JP3957536B2 - Etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an etching apparatus and an etching method suitable for use in manufacturing a semiconductor device.
[0002]
[Prior art]
A semiconductor device having a wafer level CSP (Chip Size Package) structure in which the sizes of a chip and a package are equal is known. In this type of semiconductor device, as shown in FIG. 4A, after a plurality of connection pads (aluminum electrodes) 2,..., 2 are formed on the surface (circuit surface) side of a wafer (semiconductor substrate) 1, An insulating film 3 made of silicon oxide or the like is formed so that a central portion of each connection pad 2 is opened. Thereafter, as illustrated in FIG. 4B, the protective film 4 is formed on the upper surface side of the insulating film 3 so that the central portion of each connection pad 2 is opened.
[0003]
Next, as illustrated in FIG. 4C, a seed layer 5 is formed on the central portion of each connection pad 2 and the protective film 4. When the seed layer 5 made of copper is formed directly on the protective film 4 by sputtering, adhesion is insufficient, and therefore a titanium (Ti) film 5a having a thickness of 1600 to 1700 mm is usually formed on the protective film 4. After that, a copper (Cu) film 5b is formed and a seed layer 5 is provided.
After that, as shown in FIGS. 5A and 5B, the metal layer (copper Cu layer) formed on the seed layer 5 is etched by electrolytic plating to form the rewiring 6, and further As shown in (c), columnar electrodes 7 are provided at predetermined locations on each rewiring 6. The columnar electrode 7 has a thickness of, for example, about 100 to 150 μm and is coated and cured with a photoresist for electrode formation, and an opening that exposes a predetermined portion of the rewiring 6 is formed, and electrolytic plating is performed in the opening. Is formed.
[0004]
After the rewiring 6 and the columnar electrode 7 are formed, unnecessary seed layers 5 (titanium Ti film 5a and copper Cu film 5b) are removed by etching (FIG. 6A). After the structure shown in FIG. 6A is formed in this way, the entire circuit surface side of the wafer 1 is covered with a resin such as epoxy or polyimide so as to cover the columnar electrode 7 as shown in FIG. The sealing resin layer 8 is formed by molding with a material.
Then, the upper surface side of the sealing resin layer 8 is polished to expose the end face of the columnar electrode 7, and solder balls are formed on the end face as shown in FIG. Divide into chips. As a result, a semiconductor device having a wafer level CSP structure in which the sizes of the chip and the package are equal is manufactured.
[0005]
[Problems to be solved by the invention]
Incidentally, in the manufacturing process described above, there are a wet etching method and a dry etching method as a method for removing the titanium Ti film 5a. In the wet etching method, as the number of wafers to be processed increases, the etching time changes due to an increase in the temperature of the etching solution, making the process management difficult, and the dry etching method is difficult because the management of the etching solution becomes complicated. Often used.
[0006]
As dry etching using low-temperature plasma, helicon etching and reactive ion etching are known. The etching rate when the titanium Ti film 5a is subjected to helicon etching using carbon tetrafluoride (CF ₄ ) gas under a standard apparatus configuration and recipe is about 700 Å / min. On the other hand, when the titanium Ti film 5a is subjected to reactive ion etching using carbon tetrachloride (CCl ₄ ) gas, the etching rate is about 500 Å / min, and there is a problem that the throughput is low.
[0007]
In addition, the process pressure is 0.5 Pa in the helicon etching type apparatus, and the process pressure is 4 Pa in the reactive ion etching type apparatus, and all of them use a high vacuum exhaust system such as a turbo molecular pump, an oil diffusion pump or a cryopump. In addition, the load lock chamber is indispensable in order to maintain a high vacuum in the chamber, resulting in a disadvantage that the equipment is expensive.
[0008]
Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide an etching apparatus and an etching method capable of etching a titanium Ti film with high throughput while the apparatus equipment is inexpensive. .
