JPH0354829A - Electrolytic plating process of bump electrode for integrated circuit device - Google Patents

Abstract

PURPOSE:To avoid the metallic separating and the defective contact due to any leakage current by a method wherein a metallic film connecting to underneath film is provided on the rear surface of a wafer; the wafer with its surface faced downward is brought into contact with a plating liquid PL while the rear surface metallic film is connected to a power supply to perform the plating process. CONSTITUTION:A wafer 10 is covered with an oxide film 3; electrode films 4 are arranged on the positions of oxide film 3 whereon bump electrodes are to be provided; after covering the electrode films 4 with a protective film 5, a window is made so as to coat the surface 10a side of the wafer 10 with an underneath film 7 in contact with the electrode films 4 in the window part. The periphery 6a of the underneath film 6 is coated creeping in the rear surface side chamfer 10a. The rear surface 10b is coated with a metallic film 7 connecting to the underneath film 6. Next, the other underneath films 8 are formed on the surface 10a and removed leaving the positions to provide bump electrode 11 furthermore, the films 8 are exposed to provide a photoresist film 9. Finally, the wafer 10 with its surface 10a looking downward is inserted into a plating jug 25 and then the metallic film 7 is connected to a plating power supply 30 through the intermediary of the contactors 26 of the cover 25 so that the jet stream of plating liquid PL may be brought into contact with the surface 10a to perform the electrolytic plating process for depositing the bump electrodes 11.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides bump electrodes on the surface of a wafer for the integrated circuit device in order to provide a so-called flip chip of an integrated circuit device with bump electrodes for connection with the outside. This paper relates to a method of using a base film as a plating electrode film and increasing the length by electrolytic plating. [Conventional technology] With the remarkable progress in highly integrated technology in recent years, there is a large amount of space available within small semiconductor chips. j! It has become possible to create complex integrated circuits, but at the same time it is necessary to rationalize the mounting structure, and an effective means for this is the flip-chip structure with bump electrodes or protruding electrodes for external connection. is becoming increasingly important. As is well known, flip chips can be mounted directly onto ceramic wiring boards, etc., without being packaged, which minimizes the space required for mounting and greatly saves time and effort. Furthermore, recent microbump electrodes have been reduced in size to about 10μ, making it possible to arrange hundreds of external connection points on the periphery of a small chimp with several flash angles. Such bump electrodes are often formed of noble metals such as gold, and their protrusion height from the chip surface is at least 10 μm. Usually about a few tens of nanometers is required, so
Mainly for economical reasons, it is customary to increase the length by selective electrolytic plating, which is performed on the wafer before it is isolated into chips. To ensure a reliable connection using bump electrodes during mounting, it is necessary to precisely align the heights of the bump electrodes, and in order to uniformly lengthen several thousand or more bump electrodes within a wafer by electrolytic plating. Various efforts have been made. Figure 2 shows the procedure for this typical conventional electrolytic plating. FIG. 2(a) is an enlarged view of the periphery of the wafer 10. The wafer 10 has, for example, an epitaxial layer 2 formed on a semiconductor substrate 1 to form a semiconductor layer (not shown) for integrated circuits, and as shown in the figure, the surface 10a of the wafer 10
Electrolytic plating is performed with the l1 plane and lOb on the lower side and the lOb side on the upper side. The electrodes 111i1114 arranged on the oxide film 3 covering the entire surface of the wafer 10 are covered with a protective film 5, and the bump electrodes are connected to the electrode film 4 through the metal base [6 and 8] within the window opened in this. The surface 10a is covered with a base film 6 to serve as a plating electrode at this time.
A base film 8 is patterned at a location where a bump electrode is to be provided, and the surface 10a is covered with a photoresist WX9 so as to expose the base II18. FIG. 2(b) shows this wafer 10 using a plating jig 20.
This shows how to electrolytically plate. The jig 20 includes main bodies 21 and 125 with funnel-shaped inner surfaces. A rope-shaped or perforated plate-shaped anode 22 is housed inside the main body 21, and a plating bottle 24 with a sharp tip is installed in the flange-shaped portion 2la. When the wafer 10 is placed on top of the wafer 10 with its surface 10a facing down as described above and the lid 25 is fitted onto the main body 2l along the guide 25a, the wafer 10
is pushed by the leaf spring 27 from the back side of the fob, and as shown in FIG.
is connected to. Electrolytic plating is performed by fitting the lower opening 2lb of the jig body 21 into the plating solution introduction pipe 41 of the plating tank 40, and introducing the plating solution PL.
