JP3750468B2 - Semiconductor wafer manufacturing method and semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer level CSP (chip size package) type semiconductor device compatible with high-density mounting and a method of manufacturing the same.
[0002]
[Prior art]
In recent years, along with the downsizing of devices such as mobile phones and information terminals, there has been a demand for smaller and lighter mounted components, and semiconductor devices such as LSIs have also been integrated into a conventional wafer processing process and a package assembly process. Level CSP is now supplied. The feature of the wafer level CSP is that the manufacturing cost is reduced by reducing the number of parts such as an interposer and the number of processes as compared with the conventional CSP made from a single chip, and the total cost of the package is reduced. The structure and process outline of this technology are described in, for example, the Nikkei Microdevice February issue p38 to p67 in 1999 and the electronic material September issue p21 to p85.
[0003]
These manufacturing methods are shown in FIGS. 7 and 8, for example.
[0004]
First, as shown in FIG. 7A, after opening a protective insulating layer 13 such as a silicon nitride film and a polyimide layer 14 on an Al alloy wiring pad 12 of a silicon substrate 11 in which a semiconductor element is formed, Cr is formed. Then, Cu is sputtered on the adhesion layer 15 such as TiW and TiW to form the seed layer 16, and then Cu is selectively plated using the photoresist 17 as a mask to form a rewiring layer 18 for extraction. Next, as shown in FIG. 7B, a Cu post 30 in which a barrier is stacked is formed by selectively plating a thick Cu layer of about 100 μm and a barrier layer 31 using a new photoresist 19 as a mask. Next, as shown in FIG. 8A, after the resist 19 is removed, the seed layer 16 and the adhesion layer 15 are removed by etching using the rewiring layer 18 as a mask, thereby forming separate rewirings. Further, as shown in FIG. 8B, after sealing at least the entire surface of the silicon substrate 11 with a sealing resin 21, the barrier layer 31 on the surface of the Cu post 30 is exposed by grinding or mechanical polishing the resin 21. Further, a solder ball is mounted on each post 30 region by an automatic transfer machine, and heat treatment is performed so that the solder ball is welded to the post 30 to form the external terminal 22. Thereafter, the electrical characteristics are checked, and each chip is diced and mounted on a mother board or the like of portable equipment.
[0005]
However, this technique has the following problems.
[0006]
By forming the Cu post 30 by plating, a thick resist pattern exceeding 100 μm and a long plating process are required, and costs and flow man-hours become problems. Further, since the Cu post 30 is formed vertically, the Cu post 30 is weak against a tensile stress in the vertical direction, and particularly when mounted on a flexible board, there is a problem that peeling from the rewiring layer 18 occurs. On the other hand, the polyimide layer 14 with a thickness of about several tens to 100 μm is laid to give elasticity so that the compressive stress applied to the post 30 does not give a problem to the semiconductor element on the surface of the silicon substrate 11. With the fine movement of the pad, stress concentrates on the contact area between the pad opening and the rewiring, and breaks and cracks occur around the pad 12 area in the post-process such as resin sealing, grinding process, or mounting on the board. easy.
[0007]
In addition, the thin barrier layer 31 must be ground in a reproducible manner, and there are many management items such as the thickness of the sealing resin, the grinding amount, and the plating thickness, and mass productivity is also a problem.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a low-cost and highly reliable semiconductor device and a method for manufacturing the same without increasing the number of steps in a wafer-level CSP type semiconductor device.
[0009]
[Means for Solving the Problems]
A method for producing a semiconductor wafer according to the present invention includes:
(A) A step of forming a stress relaxation layer on the protective insulating layer of the semiconductor wafer having a pad and a protective insulating layer in which the pad portion is opened. (B) Re-extending from the pad to the stress relaxing layer. (C) Step of mounting metal balls to be spherical posts on the rewiring layer (d) After sealing with resin, a desired amount of the resin is removed and a part of the spherical post (E) a step of forming an external terminal on the exposed spherical post, wherein in the step (e), the external terminal is made of a composition material having a melting point lower than that of the spherical post. And
[0010]
(A) Step of applying a rewiring layer for extracting an electrode from the final wiring pad (b) Step of mounting a metal ball to be a spherical post in a desired region of the rewiring layer (c) After sealing with resin Removing a desired amount of the resin to expose a part of the post; and (d) forming an external terminal on the exposed spherical post.
