JPH01243528A - Surface treatment - Google Patents

Abstract

PURPOSE:To enhance the performance of an element by a method wherein at least one kind out of hydrogen fluoride, ammonium fluoride and hydrofluorosilicic acid and a weak-acid nonaqueous solvent are used as an etching solution in order to remove an impurity without corroding a metal wiring part. CONSTITUTION:A substrate to be treated having a wiring layer 12 of a metal (e.g., aluminum) or a metal alloy (e.g., an aluminum alloy) which has been treated by dry etching or the like and to which an impurity containing a metal has adhered on the surface is immersed in an etching solution; its impurity 14 is removed. During this process, as this etching solution, an etching solution which contains at least one kind out of hydrogen fluoride, ammonium fluoride and hydrofluorosilicic acid and a weakly acidic nonaqueous solvent (e.g., an organic fatty acid such as glacial acetic acid or the like or phenol) and whose water content is 20% or lower in terms of its volume ratio is used. