Preparation method of semiconductor chip and semiconductor chip thereof

Abstract

The invention provides a preparation method of a semiconductor chip and the semiconductor chip, which are mainly used for forming a metal film layer on the semiconductor chip, and the preparation method comprises the following steps: providing the semiconductor chip with a laminated structure; forming a photoresist layer on the front surface of the semiconductor chip, wherein the photoresist layer covers the upper surface of the passivation layer and extends from the upper surface of the passivation layer to a part of the upper surface of the electrode layer; forming a metal film layer above the photoresist layer, wherein the metal film layer covers the photoresist layer and the exposed upper surface of the electrode layer; a thinning protection film is pasted on the upper surface of the metal film layer, and the back face of the semiconductor chip is thinned; and removing the thinning protective film to strip the metal film layer on the upper surface of the photoresist layer, and reserving the metal film layer on the upper surface of the electrode layer. According to the semiconductor chip prepared by the invention, the edge of the metal film layer is not tilted, and the product yield is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chip preparation, and particularly to a method for preparing a semiconductor chip with a metal welding layer and the semiconductor chip. Background Art

[0002] During the packaging process of a silicon carbide (SiC) semiconductor chip such as a metal-oxide-semiconductor field-effect transistor (MOSFET), it is necessary to weld and connect the chip to an external pin or a circuit board. Currently, a metal stripping process is usually used to deposit a titanium-nickel-silver metal film layer on the front metal area of the chip. This titanium-nickel-silver film layer can provide good surface conditions for welding, improve the wettability and bonding force between the chip and the welding material, make the welding process more reliable, and the welding quality higher. It can effectively avoid problems such as virtual soldering and de-soldering, enhance the mechanical stability and electrical connection performance of the device after packaging, and ensure the reliability of the device during long-term use.

[0003] The applicant of the present invention has found that the edge of the titanium-nickel-silver metal film layer prepared by the current process is prone to warping. As shown in Figure 2 the dotted box, it can be clearly seen that the warped metal film layer, and even the whole film layer falls off. Therefore, it is necessary to develop a preparation method for forming a metal film layer on the front of the semiconductor chip to avoid the warping or falling off of the edge of the film layer. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a semiconductor chip and the semiconductor chip, so as to solve the problem that the edge of the metal film layer is prone to warping when the metal film layer is prepared on the front of the semiconductor chip.

[0005] The present invention provides a method for preparing a semiconductor chip, which is mainly used for forming a metal film layer on the semiconductor chip, and includes the following steps: Provide a semiconductor chip with a stacked structure, the front of the semiconductor chip is a passivation layer and an electrode layer surrounded by the passivation layer; Form a photoresist layer on the front of the semiconductor chip, the photoresist layer covers the upper surface of the passivation layer and extends to a part of the upper surface of the electrode layer from the upper surface of the passivation layer; Form a metal film layer above the photoresist layer, the metal film layer covers the photoresist layer and the exposed upper surface of the electrode layer; Attach a thinning protective film on the upper surface of the metal film layer, and thin the back of the semiconductor chip; Remove the thinning protective film to strip the metal film layer on the upper surface of the photoresist layer, and retain the metal film layer on the upper surface of the electrode layer.

[0006] Preferably, the back surface of the semiconductor chip is a back passivation layer, the upper surface of the back passivation layer is a silicon carbide substrate, and before forming a metal film layer above the photoresist layer, the following step is further included: removing the back passivation layer.

[0007] Preferably, thinning the back surface of the semiconductor chip specifically includes: thinning the silicon carbide substrate.

[0008] Preferably, the thinning protective film is a UV film.

[0009] Preferably, the thickness of the photoresist layer at a partial upper surface of the electrode layer is 4 um to 6 um.

[0010] Preferably, forming a metal film layer above the photoresist layer specifically includes: depositing at least one layer of metal above the photoresist layer by evaporation coating.

[0011] Preferably, the metal film layer includes at least one metal layer, and the material of the metal layer includes: titanium, nickel, silver or their synthetic metals.

[0012] Preferably, after removing the thinning protective film, the following step is further included: wet-removing the photoresist layer.

[0013] Preferably, before wet-removing the photoresist layer, the following is further included: cleaning the back surface of the semiconductor chip.

[0014] The present invention further provides a semiconductor chip, on the electrode layer on the front surface of the semiconductor chip, a metal film layer is grown, and the metal film layer is prepared by the preparation method described in any one of the above.

