1. Field of the Invention
The present invention relates to a wafer processing method for processing a wafer including a silicon substrate and a plurality of devices formed on the front side of the silicon substrate, wherein each device is provided with a bonding pad, and an electrode is embedded in the silicon substrate so as to be connected to the bonding pad.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped silicon (Si) substrate to partition a plurality of regions where a plurality of semiconductor devices such as ICs and LSIs are respectively formed, thus obtaining a wafer including the silicon (Si) substrate and the plural semiconductor devices formed on the front side of the silicon (Si) substrate. The wafer is cut along the streets to thereby divide the regions where the semiconductor devices are formed from each other, thereby obtaining the individual semiconductor devices.
For the purposes of achieving smaller sizes and higher functionality of equipment, a module structure having the following configuration is in practical use. This module structure is such that a plurality of devices are stacked and bonding pads provided on each device are connected to each other. In this module structure, via holes are formed in a silicon (Si) substrate at positions corresponding to the bonding pads, and electrodes of copper, aluminum, etc. covered with an insulating material of silicon dioxide (SiO2) are embedded in the via holes so as to be connected to the bonding pads (see Japanese Patent Laid-open No. 2003-163323, for example). The copper (Cu) electrodes embedded in the silicon (Si) substrate are exposed to the back side of the silicon (Si) substrate by grinding the back side of the silicon (Si) substrate to expose the copper (Cu) electrodes to the back side of the silicon (Si) substrate and next etching the back side of the silicon (Si) substrate by using potassium hydroxide (KOH) having a high etching rate to silicon (Si) and a low etching rate to copper (Cu) as an etching liquid, thereby projecting the copper (Cu) electrodes from the back side of the silicon (Si) substrate by an amount of 5 to 10 μm.
However, potassium hydroxide (KOH) has a high etching rate also to silicon dioxide (SiO2). Accordingly, there is a problem such that the silicon dioxide (SiO2) film as an insulating film covering the copper (Cu) electrodes is etched by potassium hydroxide (KOH) to cause a reduction in insulation quality between the silicon (Si) substrate and the copper (Cu) electrodes. On the other hand, when tetramethylammonium hydroxide (TMAH) having a low etching rate to silicon dioxide (SiO2) is used as the etching liquid, there is a problem such that the copper (Cu) electrodes are etched because tetramethylammonium hydroxide (TMAH) has a high etching rate to copper (Cu).
It is therefore an object of the present invention to provide a wafer processing method for processing a wafer having embedded electrodes which can expose the electrodes from the back side of the silicon (Si) substrate without etching the silicon dioxide (SiO2) film as an insulating film covering the electrodes to cause a reduction in insulation quality and also without etching the electrodes.
In accordance with an aspect of the present invention, there is provided a wafer processing method for processing a wafer including a silicon (Si) substrate and a plurality of devices formed on the front side of the silicon (Si) substrate, wherein each device is provided with a bonding pad, and an electrode covered with a silicon dioxide (SiO2) film is embedded in the silicon (Si) substrate so as to be connected to the bonding pad, the wafer processing method including a protective member attaching step of attaching a protective member to the front side of the wafer; a back grinding step of grinding the back side of the silicon (Si) substrate of the wafer so as not to expose the electrode to the back side of the silicon (Si) substrate after performing the protective member attaching step; and an etching step of etching the back side of the silicon (Si) substrate by using an etching liquid to thereby expose the electrode to the back side of the silicon (Si) substrate after performing the back grinding step; the etching liquid including a first etching liquid having a high etching rate to silicon (Si) and a second etching liquid capable of etching silicon (Si) and having a low etching rate to silicon dioxide (SiO2); the etching step having a first etching step of etching the back side of the silicon (Si) substrate by using the first etching liquid to thereby incompletely expose the electrode covered with the silicon dioxide (SiO2) film to the back side of the silicon (Si) substrate and a second etching step of etching the back side of the silicon (Si) substrate by using the second etching liquid to thereby project the electrode covered with the silicon dioxide (SiO2) film from the back side of the silicon (Si) substrate after performing the first etching step.
Preferably, the electrode is formed of copper (Cu), the first etching liquid includes a mixture of hydrofluoric acid (HF) and nitric acid (HNO3), and the second etching liquid includes tetramethylammonium hydroxide (TMAH).
Alternatively, the electrode is formed of copper (Cu), the first etching liquid includes potassium hydroxide (KOH), and the second etching liquid includes tetramethylammonium hydroxide (TMAH).
Preferably, the wafer processing method further includes a polishing step of polishing the back side of the silicon (Si) substrate so as not to expose the electrode to the back side of the silicon (Si) substrate after performing the back grinding step and before performing the etching step, thereby removing a saw mark formed on the back side of the silicon (Si) substrate in the back grinding step.
