JP3798760B2 - Method for forming semiconductor wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a semiconductor wafer, and more particularly to a forming method for forming bump electrodes serving as electrical contacts on a circuit forming surface of a semiconductor wafer.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the improvement in performance and size and thickness of portable electronic devices such as IC cards, mobile phones, and PDAs, many surface mounting methods that can mount various electronic components on the surface of a substrate have been adopted. In the case of manufacturing such a surface mounting type electronic device, a step for forming bumps for electrodes is provided in the course of a wafer process.
[0003]
4 and 5 show a semiconductor wafer manufacturing process centering on the formation of a conventional bump electrode. Here, FIG. 4 shows a bump forming process, and FIG. 5 shows a back grinding process. In the bump formation step shown in FIG. 4, a gold vapor deposition film 3 is formed on the circuit formation surface 2 of a semiconductor wafer (wafer 1) sliced to a predetermined thickness using UMB (under metal bump) sputtering (step). a, b). Then, a resist film 4 is formed on the gold vapor deposition film 3 (step c), and a photoresist film 5 on which a bump formation pattern is drawn is deposited on the resist film 4 (step d). Next, an exposure process (step e) is performed by irradiating the photoresist film 5 with laser light or ultraviolet rays, and then a portion other than the masked with the photoresist film 5 is removed by etching. The bump electrode 7 is formed on the circuit forming surface 2 of the wafer 1 (step f).
[0004]
As shown in FIG. 5, the wafer 1 on which the bump electrode 7 is formed has the bump electrode 7 forming surface placed on a work table 8 for back grinding, and is opposite to the bump electrode 7 forming surface. The back surface 9 is pressed while rotating the back grinder 10, and is ground to a predetermined thickness to reduce the thickness (steps g and h).
[0005]
[Problems to be solved by the invention]
However, in the method in which the bump electrode 7 is formed on the wafer 1 and then the process proceeds to the back grinding process and the entire wafer 1 is ground thinly, the bump forming surface is rubbed against the work table 8 during the back grinding process. There is a problem that the shape of the formed bump electrode 7 is crushed.
[0006]
In addition, in a wafer thinned to a certain thickness (500 μm or less), the wafer may be warped or distorted without being able to withstand the load in the back grinding process or the bump forming process. For this reason, the shape of the bump electrode formed previously may be distorted or crushed.
[0007]
When the above problems occur, the wafer 1 itself is damaged, and the formation of the bump electrode 7 is also adversely affected such that the processing accuracy is deteriorated.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a semiconductor wafer in which bumps for electrodes having a constant shape are formed with high accuracy and speed by suppressing warpage and curvature associated with thinning of the semiconductor wafer. .
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, a method for forming a semiconductor wafer according to the present invention includes : placing a semiconductor wafer on a work table to be polished so that a surface side having a circuit forming surface of the semiconductor wafer is in contact; The back surface of the semiconductor wafer is polished to reduce the thickness, and a protective member made of quartz glass, metal or silicon is attached to the back surface of the thinly processed semiconductor wafer, and then the bump electrode portion is formed on the circuit forming surface of the semiconductor wafer. The back surface of the semiconductor wafer is exposed by peeling the protective member from the back surface of the semiconductor wafer after forming the bump electrode portion .
[0010]
According to the present invention, after the semiconductor wafer is thinned to a predetermined thickness in the polishing process, a protective member having a certain thickness and strength is adhered to the back surface of the semiconductor wafer, so that bump formation is performed thereafter. It is possible to prevent warping or bending of the semiconductor wafer in the process. For this reason, in the bump forming process, even if a mechanical load is applied to the semiconductor wafer or a temperature variation occurs, the bump electrode can be formed with high accuracy. Further, when the bump forming process is performed after a process in which a large load is applied to the semiconductor wafer, such as polishing, a problem such as a collapse of the previously formed bump electrode does not occur.
