, allowing for more compact device layouts and increasing the number of MOSFETs per unit area on the chip. Furthermore, by optimizing the trench depth and gate oxide thickness, on-resistance can be significantly reduced, thereby improving the efficiency of power devices.

[0004] The process of creating gate trenches in semiconductor devices involves several steps utilizing photolithography, etching, and deposition techniques. It can begin with substrate preparation, in which a high-quality silicon wafer, typically with the desired doping type (e.g., n-type or p-type) and resistivity, is thoroughly cleaned to remove any contaminants. Next, a thin layer of silicon dioxide can be thermally grown on the surface of the silicon wafer. This layer serves as a protective barrier and mask during subsequent etching processes.

[0005] After the oxide layer is formed, photolithography can be used to define the trench pattern. A photoresist layer is applied to the wafer, and the wafer is exposed to ultraviolet light through a photomask defining the trench region. The exposed photoresist is then developed, leaving patterned photoresist protecting specific areas of the oxide layer. The unprotected oxide is then etched away, exposing the silicon surface where the trenches will form.

[0006] The next step is trench etching, in which the silicon wafer undergoes anisotropic etching. This etching process creates vertical trenches with well-defined profiles in the silicon.

[0007] The subsequent step involves forming a thick bottom oxide layer on the trench base. This thick bottom oxide layer isolates the bottom of the gate from the underlying silicon, reduces parasitic capacitance, and prevents unwanted current leakage. This is achieved by growing or depositing a thicker oxide layer at the bottom of the trench after the initial etching step.

[0008] After etching the trench and forming the bottom oxide, a thin layer of silicon dioxide is grown or deposited on the trench walls to serve as the gate oxide. This step is significant because it forms an insulating barrier between the gate electrode and the silicon substrate.

[0009] Once the gate oxide is in place, the trench is filled with polysilicon, which serves as the gate electrode. The polysilicon is doped, for example, during deposition or in a subsequent doping step. The polysilicon is deposited using, for example, chemical vapor deposition (CVD) and then planarized to remove any excess material above the wafer surface. A subsequent annealing step is performed to improve the electrical properties of the polysilicon and ensure good contact with the gate oxide.

[0010] In addition to the trench structure, the surface of the substrate is typically covered with a field oxide layer (FOX). This field oxide is usually thicker than the gate oxide and can be used to isolate the active regions of the MOSFET from each other, reduce parasitic capacitance, and prevent electrical interference between adjacent devices.

[0011] For silicon-based semiconductors, field oxides are typically formed through a process known as Localized Oxidation of Silicon (LOCOS), in which silicon nitride is used as a mask to grow a thick oxide layer only in designated areas.

[0012] Finally, the source and drain regions of the MOSFET are formed by ion implantation, where dopants are introduced into the silicon substrate adjacent to the gate trench. The wafer is then subjected to a high-temperature annealing process to activate the dopants and repair any damage to the silicon lattice caused by implantation. The final steps involve forming the necessary contacts and interconnects, including depositing metal layers and patterning the metal layers to create the source, drain, and gate terminals.

[0013] In essence, creating trenches in semiconductor materials requires many subsequent steps. Any one of these steps can introduce unwanted complexity. Summary of the Invention

[0014] It would be advantageous to develop a method for fabricating trenches in semiconductor materials that requires fewer or simpler manufacturing steps. It would be further advantageous to implement a method for fabricating bottom-thick oxide (BTO) in trenches of semiconductor materials and field oxide (FOX) on top of the semiconductor material in the same manufacturing steps, as this would reduce complexity.

[0015] In a first aspect of this disclosure, a method is provided for fabricating a bottom thick oxide (BTO) in a trench of a semiconductor material and for fabricating a field oxide (FOX) on top of the semiconductor material.

[0016] The method includes the following steps:

[0017] - Provide trenches in the semiconductor material such that the trenches penetrate from the surface of the semiconductor material into the semiconductor material;

[0018] - A first material is provided on the surface of the semiconductor material and in the trenches provided;

[0019] - A mask is provided at a location above the surface of the semiconductor material, on top of the first material, the location being directly related to the location of the FOX;

[0020] - Using the mask provided on top of the first material, etch the first material on top of the surface of the semiconductor material such that the remaining first material in the trench is the BTO, or results in the BTO.

[0021] The inventors have discovered that a manufacturing process can be created in which the same manufacturing steps are used to create BTO and FOX.