[0009]
[Means for Solving the Problems]
To achieve the above object, the etching method according to claim 1 is an etching method for etching a titanium Ti film formed on a protective film made of polyimide, wherein the protective film is formed on a semiconductor substrate, A semiconductor device in which a titanium Ti film for forming a wiring is formed on the protective film is prepared, and a mixed gas composed of only carbon tetrafluoride CF ₄ and oxygen O ₂ is used as a reaction gas , and carbon tetrafluoride CF _When the flow rate of ₄ is X, the flow rate of oxygen O ₂ is Y, and the flow rate ratio Z of oxygen O ₂ is Z = {Y / (X + Y)} × 100 (%), the flow rate ratio Z of oxygen O ₂ under a predetermined process pressure Is an etching process in which the titanium Ti film of the semiconductor device mounted in the chamber is mixed in a range of 3 to 20% by a down-flow method using the reaction gas, and the etching is performed after the etching is completed. While maintaining Seth pressure, characterized by comprising: a replacement step of replacing the inside of the chamber by a gas other than the reaction gas.
The invention according to claim 2 is characterized in that the process pressure is at least 65 Pa or more.
The invention according to claim 3 is characterized in that at least one of an inert gas and a nitrogen gas is further added to the reaction gas.
The invention according to claim 4 is characterized in that in the replacing step, the inside of the chamber is replaced with at least one of nitrogen gas and inert gas.
[0017]
In the present invention, a mixed gas of carbon tetrafluoride CF ₄ and oxygen O ₂ is used, the flow rate of carbon tetrafluoride CF ₄ is X, the flow rate of oxygen O ₂ is Y, and the flow rate ratio of oxygen O ₂ is Z = {Y / When (X + Y)} × 100 (%), a semiconductor device placed in the chamber using a reaction gas mixed within a flow rate ratio Z of oxygen O ₂ within a range of 3 to 20% under a predetermined process pressure Since the titanium Ti film formed on the protective film made of polyimide is plasma-etched by the downflow method, the titanium Ti film can be etched with high throughput. In addition, after the etching is completed, the inside of the chamber is replaced with nitrogen gas or an inert gas while maintaining the process pressure, so that the titanium fluoride, which is a reaction product of the etching, is discharged from the chamber while being gasified, and enters the chamber. It becomes possible to prevent the solidification and adhesion, and the maintainability of the etching apparatus can be improved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a plasma etching apparatus 100 according to an embodiment. The plasma etching apparatus 100 includes a plasma generation unit 10 and a chamber 20. The plasma generator 10 applies, for example, a 2.45 GHz microwave output from a microwave power source 11 such as a magnetron to the outer periphery of the quartz tube 13 via the waveguide 12, and reacts under a predetermined process pressure. Plasma discharge is performed by introducing a gas (described later) into the quartz tube 13.
[0019]
In the plasma generation unit 10, ions and radicals are generated by plasma discharge, but the ions lose energy in the process of passing through the quartz tube 13 and reaching the wafer 1 placed on the stage 20 a in the chamber 20, resulting in only radicals. Is a so-called down-flow type plasma etching that hits the wafer 1 along the flow of the reaction gas.
Downflow plasma etching is a method that is applied to those that do not require resolution, such as resist ashing, which removes the resist by ashing it. The amount of radicals generated by increasing the flow rate of the reaction gas at low vacuum This increases the etching speed, thereby realizing high-speed etching.
[0020]
Next, a process for etching a titanium Ti film at high speed using the down-flow type plasma etching apparatus 100 having such characteristics will be described.
The characteristic etching process according to the present invention is as follows. (1) The titanium Ti film is etched with a reaction gas in which carbon tetrafluoride CF ₄ and oxygen O ₂ are mixed, and the flow rate of carbon tetrafluoride CF ₄ (unit: sccm). ) Is X, the flow rate of oxygen O ₂ (unit: sccm) is Y, and the flow rate ratio of oxygen O ₂ is Z = {Y / (X + Y)} × 100 (%). ₂₎ The flow rate ratio Z of 3 to 20% and (2) after etching, the inside of the chamber 20 was replaced with nitrogen N ₂ gas while maintaining the above process pressure, and then purged with nitrogen to return to atmospheric pressure. Thus, the wafer 1 is taken out from the chamber 20. Hereinafter, these characteristic points will be described.
[0021]
(1) Points in which the flow rate ratio Z of oxygen O ₂ is 3 to 20% In the down-flow type plasma etching apparatus 100 shown in FIG. 1, the amount of CF ₄ added in the reaction gas (CF ₄ + O ₂ ) is changed. As a result of an experiment for measuring the etching rate of titanium (Ti) and polyimide (PI), as shown in FIG. 2, when O ₂ addition amount is 3% or less (CF ₄ addition amount is 97% or more), titanium is added. It has been found that the etching rate of polyimide PI increases when the etching rate of Ti decreases and the O ₂ addition amount is 20% or more (CF ₄ addition amount is 80% or less). Furthermore, looking at the selection ratio Ti / PI between titanium (Ti) and polyimide (PI), as shown in FIG. 3, the selection ratio becomes 7 or more in the region where the O ₂ addition amount is 3 to 20%. In this region, the amount of polyimide etched is small relative to the amount of titanium etched, and it can be seen that almost only titanium Ti can be selectively etched. Therefore, these experimental findings, the flow ratio of oxygen O ₂ suitable to selectively etch only the titanium was found to be 3-20% is optimal.
[0022]
(2) The point in which the inside of the chamber 20 is replaced with nitrogen under the process pressure after etching. When the titanium Ti film is etched using the reaction gas (CF ₄ + O ₂ ) to which oxygen O ₂ is added at the above flow ratio, the reaction product is fluorinated. Titanium fluoride (TiFx) and titanium oxide (TixOy) are generated. Although the generation amount of titanium oxide is slight and does not cause a problem, titanium fluoride is gasified at room temperature at a process pressure (for example, 147 Pa), and when the inside of the chamber 20 is rapidly purged with nitrogen after the etching step to return to atmospheric pressure, Since the boiling point of titanium fluoride is 284 ° C., it solidifies and adheres in the chamber 20. Therefore, if the inside of the chamber 20 is replaced with nitrogen gas N ₂ while maintaining the process pressure after the etching process is completed, the titanium fluoride is discharged from the chamber 20 while being gasified, and is prevented from solidifying and adhering in the chamber 20. be able to.
[0023]
Next, a specific process including the above feature points will be described. In the down-flow type plasma etching apparatus 100 shown in FIG. 1, the wafer 1 having a titanium Ti film (film thickness 1600 to 1700 mm) to be etched is set on the stage 20a in the chamber 20 and down-flowed under the following process conditions. Perform plasma etching.
<Process conditions>
Reaction gas: Carbon tetrafluoride (CF ₄ ) + Oxygen (O ₂ )
Gas flow rate: CF ₄ : 600 sccm, O ₂ : 32 sccm
(Equivalent to 5% O ₂ addition)
Microwave output: 2.7kW
Chuck temperature ... 120 ° C
Chamber temperature ... 65 ° C
Process pressure ... 147Pa
[0024]
After the etching is completed, the supply of the reaction gas is stopped, and while maintaining the process pressure (147 Pa), the nitrogen gas N ₂ is introduced into the chamber 20 at a flow rate of 300 sccm, and the state of nitrogen replacement is maintained for 15 seconds. Thereafter, the wafer 1 having been etched by carrying out nitrogen purge three times and returning the inside of the chamber 20 to atmospheric pressure is carried out.
According to such a process, the etching rate of the titanium Ti film reaches about 2130 Å / min), and when etching a titanium Ti film having a thickness of 1600 to 1700 Å, the required time is about 50 even if the over-etching time is taken into consideration. It will be about seconds. As a result, as compared with helicon etching with an etching rate of about 700 ｍｉｎ / min and reactive ion etching with about 500 Å / min, the processing time is reduced to about ３, so that high throughput can be realized.
[0025]
Further, since the down-flow type plasma etching apparatus 100 is used, the process pressure may be a low vacuum level of about 65 to 400 Pa for plasma discharge. For this reason, there is no need for equipment for maintaining a high degree of vacuum like a helicon etching system or a reactive ion etching system, and it is possible to cope with an inexpensive apparatus configuration.
[0026]
In the embodiment described above, a reaction gas in which carbon tetrafluoride CF ₄ and oxygen O ₂ are mixed is used. However, the present invention is not limited to this, and helium, neon, argon, krypton, xenon, etc. It is also possible to increase the etching rate by adding an inert gas or increasing the radical species generated by plasma discharge by adding nitrogen or both inert gas and nitrogen.