The jet stream is brought into contact with the surface 10a of the wafer 10, and the plating t
Connect the positive terminal of if130 to lead 22g of positive 8i22,
This is carried out with the negative side terminals connected to the plating pins 24, respectively, and the base film 8 exposed within the window portion of the photoresist film 9 is used as the plating #i pole, and a bump electrode metal is grown thereon. According to the method described above, by simply setting the wafer 10 on the jig 20, the base film 6 as a plating electrode film can be easily connected to the plating power supply 30 via the plating pins 24, and in this state Using the photoresist film 9 as a mask, noble metals for bump electrodes can be selectively and wastelessly deposited over a certain length on the base film 8 by electrolytic plating. Furthermore, since the plating solution PL in contact with the wafer 10 is constantly replaced, the distribution of the plating thickness of the bump electrode metal within the wafer surface can be made uniform. [Problems to be Solved by the Invention] However, in the above-mentioned conventional method, the connection between the wafer base film and the plating pins relies on a very small area of contact between the two, and furthermore, this contact point is close to the plating liquid PL. Because the contact condition is wet during electrolytic plating, the contact condition may change during electrolytic plating, and if this causes poor contact, the distribution of plating thickness within the wafer surface becomes extremely uneven, resulting in large variations in the height of bumps W18i. There is a problem that occurs. FIG. 3 shows how this contact failure occurs.

As shown in the figure, the plated pin 24 is of course provided with an insulator 24a, but the exposed tip of the plated pin 24 that comes into contact with the base l16 gets wet with the plating solution PL, or the plated pin 24 and the photoresist film become wet. Since the plating solution PL enters the exposed tip part through the small gap between 9,
Part of the plating current leaks and metal deposits D as shown in the figure are likely to occur. In particular, as the deposition progresses, the surface area of the metal deposit D increases, so the ratio of leakage current to the plating current gradually increases, and eventually the plating bottle 24 and the base film 6
The contact resistance increases at an accelerating rate. Of course, the plated pin 24 is in contact with the base [6] at several places,
Since the bump electrode 11 near the location where the contact failure has occurred becomes extremely stunted as shown in the figure, it becomes impossible to discard the wafer as defective. The purpose of the present invention is to prevent metal deposition and poor contact caused by such leakage current during electrolytic plating, and to grow bump electrode metal with a uniform thickness over the entire wafer surface. [Means for Solving the Problems] According to the present invention, this object is achieved by forming a bump electrode on the surface of a wafer to a certain length by electrolytic plating using the underlying film as a plating electrode film as described above. A connection metal film connected to the base film on the front surface is provided on the back side, the front surface of the wafer is facing down, and only it is in contact with the plating solution, and the connection metal film on the front side of the wafer is connected to the plating power source. This can be achieved by electrolytic plating. Although it is possible to use a different material from the base film for the connecting metal film provided on the back surface of the wafer in the above structure, it is most desirable to use the same material in order to simplify the wafer process. In order to reliably connect this connection metal film to the base film on the wafer surface side, the so-called wraparound when depositing the base film and connection metal film by vapor deposition or sputtering is used to ensure that both films meet each other at the periphery of the wafer. The easiest way is to make them overlap. At this time, this overlapping can be ensured by making the chamfer around the wafer's periphery slightly larger than before. In the method of the present invention, the advantages of the jet plating method described above can be utilized as is by using a conventional plating jig whose inner surface is shaped like a funnel. At this time, by introducing a small flow of gas into the jig lid to prevent it from leaking from the periphery of the wafer, the plating solution is completely prevented from entering the back side of the wafer, and the plating solution is applied only to the surface of the wafer. It is possible to ensure the conditions of the present invention that bring the two into contact with each other. Note that the conventional temporary spring for holding down the wafer can be used in the method of the present invention as a contact for the connecting metal film. [Function] Conventionally, the problem was that the contact point of the plating bottle to the base film as the plating electrode film was wetted by the plating solution, so the method of the present invention removes the connection metal film connected to the base film from the wafer. By connecting the connecting metal film to the plating tIl on the back side of the wafer, which is not wetted by the plating solution, by making the plating solution contact only the front surface of the wafer during electrolytic plating, the plating current can be applied to the entire surface of the wafer, eliminating leakage of plating current. This is to uniformly lengthen the metal for bump electrodes. [Example] Hereinafter, an example of the present invention will be described with reference to FIG. Parts in the figure that correspond to those in Figure 2 described above are given the same reference numerals. FIG. 1(a) is an enlarged cross-section of the peripheral edge of a wafer 10 for a plurality of integrated circuit devices, which corresponds to FIG. It is preferable that the chamfer fee on the surface 10b side be larger than the chamfer 10c in the case of FIG. 2 (2), as shown, and that the slope of the chamfer 10d on the surface side be slightly gentler. As in the past, this wafer 10 was first covered with an oxide film 3, and then an electrode W14 connected to an integrated circuit was provided at a location on which a bump electrode was to be provided, and this was covered with a protective film 5 made of silicon nitride or the like. Afterwards, a window is opened on the electrode WA4, and a base film 6 of titanium or the like is deposited on the surface 10a of the wafer 10 by vapor deposition or spatter to make conductive contact with the electrode film 4 within this window. It adheres to a certain thickness. The periphery a6a of this base film 6 has a back side chamfer 10
It is usually deposited around 10n toward e. In the method of the present invention, the connecting metal film 7 is preferably deposited following the deposition with the base WA6 using the same material and method, but to a slightly thicker thickness, for example, around 0.5 nm.