[0015] The beneficial effects of the present invention are: By utilizing the process of removing the thinning protective film in the thinning process to simultaneously complete the metal stripping process, that is, when removing the thinning protective film, stripping the metal film layer located above the passivation layer and retaining the metal film layer located on the upper surface of the electrode layer. Since the metal film layer covers the photoresist layer and the exposed upper surface of the electrode layer, when attaching the thinning protective film, due to the existence of the photoresist layer, it is ensured that there is no contact between the thinning protective film and the edge of the metal film layer located on the upper surface of the electrode layer. Therefore, when removing the thinning protective film, it has no influence on the metal film layer located on the upper surface of the electrode layer, avoiding the problem of edge warping and improving the product yield. Description of the Drawings

[0016] Figure 1 It shows a schematic process flow diagram of preparing a metal film layer on the front surface of a silicon carbide chip in the prior art; Figure 2 It shows a product diagram prepared by the process flow in the prior art; Figure 3Shown is an embodiment diagram of a process flow for preparing a metal film layer on the front side of a silicon carbide chip according to the present invention; Figure 4 Shown is a schematic diagram of the product corresponding to steps S1 - S3 for preparing a metal film layer on the front side of a silicon carbide chip according to the present invention; Figure 5 Shown is a schematic diagram of the product corresponding to steps S4 - S8 for preparing a metal film layer on the front side of a silicon carbide chip according to the present invention.

[0017] Among them, 1, backside passivation layer; 2, SiC substrate; 3, electrode layer; 4, front side passivation layer; 5, photoresist layer; 6, titanium-nickel-silver film layer; 601, first metal film layer; 602, second metal film layer; 7, thinning protective film. Detailed implementation manners

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs. The words such as "including" used herein mean that the elements or items appearing before this word cover the elements or items listed after this word and their equivalents, without excluding other elements or items.

[0019] During the packaging process of a silicon carbide (SiC) chip, see Figure 1As shown, generally, a titanium-nickel-silver metal thin film is first deposited on the metal area on the front side through processes such as coating a metal lift-off glue, photolithography, development, front-side evaporation of titanium-nickel-silver metal, pasting a lift-off film, tearing the lift-off film, and wet removal of the lift-off glue. Then, a thinning process is carried out to thin the product to the target thickness. The titanium-nickel-silver metal thin film can protect the chip surface from the influence of external environmental factors such as moisture, oxygen, and corrosive gases, preventing the surface of the SiC chip from being oxidized, corroded, or eroded by other chemical substances, thereby extending the service life of the device and improving the stability and reliability of the device under different working environments. Currently, by precisely controlling the thickness, pattern, and position of the titanium-nickel-silver metal film layer, electrical isolation and insulation functions can be achieved between different electrodes of a silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET), ensuring that no short circuit or leakage occurs between the electrodes, guaranteeing the electrical performance and working safety of the device, and enabling the device to operate stably under complex working conditions such as high voltage and high frequency.

[0020] The applicant found during the formation of the titanium-nickel-silver metal thin film that: during the thinning process, when tearing the thinning protective film, the edge of the titanium-nickel-silver metal film layer is easily lifted together, as can be seen in Figure 2 the dotted box, where the lifted metal film layer can be clearly seen, causing the titanium-nickel-silver metal film layer to separate from the metal area on the front side of the chip, affecting the appearance and the subsequent packaging wire bonding yield.

[0021] In this embodiment, the SiC chip has a stacked structure. Its substrate layer is a silicon carbide substrate, the middle is a metallization and electrode layer, the front side is a passivation layer and an electrode layer surrounded by the passivation layer. The material of the passivation layer can be silicon nitride (Si3N4), silicon dioxide (SiO2), phosphosilicate glass (PSG), aluminum oxide (Al2O3), or polyimide (PI). In this embodiment, the passivation layer is specifically a PI film. In this embodiment, a back passivation layer is also provided on the bottom surface of the silicon carbide substrate, and an epitaxial layer is provided above the silicon carbide substrate. The specific structure and type of the SiC chip are not limited. For the convenience of description, this specification takes SiC MOSFET as an example, and a metal layer can be provided in the middle, or two or more metal layers can be provided to form a source, a gate, and a drain.