[0011]
In the manufacturing method of the present invention, a rewiring layer is applied to a pad for external extraction of a final wiring such as an LSI or a dummy pad opening, and a first metal ball is mounted in a desired region and welded. After being wrapped with a sealing resin and partially exposed by grinding or mechanical polishing, a second metal ball is further mounted and welded to form an external terminal.
[0012]
According to this manufacturing method, it is possible to form a post having a bow-shaped side surface and strong against a tensile stress, and therefore, the cost can be reduced and the mass productivity and the reliability can be improved by a simple process without increasing the number of steps.
[0014]
Here, in the step (b), when the rewiring layer is formed by selective plating, the metal in the rewiring layer is not plated by leaving the photoresist in the region where the first metal balls are mounted. The recess is formed in the same process, and the recess serves as a guide for absorbing the alignment error when the first metal ball is mounted and improving the placement accuracy. As a result, when the metal ball is misaligned, or when the metal ball is made of a solder material, solder flow does not occur even if the welding temperature varies, and a stable spherical post with little variation can be secured. In addition to expanding the margin of welding conditions, the post is also securely fixed, and contact failure and the like can be reduced.
[0015]
The method for manufacturing a semiconductor device according to the present invention is characterized in that, in the step (d), the removal amount of the resin is from the upper surface until reaching the maximum diameter of the spherical post.
[0017]
Here, in the steps (c) and (e), when a metal ball made of solder is used as the spherical post and the external terminal, it is welded by applying heat to the rewiring or post by heat treatment. By using a material in which the melting point of the first metal ball is higher than the melting point of the second metal ball serving as the external terminal, the temperature condition against the welding of the external terminal itself or the collapse of the shape of the post when it is mounted on a motherboard or the like As a result, a wide margin can be set, and assembly with a high yield is possible.
[0018]
Furthermore, the method for manufacturing a semiconductor device of the present invention is characterized by further comprising a step of dicing and chip-dividing each chip after the step (e).
[0019]
The step of solidifying for each chip is a step that is applied when the steps (a) to (e) are performed on a semiconductor wafer, and the steps (a) to (e) are performed as solid chips. Does not apply to
[0020]
Here, in the steps (c) and (e), when a metal ball made of solder is used as a spherical post and an external terminal, a ball having a nucleus having a melting point higher than that of solder such as Cu or Ni is used inside. Variations in height and shape of external terminals are reduced. Therefore, the yield at the time of mounting the board is improved, and also the role of stress relaxation at the time of mounting on the mother board or the like is played by the floating of the nucleus, and the control of the characteristic influence on the element and the mounting conditions becomes easy.
[0021]
According to another aspect of the present invention, there is provided a semiconductor device comprising: a stress relaxation layer formed on a protective insulating layer of a substrate having a pad and a protective insulating layer in which the pad portion is opened; and the stress relaxation layer from the pad. A rewiring layer formed up to, a spherical post made of a metal ball partially surrounded by a sealing resin in a desired region of the rewiring layer, and an external terminal formed on the spherical post, The external terminal is made of a composition material having a melting point lower than that of the spherical post.
[0022]
According to this semiconductor device, the shape of the side surface of the post covered with resin can have a region that is not at least partially perpendicular to the silicon substrate, and is mounted on a mother board of a portable device as a wafer level CSP, for example. In this case, the strength is secured against the tensile stress, and the yield and reliability can be improved. Furthermore, by providing a placement guide for the metal balls to be mounted on at least a part of the rewiring layer in the region where the posts are placed, post position control and adhesion strength can be improved.
[0023]
The semiconductor device of the present invention may be a semiconductor wafer.
[0025]
Furthermore, the semiconductor device of the present invention is characterized in that the spherical post and the external terminal are formed of a mounted metal ball.
[0026]
Alternatively, the semiconductor device of the present invention is characterized in that the mounting metal balls constituting the spherical posts and the external terminals are made of a solder material.
[0027]
Alternatively, in the semiconductor device of the present invention, in the rewiring layer for extracting the electrode from the final wiring pad, a part of the thickness of the rewiring layer in the region where the post or the external terminal is mounted mainly It is characterized by being thinner than the thickness to be formed.
[0029]
Here, when the spherical post and the external terminal are formed of a metal ball made of solder, the external terminal is made of a composition material having a melting point lower than that of the spherical post, and further inside the ball, the melting point is higher than that of the solder. For example, by holding a core such as Cu, Ni, or an alloy, it is possible to suppress variation in the shape of the external terminal, relax stress during mounting when mounting on a board, etc., and widen a mounting condition margin. Reliability can be improved.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a sectional structural view of a semiconductor device according to the first embodiment of the present invention. The structure of the semiconductor device according to the first embodiment will be briefly described. Semiconductor elements such as MOS transistors are formed on the silicon substrate 11 and these are wired with a metal such as an Al alloy via an interlayer insulating film and covered with a final protective insulating layer 13 made of a silicon oxide film, a silicon nitride film, or the like. Yes. For taking out the external electrode, for example, a pad 12 for taking out the electrode to the outside of the final wiring is provided, a necessary region of the protective insulating layer 13 is opened, and, for example, about several tens to 100 μm excluding the opening in the upper layer. The polyimide layer 14 is laminated to relieve stress on the element. The pad 12 includes an adhesion layer 15 made of TiW, a Cu seed layer 16, and a rewiring layer 18 on which Cu having a thickness of several μm is plated. A spherical post 20 mounted with a first metal ball and welded by heat treatment is formed in a predetermined region on the rewiring layer 18, and the periphery thereof is wrapped with a sealing resin 21 such as epoxy, and the surface is ground with substantially the same surface. As a result, the side surface of the post 20 has an arcuate shape. An external terminal 22 having a second metal ball mounted on the exposed head is formed on the desired post 20 by welding. Electrical connection is made from the internal element to the external terminal 22 via the pad 12, the rewiring layer 18, the spherical post 20, and the like.
[0031]
Next, a method for manufacturing the semiconductor device according to the first embodiment will be described. 2 and 3 are schematic cross-sectional views for explaining this in the order of steps.
[0032]
As shown in FIG. 2A, first, an Al alloy final wiring including pads 12 is formed on a silicon substrate 11 on which a semiconductor element or the like is formed and a protective insulating layer 13 such as a silicon nitride film is formed by plasma CVD to a thickness of about 1000 nm. Then, the insulating layer 13 in a desired region is selectively etched to form a hole. Further, a polyimide layer 14 having a thickness of about several tens to 100 μm is formed for stress relaxation, and the pad opening is selectively removed. The protective insulating layer 13 and the polyimide layer 14 may be selectively opened with the same photomask. However, in order to taper the opening step shape around the pad 12 and prevent disconnection in the rewiring process described later, separate steps are required. It was done in. Moreover, when photosensitive polyimide is used, the step of opening the polyimide layer is simplified. Subsequently, TiW of about several tens to 100 nm and Cu of about 100 to 1000 nm are continuously sputtered to form the adhesion layer 15 and the seed layer 16, and then a photoresist 17 is patterned to have a thickness of about several hundred to several thousand nm. Then, a re-wiring layer 18 is formed by continuously plating, for example, Ni thinly as a cap metal for preventing oxidation of the Cu surface. The adhesion layer 15 may be made of refractory metal such as Cr, Ni, Ti, TiCu, or Pt or an alloy thereof in addition to Tiw. In addition to Cu, Ni, Ag, Au, or an alloy thereof can be applied to the seed layer 16. Furthermore, Au, Pt, Pd, or an alloy thereof can be applied in addition to Ni as a cap metal.
[0033]
Next, as shown in FIG. 2B, after the photoresist 17 is peeled off, a flux is spin-coated as necessary, and then a first metal having a diameter of about 100 to 150 μm is formed in a desired region of the rewiring layer 18. The ball 200 is mounted by an automatic transfer machine. As the ball composition, a high-temperature solder material having a composition of Pb85 to 97 wt% / Sn was used.
[0034]
Next, as shown in FIG. 2C, when heat treatment is performed for several tens of minutes in a nitrogen atmosphere at about 180 to 230 ° C., the metal balls 200 are somewhat flowed and welded to the rewiring layer 18 to form spherical posts 20. Is formed.
[0035]
Thereafter, the rewiring is separated by selectively removing the seed layer 16 and the adhesion layer 15 in the unnecessary region using ion milling with the rewiring layer 18 as a mask. This removal process may be a wet etch such as aqua regia, an aqueous solution of ceric ammonium nitrate or potassium hydroxide. However, when considering the side etch of each metal layer constituting the rewiring and the thickness reduction, dry etcher or milling Etch back by such as is preferable. The etch back process may be performed before the metal ball is mounted, but it is preferable to weld the spherical post 20 in consideration of the reduction of the cap metal.
[0036]
Subsequently, as shown in FIG. 3 (A), sealing is performed so that the spherical post 20 is sufficiently covered with a sealing resin 21 such as epoxy in a molding apparatus, and further, as shown in FIG. 3 (B), with a grinder. Grind so that the post 20 is exposed. At this time, the amount of grinding is controlled within a range of 1/5 to 4/5 of the distance from the top of the spherical post 20 to the maximum diameter, and the margin of the amount of grinding is sufficiently larger than when using a conventional Cu post. it can. Here, the point is that the post 20 is encased by the sealing resin 21 from the upper surface. In addition, although the grinder was used for grinding the resin 21, a method of batch mechanical polishing of the entire surface of the wafer-like silicon substrate, or etch back using a dry etcher using oxygen, CF4, NF3, or a mixed gas thereof can be applied. .
[0037]
Next, as shown in FIG. 3C, a flux is applied if necessary, and the second metal ball 220 made of a low-temperature solder material of Pb / Sn 60 to 70 wt% is used for the spherical post 20 necessary for the automatic transfer machine. When placed above and heat-treated in a nitrogen atmosphere at about 170 to 200 ° C., the external terminals 22 welded to the spherical posts 20 are formed as shown in FIG. Although the size of the second metal ball 220 is 150 to 300 μm for BGA (Boll Grid Array), it is not particularly limited depending on the application. The second metal ball 220 for the external terminal 22 is made of a material having a lower melting point than the first metal ball 200 used for the spherical post 20, and the deformation of the external terminal varies because the deformation of the post is less during heat treatment. Few. Also, instead of mounting the metal ball 220 as the external terminal, it is possible to form a solder layer for the external terminal by a printing method, a plating method or a metal jet method, but the man-hours, cost, and shape reproducibility are inferior to the ball mounting method. .
[0038]
According to the first embodiment, the side surface of the post 20 is fixed so as to be wrapped with the sealing resin 21 while maintaining a bow shape. Therefore, the adhesion force of the post 20 can be secured against the stress from each direction generated in the post-process, and the adhesion force against the stress in the pulling direction is greatly improved as compared with the conventional method, and the yield and reliability can be improved. . In addition, the formation of the post 20 does not require plating or a photo process for the thick Cu layer, thereby improving throughput and cost. Further, the melting point of the material constituting the external terminal 22 is made lower than that of the constituent material of the post 20, and the CSP mounting yield and reliability to the mother board and the like including the stabilization of the shape of the external terminal 22 are ensured.
[0039]
(Other embodiments)
The first metal ball 200 is mounted on the rewiring layer 18 to form a spherical post. However, in rare cases, the alignment error during mounting or the ball may be out of the predetermined position during heat treatment. Therefore, as shown in FIG. 4A, in the photo process for forming the rewiring layer 18, a pattern resist 170 is formed in the same process in the region where the rewiring layer is formed, and Cu plating is performed. Then, after selectively plating the rewiring layer 18 and the Ni cap layer, the resists 17 and 170 are peeled off, as shown in FIG. 4B, in the rewiring layer 18 region on which the first metal balls 200 are mounted. A dent 40 can be formed. Next, a flux is spin-coated, and a first metal ball 200 made of a solder material is automatically mounted thereon. Subsequently, as shown in FIG. 5A, when the heat treatment is performed, the metal ball 200 is somewhat flowed to form the spherical post 20 welded to the rewiring layer 18 and the recessed portion 40.
[0040]
Thereafter, the rewiring is separated from each other by selectively removing the seed layer 16 and the adhesion layer 15 in the unnecessary region using ion milling or the like using the rewiring layer 18 as a mask.
[0041]
Next, as shown in FIG. 5B, the spherical post 20 is sufficiently covered with a sealing resin 21 such as epoxy with a molding apparatus, and then the post 20 is exposed with a grinder, and the post 20 Is ground from the upper surface with the sealing resin 21, and the second metal ball 220 made of solder material is placed on the spherical post 20 required by the automatic transfer machine, and is about 170 to 200 ° C. When heat treatment is performed using a belt furnace, the external terminals 22 welded to the spherical posts 20 are formed. Although the first metal ball 200 has a diameter of 100 to 150 μm and the second metal ball 220 has a diameter of 150 to 300 μm, it is not particularly limited depending on the application.
[0042]
In the semiconductor device thus configured, even if the mounting alignment error of the first metal ball is about several to 10 μm, the indented portion 40 serves as a guide for the first metal ball 200 and is positioned at the assumed coordinate position of the post 20. Can be dropped into the array. Further, when applying the flux, the dent portion 40 becomes a flux reservoir, so that no problem occurred in the adhesiveness, shape, etc. even if the application thickness was ½ or less of the conventional thickness.
[0043]
Further, as an effect of the dent portion 40, when the temperature becomes high due to variations in the heat treatment apparatus, the phenomenon that the solder flows on the surface of the rewiring layer 18 is eliminated, and further, the rewiring layer 18 and the post 20 The adhesion area increased and the strength increased. As described above, without increasing the number of steps, it is possible to stabilize the adhesion strength and shape of the post and reduce the flux cost, thereby providing a mass-productive semiconductor device. Further, even when a structure in which the external terminal is directly taken out from the rewiring layer without using the post is formed, the formation of the recessed portion 40 is effective for collecting flux or stabilizing the position and shape of the solder material. .
[0044]
In addition, in the embodiment, the metal balls used as posts and external terminals are made of solder material. However, as shown in FIG. 6, Ni cores 50 having a high melting point are included inside, and the outer periphery is covered with conventional solder material. As a result of trial application of the broken ball, the shape of the post 20 and the external terminal 22 can be stabilized as compared with the conventional case. In the process of attaching the CSP to the motherboard, reliable contact and fixation are ensured even if the height of the external terminals varies due to the floating movement of the core during solder welding, resulting in a wider welding pressure and temperature control margin. As a result, the assembly yield was improved.
[0045]
In the embodiments described so far, the case where the wiring of the semiconductor device is made of an Al alloy has been described. However, Cu, a refractory metal material, a laminate thereof, or an alloy wiring layer is also possible. Further, the present invention can be applied to a semiconductor device in which a wiring layer is formed by a damascene method. In particular, when Cu or Ni rewiring is formed on damascene wiring using Cu, the flatness and the compatibility with the pad material are good.
[0046]
In addition to the Pb / Sn solder, the metal ball in the embodiment can be applied to a solder material containing Sn, Ag, Cu, Bi, etc. as a solder material that does not contain Pb. As a material, a ball made of Ni, Cu, Au, other refractory metals, or various alloys can be used.
[0047]
Further, a belt furnace is used for welding each metal ball. However, in the automatic ball transfer machine, the heat treatment can be performed simultaneously with the mounting of the ball while heating the substrate, and the welding can be continued.