[0011]
In addition, since quartz glass is used as the protective member to be attached to the semiconductor wafer, resistance to impact and temperature change is increased, so that the semiconductor wafer can be further reduced in thickness.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for forming a semiconductor wafer according to the present invention will be described with reference to the accompanying drawings. 1 to 3 are process diagrams showing the flow from the back grinding process of a semiconductor wafer to the formation of bump electrodes.
[0013]
The method for forming a semiconductor wafer in the present embodiment is a process in which there are a number of semiconductor wafers (hereinafter simply referred to as wafers), and is centered on processes related to the formation of bump electrodes. This series of processes includes a back grinding process for polishing a wafer to a constant thickness, a protective member attaching process for attaching a reinforcing protective member to the wafer, and a bump forming process for forming electrode bumps on the wafer surface. And a protective member peeling step. The operations in the series of steps are performed under a certain decompression condition in which the temperature and humidity are controlled so that the wafer being processed does not become dusty or deforms due to changes in temperature or humidity.
[0014]
In the back grinding process, an operation of polishing and flattening the back surface of the wafer on which the circuit forming surface is formed in a pre-processing process (not shown) is performed. Here, as shown in FIG. 1 (steps a and b), the circuit forming surface 22 of the wafer 21 is covered with a protective sheet (not shown) and placed on the work table 28 with the circuit forming surface 22 facing down. The back grinder 10 is pressed against the back surface 29 of the wafer 21 while rotating, and the wafer 21 is uniformly polished to a predetermined thickness. By this back grinding process, the wafer 21 is usually polished from a thickness of about 500 μm to a thickness of about 250 μm. However, when used for a product corresponding to a reduction in thickness, it can be polished to about 30 μm. is there.
[0015]
In the next protective member attaching step, a glass substrate as a protective member is attached to the back surface 29 of the wafer 21 that has been thinned in the back grinding step. In attaching the glass substrate, first, a resist film 31 is formed on the back surface 29 of the thinned wafer 21 (step c). Then, a wax 32 as an adhesive is uniformly applied to the surface on which the resist film 31 is formed (step d). The wax 32 is a liquid material made of a material in which a resin and alcohol are mixed, and can maintain a certain adhesive force even at a high temperature of about 200 ° C. after solidification. Subsequently, the glass substrate 33 is placed on the surface coated with the wax 32 and pressed to join the wafer 21 (step e). The glass substrate 33 is formed in a plate body having the same diameter as the wafer 21 to be adhered or a size larger than that, and quartz glass having a thickness of about 1000 μm is used. Such quartz glass can suppress the occurrence of deformation, corrosion and the like against external impacts and temperature fluctuations applied during the wafer process. In order to increase the adhesion to the glass substrate 33, the wafer 21 is heated to 100 to 130 ° C. to soften the wax 32, and an equal pressure is applied so that bubbles do not enter the bonding surface. Do it while hanging.
[0016]
In the bump forming step shown in FIG. 2, the wafer 21 with the adhered glass substrate 33 is placed on a work table (step f), and a gold deposited film is formed on the circuit forming surface 22 exposed on the upper surface by UMB sputtering. 23 is formed (step g). The gold vapor deposition film 23 is a base member for the bump electrode and has good conductivity. Next, a resist film 24 is formed on the gold vapor deposition film 23 (step h), and a photoresist film 25 having a bump electrode pattern formed thereon is deposited thereon (step i). Then, the photoresist film 25 and the photoresist film 25 other than the bump electrode pattern are removed by irradiating the photoresist film 25 with laser light or ultraviolet light and performing exposure (step j). Subsequently, etching is performed leaving a portion masked by the resist film 24 and the photoresist film 25. Finally, the resist film 24 and the photoresist film 25 remaining on the bump electrode 27 are removed cleanly to expose the bump electrode 27 on the upper surface (step k).