[0022] The embodiment of the present invention provides a method for manufacturing a semiconductor chip, mainly used for forming a metal film layer on the semiconductor chip, which includes the following steps: as shown in Figure 3 shown, A semiconductor chip with a stacked structure is provided. The front side of the semiconductor chip is a passivation layer and an electrode layer surrounded by the passivation layer. In this embodiment, the semiconductor chip can be a SiC MOSFET; A photoresist layer is formed on the front side of the semiconductor chip (i.e., lift off resist coating, lithography, and development). The photoresist layer covers the upper surface of the passivation layer and extends to a part of the upper surface of the electrode layer from the upper surface of the passivation layer; A metal film layer is formed above the photoresist layer. The metal film layer covers the photoresist layer and the exposed upper surface of the electrode layer; A thinning protective film is attached to the upper surface of the metal film layer, and the back side of the semiconductor chip is thinned; The thinning protective film is removed to strip the metal film layer on the upper surface of the photoresist layer, and the metal film layer on the upper surface of the electrode layer is retained.

[0023] In this embodiment, on the one hand, the metal film layer serves as a protective layer for the front electrode of the silicon carbide (SiC) chip, and on the other hand, it serves as a metal welding layer required in the subsequent packaging process. In this embodiment, when attaching the thinning protective film, the photoresist in the process of forming the metal film layer is not removed. Thus, when the thinning protective film transitions from above the photoresist layer to above the electrode layer, due to the presence of the photoresist layer, there is a gap between the thinning protective film and the metal film layer at the transition. See Figure 5 the schematic cross-sectional view of the product corresponding to step S4 in. This gap causes that during the process of removing the thinning protective film 7, the edge of the metal film layer on the upper surface of the electrode layer will not be lifted, that is, the problems of edge warping or detachment of the metal film layer are avoided. On the other hand, since metal stripping is not achieved before the thinning process, that is, there is no need to attach a lift off film. Instead, metal stripping is performed when tearing the thinning protective film after thinning, saving a lift off film, shortening the process flow, and greatly reducing the preparation cost of the metal film layer. Compared with the above production process of attaching a lift off film, tearing the lift off film and then thinning, the economic cost is saved by at least 30%.

[0024] In a specific embodiment, the back side of the above semiconductor chip is a back side passivation layer, and the upper surface of the back side passivation layer is the above silicon carbide substrate. Before forming the metal film layer above the photoresist layer, the step of removing the back side passivation layer is further included. The back side passivation layer mainly plays a surface protection role, preventing contamination and oxidation, blocking the penetration of external impurities (such as metal ions, water vapor) into the silicon carbide substrate, and avoiding the degradation of electrical performance, etc. The material of the back side passivation layer can be: silicon nitride (Si3N4), silicon dioxide (SiO2), and aluminum oxide (Al2O3). Further, thinning the back side of the semiconductor chip specifically includes: thinning the silicon carbide substrate.

[0025] In a specific embodiment, the thinning protective film is a UV film. In this embodiment, the viscosity of the UV film is utilized to remove the metal film layer and part of the photoresist on the upper surface of the non-electrode layer. That is, when removing the thinning protective film after thinning, there is no need to desolve the UV and directly tear the film.

[0026] In a specific embodiment, the thickness of the photoresist layer at a part of the upper surface of the electrode layer is 4 μm to 6 μm, such as 4 μm, 5 μm or 6 μm. In this embodiment, through the thickness of the photoresist layer, the metal film layer on the upper surface of the electrode layer can be better controlled, and the height difference between it and the metal film layer on the upper surface of the photoresist layer is formed to form a step, so that there is a gap between the thinning protective film and the metal film layer on the upper surface of the electrode layer at this step, without contact, and the edge of the metal film layer will not be lifted when removing the thinning protective film, avoiding problems such as warping.

[0027] In a specific embodiment, forming a metal film layer above the above-mentioned photoresist layer specifically includes: depositing at least one layer of metal above the photoresist layer by evaporation. The evaporation process of this embodiment can specifically be thermal evaporation or electron beam evaporation. Preferably, the metal film layer includes at least one metal layer, and the materials of the metal layer include: titanium, nickel, silver or their synthetic metals. The metal film layer of this embodiment can be a titanium-nickel-silver film layer, which can provide good surface conditions for welding, improve the wettability and bonding force between the chip and the welding material, make the welding process more reliable, the welding quality higher, effectively avoid problems such as false soldering and de-soldering, enhance the mechanical stability and electrical connection performance of the device after packaging, and ensure the reliability of the device during long-term use.

