JPS6358948A - Formation of solder bump - Google Patents

Abstract

PURPOSE:To form a solder bump directly without incurring an erosion phenomenon of an electrode by a method wherein a covering layer to be destroyed by ultrasonic waves is formed on an electrode part and a location corresponding to the electrode part is brought into contact with molten solder so that ultrasonic waves can be applied to the molten solder or a substrate. CONSTITUTION:At a silicon wafer 11 an electrode 14 is formed on a silicon substrate 12 via an insulating film 13, the electrode 14 is not covered with a passivating film 15 coating the whole surface, and additionally a covering layer 16 is formed on the whole surface. A glass plate to which a double-faced adhesive tape for high-temperature use is glued is attached to the reverse side of the silicon wafer 11, and this assembly is then dipped into spouting molten solder 23 by keeping it in a vertical position. Then, an ultrasonic vibrator 25 is inserted into the molten solder 23 at a location near the silicon wafer 11, and ultrasonic waves are applied to the molten solder 23. Therefore, the covering layer 16 on the electrode 14 and a natural oxide film are removed and a mountain-like solder bump 17 is bonded directly on the electrode 14.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a method of forming solder bumps, particularly for use in the semiconductor industry.

(Prior Art) Bonding technology for semiconductor devices is roughly divided into two types: wire bonding technology and wireless bonding technology.

The former method connects electrodes of a semiconductor chip and lead terminals of a lead frame using wires. This technology is sufficient when the number of connections is small, but with the increase in the number of connections, as the electrode size becomes less than 100 m + electrodes and the density becomes higher, problems arise especially in terms of reliability. Become.

On the other hand, the latter method involves bonding the electrodes of the semiconductor chip and the lead terminals of the lead frame or the electrodes on the glass or ceramic substrate all at once.
It has been put into practical use to ensure reliability in response to higher integration of elements.

As this wireless bonding technology, for example, tape automated bonding method (TAB method) is used.
, a flip-chip method, a CCB method, and the like are known, and in these methods, bumps are usually formed on electrodes (pads) of a semiconductor chip. For this bump, inexpensive pb-13n solder has been considered.

Conventionally, bumps made of PB-3N solder formed on the electrodes of semiconductor chips are as shown in FIG. In FIG. 7, an electrode 3 made of 8β or An alloy is patterned on a silicon substrate 1 through an insulating film 2 such as a silicon oxide film, and a passivation film 4 made of silicon nitride or the like is formed on the entire surface. of? l! After covering, the passivation film 4 on the electrode 3 is selectively etched to expose the electrode 3. On the exposed electrode 3, cr,
Base metal R consisting of N', Mos Cu, Au, Heq, etc.
5 is formed. Further, solder bumps 6 are formed on the base metal R5.

The base metal R5 is provided to improve bondability with solder. For this purpose, one to three metal layers are provided as the base metal 5, and various combinations are being considered.

Incidentally, the solder bumps 6 are usually formed by plating or vapor deposition, and various methods have been proposed, but all of these methods have drawbacks as described below.

In the plating method, for example, after the electrode hole-drilling process is completed, the natural oxide film on the electrode is removed by ion etching, one to three layers of base metal are deposited on the entire surface, and the electrode part is formed into a tight resist with the hole formed. The process involves coating only the base metal on the electrode, performing solder plating only on the base metal, and etching unnecessary parts of the plating resist and base metal.

However, although this method has no problems when forming gold bumps, when it is applied to forming solder bumps, the chemical resistance of the solder is poor, so when etching the underlying metal, the solder is also etched. It has the disadvantage of being eroded by liquids.Therefore, a method is used in which 3n and PB are plated in sequence, and after the base metal is etched, they are heated and alloyed.

In addition, in the vapor deposition method, for example, after the electrode drilling process is completed, the natural oxide film on the N electrode is removed by ion etching, one to three layers of base metal are vapor deposited on the entire surface, patterned, and then After coating a resist with holes only on the base metal, solder is vapor-deposited, and the resist is removed as well as the solder in unnecessary parts. However, when using the vapor deposition method, the pb and 3n in the solder
The disadvantage is that it is difficult to form solder bumps with a eutectic composition because the vapor pressure is different from that of the eutectic composition.

In any case, the conventional method uses a base metal and has basic problems that make the process complicated, such as the need to form a mask to prevent solder from being plated or vapor-deposited on parts other than the electrode part. be.