Furthermore, in the present embodiment, the inside of the chamber 20 is replaced with nitrogen while maintaining the process pressure after the etching is finished. However, the present invention is not limited to this, and an inert gas can also be used.
[0027]
【The invention's effect】
According to the first aspect of the present invention, a mixed gas composed of only carbon tetrafluoride CF ₄ and oxygen O ₂ is used as a reaction gas, the flow rate of carbon tetrafluoride CF ₄ is X, and the flow rate of oxygen O ₂ is Y. When the flow rate ratio of oxygen O ₂ is Z = {Y / (X + Y)} × 100 (%), the reaction gas mixed within a range of 3 to 20% of the flow rate ratio of oxygen O ₂ under a predetermined process pressure Since the titanium Ti film formed on the protective film made of polyimide of the semiconductor device mounted in the chamber is plasma-etched by the downflow method, the titanium Ti film can be etched with high throughput. In addition, after the etching is completed, the inside of the chamber is replaced with a gas other than the reaction gas while maintaining the process pressure, so that titanium fluoride, which is a reaction product by etching, can be prevented from solidifying and adhering in the chamber. Thus, the maintainability of the etching apparatus can be improved.
According to the invention described in claim 2, since the process pressure is set to at least 65 Pa or more, the equipment for maintaining a high degree of vacuum becomes unnecessary as in the case of the helicon etching method and the reactive ion etching method. An inexpensive apparatus configuration can be achieved.
According to the invention described in claim 3, since at least one of an inert gas and a nitrogen gas is further added to the reaction gas, the radical species generated by the plasma discharge is increased to increase the etching rate. Can be made.
According to the invention described in claim 4, since the inside of the chamber is replaced with at least either nitrogen gas or inert gas after the etching is completed, the cost of the gas used for replacement can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a plasma etching apparatus 100. FIG.
FIG. 2 is a diagram showing results of an experiment in which the etching rate of titanium Ti and polyimide PI is measured by changing the amount of CF ₄ added to the reaction gas (CF ₄ + O ₂ ) in the plasma etching apparatus 100 shown in FIG. is there.
FIG. 3 is a diagram showing a selection ratio Ti / PI of titanium Ti and polyimide PI obtained from the experimental result shown in FIG. 2;
FIG. 4 is a cross-sectional view showing a manufacturing process of a semiconductor device having a wafer level CSP structure.
FIG. 5 is a cross-sectional view showing a manufacturing step that follows FIG. 4;
6 is a cross-sectional view showing a manufacturing step that follows FIG. 5; FIG.
[Explanation of symbols]
1 Wafer 10 Plasma Generator 11 Microwave Power Supply 11
12 Waveguide 13 Quartz tube 20 Chamber

Claims (4)

An etching method for etching a titanium Ti film formed on a protective film made of polyimide,
A semiconductor device is prepared in which the protective film is formed on a semiconductor substrate, and a titanium Ti film is formed on the protective film to form a wiring.
A mixed gas consisting of only carbon tetrafluoride CF ₄ and oxygen O ₂ is used as a reaction gas, the flow rate of carbon tetrafluoride CF ₄ is X, the flow rate of oxygen O ₂ is Y, and the flow rate ratio of oxygen O ₂ is Z = {Y / (X + Y)} If you × 100 (%) and the placed in the chamber with the reaction gas flow ratio Z of the oxygen O ₂ are mixed in the range of 3-20% at a predetermined process pressure and etching step of plasma etching in a down-flow manner the titanium Ti film of a semiconductor device,
After the etching is completed, while maintaining the above process pressure, a replacement process for replacing the inside of the chamber with a gas other than the reaction gas,
Etching method characterized by comprising. Said process pressure, etching method of claim 1, wherein the at least 65Pa or more. Wherein the reaction gas further etching method according to claim 1, wherein the addition of at least one inert gas or nitrogen gas. The substitution process, etching process of claim 1, wherein replacing the chamber with one of at least a nitrogen gas or an inert gas.

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