Process arrangement for the production of a semiconductor device and a method for the production of a semiconductor device

Abstract

The invention relates to a process arrangement for manufacturing a semiconductor device (1) with a semiconductor chip (3) connected to a substrate (5), comprising a process chamber (17) in which an joining process (IV) for contacting the semiconductor chip (3) on the substrate (5) can be carried out, wherein, in preparation for the joining process (IV), at least one rinsing process (I, III) using technically pure protective gas (S T ) so that the joining process (IV) takes place in the process chamber (17) under a protective gas atmosphere. According to the invention, the technically pure protective gas (S T ) can be pretreated with silane before being introduced into the process chamber (17), thereby removing residual oxygen from the protective gas so that the protective gas atmosphere is oxygen-free in order to prevent oxide formation on the contact surfaces to be joined.

Description

[0001] The invention relates to a process arrangement and a method for manufacturing a semiconductor device according to the preamble of claim 1 and claim 10.

[0002] In a typical power electronics circuit of a pulse inverter, a semiconductor chip of a power module has a bottom-side contact on its underside, which is sintered or soldered onto an aluminum- or copper-based substrate in a joining process. The substrate can be designed as a three-layer structure with a middle ceramic layer coated on both sides with an aluminum or copper layer. In common practice, the top-side electrical contact of the semiconductor chip is achieved in a bonding process in which aluminum or copper bonding wires or a copper clip are joined to a top-side contact pad of the chip using a friction welding process.

[0003] A process arrangement of this type includes a process chamber in which the joining process described above is carried out. In preparation for the joining process, a surface treatment step is performed, in which the contact surfaces to be joined are pretreated with a reducing agent, particularly formic acid, under heat to reduce oxide layers on the contact surfaces. Such oxide layers delay the formation of the joint or impair its properties, for example, with regard to strength and thermal conductivity. Following the surface treatment, a rinsing process is carried out. The rinsing process includes at least one evacuation / flooding cycle in which the process chamber is first evacuated and then flooded with a technically pure inert gas.

[0004] During the preparation of the joining process described above, the following problem was identified: The technically pure protective gas used in the purging process still contains a small amount of residual oxygen, for example, 5 ppm. Furthermore, the surface treatment step is carried out under heat. Therefore, a high process temperature is still present in the process chamber during the subsequent purging process. In such a high-temperature process situation, the contact surfaces to be joined react abruptly with the residual oxygen in the introduced protective gas and are coated with new oxide layers.

[0005] WO 2012 / 104 010 A1 discloses a method for soft, hard, or high-temperature soldering in a soldering furnace using a protective gas, wherein the protective gas contains a silane-containing protective gas additive consisting of at least one linear, branched, or cyclic silane having at least three silicon atoms, which is liquid at normal pressure in the temperature range of 1°C to 50°C. US 4,646,958 A discloses a soldering reflow or chip joining process that can be carried out in a fluxless system. The process is carried out in a carrier gas containing approximately 0.1 to approximately 10% by volume SiH4.

[0006] German patent DE 10 2022 125 415 A1 relates to a method for joining a first and a second workpiece using a fastener, and to a joining product produced by this method. The method is suitable for various joining techniques such as soldering, sintering, or bonding, and in particular allows for the gentle joining of even sensitive workpieces such as films, printed circuit boards, or optical components. Optionally, at least one of the workpieces can be pre-metallized to increase the degree of wetting at the joining point and to achieve improved cross-linking with the fastener.

[0007] DE 103 54 353 A1 relates to a process for purifying protective gases, such as those used in heat treatment and brazing processes. For this purpose, a highly reactive, strongly reducing gaseous agent, preferably silanes or boranes, is added to the protective gas. This agent reacts quantitatively with reducible impurities, especially water and oxygen, even at room temperature. In this way, a self-cleaning protective gas atmosphere is provided, which ensures a consistently high-quality, oxidation-free process atmosphere even with inferior protective gas quality or air ingress.