[0022] The method steps described above thus enable the fabrication of a combination of TBO and FOX. TBO is used to ensure gate oxide integrity in the gate dielectric of the metal-oxide-semiconductor (MOS) field-effect transistor (FET), and FOX is used to reduce gate capacitance and ensure gate oxide integrity of the MOSFET.

[0023] In the combined process, namely before the formation of the gate oxide, the fabrication of both TBO and FOX simplifies the manufacturing process, requiring less effort and reducing the risk of manufacturing problems caused by the interaction of subsequent oxide layer fabrication (such as deposition, photolithography, and etching).

[0024] The invention will now be disclosed in more detail with reference to specific examples.

[0025] In the first example, the first material includes an oxide, typically silicon dioxide. The oxide can be deposited using a variety of techniques.

[0026] Thermal oxidation is a process that involves exposing semiconductor material to a high-temperature oxidizing environment, causing a silicon dioxide layer to grow on the surface and in trenches. The resulting silicon dioxide layer is essential for MOSFET performance, providing a reliable insulating barrier that can be critical for device operation.

[0027] Chemical vapor deposition (CVD) technologies, such as low-pressure CVD (LPCVD) and plasma-enhanced CVD (PECVD), can be used to deposit oxide layers with precise control over their thickness and composition. High-density plasma CVD (HDP-CVD) is a special type of CVD that utilizes high-density plasma to enhance the deposition process.

[0028] In one instance, the method includes the following steps:

[0029] - Etching provides the first material onto the surface of the semiconductor material such that the thickness of the first material on the top of the surface is the desired thickness of the FOX.

[0030] It may be advantageous to first etch the first material as an oxide, so that an oxide layer of a certain thickness is retained on the surface of the semiconductor material. This thickness is the same as the desired thickness of the FOX layer. Therefore, this etching step can be matched with the required or desired thickness of the FOX layer.

[0031] Subsequent steps in the process, such as masking and additional etching, will then create TBOs and FOXes with the desired thickness.

[0032] In a specific example, the method includes the following steps:

[0033] - After the step of etching the first material with the mask, remove the mask;

[0034] - Etching the first material provided on the surface of the semiconductor material and the first material provided in the trench, such that the thickness of the first material on the top of the surface is the desired thickness of the FOX.

[0035] These two additional steps describe the method in more detail. First, an oxide material is provided on the surface of the semiconductor material and in the trenches. Essentially, the trenches are completely filled with the oxide material. Then, the oxide material is etched to the desired thickness. The result of this etching step is that the oxide material layer remaining on the surface of the semiconductor material is equal to the desired thickness of the FOX.

[0036] Next, a mask is provided on top of the oxide material in the areas where FOX is needed. Then, a photolithography step is performed to remove the oxide material from the surface of the semiconductor material. Finally, a recess is made to reduce the oxide thickness to TBO.

[0037] In another example, the first material comprises polycrystalline silicon (PolySi), and the method further comprises the following steps:

[0038] - The polycrystalline silicon on the top of the first surface and in the trench is oxidized to form the BTO and FOX.

[0039] The inventors have discovered that using polycrystalline silicon (PolySi) as the primary material can also be advantageous. In this case, an additional step is required to oxidize the PolySi to obtain the oxide material. This additional step thus creates FOX and TBO.

[0040] In a specific example, the method further includes the following steps:

[0041] - Etching provides the first material onto the surface of the semiconductor material such that the thickness of the first material on the top of the surface is related to the desired thickness of the FOX.

[0042] Note that etching the first material into PolySi may result in a slightly smaller thickness compared to the thickness of the FOX, as the oxidation process may add a little thickness to the resulting FOX and / or TBO.

[0043] In a specific example, the method includes the following steps:

[0044] - After the step of etching the first material with the mask, remove the mask;

[0045] - Etching the first material provided on the surface of the semiconductor material and the first material provided in the trench, such that the thickness of the first material on the top of the surface is related to the desired thickness of the FOX.

[0046] In another embodiment of this disclosure, the step of providing the first material on the surface of the semiconductor material and in the trench includes:

[0047] - A polysilicon layer having a substantially uniform thickness is provided on the surface of the semiconductor material and in the trench;

[0048] - Nitride spacers are provided on the sidewalls of the PolySi provided in the trench.

[0049] It was discovered that the trench does not need to be completely filled with the first material. A PolySi layer can be provided on top of the semiconductor material surface and within the trench. This means the trench is not completely filled with PolySi. PolySi layers are provided on the sidewalls of the trench and on the bottom of the trench.