For this reason, a method has been proposed in which bumps are formed on the AJ2 electrode by soldering using ultrasonic waves (Japanese Patent Laid-Open No. 53-89368). However, since the solder used in this method uses 3n, Zn1tylo, B1, and Sb as standard components, it adheres to parts other than the AQ and electrodes, and there is a problem that the A2 electrode is bent and the ffl phenomenon occurs. There is.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems. The object of the present invention is to provide a method in which solder bumps can be selectively and directly formed without providing a base metal on top, and the process can be simplified.

[Structure of the Invention] (Means and Effects for Solving the Problems) The method for forming solder bumps of the present invention provides a coating layer that can be destroyed by ultrasonic waves on at least the electrode portion of the substrate surface, and A molten solder is brought into contact with the corresponding portion and an ultrasonic wave is applied to at least either the molten solder or the substrate to destroy the N layer and the natural oxidation film on the electrode and selectively form an alloy with the electrode. It is characterized by attaching solder to the solder.

The method of the present invention will be explained in more detail as follows.

For example, after the N-electrode drilling step, a coating layer is first provided on at least the electrode portion of the substrate surface. This 11th layer may be made of organic matter or inorganic material, but is preferably solid. From the viewpoint of ease of coating, polyimide and organic metal oxide are preferable. For example, the organometallic oxide is applied in a liquid state onto a substrate and solidified by applying a temperature of about 50 to 150°C. The thickness of this coating layer is preferably 10p or less, more preferably 50 people to 3JR. Of course, other metals such as A2, Ti, Mo, Cr, ■, N1, etc. may be coated. Also, before coating these coating layers,
There is no need to etch the electrode surface.

In addition, for example, in the electrode hole drilling process, etching is performed at t.
IIJi! I! Insulation 1 that covers the electrode so that it is not completely exposed! ! This insulating film may be used as the 11th layer by leaving a small amount (PSG film or silicon nitride film).

The thickness of the insulating film serving as the covering layer is preferably thinner than the thickness of the insulating film in other parts, and is preferably 4000 Å or more. This is because if the thickness of the insulating film is less than 4,000 mm, the impact caused by ultrasonic waves will reach the electrodes, making it easy for the electrodes to bend. In addition, there is no coating on the electrode!
As a method of leaving an insulating film as a layer, two different types of insulating films are formed on the electrode, and the upper layer of insulation II! is formed in the electrode hole drilling process. l (for example, only the silicon nitride film is removed,
Lower layer insulation I! (For example, a PSG film) may be left.

In the latter method, the thickness of the insulating film serving as the covering layer can be easily controlled. The method of leaving the insulating film as described above can simplify the process compared to the method of forming a new covering layer after the electrode hole drilling step.

Next, when ultrasonic waves are applied to the molten solder or the substrate with the molten solder in contact with the electrode portion, metal vapor bubbles are generated in the molten solder due to the ultrasonic energy. These bubbles grow and disappear instantly, creating localized high temperatures and pressures. When this high-pressure bubble bursts, it applies a strong impact to the electrode surface, thereby destroying the coating layer and natural oxide film on the electrode, and selectively soldering the exposed new surface of the electrode. In this way, solder bumps are formed by bonding directly onto the electrodes.

When applying ultrasonic waves to molten solder, specific methods include immersing the board in molten solder in a solder bath, inserting an ultrasonic vibrator, and applying ultrasonic waves to molten solder, or applying ultrasonic waves to molten solder. You can apply ultrasonic waves to the molten solder by applying ultrasonic waves to the solder bath eye, or you can apply ultrasonic waves to the molten solder at the same time as you bring the molten solder into contact with the electrode using a soldering iron that can vibrate ultrasonic waves. It's okay. Note that the surface of old electrodes may be covered with contaminants.
In this case, ozone may be sprayed as a pretreatment.

The components of the solder are normal Pb-3n series, Pb-Cd series, z
n-3n system, Cd-Zn system, Pb-1n system, AQ-1n
(7) Solder may also be used. Of course, low melting point metals such as in can be used alone.

The method of the present invention is equally applicable whether the substrate is a semiconductor substrate or an insulating substrate such as glass or ceramic. When these substrates are immersed in molten solder as described above, the entire substrate may be immersed, or it may be partially immersed. Further, since solder does not adhere to insulating films such as passivation films other than electrodes, there is no need to cover them with the FM layer, but if metal other than electrodes is exposed, it is necessary to protect them. When immersing a semiconductor wafer in molten solder, after blade dicing, the semiconductor chips may crack along the dicing lines and separate. It is desirable to attach a high-temperature adhesive tape to the wafer, and then to adhere it to metal, glass, etc., or to suction the back side of the wafer with a vacuum chuck or the like. Further, blade dicing may be performed after forming the solder bumps.

