JPH04217323A - Manufacture of bump electrode for semiconductor device - Google Patents

Abstract

PURPOSE:To rationalize the manufacture by reducing the number of photoprocessess in manufacturing process for building a bump electrode in a flip chip and prevent the drop of the mechanical strength by the corrosion of the metal at the root of the bump electrode or the overetching in manufacturing process. CONSTITUTION:The whole face of a wafer on which to provide a bump electrode is coated with a composite base film, where at least two kinds of metals are put upon the other, and with this base electrode as a plating electrode, a metal for a bump electrode is grown by electrolytic plating, and with this metal for bump electrode as a mask, the upper base film is removed by chemical etching or the like, and next the remaining lower base film is removed by dry etching, and it is put in complete condition. Moreover, at need, after etching of the upper base film, Au plating is applied to the etched face to improve the corrosion resistance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing bump electrodes for connecting chips of semiconductor devices such as integrated circuit devices to the outside.

0002

2. Description of the Related Art As is well known, as a means or structure for mounting semiconductor devices such as integrated circuit devices on various wiring boards, etc., there are two methods for mounting semiconductor devices such as integrated circuit devices on various wiring boards, etc. In some cases, it is mounted in the form of a flip chip with bump electrodes, and for mass-produced electronic circuits and electronic devices, the latter can reduce the mounting space, reduce the overall size, and reduce the mounting effort. It's great because it saves money. Metals such as solder, Cu, and Au are used for the bump electrodes of flip chips, and their sizes vary, but in all cases, the metal for the bump electrodes is electrolyzed in the wafer state before it is isolated into flip chips. Grown by plating method. The present invention relates to a bump electrode suitable for using Cu or Au, and a typical conventional manufacturing method thereof will be briefly explained below with reference to FIG. 2.

FIG. 2 is a cross-sectional view showing the state of a small portion of a semiconductor wafer or substrate 1 where bump electrodes are provided at each major step. In the state shown in FIG. 1(a), the surface of the substrate 1 is covered with an oxide film 2 such as phosphorus silicate glass, on which a metal film 3 such as aluminum for connection or wiring is disposed in a predetermined pattern. A small window 5 is formed in the insulating film 4, which is a so-called protective film such as silicon nitride, covering the insulating film 4, and a thin base film 10 is formed on the wafer in order to provide a bump electrode connected to the metal film 3 through this window 5. Covered all over. This base film 10 is of course a metal film, and in order to grow bump electrodes thereon by electrolytic plating, it is made into a composite film consisting of a lower base film 11 such as Ti and an upper base film 12 such as Cu or Pd. Ru.

In the step shown in FIG. 2B, the upper base film 12 is etched into a rectangular or circular pattern for a bump electrode using the photoresist film 13 as a mask. The next figure (c) shows the growth process of the bump electrode, in which another photoresist film 21 is formed by a photo process so as to expose only the upper base film 12 patterned as above, and this is covered with a mask. The metal 20, such as Cu or Au, for bump electrodes is coated with a thickness of several tens of μm, for example, by electrolytic plating.
grow to a certain height. At this time, the lower base film 11 is used as a plating electrode for the entire surface of the wafer, and electrolytic plating is performed while it is connected to the cathode of a plating power source, thereby simultaneously growing bump electrode metal 20 at multiple locations within the wafer.

In the final step shown in FIG. 4(d), after removing the photoresist film 21, the lower base film 11 is removed by chemical etching using the bump electrode metal 20 as a mask, resulting in the completed state shown in the figure. . Note that the lower base film 11 in the base film 10 is used as the above-mentioned plating electrode film, and also serves as a barrier film to prevent aluminum, etc. of the metal film 3 from diffusing toward the bump electrodes. The base film 12 serves to connect the bump electrode metal 20 to the lower base film 11 at a relatively narrow base of the bump electrode with a low resistance value and high mechanical strength.

[0006]

[Problems to be Solved by the Invention] As is well known, the manufacturing cost of semiconductor devices is largely influenced by the number of photoprocesses performed on the wafer, but in the conventional bump electrode manufacturing method shown in FIG. Since a total of two photo processes are required, one for etching the base film 12 and the other for forming the pattern for the electrolytic plating mask shown in FIG. There is. Another problem with the conventional technology is that troubles tend to occur at the base of the bump electrode. explain.

As shown in FIG. 3(a), one of the problems is that, especially when the upper base film 12 is made of Cu, its peripheral surface is exposed, so corrosion is likely to occur under high temperature and high humidity conditions. As shown in C1 in the figure, the bump electrode swells and easily falls off due to corrosion, and as shown in C2, the corroded area is missing and the mechanical strength of the base of the bump electrode decreases. Another problem is that over-etching E occurs in the lower base film 11, as shown in FIG. 2(b), which reduces the mechanical strength of the base of the bump electrode or increases the connection resistance with the metal film 3. At a certain point, this over-etching E tends to occur at the bump electrode connected to the substrate 1 via the metal film 3 as shown in the figure. This is because the etching solution naturally comes into contact with the substrate 1 during chemical etching, so the electrochemical conditions differ depending on the resistance between the lower base film 12 and the substrate 1, and the lower base film has a lower resistance. 12
It is thought that etching is promoted. In other words, the etching rate for the lower base film 12 varies within the wafer surface, so if an attempt is made to remove the lower base film 12 at a location where the etching rate is slow, over-etching will occur at a location where the etching rate is fast. It is.

The main object of the present invention is to solve these problems and provide a bump electrode for a semiconductor device that can reduce the manufacturing cost of a flip chip and prevent over-etching of the lower base film at the root of the bump electrode. The purpose is to provide a manufacturing method. A further object of the present invention is to prevent corrosion of the upper base film at the base of the bump electrode.

[0009]

[Means for Solving the Problems] According to the method of the present invention, the object is to provide at least two types of A process of depositing a base film as a metal composite film on the entire surface, a process of selectively growing the metal for the bump electrode on the window part of the insulating film by electrolytic plating using the base film as a plating electrode, and a process of selectively growing the metal for the bump electrode on the window part of the insulating film using the base film as a plating electrode. This is achieved by providing the bump electrode through sequential steps of removing the upper base film by etching using a mask and removing the lower base film by dry etching.

As mentioned above, it is preferable to use either Au or Cu as the metal for the bump electrode according to the method of the present invention.

[0011] Furthermore, it is preferable to use a chemical etching method in the step of removing the upper base film, and if the metal for the bump electrode is a metal that is easily corroded such as Cu, in order to prevent corrosion during this chemical etching, It is desirable that the surface grown by electrolytic plating be covered with a plating film of a highly corrosion-resistant metal such as Au with a film thickness of approximately 2 μm or more.

Furthermore, in order to prevent corrosion of the upper base film at the base of the bump electrode, the lower base film remaining after the removal process of the upper base film is used as a plating electrode, and a highly corrosion-resistant metal such as Au is used for the bump electrode. It is very effective to insert an electrolytic plating process between the metal and the surface to be etched of the upper base film, and it is desirable that the thickness of this Au plating is 2 μm or more.

[0013] The metal for the lower base film is either Ti or Cr, and the metal for the upper base film is Cu, Pd,
It is preferable to use either Ni or Au alone or in combination, and in some cases it is desirable to interpose an intermediate film made of W or the like between the base films on both sides.

[0014]

[Operation] In the conventional method, as mentioned above, the bump electrode growth process by electrolytic plating was performed after the etching process for the upper base film in the base film, so a photo process was required for both processes. The method of the invention is to grow the bump electrode immediately after depositing the base film as described in the previous section, and remove the upper base film by etching using the bump electrode as a mask, thereby converting the photo process into electrolytic plating of the bump electrode. We succeeded in patterning the mask only once. Furthermore, in the conventional method, the lower base film was removed using a chemical etching method using the bump electrode as a mask, but the method of the present invention uses the bump electrode as a mask, but removes it using a dry etching method. This eliminates variations in etching rate caused by conventional bump electrodes and prevents over-etching.

Furthermore, in the present invention, as the next step after the step of removing the upper base film, there is a step of electrolytically plating, for example, Au on the surface to be etched of the upper base film, using the lower base film still remaining at that time as a plating electrode. By inserting
The risk of corrosion of the upper base film during use can be significantly reduced.

[0016]

[Embodiment] An embodiment of the method for manufacturing a bump electrode according to the present invention will be described below with reference to FIG. FIG. 1 is a partially enlarged cross-sectional view showing the state of each main process in the same way as FIG. 2 described above, and the same parts are given the same reference numerals. FIG. 1(a) shows the state of the wafer before bump electrodes are formed, and as mentioned above, the normal bump electrodes are formed on the oxide film 2 or phosphorus silicate glass film covering the silicon substrate 1, which is the main body of the wafer. A part of the metal film 3 with a thickness of 1 to 1.5 μm made of aluminum containing some silicon is 1 to 2 μm thick.
It is exposed in a window 5 opened in a predetermined rectangular or circular pattern in an insulating film 4 made of silicon nitride or the like having a film thickness of m.

From FIG. 1(b) onwards, the bump electrode is manufactured. In the base film deposition step shown in FIG. 1(b), conductive contact is made with the metal film 3 within the window 5 of the insulating film 4 on the surface of the wafer. A base film 10, which is a composite film of a lower base film 11 and an upper base film 12, is deposited over the entire surface by, for example, sputtering. The metal of the lower base film 11 is Ti or Cr, which has a barrier effect against the diffusion of aluminum in the metal film 3, and the metal of the upper base film 12 is used for the lower base film 11 and bumps. Cu, Pd, N, which are compatible with electrode metals
i, Au, etc. alone or Ni and Au,
Pd and Au, W and Cu, etc. are used in combination, but in this embodiment, Ti is used as the lower base film 11.
However, it is assumed that Cu is used for the upper base film 12. Note that the thickness of the lower base film 11 is usually 0.1
~0.3 μm, the thickness of the upper base film 12 is ~0.2 μm
It is estimated to be about 0.6 μm.

FIG. 1(c) shows the process of growing bump electrodes by electrolytic plating. For this purpose, a photoresist film 21 is first spin-coated on the entire surface, and a layer larger than the window 5 of the insulating film 5 is formed by a photo process. A plating window is opened in the pattern, and using this as a mask and the base film 10 as a plating electrode, bump electrode metal 20 is grown to a thickness of, for example, 30 to 50 μm by electrolytic plating. As mentioned above, Cu or Au is used as the metal 20.
In this embodiment, Au is used. In addition, when Cu is used for the bump electrode metal 20, it is desirable to apply, for example, Au to a thin film thickness of 2 μm or more by electrolytic plating thereon.

The next step shown in FIG. 1(d) is the step of removing the upper base film. For this reason, first remove the photoresist film 21 from the state shown in FIG. 1(c), and then remove the bump electrode metal 21.
In this embodiment, the upper base film 12 is removed by chemical etching using 0 as a mask. The etching solution at this time is one that has the selectivity to dissolve the upper base film 12 but not the lower base film 11, and as in this example, the lower base film 11 is Ti and the upper base film 12 is In the case of Cu, by using a thin aqua regia, the upper base film 12 can be selectively etched within a short time, leaving the lower base film 11.

In this embodiment, since Cu is used for the upper base film 12, there is a risk that corrosion may occur during use, so an Au plating process shown in FIG. 1(e) is inserted. In this step, the remaining lower base film 11 is used as a plating electrode.
Au plating 30 is applied to the peripheral surface etched in the previous step of the upper base film 12 to a thickness of 2 μm or more, for example, 2 to 5 μm, by electrolytically plating a highly corrosion-resistant metal such as U or the like. In this example, this Au plating 30 is also attached to the surface of the Au bump electrode metal 20 as shown in the figure, but due to the selection of the plating voltage, the ionization tendency is quite different from that of Au.
It is possible to provide good plating selectivity with almost no adhesion to the lower base film 11 of i.

In the final lower base film removal step shown in FIG. 1(f), the remaining lower base film 11 is dry-etched using the bump electrode metal 20 or the Au plating applied in the previous process as a mask. The completed state shown in the figure is obtained by removing the material using a method. This dry etching can be carried out under an ambient pressure of about 2 Torr using, for example, carbon tetrafluoride or carbon tetrachloride containing about 4% oxygen as a reaction gas. Good selectivity for etching Ti of the base film 11 at high speed is obtained. Moreover, unlike chemical etching, the speed of this dry etching is virtually unrelated to the connection resistance between the substrate 1 and the metal film 5, so the lower base film 11 near all bump electrodes in the wafer is etched at a uniform rate. It is possible to completely prevent over-etching.

The flip chip equipped with bump electrodes according to this embodiment uses the so-called COG method (Chip On
It is particularly suitable for mounting on a ceramic wiring board using a conductive resin or the like and connecting bump electrodes to the wiring conductors of the ceramic wiring board. For example, the size of the bump electrode in a flip chip for mounting using the COG method is 1.
It is approximately 00 μm square or in diameter, and its height is approximately 50 μm.

Bump electrodes manufactured by the method of the present invention have significantly reduced variations in mechanical strength at their bases than conventional ones, and there is no problem of corrosion of the upper base film throughout the storage period of the flip chip before mounting and the period of use after mounting. It has been confirmed that no outbreak has occurred.

[0024]

[Effects of the Invention] As described above, the method of the present invention includes the steps of fully depositing a base film as a composite film of at least two types of metals on the surface of a wafer, and electrolytically plating metal for bump electrodes using the base film as a plating electrode. a step of selectively growing the insulating film on the window portion by using a method, a step of removing the upper base film by etching using the bump electrode metal as a mask, and a step of removing the remaining lower base film by dry etching. Since the bump electrode is manufactured after the process, the following effects can be obtained.

(a) Following the deposition of the lower base film and the upper base film, a bump electrode is grown by electrolytic plating, and the upper base film is removed by etching using the bump electrode as a mask. It is possible to reduce the manufacturing cost of flip chips by omitting the photo process that was conventionally required for patterning the bump electrodes and requiring only one photo process to pattern the electrolytic plating mask for the bump electrodes. can.

(b) Since the lower base film is removed by a dry etching method using the bump electrodes as a mask, the etching rate becomes uniform for all bump electrodes within the wafer, and unlike the conventional method, the etching rate is uniform for all bump electrodes on the wafer. The risk of over-etching of the lower base film is significantly reduced, and the manufacturing yield of flip chips can be improved by virtually eliminating problems such as a decrease in mechanical strength at the base of the bump electrode and an increase in connection resistance.

(c) Since the electrolytic plating of the bump electrode metal is performed using the lower base film and the upper base film as the plating electrodes, compared to the conventional case where electrolytic plating was performed using only the lower base film as the plating electrode. The electrical resistance of the plated electrode is reduced to a fraction of a fraction, which reduces the variation in the growth height of bump electrodes within the wafer, increases the yield of flip chips, and facilitates their mounting on wiring boards, etc. Moreover, the connection with the wiring conductor can be ensured.

(d) When a metal that is easily corroded, such as Cu, is used for the upper base film, by inserting an Au plating process on the side surface, its corrosion resistance can be improved and the flip chip can be easily removed during storage or after mounting. Troubles caused by corrosion of the upper base film can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of a main part of a wafer in which bump electrodes are provided, showing an embodiment of the method for manufacturing bump electrodes for semiconductor devices according to the present invention, showing the state of each main process in FIGS. It is.

FIG. 2 is an enlarged cross-sectional view of a main part of a wafer shown in FIGS. 1A to 1D, in a manner corresponding to FIG. 1, showing a conventional method for manufacturing bump electrodes.

[Fig. 3] The problem of the bump electrode according to the conventional method is shown in the same figure (a
) and (b) are enlarged cross-sectional views of essential parts of the wafer.

[Explanation of symbols]

1 Wafer substrate 3 Metal film 4 Insulating film 5 Window 10 Base film 11 Lower base film 12 Upper base film 20 Bump electrode or bump electrode metal 30
Au plating

Claims (7)

[Claims] 1. A step of fully depositing a base film, which is a composite film of at least two types of metals, on the surface of the wafer where the metal film portion to which the bump electrode is to be connected is exposed within the window formed in the insulating film. , a step of selectively growing bump electrode metal on the window portion of the insulating film by electrolytic plating using the base film as a plating electrode, a step of removing the upper base film by etching using the bump electrode metal as a mask, and a step of removing the upper base film by etching using the bump electrode metal as a mask. 1. A method for manufacturing a bump electrode for a semiconductor device, comprising the step of removing a lower base film by dry etching. 2. The method of manufacturing a bump electrode for a semiconductor device according to claim 1, wherein either Au or Cu is used as the metal for the bump electrode. 3. The method of manufacturing a bump electrode for a semiconductor device according to claim 1, wherein the upper base film is removed by a chemical etching method using a bump electrode metal as a mask. 4. The method of manufacturing a bump electrode for a semiconductor device according to claim 3, wherein Cu is used as the metal for the bump electrode, and the surface of the bump electrode is plated with Au after electrolytic plating. 5. The method according to claim 1, in which the lower base film remaining after the removal step of the upper base film is used as a plating electrode, and Au is electrolytically plated on the bump electrode metal and the surface to be etched of the upper base film. 1. A method for manufacturing a bump electrode for a semiconductor device, the method comprising: inserting a bump electrode for a semiconductor device. 6. The method of manufacturing a bump electrode for a semiconductor device according to claim 1, wherein either Ti or Cr is used as the metal for the lower base film. 7. The method of manufacturing a bump electrode for a semiconductor device according to claim 1, wherein at least one of Cu, Pd, Ni, Au and W is used as the metal for the upper base film. .