[0048]
【The invention's effect】
As described above, according to the present invention, a spherical post and an external terminal are formed by a mounted metal ball in a wafer level CSP, and further, the post is rewrapped from the rewiring to the post as a form of wrapping with the sealing resin. In addition, a highly reliable semiconductor device can be supplied at low cost by increasing the external terminal strength. Further, by holding a metal core having a melting point higher than that of the solder material inside the solder external terminal, and forming a recess for a metal ball arrangement guide in the rewiring layer immediately below the spherical post, etc. It is possible to supply a fine CSP type semiconductor device with high reliability and high mass productivity by suppressing variation in the shape of the constituent members, improving the yield when the CSP is mounted on the motherboard, and reducing the stress applied to the semiconductor element.
[Brief description of the drawings]
FIG. 1 is a sectional structural view of a semiconductor device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional structure diagram showing an example of the manufacturing method of the semiconductor device according to the first embodiment of the present invention in the order of steps.
3 is a cross-sectional structure diagram showing an example of the manufacturing method of the semiconductor device according to the first embodiment of the present invention performed subsequent to the process shown in FIG.
FIG. 4 is a cross-sectional structure diagram showing an example of a method of manufacturing a semiconductor device according to another embodiment of the present invention in the order of steps.
5 is a cross-sectional structure diagram showing an example of a method of manufacturing a semiconductor device according to another embodiment of the present invention, which is performed subsequent to the process shown in FIG. 4; FIG. 1 is a cross-sectional structure diagram illustrating a semiconductor device according to an embodiment.
FIG. 7 is a cross-sectional structure diagram showing an example of a conventional method of manufacturing a semiconductor device in order of steps.
8 is a cross-sectional structure diagram showing an example of a conventional method of manufacturing a semiconductor device performed following the process shown in FIG. 7 in order of processes.
[Explanation of symbols]
11 Silicon substrate 12 Pad 13 Protective insulating layer 14 Polyimide layer 15 Adhesion layer 16 Seed layers 17, 19, 170 Resist 18 Rewiring layer 20 Spherical post 21 Sealing resin 22 External terminal 30 Cu post 31 Barrier layer 40 Recessed portion 50 Core 200 First metal ball 220 second metal ball

Claims (8)

(A) A step of forming a stress relaxation layer on the protective insulating layer of the semiconductor wafer having a pad and a protective insulating layer in which the pad portion is opened. Step of applying wiring layer (c) Step of mounting metal ball to be spherical post on the rewiring layer (d) After sealing with resin, a desired amount of the resin is removed and part of the spherical post (E) a step of forming an external terminal on the exposed spherical post, wherein in the step (e), the external terminal is made of a composition material having a melting point lower than that of the spherical post. A method for manufacturing a semiconductor wafer. In claim 1,
In the step (d), the amount of the resin removed is from the upper surface until reaching the maximum diameter of the spherical post. In claim 1,
The method for manufacturing a semiconductor wafer, further comprising a step of dicing each chip after the step (e). A chip size package type semiconductor device,
A stress relaxation layer formed on the protective insulating layer of the substrate having a pad and a protective insulating layer in which the pad portion is opened; and
A rewiring layer formed from the pad to the stress relaxation layer;
A spherical post made of a metal ball partially surrounded by a sealing resin in a desired region of the rewiring layer;
An external terminal formed on the spherical post;
Have
The semiconductor device, wherein the external terminal is made of a composition material having a melting point lower than that of the spherical post. In claim 4,
The semiconductor device is a semiconductor wafer. In claim 4,
The spherical post and the external terminal are formed of a mounted metal ball. In claim 6,
The mounting metal ball constituting the spherical post and the external terminal is formed of a solder material. In the rewiring layer for extracting electrodes from the final wiring pad, a part of the rewiring layer thickness in the area where the post or external terminal is mounted is thinner than the thickness that mainly forms the rewiring layer. A semiconductor device characterized by the above.

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