Further, it is desirable that the treatment in the method of the present invention be carried out in a non-oxidizing atmosphere by flowing an inert gas. When the atmospheric gas contains 5% or more oxygen, A, which is a constituent element of the electrode,
This is because 2 causes oxidation, resulting in poor wetting with solder, and in the worst case, a defect occurs in which the bumps are connected to each other.

In the method of the present invention, the frequency of the applied ultrasound is 10~
It may be about 60 kHz, preferably 15 to 40 kHz. This is because if the frequency is too low, the above-mentioned effect is difficult to occur, whereas if the frequency is too high, there is a risk of peeling of the electrodes, etc.

Further, the output of the ultrasonic wave may be about 2 to 500 W, but preferably 10 to 300'vV. On the other hand, the temperature of molten solder is about 230-350℃, and the processing time is 0.1-1
It is about 0 seconds. This is because if the temperature is high and the treatment time is long, the 8λ, which is the constituent element of the electrode, will dissolve, whereas if the temperature is low (
This is because if the processing time is short, alloying of Al1 and solder will not occur.

Preferably, the molten solder temperature is about 240 to 320°C and the processing time is about 0.5 to 5 seconds. Note that since glass or ceramic substrates are less likely to break than silicon or compound semiconductor substrates, the frequency and output of ultrasonic waves, the temperature of molten solder, etc. can be increased. Furthermore, since the temperature at which the solder becomes liquid differs depending on the solder component, it is best to select a temperature that matches the solder component.

The board on which the solder bumps are formed as described above is mounted using wireless bonding technology.

For example, in the TAB method, a semiconductor substrate on which solder bumps are formed and a lead frame (tape) are aligned and bonded by thermocompression. In this case, the conductive metal that makes up the lead frame is Cu, Fe, Al1, Fe-Ni alloy, Aus
AQ, Sn, etc. are used. It may be plated with these metals. However, the lead frame side is Fe-N.
In the case of i-alloy, it is desirable to use flux, and in the case of Au, it is desirable to apply solder in a similar manner.

Furthermore, in the flip-chip method or the CCB method, a semiconductor chip on which solder bumps are formed and bumps on a glass or ceramic substrate on which solder bumps are formed are bonded together by thermal a-bonding.

As described above, according to the present invention, the i-layer prevents the phenomenon of electrode bending, and it is possible to selectively form solder bumps directly on the electrodes without using a base metal, simplifying the process and greatly improving the process. Time savings can be achieved.

Further, the subsequent wireless bonding process can also be easily performed.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Example 1 First, a silicon wafer 11 was prepared in which wiring and electrodes were formed by a normal wafer process, a passivation film was deposited on the entire surface, and openings for contact pads were formed. The wiring electrode is made of A2-2% 5i-2% Cu with a film thickness of 1- formed by a sputtering device.
A silicon nitride film is used as the passivation film. And this silicon wafer 1
Each chip formed in No. 1 has 48 electrodes (contact pads) each having a width of 90 m. Note that this silicon wafer 11 was not subjected to blade dicing. Next, an organic silicon oxide liquid was applied to the entire surface of the silicon wafer 11, and then heat-treated at 120° C. for 30 minutes to evaporate the organic components to form a 2,000-layer silicon oxide coating layer. This was repeated 5 times to obtain a coating layer with a thickness of 1 U++. To illustrate this state, as shown in FIG. 1(a), an electrode 14 is formed on a silicon substrate 12 with an insulating film 13 interposed therebetween, the electrode 14 is exposed from a passivation film 15 covering the entire surface, and then the electrode 14 is exposed from a passivation film 15 covering the entire surface. A covering layer 16 is formed on.

Next, solder bumps were formed on the electrodes of this silicon wafer 11 using an ultrasonic soldering apparatus as shown in FIG. In FIG. 2, a solder return path 22 is formed in a solder bath 21, and molten solder 23 is accommodated therein. This molten solder 23 passes through the reflux path 22 by a stirring rod 24 rotated by a motor (not shown), and is ejected above the liquid level and refluxed. The silicon wafer 11 has a high-temperature double-sided adhesive tape affixed to its back surface, is further adhered to a glass plate (not shown), is held vertically, and is immersed in the spouting molten solder 23. Then, an ultrasonic vibrator 25 is inserted into the molten solder 23 near the silicon wafer 11 to apply ultrasonic waves to the molten solder 23.