[0050] The thickness of the PolySi layer may be related to the required thickness of the FOX. As mentioned above, the PolySi layer can undergo an oxidation process, which can increase the thickness of the resulting FOX and / or BTO. Therefore, the PolySi layer can have a smaller thickness compared to the desired or required thickness of the FOX and / or BTO.

[0051] Nitride separators are used to prevent PolySi on the sidewalls of the trench from participating in the oxidation process. Therefore, the PolySi on the sidewalls of the trench will not oxidize.

[0052] Finally, after the oxidation process, the nitride separators and PolySi provided on the sidewalls of the trench can be removed.

[0053] In another instance, the method includes the following steps:

[0054] - After the step of etching the first material with the mask, remove the mask;

[0055] - The polycrystalline silicon on the top of the first surface and in the trench is oxidized to form the BTO and FOX.

[0056] In other examples, the semiconductor material is any one of silicon, silicon carbide (SiC), and gallium nitride (GaN).

[0057] In the fabrication of gate trench MOSFETs, the semiconductor material used can be silicon or silicon carbide (SiC), etc. Silicon has excellent electrical properties, is a mature processing technology, and is cost-effective.

[0058] On the other hand, silicon carbide (SiC) is a semiconductor material that offers improved performance in high-temperature, high-pressure, and high-frequency applications. SiC devices can operate at higher temperatures and voltages than silicon devices, making them ideal for power electronics, such as inverters for electric vehicles, power supplies for industrial applications, and power management systems for renewable energy. SiC's wider bandgap, higher thermal conductivity, and higher breakdown electric field strength make it a good choice for these demanding applications.

[0059] Other semiconductor materials used in specific applications include gallium nitride (GaN), which exhibits high electron mobility and efficiency in high-frequency and high-power applications. GaN is increasingly being used in RF components, power amplifiers, and LED technology.

[0060] For example, using silicon carbide could be advantageous. The inventors have recognized that the LOCOS process for growing oxides allows for self-aligned fabrication techniques that cannot be easily transferred to silicon carbide. This is one reason why those skilled in the field of silicon carbide do not consider the LOCOS process a direct process for FOX manufacturing. Due to the low oxidation rate of SiC, the application of LOCOS in SiC technology has not yet been adopted.

[0061] In another example, a method for fabricating a metal-oxide-semiconductor (MOS) field-effect transistor (FET) in a semiconductor material is provided, wherein the steps for fabricating the MOSFET include the steps of any of the foregoing examples.

[0062] The inventors have discovered that, as explained in the preceding examples, trench fabrication is particularly useful when manufacturing MOSFETs.

[0063] In a specific instance, the trench is the gate trench of the MOSFET.

[0064] In a second aspect of this disclosure, a semiconductor device embodied in a semiconductor material is provided, the semiconductor device comprising a bottom thick oxide BTO in a trench of the semiconductor material and a field oxide FOX on top of the semiconductor material, wherein the BTO and the FOX are manufactured according to any of the examples provided above.

[0065] It should be noted that the advantages explained by referring to the first aspect of this disclosure, namely the method of fabricating a bottom thick oxide (BTO) in a trench of semiconductor material and fabricating a field oxide (FOX) on top of semiconductor material, also apply to the second aspect of this disclosure, namely semiconductor devices.

[0066] In the accompanying drawings, similar parts and / or features may have the same reference numerals. Furthermore, various parts of the same type can be distinguished by adding a dash and a second reference numeral after the reference numeral, the second reference numeral used to distinguish similar parts. If only the first reference numeral is used in the description, the description applies to any one of the similar parts having the same first reference numeral, regardless of the second reference numeral.

[0067] The foregoing and other aspects of this disclosure will become apparent from the examples described below, and are illustrated with reference to the examples described below. Attached Figure Description

[0068] Figures 1a to 1d disclose processes for fabricating bottom thick oxide (BTO) in trenches of semiconductor material and fabricating field oxide (FOX) on top of semiconductor material according to examples of the present disclosure.

[0069] Figures 2a to 2c show process variations of the processes disclosed in Figures 1a to 1d;

[0070] Figures 3a to 3d disclose processes for fabricating bottom thick oxide (BTO) in trenches of semiconductor material and fabricating field oxide (FOX) on top of semiconductor material according to other embodiments of the present disclosure.

[0071] Figures 4a to 4d show process variations of the processes disclosed in Figures 3a to 3d;

[0072] Figures 5a and 5c disclose a process for fabricating a bottom thick oxide (BTO) in a trench of a semiconductor material and a field oxide (FOX) on top of a semiconductor material, according to another example of the present disclosure. Detailed Implementation

[0073] Note that in the description of the accompanying drawings, the same reference numerals refer to the same or similar parts that perform the same or substantially similar functions.

