Semiconductor device and method of manufacturing the same

Abstract

The application provides a semiconductor device and a preparation method thereof. The method comprises the following steps: providing a plurality of wafers, the front surface of the wafer being coated with a protective film, and the back surface of the wafer being formed with a metal layer; stacking the plurality of wafers in a heating pipe at intervals, and the inner wall of the cavity of the heating pipe being previously attached with the protective film; and heating the wafer by using a first temperature, so that part of the protective film volatilizes and is uniformly distributed in the cavity of the heating pipe. In the process of heating the wafer, the protective film on the front surface of the wafer and the inner wall of the cavity of the heating pipe volatilize. Due to the flow of the airflow in the heating pipe, the volatilized part of the protective film on the front surface of the wafer is mainly distributed in the central region of the wafer, and less in the edge region. The volatilized protective film on the inner wall of the cavity of the heating pipe can make up for the problem that the volatilized component in the edge region of the wafer is less, so that the volatilized components of the protective film are uniformly distributed in the cavity of the heating pipe, the volatilized component amount contacted by the metal layer at each position is balanced, the color difference of the metal layer is avoided, and the visual inspection result is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a semiconductor device and its fabrication method. Background Technology

[0002] To improve the electrical performance and reliability of chips, current processes often coat the chip surface with a layer of polyimide (PI). PI refers to a type of polymer containing imide rings in its main chain, possessing properties such as high-temperature resistance, low-temperature resistance, flame retardancy, corrosion resistance, and non-toxicity, which can enhance the mechanical properties of the chip. Simultaneously, to improve the chip's on-resistance, current processes also employ back-side metallization, depositing a metal layer on the back of the wafer as lead-out electrodes. In the back-side metallization process, aluminum, titanium, nickel, and silver are generally chosen as the four back-side metal layers. Because silver has good conductivity and good miscibility with solder paste, it is generally used as the outermost layer of the back-side metal.

[0003] Currently, existing back-side alloying processes improve ohmic contact by controlling process temperature, gas flow rate, and process time. The temperature range for back-side alloying is typically 300℃ to 400℃. Figure 1 It is known that under a process environment of 300℃~400℃, PI is exactly in the fourth state (T4), i.e., a fully amination state. The solvent volatilized from PI readily reacts with the active silver layer on the back side. Based on this, if... Figure 2 As shown, when there is a difference in atmosphere between the center and edge of wafer W, a significant color difference D will form in the silver layer on the back of wafer W, severely affecting the visual inspection results of wafer W. Current solutions only involve verifying the electrical parameters of the chip for graded shipment, which cannot resolve the color difference D problem in the silver layer on the back of the wafer.

[0004] Therefore, a new preparation process is urgently needed to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a semiconductor device and its fabrication method to solve at least one of the problems of how to alleviate the color difference of the silver layer on the back side of a wafer and how to improve the visual inspection results of the wafer.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for fabricating a semiconductor device, comprising:

[0007] A plurality of wafers are provided, wherein a protective film is coated on the front side of the wafers and a metal layer is formed on the back side of the wafers;

[0008] The plurality of wafers are stacked at intervals inside the heating tube, and the inner wall of the heating tube is pre-adhered with the protective film;

[0009] The wafer is heated to a first temperature, causing a portion of the protective film to evaporate and distribute evenly within the cavity of the heating tube.

[0010] Optionally, in the semiconductor device fabrication method, during the process of heating the wafer at a first temperature, one end of the heating tube vents air into the cavity, while the other end draws air from the cavity, and the air intake and / or air intake of the heating tube are adjusted to control the air pressure inside the heating tube within a preset range.

[0011] Optionally, in the method for fabricating the semiconductor device, the preset range is 135 Pa to 155 Pa.

[0012] Optionally, in the method for fabricating the semiconductor device, the process of pre-adhering the protective film to the inner wall of the heating tube includes:

[0013] A plurality of test pieces are provided, the surface of which is coated with the protective film;

[0014] The test pieces are stacked at intervals inside the heating tube, and the test pieces are heated at a second temperature, so that at least part of the protective film evaporates and adheres to the inner wall of the heating tube.

[0015] Optionally, in the method for fabricating the semiconductor device, the second temperature is higher than the first temperature.

[0016] Optionally, in the method for fabricating the semiconductor device, the protective film may be made of polyimide.