[0008] The object of the invention is to provide a process arrangement and a method for manufacturing a semiconductor component by means of which improved connection properties can be produced for the contact surfaces to be joined in the joining process compared to the prior art.

[0009] The problem is solved by the features of claim 1 or 10. Preferred embodiments of the invention are disclosed in the dependent claims.

[0010] The invention relates to a process arrangement for manufacturing a semiconductor device with a semiconductor chip that is bonded to a substrate, in particular made of copper or aluminum. The process arrangement includes a process chamber in which an joining process for contacting the semiconductor chip on the substrate can be carried out. The joining process can, by way of example, comprise a sintering process and / or a soldering process. In preparation for the joining process, at least one purging process is carried out using a technically pure protective gas so that the joining process can take place in the process chamber under a protective gas atmosphere. According to the characterizing part of claim 1, the following measures are taken to prevent oxide formation on the contact surfaces to be joined: The technically pure protective gas can be pretreated with silane before being introduced into the process chamber.In this way, residual oxygen is removed from the protective gas, so that the protective gas atmosphere is completely oxygen-free.

[0011] Pretreating the protective gas with silane ensures that the atmosphere in the process chamber is completely oxygen-free. This prevents the formation of oxides on the contact surfaces, significantly improving the quality of the connection between the semiconductor chip and the substrate. A further advantage is the ability to use less noble metals on the underside of the chip, as no oxide layers form that could impair the connection. Compared to conventional protective gas systems, this results in higher mechanical bond strength and improved thermal conductivity.

[0012] As explained above, the substrates consist of copper or aluminum. Conventionally, copper or aluminum is often additionally metallized, e.g., with nickel, if difficulties in the joining technology and the durability of the connection are anticipated. With the present invention, this additional metallization could be eliminated, as the process can be carried out completely oxygen-free.

[0013] The top or bottom surfaces of the dies (chips), intended for further contacting, are also metallized. Conventionally, layers of gold, palladium, or silver, only a few micrometers thick, are used there. According to the invention, however, less expensive metallizations can be used, since oxide-free surfaces and oxygen-free processing are ensured.

[0014] The joining process for contacting the semiconductor chip on the substrate can be carried out as a sintering process, as described above. In the prior art, only silver sintering pastes have proven successful in sintering technology for chips or modules. The copper alternative has not demonstrated the required properties in the prior art. Processing with copper currently requires significantly higher temperatures (280 °C and above) than with silver (220–230 °C). The present invention offers significant potential for improvement (cost reduction) because copper pastes can be used instead of silver pastes. The pastes consist of micrometer-sized copper flakes and various additives. The flakes represent vast surface areas that are used / required for the diffusion processes during sintering.

[0015] In the prior art, the high process temperatures during copper sintering would cause the surfaces of the flakes to be quickly covered with the residual oxygen from the protective gas atmosphere, which would suppress the diffusion processes. The completely oxygen-free processing according to the invention offers improvements in this regard; the temperature could also potentially be lowered, thus reducing stress on the chips.

[0016] In one technical implementation, the process arrangement can include a pretreatment station upstream of the process chamber, in which the technically pure protective gas, in particular nitrogen, is reacted with silane. The solid SiO2 deposited by the reaction of silane with the residual oxygen is preferably collected in the pretreatment station, i.e., not introduced into the process chamber.

[0017] The pretreatment station enables the efficient removal of residual oxygen through reaction with silane, with the resulting silicon dioxide being retained within the pretreatment station. This keeps the process chamber free of solid silicon dioxide impurities. The process chamber is thus protected from contamination, increasing the stability of the joining process and preventing potential malfunctions. This also reduces maintenance costs and extends the service life of the process chamber.

[0018] In a first implementation variant, the amount of silane used for protective gas pretreatment can be precisely measured so that the oxygen-free protective gas introduced into the process chamber is free of silane. This prevents a precipitation reaction of silane to SiO2 in the process chamber. The precise measurement of the silane content avoids the precipitation of silicon oxide in the process chamber, thus ensuring the purity and stability of the process. This minimizes unwanted deposits that could negatively affect the process parameters and the quality of the semiconductor devices.

[0019] In a second embodiment, the amount of silane used for protective gas pretreatment can be precisely measured so that the completely oxygen-free protective gas, containing a residual amount of silane, can be introduced into the process chamber. This allows the silane to react with any oxygen present in the process chamber. The residual silane thus enables an additional reaction with any oxygen that may remain in the process chamber. This renders the atmosphere completely inert and effectively prevents oxide formation. This improves the safety and robustness of the process, particularly in applications where small amounts of residual oxygen cannot be completely eliminated.

[0020] A silane-containing carrier gas can be supplied to the pretreatment station. The silane in the carrier gas reacts with the residual oxygen contained in the technically pure protective gas within the pretreatment station. A noble gas, particularly argon, is used as the carrier gas. The use of a silane-containing carrier gas enables precise dosing of the silane, resulting in optimal reaction with the residual oxygen in the protective gas within the pretreatment station. Argon, as a noble gas, is inert and prevents additional chemical reactions, further increasing process stability.

[0021] As further preparation for the joining process, the following measure can be taken: Before the rinsing process, a surface treatment step can be performed in which the contact surfaces to be joined are pretreated with a reducing agent, particularly formic acid, under the influence of heat. This reduces oxide layers on the contact surfaces. The surface treatment with formic acid removes existing oxide layers, thus ensuring that the metallic contact surfaces remain reactive. This significantly improves the electrical and mechanical connection and reduces the process's susceptibility to residual oxides.

[0022] During the surface treatment described above, residues or reaction products remain in the process chamber. These can be removed from the process chamber by means of the subsequent rinsing process. Due to the heat input during the surface treatment, the process temperature in the process chamber remains significantly elevated even after the surface treatment has ended. Therefore, the introduction of (only) technically pure protective gas containing residual oxygen during the subsequent rinsing process would—due to the high process temperature—cause an immediate oxide formation on the contact surfaces to be joined. Consequently, the use of completely oxygen-free protective gas according to the invention is crucial, especially at this stage of the process, for preventing oxide layers from forming on the contact surfaces to be joined.

[0023] The purging process includes at least one evacuation / flooding cycle in which the process chamber is first evacuated and then flooded with protective gas. In a specific embodiment, at least one further purging process can take place before the surface treatment step. The evacuation / flooding cycle increases the efficiency of removing residual gases, including oxygen, from the process chamber. Multiple purging cycles before the surface treatment increase the purity of the atmosphere and improve the overall process quality. Preferably, in the further purging process, completely oxygen-free protective gas, also pretreated with silane, is introduced into the process chamber to ensure maximum purity of the process atmosphere.

[0024] An exemplary embodiment is described below with reference to the attached figures.

[0025] They show: Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. Six different views are shown, illustrating the process steps for preparing a joining process to contact the semiconductor chip on the substrate.

[0026] In the Fig. Figure 1 is a semiconductor device 1, indicated to the extent necessary for understanding the invention. Accordingly, the semiconductor device 1 comprises a semiconductor chip 3, the underside contact of which is sintered onto a copper-based substrate 5 via a solder / sintered layer 2. In the Fig. 1. The copper-based substrate 5 is formed in three layers with a middle ceramic layer 7, which is coated on both sides with a copper layer 9. The in the Fig. The upper copper layer 9 of the substrate 5 forms a current-carrying conductor track on which a chip connection pad of the semiconductor chip 3 is attached with an intermediate layer of solder / sintered layer 2. The underside of the substrate 5 is attached to a coolant-flowing cooler 13 via another solder / sintered layer 11. In the Fig. In Figure 1, the semiconductor chip 3 is encased in a potting compound 13, of which only the outline is indicated. In the Fig. Figure 2 shows a top-side contact of the semiconductor chip 3, whereby, as an example, a copper bonding wire 6 is attached to the top-side chip contact surface in a bonding process similar to friction welding. Alternatively, in the Fig. 3. Instead of the copper bond wire 6, a copper clip 8 is attached to the upper chip contact surface. Both the upper and lower chip contact surfaces are formed by metallization layers made of, for example, copper. Such a semiconductor device 1 can be part of a power module of power electronics for a pulse inverter.

[0027] During operation, adequate heat dissipation from the semiconductor chip 3 must be ensured. In the Fig. 1, Fig. 2 to Fig. 3. Heat dissipation occurs via the solder / sintered layer 2 to the substrate 5 and from there via the solder / sintered layer 11 to the cooler 13. The following problem has arisen: If the contact surfaces to be joined between the lower chip termination surface and the cooler 13 are coated with oxide layers before the contact surfaces of the semiconductor element 1 are joined, the formation of the connection during the joining process is impaired, as are the properties of the connection, for example, with regard to strength and thermal conductivity. Against this background, a key aspect of the invention is to carry out the joining process of the contact surfaces of the semiconductor element 1 completely oxygen-free, so that oxide formation on the contact surfaces to be joined is prevented.

[0028] The procedural order provided for this purpose designates a procedural chamber 17 ( Fig. 4) in which the components of the semiconductor device 1, namely the substrate 5 and the semiconductor chip 3, are already loosely stacked on top of each other with a solder / sinter preform 19 in between. In preparation for the joining process, a protective gas purge is carried out in the process chamber 17. For this purpose, a protective gas line 23 leads into the process chamber 17 at a protective gas inlet 21, through which a protective gas (e.g., nitrogen) can be introduced. The process chamber 17 also has an outlet 25 to which an extraction line 26 of an extraction device is connected. Protective gas is introduced via the protective gas inlet 21, while the process chamber 17 can be evacuated via the outlet 25.

[0029] According to the Fig. 4. The protective gas line 23 is connected to a pretreatment station 27. A technically pure protective gas S is supplied to the pretreatment station 27. T supplied. Under the technically pure protective gas ST This refers to a highly purified shielding gas (i.e., nitrogen gas) suitable for welding and inerting applications. Such a technically pure shielding gas is called S T It is used in processes requiring a low-oxygen or inert environment, such as welding, metal protection, or chemical reactions. The technically pure shielding gas S T However, it still contains a residual oxygen, for example 5 ppm oxygen.

[0030] In the block diagram of Fig. Figure 6 indicates a process chain for preparing and carrying out joining process IV. Accordingly, at least one, preferably two or three, rinsing processes I are performed first. Rinsing process I comprises an evacuation / flooding cycle in which process chamber 17 is first evacuated using the extraction device, and then the evacuated process chamber 17 is flooded with protective gas via the protective gas line 23. This is followed by surface treatment II, in which the components to be joined are heated and pretreated with formic acid to reduce oxide layers on the contact surfaces to be joined. After completion of surface treatment step II, a further rinsing process III is carried out to remove reaction products of surface treatment II from process chamber 17. Following this, joining process IV starts ( Fig.5), in which the process chamber 17 is heated to a soldering / sintering temperature, whereby the semiconductor chip 3 is pressed against the substrate 5 located on a counter-holder 31 by means of a hold-down device 29. After completion of the joining process, the manufactured semiconductor device 1 is cooled in the oxygen-free protective gas atmosphere or in air and then removed from the process chamber 17.

[0031] As described in the preliminary section, the surface treatment is carried out under heat. Therefore, a high process temperature is still present in process chamber 17 during the subsequent rinsing process. It has been shown that in such a high-temperature process situation, the contact surfaces to be joined react abruptly with residual oxygen and are coated with new oxide layers. To prevent such renewed oxide formation, the aforementioned pretreatment station 27 is provided according to the invention. In the pretreatment station 27, the technically pure protective gas S, which still contains a small residual amount of oxygen, is used. TThe material is mixed with silane, which is supplied to pretreatment station 27 in a carrier gas TG (argon). Silicon oxide is deposited in pretreatment station 27 in this way. The silicon oxide remains in pretreatment station 27, forming a completely oxygen-free protective gas S, which is introduced from pretreatment station 27 into process chamber 17 via protective gas line 23. This reliably prevents the formation of new oxide layers on the contact surfaces to be joined after the high-temperature surface treatment (i.e., during the subsequent rinsing process). Reference symbol list 1 Semiconductor device 2 Lot / Sintered layer 3 Semiconductor chips 4 lower chip connection area 5 Substrat 6 copper bonding wire 7 middle ceramic layer 8 copper clips 9 copper layers 11 additional solder / sinter layer 13 coolers 17th Tribunal 19 Lot / Sintered Preform 21 Shielding gas inlet 23 Shielding gas line 25 Outlet 26 Suction line 27 Pre-treatment ward 29 hold-down devices 31 Counterhold I. Rinsing process II Surface treatment III. Rinsing process IV Joining process S T technically pure protective gas oxygen-free protective gas TG carrier gas

Claims

[1] Process arrangement for the manufacture of a semiconductor device (1) comprising a semiconductor chip (3) connected to a substrate (5), comprising a process chamber (17) in which an joining process (IV) for contacting the semiconductor chip (3) on the substrate (5) can be carried out, wherein, in preparation for the joining process (IV), at least a rinsing process (I, III) using technically pure protective gas (S T ) so that the joining process (IV) takes place in the process chamber (17) under a protective gas atmosphere, characterized by that the technically pure protective gas (S T ) can be pretreated with silane before being introduced into the process chamber (17), thereby removing residual oxygen from the protective gas so that the protective gas atmosphere is oxygen-free in order to prevent oxide formation on the contact surfaces to be joined. [2] Process arrangement according to claim 1, characterized by, that the process arrangement includes a pretreatment station (27) in which the technically pure protective gas (S T ), in particular nitrogen, is reacted with silane, and in particular the solid silicon dioxide deposited by reaction of silane with the residual oxygen remains in the pretreatment station (27). [3] Process arrangement according to claim 1 or 2, characterized by , that the amount of silane used for protective gas pretreatment is such that the oxygen-free protective gas (S) introduced into the process chamber (17) is free of silane, so that a precipitation reaction of silane to silicon oxide in the process chamber (17) is prevented. [4] Process arrangement according to claim 1 or 2, characterized by, that the amount of silane used for protective gas pretreatment is such that the oxygen-free protective gas (S) with a residual silane content can be introduced into the process chamber (17) so that the silane may react with any oxygen that may be present in the process chamber (17). [5] Process arrangement according to one of claims 2 to 4, characterized by , that a silane-containing carrier gas (TG) can be supplied to the pretreatment station (27), and that the silane content in the carrier gas (TG) in the pretreatment station (27) is comparable to that in the technically pure protective gas (S T ) containing residual oxygen, and that in particular the carrier gas (TG) is a noble gas, especially argon. [6] Process arrangement according to one of the preceding claims, characterized by, that prior to carrying out the rinsing process (III) a surface treatment step (II) is performed in which the contact surfaces to be joined can be pretreated with a reducing agent, in particular formic acid, under heat in order to reduce oxide layers on the contact surfaces to be joined. [7] Process arrangement according to claim 6, characterized by , that residues or reaction products of the surface treatment (II) can be removed from the process chamber (17) by means of the subsequent rinsing process (III). [8] Process arrangement according to one of the preceding claims, characterized by , that the rinsing process (III) includes at least one evacuation / flooding cycle in which the process chamber (17) is first evacuated and then the evacuated process chamber (17) is flooded with protective gas (S), and / or that, in particular, at least one further rinsing process (I) takes place before the surface treatment step (II) is carried out. [9] Process arrangement according to claim 8, characterized by , that in the further purging process (I) also pretreated with silane, completely oxygen-free protective gas (S) can be introduced into the process chamber (17). [10] Method for manufacturing a semiconductor device (1) in a process arrangement according to one of the preceding claims.

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