[0028] A specific evaporation process of the titanium-nickel-silver film layer can be: loading the pre-cleaned and pre-treated SiC chip into an evaporation chamber, vacuum coating with an electron beam evaporation source, first performing thermal baking on the SiC chip under a certain vacuum degree and maintaining a constant temperature for a certain time; then starting evaporation, and the evaporation sequence is titanium-nickel-silver in turn. After evaporation and cooling, take out the chip to obtain the front side of the chip with a metal film layer. The thickness of the evaporated metal titanium is 100 nm - 300 nm, the thickness of the metal nickel is 200 nm - 1000 nm, and the thickness of the metal silver is 200 - 2000 nm. More specifically, preferentially evaporate titanium as the bottom layer, control the film thickness by adjusting the electron beam power (usually 0.5 kW - 10 kW) and evaporation rate (0.1 - 2 nm / s), deposit nickel on the titanium layer, use electron beam evaporation and maintain the temperature of the SiC chip at 0 - 300 °C to optimize the interfacial bonding force. Finally, evaporate the silver layer. Since the evaporation rate of silver is relatively fast, up to 1.5 nm / s, the resistance heating temperature is controlled at 1200 - 2800 °C, and the coating area accuracy is controlled by a mask.

[0029] Another specific embodiment of the titanium-nickel-silver film layer is as follows: titanium, nickel, and silver are synchronously deposited using multiple evaporation sources, and the alloy composition is regulated by adjusting the evaporation rate of each source.

[0030] In a specific embodiment, after removing and thinning the protective film, the following steps are further included: wet-etching the photoresist layer that has not been peeled off by the thinned protective film. Further, before wet-etching the photoresist layer, the following is also included: cleaning the back surface of the semiconductor chip.

[0031] Taking the formation of a titanium-nickel-silver film layer on the front electrode layer of a SiC MOSFET chip as an example, the specific preparation steps are as follows: see Figures 4 to 5 The figure shows a schematic cross-sectional view of the product formed in each step. Incoming material, that is, a SiC MOSFET chip with a stacked structure is provided. The stacked structure of the SiC MOSFET chip from bottom to top is a back passivation layer 1, a SiC substrate 2, an electrode layer 3, and a front passivation layer 4 at the top. The front of the SiC MOSFET chip is the front passivation layer 4 and the electrode layer 3 surrounded by the front passivation layer 4. In this embodiment, the material of the front passivation layer 4 can be polyimide (PI), and the metal material of the electrode layer can be aluminum (Al), copper (Cu), gold (Au), silver (Ag), platinum (Pt), tungsten (W), or their composite alloy; Step S1, a photoresist layer 5 is formed on the front of the incoming material through lift-off glue coating, photolithography, and development processes. The photoresist layer 5 covers the upper surface of the front passivation layer 4 and extends to a part of the upper surface of the electrode layer 3 from the upper surface of the front passivation layer 4, that is, the upper surface of the electrode layer near the front passivation layer 4 is covered with photoresist; Step S2, the back passivation layer 1 of the above SiC MOSFET chip is removed to expose the SiC substrate 2; Step S3, a titanium-nickel-silver film layer 6 is formed above the photoresist layer 5 by evaporation plating. The titanium-nickel-silver film layer 6 covers the upper surfaces of the photoresist layer 5 and the exposed electrode layer 3, specifically including: a first metal film layer 601 on the upper surface of the exposed electrode layer, and a second metal film layer 602 on the upper surface of the photoresist layer. Due to the presence of the photoresist layer 5, there is a height difference between the first metal film layer 601 and the second metal film layer 602, showing a stepped shape. The evaporation plating process for forming the titanium-nickel-silver film layer 6 will not be elaborated here, and it can use thermal evaporation or electron beam evaporation; Step S4, a thinning protective film 7 is attached to the upper surface of the titanium-nickel-silver film layer 6. There is a gap between the thinning protective film 7 and the first metal film layer 601 at the above stepped part. The thinning protective film 7 in this embodiment is a UV film; Step S5, back thinning, that is, thinning the SiC substrate 2; Step S6: Remove the thinning protective film 7. When peeling off the thinning protective film 7, there is no need to remove the UV. By using its own adhesiveness, the second metal film layer 602 and part of the photoresist are torn off, while the first metal film layer 601 is retained. Due to the existence of the above-mentioned gap, the edge of the first metal film layer 601 will not be lifted when peeling off the thinning protective film 7, avoiding the problems of the edge of the first metal film layer 601 warping or detaching from the electrode layer 3. Step S7: Backside cleaning; Step S8: Remove the remaining photoresist by wet process to prepare a SiC MOSFET chip with a titanium-nickel-silver film layer 6 covering the front electrode layer. The titanium-nickel-silver film layer 6 can be used as a metal welding layer in the subsequent packaging process.

[0032] In this embodiment, by performing the metal stripping process and the backside thinning process simultaneously, when peeling off the thinning protective film 7 attached to the front side, since the lift off glue has not been removed, the thinning protective film 7 does not contact the edge of the first metal film layer 601. Therefore, the phenomenon of lifting the titanium-nickel-silver metal will not occur during film peeling. The entire process requires a total of eight steps, namely steps S1 - S8, only consumes one thinning protective film, and does not require the use of a lift off film. The thinning protective film realizes two functions: ① protecting the front side during thinning; ② stripping the excess metal on the front side (i.e., stripping the second metal film layer 602), reducing the production cost.

[0033] An embodiment of the present invention also provides a semiconductor chip. A metal film layer is grown on the electrode layer on the front side of the semiconductor chip. See Figure 5 the product cross-sectional schematic diagram corresponding to step S8 in the figure. It includes, from bottom to top: a SiC substrate 2, an electrode layer 3, a front passivation layer 4, and a first metal film layer 601 surrounded by the passivation layer and located on the upper surface of the electrode layer. The metal film layer can specifically be a titanium-nickel-silver film layer. The metal film layer is prepared by the preparation method described in any one of the above. The production cost of this semiconductor chip is low.

[0034] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes fall within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A method for preparing a semiconductor chip, mainly used for forming a metal film layer on the semiconductor chip, characterized in that, Including the following steps: Providing a semiconductor chip with a stacked structure, the front side of the semiconductor chip being a passivation layer and an electrode layer surrounded by the passivation layer; Forming a photoresist layer on the front side of the semiconductor chip, the photoresist layer covering the upper surface of the passivation layer and extending from the upper surface of the passivation layer to a part of the upper surface of the electrode layer; Forming a metal film layer above the photoresist layer, the metal film layer covering the photoresist layer and the exposed upper surface of the electrode layer; Attaching a thinning protective film on the upper surface of the metal film layer and thinning the back side of the semiconductor chip; Removing the thinning protective film to strip the metal film layer on the upper surface of the photoresist layer and retaining the metal film layer on the upper surface of the electrode layer.

2. The method for manufacturing a semiconductor chip according to claim 1, wherein: The back side of the semiconductor chip is a back side passivation layer, the upper surface of the back side passivation layer being a silicon carbide substrate, and before forming the metal film layer above the photoresist layer, there is also a step of removing the back side passivation layer.

3. The method for manufacturing a semiconductor chip according to claim 2, wherein: The thinning of the back side of the semiconductor chip specifically includes thinning the silicon carbide substrate.

4. The manufacturing method of the semiconductor chip according to claim 1, wherein: The thinning protective film is a UV film.

5. The method for preparing a semiconductor chip according to claim 1, wherein: The thickness of the photoresist layer at a part of the upper surface of the electrode layer is 4um to 6um.

6. The manufacturing method of the semiconductor chip according to claim 1, characterized in that: Forming the metal film layer above the photoresist layer specifically includes depositing at least one layer of metal above the photoresist layer by evaporation.

7. The method for preparing a semiconductor chip according to claim 1 or 6, characterized in that: The metal film layer includes at least one metal layer, and the material of the metal layer includes titanium, nickel, silver or their alloyed metals.

8. The method for manufacturing a semiconductor chip according to claim 1, wherein: After removing the thinning protective film, there is also a step of wet-removing the photoresist layer.

9. The method for manufacturing a semiconductor chip according to claim 8, wherein: Before wet-removing the photoresist layer, there is also a step of cleaning the back side of the semiconductor chip.

10. A semiconductor chip, characterized in that, A metal film layer is grown on the electrode layer on the front side of the semiconductor chip, and the metal film layer is prepared by the preparation method according to any one of claims 1 to 9.

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