[0017] Optionally, in the method for fabricating the semiconductor device, the first temperature range is 300℃~400℃, and the second temperature range is 550℃~600℃.

[0018] Optionally, in the method for preparing the semiconductor device, the heating time range for heating the test piece at the second temperature is 8h to 20h.

[0019] Optionally, in the method for fabricating the semiconductor device, the metal layer includes at least a silver layer.

[0020] Based on the same inventive concept, the present invention also provides a semiconductor device, which is prepared by the semiconductor device preparation method described above.

[0021] In summary, this invention provides a semiconductor device and a method for fabricating the same. The method includes: providing a plurality of wafers, each wafer having a protective film coated on its front side and a metal layer formed on its back side; stacking the plurality of wafers at intervals within a heating tube, wherein the protective film is pre-adhered to the inner wall of the heating tube cavity; and heating the wafers at a first temperature, causing a portion of the protective film to evaporate and distribute evenly within the cavity of the heating tube. Compared to existing technologies, this application pre-adheres the protective film to the inner wall of the heating tube, so during the heating process, both a portion of the protective film on the front side of the wafer and a portion of the protective film on the inner wall of the heating tube will evaporate. Due to the airflow within the heating tube, the evaporated portion of the protective film on the front side of the wafer is mainly distributed in the central region of each wafer, with less evaporation at the edges. The volatile protective film on the inner wall of the heating tube can compensate for the low volatile content in the wafer edge region, ensuring a uniform distribution of the volatile components within the heating tube cavity. This results in a balanced amount of volatile components from the protective film at all points of contact with the metal layer. Therefore, this application alleviates the problem of atmosphere differences between the central and edge regions of the wafer, avoids color differences in the metal layer, and improves visual inspection results. Attached Figure Description

[0022] Those skilled in the art will understand that the accompanying drawings are provided to better understand the invention and do not constitute any limitation on the scope of the invention. Wherein:

[0023] Figure 1 This is a temperature-state diagram of polyimide.

[0024] Figure 2 This is a schematic diagram of the silver layer color difference in wafers in the existing technology.

[0025] Figure 3 This is a flowchart of the semiconductor device fabrication method in an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of the wafer structure in an embodiment of the present invention.

[0027] Figure 5 This is a schematic diagram of the heating tube in an embodiment of the present invention.

[0028] Figure 6 This is a schematic diagram of the molecular distribution on the back side of the wafer in an embodiment of the present invention.

[0029] Figure 7 This is a schematic diagram of the heating tube with a protective film attached to the inner wall of the cavity in an embodiment of the present invention.

[0030] Figure 8This is a schematic diagram of a heating tube with a protective film attached to the inner wall of the cavity used to heat a wafer in an embodiment of the present invention.

[0031] Figure 9 This is a schematic diagram of a wafer heated by a heating tube with a protective film attached to the inner wall of the cavity, as described in an embodiment of the present invention.

[0032] In the attached image:

[0033] 10 - Wafer; 100 - Device layer; 101 - Protective film; 1011 - Molecule; 102 - Metal layer;

[0034] 20 - Heating element; 200 - Body; 201 - Inlet pipe; 202 - Outlet pipe;

[0035] D - wafer; W - color difference; T1 - first state; T2 - second state; T3 - third state; T4 - fourth state; T5 - fifth state. Detailed Implementation

[0036] To make the objectives, advantages, and features of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to facilitate and clarify the explanation of the embodiments of this invention. Furthermore, the structures shown in the drawings are often part of the actual structures. In particular, different figures may emphasize different aspects and may sometimes use different scales.

[0037] As used in this invention, the singular forms “a,” “an,” and “the” include plural objects; the term “or” is generally used to mean “and / or”; the term “a number” is generally used to mean “at least one”; and the term “at least two” is generally used to mean “two or more”. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature. The terms “installed,” “connected,” and “linked” should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral part; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; they may refer to the internal communication of two elements or the interaction between two elements. Furthermore, as used in this invention, the phrase "one element is disposed on another element" generally only indicates that there is a connection, coupling, cooperation, or transmission relationship between the two elements, and the connection, coupling, cooperation, or transmission between the two elements can be direct or indirect through an intermediate element. It should not be construed as indicating or implying a spatial positional relationship between the two elements, i.e., one element can be located arbitrarily inside, outside, above, below, or to one side of the other element, unless otherwise explicitly stated. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] Please see Figure 3 This embodiment provides a method for fabricating a semiconductor device, including:

[0039] Step 1 S10: Provide a plurality of wafers, wherein the front side of the wafers is coated with a protective film and the back side of the wafers is formed with a metal layer;

[0040] Step 2 S20: The plurality of wafers are stacked in the heating tube, and the inner wall of the heating tube is pre-adhered with the protective film;

[0041] Step 3 S30: Heat the wafer at a first temperature, causing some of the protective film to evaporate and be evenly distributed within the cavity of the heating tube.

[0042] Therefore, as can be seen, the method provided in this embodiment pre-adheres the protective film to the inner wall of the heating tube. During the heating of the wafer, both the portion of the protective film on the front side of the wafer and the portion of the protective film on the inner wall of the heating tube will evaporate. Due to the airflow within the heating tube, the evaporating portion of the protective film on the front side of the wafer is mainly distributed in the central region of each wafer, with less evaporation at the edges. The evaporating protective film on the inner wall of the heating tube compensates for the lower evaporation at the wafer edges, resulting in a uniform distribution of the volatile components within the heating tube cavity. This ensures a balanced amount of volatile components in the protective film at all points of contact with the metal layer. Therefore, the method provided in this embodiment alleviates the problem of atmosphere differences between the central and edge regions of the wafer, avoids color differences in the metal layer, and improves visual inspection results.

[0043] The following combination Figures 3-9 The method for fabricating the semiconductor device provided in this embodiment will be described in detail.

[0044] Step 1 S10: Please refer to Figure 4 A plurality of wafers 10 are provided, wherein a protective film 101 is coated on the front side of the wafers 10 and a metal layer 102 is formed on the back side of the wafers 10.

[0045] Specifically, in this embodiment, the wafer 10 is composed of at least a device layer 100, a protective film 101, and a metal layer 102. The device layer 100 has a device structure formed thereon, such as an IGBT, a MOSFET, or other semiconductor device. The protective film 101 is used to enhance the performance of the device structure, and the material of the protective film 101 is preferably polyimide. The metal layer 102 is used to improve the contact effect of the device structure and reduce contact resistance. Further, the metal layer 102 is composed of various metal film layers, such as aluminum, titanium, nickel, silver, etc. Preferably, the outermost layer of the metal layer 102 is a silver layer.

[0046] Step 2 S20: Please refer to Figures 4-7 The plurality of wafers 10 are stacked at intervals inside the heating tube 20, and the inner wall of the heating tube 20 is pre-adhered with the protective film 101.

[0047] It should be noted that during the back-side alloying process, the wafer 10 with the metal layer 102 formed thereon needs to be placed inside the heating tube 20 for heating treatment. This reduces the contact resistance between the metal in the metal layer 102 and the semiconductor structure in the device layer 100, increases the adhesion of the metal to the semiconductor, and improves the mechanical strength of the metal layer 102. Preferably, to improve fabrication efficiency, multiple wafers 10 can be carried in a quartz boat for simultaneous heating.

[0048] Please see Figure 5 In this embodiment, the heating tube 20 is a quartz tube. Quartz tubes possess excellent high-temperature resistance, corrosion resistance, thermal stability, and light transmittance, making them widely suitable for semiconductor furnace tube processes. Furthermore, during the heating of the wafer 10, to prevent oxidation of the metal layer 102 by oxygen, nitrogen or a mixture of nitrogen and hydrogen is introduced into the heating tube 20 during heating to ensure the quality of metal sintering. Based on this, the heating tube 20 consists of a tube body 200, an inlet pipe 201, and an outlet pipe 202. The inlet pipe 201 and the outlet pipe 202 are located at opposite ends of the tube body 200 and are connected to the inner cavity of the tube body 200. During heating, gas enters through the inlet pipe 201 and is then extracted through the outlet pipe 202.