In addition, 1% warm solder of 95Pb-3n was used as the solder. ! The temperature was maintained at 320°C. Also,
A frequency of 28k is applied to the molten solder 23 by the ultrasonic vibrator 25.
Ultrasonic waves with a frequency of Hz and an output of 100 W were applied, and the immersion time of the silicon wafer 11 was 1 second. During this soldering operation, nitrogen gas was passed around at a flow rate of 20 2 /min to prevent oxidation of aluminum, which is a constituent element of the electrode, and tin in the solder.

By this operation, the iI layer 16 on the electrode 14 and the natural oxide film (not shown) are removed as shown in FIG. 1(b), and the solder bump 17 is removed on the electrode 414 as shown in FIG. were directly joined to form a mountain shape. The height of this solder bump 17 was 25 m. In addition, electrode 1
A thin alloy layer of A2 and 3n was formed on the bonding surface between A2 and the solder bump 17.

Next, the silicon wafer 11 was separated into individual chips by blade dicing. Separately, a TAB type tape was prepared in which a copper lead frame was formed and the surface thereof was gold-plated. Then, align the bumps on the chip and the lead terminals on the tape and heat them both at 190℃!
I watched it. No problems occurred in this inner lead bonding process either.

Example 2 First, a silicon wafer 11 similar to that in Example 1 was prepared. In this case, A2-1% Si is used for the wiring and electrodes, and each chip formed on the silicon wafer 11 has 64 electrodes (contact pads) each having a width of 70 Jm.
Individually formed. It should be noted that this silicon wafer 11 had undergone a period of warping after the formation of the elements, and since it was expected that the electrode surface would be covered with a hard oxide film, ozone cleaning was performed. In addition, the coating layer 16 has a thickness of 3 on the entire surface.
000 carbon film was formed by vapor deposition.

Solder bumps were formed on the electrodes of this silicon wafer 11 using an ultrasonic soldering apparatus as shown in FIG. In FIG. 3, a solder reflux path 32 is formed within the solder side 31, and molten solder 33 is accommodated therein.

This molten solder 33 is passed through the reflux path 32 by a stirring rod 34 rotated by a motor (not shown), and then passed through the solder bath 31.
It spews out above the liquid level in the center and refluxes. The silicon wafer 11 is immersed in the surface of the spouted molten solder 33 so that the entire surface on which the electrodes are formed is immersed in the liquid surface of the molten solder 33, with the back surface being attracted by a vacuum chuck. Then, an ultrasonic vibrator 35 is inserted from the bottom of the solder bath 31, and ultrasonic waves are applied to the molten solder 33 near the silicon wafer 11.

Note that 30Zn-8n solder was used as the solder, and the solder bath temperature was maintained at 250°C.

Further, ultrasonic waves with a frequency of 30 kHz and an output of 50 W were applied to the molten solder 33 by the ultrasonic vibrator 35, and the immersion time of the silicon wafer 11 was 3 seconds.

During this soldering operation, Ar gas is applied to the surrounding area at 202/min. It was washed away.

Through this operation, solder bumps 17 were formed as shown in FIG. 1(C). The height of this solder bump 17 is 20
It was pR.

Next, after cutting the silicon wafer 11 into individual chips by blade dicing, inner lead bonding was performed with a TAB tape in the same manner as in Example 1, but no problems occurred.

Example 3 First, a silicon wafer 11 similar to that in Example 1 was prepared. In this case, A2-1% Si is used for the wiring/lti, and two 500x electrodes (contact pads) are formed on each chip formed on the silicon wafer 11. Further, as the covering layer 16, CrWA with a thickness of 2,000 yen was formed over the entire surface by vapor deposition.

Next, using a soldering iron 41 capable of applying ultrasonic waves as shown in FIG. 4, molten solder 42 was dropped onto the silicon wafer 11, and ultrasonic waves were applied.

Note that 95Sn-AQ solder was used as the solder, and the soldering temperature was maintained at 240°C. Further, ultrasonic waves with a frequency of 40 kHz and an output of 30 W were applied to the molten solder 42, and the soldering time was increased by 10 seconds. In addition, since the soldering area was large in this case, there was no need to flow inert gas around it. Through this operation, solder bumps 17 were formed as shown in FIG. 1(C). The height of this solder bump 17 was 120 m.

Subsequently, the ultrasonic wave of the soldering iron 41 was stopped, and further pb-sn eutectic solder was dropped onto the solder bumps 17. At this time, the molten solder temperature was 200°C. In addition, rosin-based flux was used in areas where solder is difficult to adhere. By this operation, a second layer of solder bumps (not shown) is formed on the solder bumps 17, and the total height of both is 1.
It became 60JiI11.

Next, after cutting the silicon wafer 11 into individual chips by blade dicing, inner lead bonding was performed with a TAB tape in the same manner as in Example 1, but no problems occurred.

The ultrasonic soldering apparatus used in the present invention is not limited to those used in Examples 1 to 3 above, and may be, for example, as shown in FIG. 5.

In the ultrasonic soldering apparatus shown in FIG. 5, a solder rod 51 itself emits ultrasonic waves and applies ultrasonic waves to molten solder 52.

In addition, in Examples 1 to 3 above, a coating layer made of silicon oxide, carbon, or Cr was provided after the electrode drilling process, but in the N electrode drilling process, a part of the insulating film covering the electrode was left behind. A membrane may also be used as a covering layer.

Further, in Examples 1 to 3 above, the case where the present invention is applied to TAB type wireless bonding has been explained, but the present invention is not limited to this, and the present invention can be applied to other wireless bonding such as flip chip type or CCB type. Applicable. In this case, first, as shown in FIG. 6(a), an electrode 62 is formed on a silicon substrate 61 via an insulating film,
After covering the entire surface with a passivation film 63, the electrode 62
An electrode 72 is formed on a glass or ceramic substrate 71 as shown in FIG. For each hole, solder bumps 64.74 are formed on electrodes 62.72 in the manner described in Examples 1-3. Next, as shown in FIG. 6(C), a joint portion 80 is formed by thermally bonding the solder bumps 64 and 74 of the two together.

Furthermore, in Examples 1 to 3 above, the present invention was described with respect to the formation of solder bumps on electrodes containing A2 as a main component and additives such as St and Cu. Alternatively, even silicides of these metals can be applied to @-like.

[Effects of the Invention] As detailed above, according to the method for forming solder bumps of the present invention, solder bumps can be selectively formed directly on electrodes in an extremely simple process without causing the phenomenon of electrode bending. This makes it possible to easily introduce wireless bonding technology, and to manufacture semiconductor devices with high bonding reliability in response to the miniaturization of elements.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are cross-sectional views of the electrode portion of a silicon wafer showing the steps of the method of the present invention, and FIG. 2 is Example 1 of the present invention.
FIG. 3 is an explanatory diagram showing the method for forming solder bumps in Example 2 of the present invention, and FIG. 4 is an explanatory diagram showing the method for forming solder bumps in Example 3 of the present invention. An explanatory diagram, FIG. 5 is an explanatory diagram showing a method of forming solder bumps in another embodiment of the present invention,
6(a) to 6(C) are cross-sectional views showing the wireless bonding process in another embodiment of the present invention, and FIG. 7 is a cross-sectional view of the electrode portion of a silicon wafer on which conventional solder bumps are formed. . 11... Silicon wafer, 12... Silicon substrate,
13... Insulating film, 14... Snow scraper, 15... Passivation film, 16... Covering layer, 17... Solder bump, 21... Solder bath, 22... Circulation path, 23・
... Molten solder, 24 ... Stirring bar, 25 ... Ultrasonic vibrator, 31 ... Solder oval, 32 ... Reflux path, 33
... Molten solder, 34 ... Stirring bar, 35 ... Ultrasonic vibrator, 41 ... Soldering iron, 42 ... Molten solder, 51 ... Solder bath, 52 ... Molten solder , 61
... silicon substrate, 62 ... electrode, 63 ... passivation film, 71 ... glass or ceramics substrate, 72 ... electrode, 73 ... insulating film, 80 ... joint portion. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 5 (a) (b) Figure 6 Figure 7

Claims (6)

[Claims] (1) A coating layer that can be destroyed by ultrasonic waves is provided on at least the electrode portion of the surface of the substrate, and molten solder is brought into contact with at least a portion corresponding to the electrode portion, and ultrasonic waves are applied to at least either the molten solder or the substrate. 1. A method for forming solder bumps, which comprises applying a pressure to destroy a coating layer and a natural oxide film on an electrode, and selectively attaching solder by alloying with the electrode. (2) The method for manufacturing a solder bump according to claim 1, wherein the thickness of the coating layer is 10 μm or less. (3) The method for forming solder bumps according to claim 1, characterized in that the substrate is immersed in a bath of molten solder. (4) The method for forming solder bumps according to claim 1, wherein the substrate is a semiconductor substrate or a glass or ceramic substrate. (5) The method for forming a solder bump according to claim 1, wherein the electrode is mainly composed of aluminum. (6) The method for forming solder bumps according to claim 1, wherein the process is performed in a non-oxidizing atmosphere.