[0017]
In the protective member peeling step shown in FIG. 3, the glass substrate 33 is peeled from the wafer 21 on which the bump electrodes 27 are formed in the bump forming step (step l). In this peeling operation, the wax 32 present between the glass substrate 33 is melted and then gently peeled off so as not to damage the surface of the wafer 21. Finally, the process moves to the cleaning process of the wafer 21, and the wax 32 and minute dust remaining after the glass substrate 33 is peeled off are washed away (process m). The wafer 21 that has undergone such a series of steps shifts to a post-processing step such as a dicing step or an assembly step, and individual semiconductor chips are formed.
[0018]
As described above, by providing the protective member attaching step during the transition from the back grinding step to the bump forming step, the thinly ground wafer 21 can be reinforced, and subsequent bump forming processing is easy. It became. In the conventional forming method, when the wafer thickness is 250 μm or less, the defective formation rate of the bump electrode is increased, so that the thinning is limited. However, according to the forming method of the present invention, it is possible in the back grinding process. The bump electrode can be formed with high accuracy even for a thickness of about 30 μm. In addition, by performing the bump forming process after the back grinding process, it is possible to reduce bump formation defects such as variations in the shape of the formed bumps or deformation.
[0019]
In the above embodiment, the raw material constituting the wafer is silicon. However, the present invention can be applied to wafers made of oxides such as selenium and germanium in addition to silicon, and the size of the wafer is not limited. .
[0020]
In this embodiment, quartz glass is used for the protective member to be attached to the wafer, but metal or silicon can be used without any problem as long as the material has the same strength and thickness without using such quartz glass. can do.
[0021]
【The invention's effect】
As described above, according to the method for forming a semiconductor wafer according to the present invention, when a back grinding process or a bump electrode forming process is performed on the semiconductor wafer, a reinforcing support member is attached to the semiconductor wafer. Therefore, there is no deformation due to impact or temperature change during the back grinding operation or bump forming operation. For this reason, it is possible to mass-produce semiconductor chips having a stable quality while being thin.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a back grinding process and a protective member attaching process in a method for forming a semiconductor wafer according to the present invention.
FIG. 2 is an explanatory view showing a bump forming step in the semiconductor wafer forming method.
FIG. 3 is an explanatory view showing a protective member peeling step in the method for forming a semiconductor wafer.
FIG. 4 is an explanatory view showing a bump forming step in a conventional method for forming a semiconductor wafer.
FIG. 5 is an explanatory view showing a back grinding process in the conventional method for forming a semiconductor wafer.
[Explanation of symbols]
21 Wafer 22 Circuit formation surface 23 Gold vapor deposition film 24 Resist film 25 Photoresist film 27 Bump electrode 32 Wax 33 Glass substrate (protective member)

Claims (3)

After placing the semiconductor wafer on the workbench to be polished so that the surface side having the circuit forming surface of the semiconductor wafer is in contact, the back surface of the semiconductor wafer is polished to reduce the thickness, and this thinly processed semiconductor wafer After attaching a protective member made of quartz glass, metal or silicon on the back surface of the semiconductor wafer, a bump electrode portion is formed on the circuit forming surface of the semiconductor wafer, and after forming the bump electrode portion, the protective member is applied from the back surface of the semiconductor wafer. A method of forming a semiconductor wafer , wherein the back surface of the semiconductor wafer is exposed by peeling . After the semiconductor wafer is placed so that the surface side having the circuit forming surface of the semiconductor wafer is in contact with the work table to be polished, a back grinding process for polishing the back surface of the semiconductor wafer to reduce the thickness, A protective member attaching step for attaching a protective member made of quartz glass, metal or silicon ; a sputtering step for forming gold plating from the surface side of the semiconductor wafer; and a photoresist step for forming an electrode pattern on the gold plating; A method for forming a semiconductor wafer , comprising: a bump forming step for forming a bump electrode on the electrode pattern; and a protective member peeling step for peeling the protective member after the bump electrode is formed . 3. The semiconductor wafer formation according to claim 1, wherein the protective member is attached via a resist film formed on a back surface of the thinly processed semiconductor wafer and an adhesive applied on the resist film. Method.

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