[0074] A more detailed description is provided with reference to specific examples, some of which are illustrated in the accompanying drawings, to enable a more detailed understanding of the features of this disclosure. Note that the drawings show only typical examples and should therefore not be considered as limiting the scope of the claims. The drawings are incorporated for ease of understanding of this disclosure and are therefore not necessarily drawn to scale. Upon reading the specification in conjunction with the drawings, the advantages of the claimed subject matter will become apparent to those skilled in the art.

[0075] The foregoing description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of this disclosure. Rather, the subsequent description of preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing preferred exemplary embodiments of this disclosure. It should be understood that various changes may be made to the functionality and layout of elements, including combinations of features from different embodiments, without departing from the scope of this disclosure.

[0076] Unless the context explicitly requires otherwise, throughout the specification and claims, the terms “comprise,” “comprising,” etc., shall be interpreted in a sense of inclusion, rather than exclusion or exhaustion; that is, in the sense of “including but not limited to.” As used herein, the terms “connection,” “coupling,” or any variation thereof mean any direct or indirect connection or coupling between two or more elements; the coupling or connection between elements may be physical, logical, electromagnetic, or a combination thereof. Furthermore, when used in this application, the terms “in this document,” “above,” “below,” and similar terms refer to the application as a whole, and not to any particular part of the application. Where the context permits, singular or plural terms used in the specific embodiments may also include the plural or singular, respectively. The word “or,” referring to a list of two or more items, covers all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list.

[0077] These and other modifications can be made to the technology in light of the following detailed description. While the specification describes certain examples of the technology and outlines the expected best practices, the technology can be practiced in a variety of ways, no matter how detailed the specification may appear. The details of the system can vary considerably in its specific implementation, while still being covered by the technology disclosed herein.

[0078] Figures 1a to 1d disclose processes for fabricating bottom thick oxide (BTO) in trenches of semiconductor material and fabricating field oxide (FOX) on top of semiconductor material according to examples of the present disclosure.

[0079] Figure 1a illustrates the starting point of this disclosure. Here, trenches are provided in a semiconductor material. An oxide is provided on top of the surface and within the trench. The trench is completely filled with oxide.

[0080] Figure 1b shows the oxide being etched to a specific thickness. This thickness matches or is related to the desired thickness of FOX.

[0081] Figure 1c shows a mask provided on top of an oxide layer at the surface of a semiconductor material. The mask is provided over the region of oxide in which FOX is to be created.

[0082] The oxide can then be etched onto the surface of the semiconductor material.

[0083] Figure 1d shows that the trench can be etched to a specific depth so that the TBO remains in the trench.

[0084] Figures 2a to 2c relate to the processes disclosed in Figures 1a to 1d and briefly discussed below.

[0085] Figure 2a shows the same starting point as disclosed in Figure 1a.

[0086] Instead of etching the oxide to the desired thickness, the example shown in Figure 2 first places a mask at the location where the FOX will be created. This means the oxide is still thicker than the required thickness of the FOX. Then, as shown in Figure 2b, an etching process is performed to remove the oxide present on the surface of the semiconductor material. Of course, the oxide under the mask is not removed, which is why a mask is used. Finally, as shown in Figure 2c, the remaining oxide on the surface of the semiconductor material, as well as the oxide present in the trenches, can be recessed to create the desired thickness of the TBO and FOX.

[0087] Figures 3a to 3d disclose further examples of the present disclosure, which are processes for fabricating a bottom thick oxide (BTO) in a trench of a semiconductor material and fabricating a field oxide (FOX) on top of the semiconductor material.

[0088] In this specific case, the first material is PolySi. The steps shown in Figures 3a to 3c are similar to those shown in Figures 1a to 1c. However, in Figure 3d, an additional step is shown: oxidizing PolySi to create oxides for FOX and TBO.

[0089] Figures 4a to 4c disclose process variations of the process disclosed in Figures 3a to 3d. The steps shown in Figures 4a to 4c are similar to those shown in Figures 1a to 1c. The additional step 4d is similar to the steps shown in Figure 3d.

[0090] Figures 5a to 5c disclose another embodiment of the present disclosure, which describes a process for fabricating a bottom thick oxide (BTO) in a trench of semiconductor material and a field oxide (FOX) on top of semiconductor material.