As described above, the wafer processing method according to the present invention includes the protective member attaching step of attaching the protective member to the front side of the wafer, the back grinding step of grinding the back side of the silicon (Si) substrate of the wafer so as not to expose the electrode to the back side of the silicon (Si) substrate, and the etching step of etching the back side of the silicon (Si) substrate by using the etching liquid to thereby expose the electrode to the back side of the silicon (Si) substrate. The etching liquid includes the first etching liquid having a high etching rate to silicon (Si) and the second etching liquid capable of etching silicon (Si) and having a low etching rate to silicon dioxide (SiO2). The etching step includes the first etching step of etching the back side of the silicon (Si) substrate by using the first etching liquid to thereby incompletely expose the electrode covered with the silicon dioxide (SiO2) film to the back side of the silicon (Si) substrate and the second etching step of etching the back side of the silicon (Si) substrate by using the second etching liquid to thereby project the electrode covered with the silicon dioxide (SiO2) film from the back side of the silicon (Si) substrate after performing the first etching step.
Accordingly, the etching rate to the silicon dioxide (SiO2) film covering the electrode in the second etching step is low, so that the electrode can be projected from the back side of the silicon (Si) substrate so as not to be etched.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.
A preferred embodiment of the wafer processing method according to the present invention will now be described in detail with reference to the attached drawings.
There will now be described a processing method for exposing the copper (Cu) electrodes 214 to the back side 21b of the silicon (Si) substrate 21 of the wafer 2 so that the copper (Cu) electrodes 214 project from the back side 21b. First, as shown in
After performing the protective member attaching step mentioned above, a back grinding step is performed in such a manner that the back side 21b of the silicon (Si) substrate 21 of the wafer 2 is ground so as not to expose the copper (Cu) electrodes 214. This back grinding step is performed by using a grinding apparatus 4 essentially shown in
The back grinding step using this grinding apparatus 4 is performed in the following manner. First, the wafer 2 is placed on the chuck table 41 in the condition where the protective member 3 attached to the front side of the wafer 2 comes into contact with the upper surface (holding surface) of the chuck table 41 as shown in
After performing the back grinding step mentioned above, a polishing step is performed to remove a saw mark formed on the back side 21b of the silicon (Si) substrate 21 in the back grinding step, planarizing the back side 21b of the silicon (Si) substrate 21. This polishing step is performed by using a polishing apparatus 5 shown in
The polishing step using the polishing apparatus 5 is performed in the following manner. First, the wafer 2 is placed on the chuck table 51 in the condition where the protective member 3 attached to the front side of the wafer 2 comes into contact with the upper surface (holding surface) of the chuck table 51 as shown in
After performing the polishing step mentioned above, an etching step is performed in such a manner that the back side 21b of the silicon (Si) substrate 21 of the wafer 2 is etched by an etching liquid to thereby expose the copper (Cu) electrodes 214 to the back side 21b of the silicon (Si) substrate 21. This etching step is performed by using an etching apparatus 6 shown in
The spinner table accommodating means 62 includes a receptacle 621, three support legs 622 for supporting the receptacle 621 (two of the three support legs 622 being shown in
The etching apparatus 6 further includes a first etching liquid supplying mechanism 64 for supplying a first etching liquid to the workpiece held on the spinner table 611. The first etching liquid supplying mechanism 64 includes a first etching liquid supplying nozzle 641 for supplying the first etching liquid toward the workpiece held on the spinner table 611 and a reversible electric motor 642 (see
The etching apparatus 6 further includes a second etching liquid supplying mechanism 65 for supplying a second etching liquid to the workpiece held on the spinner table 611. The second etching liquid supplying mechanism 65 includes a second etching liquid supplying nozzle 651 for supplying the second etching liquid toward the workpiece held on the spinner table 611 and a reversible electric motor 652 (see
The etching apparatus 6 further includes a cleaning water supplying mechanism 66 for supplying a cleaning water to the workpiece held on the spinner table 611. The cleaning water supplying mechanism 66 includes a cleaning water supplying nozzle 661 for supplying the cleaning water toward the workpiece held on the spinner table 611 and a reversible electric motor 662 (see
There will now be described with reference to
The etching step to be performed by using the etching apparatus 6 will now be described. First, the wafer 2 (with the protective member 3 attached to the front side) polished by the polishing step mentioned above is placed on the vacuum chuck 611a of the spinner table 611 constituting the etching apparatus 6 in the condition where the protective member 3 attached to the front side of the wafer 2 comes into contact with the vacuum chuck 611a. In this condition, the suction means is operated to hold the wafer 2 through the protective member 3 on the vacuum chuck 611a under suction. Accordingly, the back side 21b of the silicon (Si) substrate 21 of the wafer 2 held through the protective member 3 on the vacuum chuck 611a is oriented upward. At this time, the spinner table 611 is set at the load/unload position shown in