[0049] Please see Figure 5 and Figure 6 During the heating of the wafer 10 using the heating tube 20, multiple wafers 10 are stacked along the axial direction of the heating tube 20 within the inner cavity of the tube body 200, and are spaced apart from each other for sufficient heating. The protective film 101 on the front side of the wafer 10 evaporates due to heating, forming numerous suspended molecules 1011 that fill the inner cavity of the tube body 200. However, because there is flowing gas within the cavity of the tube body 200, and the airflow velocity is higher at the edges of the wafer 10 and lower at the center, some of the molecules 1011 suspended at the edges of the wafer 10 flow out of the tube body 200 with the airflow. Therefore, more molecules 1011 accumulate in the center of the wafer 10, while fewer molecules 1011 accumulate in the edges. Based on this, the molecules 1011 emitted by the protective film 101 react with the silver layer mainly in the central region of the wafer 10, which will result in silver layer color difference.

[0050] In this embodiment, the heating tube 20, with the protective film 101 pre-adhered to its inner wall, is used to heat the wafer 10. This utilizes the protective film 101 adhering to the inner wall of the heating tube 20 to even out the number of molecules 1011 corresponding to each region in the metal layer 102. For details, please refer to... Figure 7The process of pre-adhering the protective film 101 to the inner wall of the heating tube 20 includes: first, providing a plurality of test pieces, the surface of which is coated with the protective film 101 of a certain thickness. Then, stacking the plurality of test pieces at intervals inside the heating tube 20, and heating the test pieces at a second temperature. Finally, at least a portion of the protective film 101 evaporates and adheres to the inner wall of the heating tube 20.

[0051] Furthermore, since the main component of the protective film 101 is polyimide, and polyimide exhibits different states at different temperatures. For example... Figure 1 As shown, when the polyimide is between 110℃ and 160℃, it is in the first state T1, where a large amount of polyimide volatilizes; when the polyimide is between 160℃ and 250℃, it is in the second state T2, where the volatilization of polyimide intensifies; when the polyimide is between 250℃ and 300℃, it is in the third state T3, where the polyimide is basically amination-completed; when the polyimide is between 300℃ and 400℃, it is in the fourth state T4, where the polyimide is fully amination-completed; and when the polyimide is at or above 400℃, it is in the fifth state T5, where the polyimide begins to decompose. Therefore, in this embodiment, the preferred range of the second temperature is 550℃ to 600℃, during which the polyimide in the protective film 101 begins to decompose, and the heating time is between 8h and 20h, so as to fully bake the test piece and ensure that the protective film 101 is stably attached to the inner wall of the heating tube 20. For example, the second temperature is 550℃, 580℃, or 600℃, and the heating time is 8h, 15h, or 20h. It should be noted that this embodiment does not limit the specific thickness of the protective film 101 coated on the test piece, nor the specific thickness of the protective film 101 attached to the inner wall of the tube 200. The thickness can be selected according to the device product, process requirements, and the service life of the heating tube 20.

[0052] Step 3 S30: Please refer to Figure 8 and Figure 9 The wafer 10 is heated at a first temperature, causing a portion of the protective film 101 to evaporate and be evenly distributed within the cavity of the heating tube 20.

[0053] As described in step S20, in this example, the heating tube 20, whose inner wall is pre-adhered with the protective film 101, is used to heat the wafer 10. During the heating process of the wafer 10, both the portion of the protective film 101 on the front side of the wafer 10 and the portion of the protective film 101 on the inner wall of the heating tube 20 will evaporate. The evaporated protective film 101 on the inner wall of the heating tube 20 can compensate for the low number of molecules 1011 suspended in the edge region of the wafer 10, thus supplementing the number of molecules 1011 in the edge region of the wafer 10. This ensures that the molecules 1011 evaporated from the protective film 101 are evenly distributed within the cavity of the heating tube 20, resulting in a balanced number of molecules 1011 in contact with the metal layer 102. This alleviates the problem of atmosphere differences between the central and edge regions of the wafer 10, avoids color differences in the metal layer 102, and improves visual inspection results.

[0054] To further ensure a uniform atmosphere between the central and edge regions of the wafer 10, during the heating of the wafer 10 at the first temperature, the exhaust or intake air volume of the heating tube 20 is adjusted, or both are adjusted simultaneously, so that the internal air pressure of the heating tube 20 is controlled within a preset range. This ensures that the atmosphere within the heating tube 20 is saturated, avoids the formation of silver layer color differences, and improves visual inspection results. Preferably, the preset range is 135 Pa to 155 Pa.