During vapor deposition or sputtering, the peripheral edge 7a wraps around the side chamfer 10d of the wafer surface and is deposited as before, thereby connecting it to the base film 6 with very low contact resistance.
Next, in the same manner as in the past, copper, for example, is deposited on the entire surface of the wafer as the base film 8 on the bump electrode side to a thickness of 0.5 to 1 nm, and is removed by photo-etching, leaving only the areas where the bump electrodes are to be provided. Further, a photoresist film 9 is provided on the surface 10a side by a photo process so as to expose the base film 8. This FIG. 1(a) shows the state in which the preparation for electrolytic plating of the wafer 1o is completed, and the connecting metal M7 on the back surface 1Ob side is connected to the surface 10.
The surface 10a of the wafer 10 in contact with the plating solution and its chamfered portion 10d are securely connected to the base film 6 as the plating electrode film on the a side by the overlapping of the above-mentioned peripheral edges, and the surface 10a of the wafer 10 that contacts the plating solution and its chamfered portion 10d are the base film on the bump electrode side! I! All parts except 8 are covered with a photoresist film 9. Figure 1 shows the state of electrolytic plating. Plating jig 20
is equipped with a main body 21 having a funnel-shaped inner surface and a lid 25, and the wafer 10 is loaded into the main body 21 with the surface 10a facing downward, as in the conventional case.
The difference is that a is provided with supporting pins 23 for the wafer 10 at a plurality of locations, for example, three locations in the circumferential direction, and a small diameter gas introduction pipe 25b and a contactor 26 are provided at 125. The support pins 23 on the side of the main body 21 are made of an insulating material or a metal wire covered with an insulating material, and their tips serve to support the peripheral edge of the wafer 10 at a plurality of locations. The positive 8i22 is the same as the conventional one, but a platinum-plated titanium mesh is used for gold plating, and a perforated solder plate is used for solder plating. The contactor 26 on the lid 25 side may be the same leaf spring as the conventional one, but the wafer rich surface 1
Since it makes conductive contact with the connecting metal film 7 of 0b, it is desirable to plate it with platinum or the like. A small flow rate of nitrogen gas N or the like is introduced between the lid 25 and the wafer 10 from the gas introduction pipe 25b, and is allowed to leak slightly from the periphery of the wafer 10, thereby completely preventing wetting of the back surface 10b of the wafer by the plating solution. This can be prevented. During electrolytic plating, the wafer 10 is placed on the support pin 23 of the jig main body 21 in which the lower opening 2lb is fitted into the plating solution introduction pipe 41 of the plating PL 40, with its surface 10a facing downward, and the lid 25 is covered. By doing this, the contactor 26 is connected to the connection gold i film 7 on the back surface 10b of the wafer, and the wafer 10 is pressed against the support pin 23 for accurate positioning.
Next, the jet stream of the plating solution PL is brought into contact with the wafer surface 10a, and preferably with nitrogen gas N etc. introduced from the gas introduction pipe 25b, the lead 22a for the anode 22 and the contactor are connected to the positive and negative terminals of the plating $B30. Connect 26 and perform electrolytic plating. FIG. 1(C) shows the complete state of the wafer 10. After the bump electrodes 11 made of gold, solder, etc. are made to a certain length on the base film 8 by the above-mentioned electrolytic plating, the photoresist M9 shown in FIG. 1(a) is formed.
Then, using the base layer M8 and the bump t-electrode 11 as a mask, the base film 6 of the wafer surface TliflOa and the connection metal M7 between the vertical plane 10b are chemically etched to obtain the state shown in the figure. Connecting metal! If l7 is the same titanium film as base film 6, both films can be easily removed by simultaneous etching with a thin acid solution. In the above-described method of the present invention, the plating solution PL contacts only the surface 10a of the wafer 10, which is the target of electrolytic plating,
Connection gold II on the back side 10b! Since the connection point between the Wl47 and the contact 26 is not wetted by the plating liquid PL, there is no risk of leakage of plating current unlike in the conventional method, and this connection state is always kept stable during electrolytic plating to cover the entire surface of the wafer. The metal for the rebump electrode can be made uniformly long. By implementing the present invention, variations in the height of bump electrodes for all S-product circuit chips on the same wafer can be suppressed to ±10% or less, and the defect rate due to uneven height can be reduced from a few liters to 10 It can be reduced to one-fold. The method of the present invention is not limited to the embodiments described above, and the method of the present invention can be implemented in various ways. For example, various selections are possible depending on the type of electrolytic plating, as well as the materials for the connecting metal film and base film, and the structure of the electrolytic plating jig is a desirable example, but it is just an example. The present invention can be carried out using structures or structures that are variously modified depending on work conditions and needs. [Effects of the Invention] As is already clear from the above description, in the method of the present invention, when a bump electrode is formed on the surface of a wafer for an integrated circuit device by electrolytic plating using the underlying film as a plating electrode film, a bump electrode is formed on the back surface of the wafer. A connecting metal film is provided that is connected to the base film on the front surface, and electrolytic plating is performed with the front surface of the wafer facing down, allowing the plating solution to contact only that layer, and with the connecting metal film on the back side of the wafer being connected to the plating power source. By doing so, the base film as the Plating Electrolyte 8i film can be connected to the plating power supply via the connecting metal film connected to it on the back side of the wafer, which is not wetted by the plating solution. It completely prevents metal deposition and poor contact caused by leakage current, and allows the bump electrode metal to be made to have a uniform thickness over the entire wafer. The method of the present invention is particularly suitable for manufacturing integrated circuit devices in which a large number of small bump electrodes are provided, and can improve the reliability of the connection during mounting by making the height of the bump electrodes uniform. To carry out the present invention, it is necessary to add a step of depositing a connecting metal film on the back side of the wafer, but preferably this and a base film are subsequently deposited using the same material and the same method, so that it is substantially the same as in conventional methods. The connecting metal film can be provided in the same process as the conventional method, and both films can be removed in one step after electrolytic plating of the bump electrode. Furthermore, as in the embodiments, the present invention can be implemented by only slightly changing the structure of a conventional jet plating jig, for example, while taking advantage of the advantages of easy loading and unloading of wafers and easy control of plating conditions. This drawback can be overcome and the uniformity of plating thickness can be improved. In this way, the method of the present invention grows bump electrodes to a uniform height over the entire wafer surface while proceeding with electrolytic plating using substantially the same process and equipment as conventional methods, thereby reducing the defective rate due to uneven heights. As mentioned above, it can be applied to small flip-chip chips with a high degree of integration and a large number of bump electrodes, and can be particularly effective in increasing connection reliability during mounting.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view of the periphery of a wafer before and after electrolytic plating of metal for bump electrodes according to the method of the present invention, and a cross-sectional view of a plating jig showing the steps of electrolytic plating. Figure 2 and subsequent figures relate to the prior art; Figure 2 is an enlarged cross-sectional view of the circumference of a wafer before electrolytic plating of bump electrode metal according to the conventional method, and a cross-sectional view of a plating jig showing the steps of electrolytic plating; This is an enlarged cross-sectional view of the wafer periphery showing the problem. In the figure, 1: semiconductor substrate for integrated circuit device, 2: epitaxial layer, 3: oxide film, 4: electrode film on which bump t8i is to be provided, 5: protective film, 6: base film as plating electrode film, 6a: [Edge of base film, 7: Connecting metal film, 7a: Periphery of connecting metal film,
8: Bump electrode side base film, 9: Photoresist a, 10
: Wafer for integrated circuit device, 10a : Surface of wafer, l
Ob; back surface of wafer, 10c to 10e: chamfering of wafer periphery, llj bump electrode, 20: plating jig, 21: main body of jig, 21a: flange-shaped portion, 21b two lower openings,
22: Electrolytic plating anode, 22a: Anode lead, 23
Niueno) Supporting pin, 24: Conventional pin, 24a
: Insulation coating of plating pin, 25: Jig lid, 25a + guide, 25b = gas introduction pipe, 26: Contact for connection to connecting metal WAVA, 27: Leaf spring, 30: Plating power supply, 40
: Plating tank, 41: Plating solution introduction pipe, D: Metal deposition, N
：Ni7 cold transfer I0b

Claims (1)

[Claims] This is a method of growing bump electrodes on the surface of a wafer for integrated circuit devices by electrolytic plating, using the base film as a plating electrode film. A method for electrolytic plating of bump electrodes for integrated circuit devices, characterized in that electrolytic plating is carried out with the wafer facing downward and in contact with a plating solution only on this surface, and with the connecting metal film on the back side of the wafer connected to a plating power source. .