[0091] The difference in this example compared to the previous one is the provision of a thin layer of PolySi instead of completely filling the trench. This requires an additional step of providing a nitride separator to the sidewalls of the trench to prevent the polysilicon positioned on the sidewalls of the trench from being oxidized during the oxidation process.

[0092] As stated above, certain terms used in describing certain features or aspects of this technology should not be construed as implying that such terms are redefined herein as limited to any specific characteristic, feature, or aspect of the technology associated with that term. In general, the terms used in the appended claims should not be construed as limiting the technology to the specific instances disclosed in the specification, unless such terms are expressly defined in the detailed description section. Therefore, the actual scope of this technology covers not only the disclosed instances but also all equivalent ways of practicing or implementing the technology under the claims.

[0093] List of reference numerals

[0094] 1 Oxide

[0095] 2 Semiconductor materials 3 Semiconductor materials 4 Semiconductor materials 5 Photoresist

[0096] 6FOX

[0097] 7BOX

[0098] 8 Polycrystalline silicon

[0099] 10 Polycrystalline Silicon

[0100] 11p+

[0101] 12 p well

[0102] 13 Semiconductor Materials 14n+

[0103] 15n-CSL

[0104] 16SixNy.

Claims

1. A method of manufacturing a bottom thick oxide, BTO, in a trench in a semiconductor material, and a field oxide, FOX, on top of the semiconductor material, the method comprising the steps of: - providing a trench in the semiconductor material, such that the trench penetrates into the semiconductor material from a surface of the semiconductor material; - providing a first material on the surface of the semiconductor material, and in the provided trench; - providing a mask on top of the first material at a location above the surface of the semiconductor material, the location being directly related to a location of the FOX; - etching the first material on top of the surface of the semiconductor material with the mask provided on top of the first material, such that the first material remaining in the trench is, or results in, the BTO.

2. The method according to claim 1, wherein the first material comprises an oxide.

3. The method according to any of the preceding claims, wherein the step method further comprises the step of: - etching the first material provided on the surface of the semiconductor material, such that a thickness of the first material on top of the surface is a required thickness of the FOX.

4. The method according to any of the claims 1-2, wherein the method comprises the steps of: - removing the mask after the step of etching the first material with the mask; - etching the first material provided on the surface of the semiconductor material, and the first material provided in the trench, such that a thickness of the first material on top of the surface is a required thickness of the FOX.

5. The method according to claim 1, wherein the first material comprises poly-silicon, PolySi, and wherein the method further comprises the step of: - oxidizing the PolySi on top of the first surface and in the trench, thereby forming the BTO and FOX.

6. The method according to claim 5, wherein the method further comprises the step of: - etching the first material provided on the surface of the semiconductor material, such that a thickness of the first material on top of the surface is related to a required thickness of the FOX.

7. The method according to claim 5, wherein the method comprises the steps of: - removing the mask after the step of etching the first material with the mask; - etching the first material provided on the surface of the semiconductor material, and the first material provided in the trench, such that a thickness of the first material on top of the surface is related to a required thickness of the FOX.

8. The method according to claim 1, wherein the step of providing the first material on the surface of the semiconductor material, and in the trench comprises: - providing a layer of poly-silicon, PolySi, on the surface of the semiconductor material, and in the trench, the layer having a substantially uniform thickness. - providing a nitride spacer at the sidewalls of the provided PolySi in the trench.

9. The method according to claim 8, wherein the thickness of the PolySi layer is related to the required thickness of the FOX.

10. The method according to any of claims 8 to 9, wherein the method further comprises the steps of: - removing the nitride spacer and the PolySi provided at the sidewalls of the trench.

11. The method according to any of claims 10, wherein the method comprises the steps of: - removing the mask after the step of etching the first material with the mask; - oxidizing the poly-silicon on top of the first surface and in the trench, thereby forming the BTO and FOX.

12. The method according to any of the preceding claims, wherein the semiconductor material is any of silicon, silicon carbide SiC, and gallium nitride GaN.

13. A method of manufacturing a metal oxide semiconductor, MOS, field effect transistor, FET, in a semiconductor material, wherein the steps of manufacturing the MOSFET comprise the steps according to any of the preceding claims.

14. The method according to claim 13, wherein the trench is a gate trench of the MOSFET.

15. A semiconductor device embodied in a semiconductor material, the semiconductor device comprising a bottom thick oxide, BTO, in a trench of the semiconductor material, and a field oxide, FOX, on top of the semiconductor material, wherein the BTO and the FOX are manufactured according to any of claims 1 to 12.

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