[0055] Furthermore, during normal heating, the first temperature is generally lower than the second temperature, so only a portion of the protective film 101 evaporates with each heating, increasing the reusability of the heating tube 20. That is, it is unnecessary to pre-bake the test wafer each time the wafer 10 is heated, so that the protective film 101 adheres to the inner wall of the heating tube 20; the heating tube 20 can be reused for a long time after only one baking of the test wafer, until the thickness of the protective film 101 adhering to the inner wall of the heating tube 20 is small. Preferably, the range of the first temperature is 300℃~400℃. Exemplarily, the first temperature is 300℃, 350℃, or 400℃.

[0056] Based on the same inventive concept, this embodiment also provides a semiconductor device. The semiconductor device is fabricated using the aforementioned semiconductor device fabrication method, exhibiting superior visual inspection results and a high chip survival rate. Furthermore, as verified by the applicant, the semiconductor device fabricated using the semiconductor device fabrication method provided in this embodiment demonstrates superior test results for hole testing, wetting testing, contact resistance testing, and peeling testing.

[0057] In summary, this embodiment provides a semiconductor device and its fabrication method. The method involves pre-adhering a protective film 101 to the inner wall of the heating tube 20. During the heating of the wafer 10, both a portion of the protective film 101 on the front side of the wafer 10 and a portion of the protective film 101 on the inner wall of the heating tube 20 will volatilize. Due to the airflow within the heating tube 20, the volatilized portion of the protective film 101 on the front side of the wafer 10 is mainly distributed in the central region of each wafer 10, with less volatilization at the edges. The volatilized protective film 101 on the inner wall of the heating tube 20 compensates for the lower volatilization at the edges of the wafer 10, resulting in a uniform distribution of the volatilized components within the heating tube 20. This ensures a balanced amount of volatilized components from the protective film 101 at all points of contact with the metal layer 102. Meanwhile, this embodiment also adjusts the gas pressure within the heating tube 20 during the heating of the wafer 10 to saturate the atmosphere within the heating tube, thereby further ensuring that the volatilized molecules 1011 can be evenly distributed. Therefore, the semiconductor device and its fabrication method provided in this embodiment effectively alleviate the problem of atmosphere differences between the central and edge regions of the wafer 10, avoid color differences in the metal layer 102, and improve visual inspection results.

[0058] Furthermore, it should be understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for fabricating a semiconductor device, characterized in that, include: A plurality of wafers are provided, wherein a protective film is coated on the front side of the wafers and a metal layer is formed on the back side of the wafers; The plurality of wafers are stacked at intervals inside the heating tube, and the inner wall of the heating tube is pre-adhered with the protective film; The wafer is heated to a first temperature, causing a portion of the protective film to evaporate and distribute evenly within the cavity of the heating tube.

2. The method for fabricating a semiconductor device according to claim 1, characterized in that, During the heating of the wafer at the first temperature, one end of the heating tube vents air into the cavity, while the other end draws air out of the cavity. The air intake and / or air intake of the heating tube are adjusted to control the air pressure inside the heating tube within a preset range.

3. The method for fabricating a semiconductor device according to claim 2, characterized in that, The preset range is 135Pa to 155Pa.

4. The method for fabricating a semiconductor device according to claim 1, characterized in that, The process of pre-adhering the protective film to the inner wall of the heating tube includes: A plurality of test pieces are provided, the surface of which is coated with the protective film; The test pieces are stacked at intervals inside the heating tube, and the test pieces are heated at a second temperature, so that at least part of the protective film evaporates and adheres to the inner wall of the heating tube.

5. The method for fabricating a semiconductor device according to claim 4, characterized in that, The second temperature is higher than the first temperature.

6. The method for fabricating a semiconductor device according to claim 4, characterized in that, The protective film is made of polyimide.

7. The method for fabricating a semiconductor device according to claim 6, characterized in that, The first temperature range is 300℃~400℃, and the second temperature range is 550℃~600℃.

8. The method for fabricating a semiconductor device according to claim 7, characterized in that, The heating time range for heating the test piece at the second temperature is 8h to 20h.

9. The method for fabricating a semiconductor device according to claim 1, characterized in that, The metal layer includes at least a silver layer.

10. A semiconductor device, characterized in that, It is prepared by the method of preparing a semiconductor device as described in any one of claims 1 to 9.

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