After holding the wafer 2 through the protective member 3 on the vacuum chuck 611a of the spinner table 611 under suction as mentioned above, a first etching step is performed in such a manner that the back side 21b of the silicon (Si) substrate 21 is etched by using the first etching liquid having a high etching rate to silicon (Si) to thereby incompletely expose the copper (Cu) electrodes 214 covered with the silicon dioxide (SiO2) film 215 to the back side 21b of the silicon (Si) substrate 21. In performing the first etching step, the spinner table 611 is lowered to the working position in the condition where the wafer 2 is held through the protective member 3 on the vacuum chuck 611a under suction, and the nozzle portion 641a of the first etching liquid supplying nozzle 641 is swiveled about the axis of the support portion 641b so that the front end of the nozzle portion 641a comes to a position directly above the center of the back side 21b of the silicon (Si) substrate 21 of the wafer 2 held on the spinner table 611 as shown in
The mixture of hydrofluoric acid (HF) and nitric acid (HNO3) supplied to the center of the back side 21b of the silicon (Si) substrate 21 is spread toward the outer circumference of the wafer 2 by a centrifugal force to thereby etch the back side 21b of the silicon (Si) substrate 21. The first etching step is performed for three minutes, so that the back side 21b of the silicon (Si) substrate 21 is etched by an amount of 9 μm, for example, thereby reducing the thickness of the wafer 2 to 50 μm, for example, as shown in
After performing the first etching step mentioned above, a second etching step is performed in such a manner that the back side 21b of the silicon (Si) substrate 21 is etched by using the second etching liquid capable of etching silicon (Si) and having a low etching rate to silicon dioxide (SiO2) to thereby project the copper (Cu) electrodes 214 covered with the silicon dioxide (SiO2) film 215 from the back side 21b of the silicon (Si) substrate 21. In performing the second etching step, the first etching liquid supplying nozzle 641 is retracted to the standby position and the nozzle portion 651a of the second etching liquid supplying nozzle 651 is swiveled about the axis of the support portion 651b so that the front end of the nozzle portion 651a comes to a position directly above the center of the back side 21b of the silicon (Si) substrate 21 of the wafer 2 held on the spinner table 611 as shown in
The tetramethylammonium hydroxide (TMAH) supplied to the center of the back side 21b of the silicon (Si) substrate 21 is spread toward the outer circumference of the wafer 2 by a centrifugal force to thereby etch the back side 21b of the silicon (Si) substrate 21. The second etching step is performed for five minutes, so that the back side 21b of the silicon (Si) substrate 21 is etched by an amount of 5 μm, for example. As a result, the copper (Cu) electrodes 214 covered with the silicon dioxide (SiO2) film 215 projects by the amount of 5 μm from the back side 21b of the silicon (Si) substrate 21. The tetramethylammonium hydroxide (TMAH) used as the second etching liquid in the second etching step can etch silicon (Si) and has a low etching rate to silicon dioxide (SiO2). Further, etching time is short in the second etching step. Accordingly, the etching amount of the silicon dioxide (SiO2) film 215 covering the copper (Cu) electrodes 214 is small, so that the copper (Cu) electrodes 214 are not etched to be maintained.
After performing the second etching step mentioned above, a cleaning step of cleaning the wafer 2 etched above is performed. In performing the cleaning step, the second etching liquid supplying nozzle 651 is retracted to the standby position and the nozzle portion 661a of the cleaning water supplying nozzle 661 is swiveled about the axis of the support portion 661b so that the front end of the nozzle portion 661a comes to a position directly above the center of the back side 21b of the silicon (Si) substrate 21 of the wafer 2 held on the spinner table 661. Thereafter, the electric motor 612 is operated to rotate the spinner table 611 at a rotational speed of 800 rpm, for example, and the cleaning water supplying means 660 is operated to supply a cleaning water from the nozzle portion 661a of the cleaning water supplying nozzle 661 to the back side 21b of the silicon (Si) substrate 21. The nozzle portion 661a is preferably provided by a so-called two-fluid nozzle such that about 0.2 MPa of water and about 0.3 to 0.5 MPa of air are supplied and the water is sprayed by the pressure of the air to effectively clean the back side 21b of the silicon (Si) substrate 21 of the wafer 2. At this time, the electric motor 662 is operated to swing the nozzle portion 661a of the cleaning water supplying nozzle 661 in a required angular range from the center of the wafer 2 to the outer circumference thereof. As a result, the back side 21b of the silicon (Si) substrate 21 of the wafer 2 can be reliably cleaned.
After performing the cleaning step mentioned above, the rotation of the spinner table 611 is stopped and the cleaning water supplying nozzle 661 is retracted to the standby position. Thereafter, the spinner table 611 is raised to the load/unload position shown in
The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
Number | Date | Country | Kind |
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2011-075083 | Mar 2011 | JP | national |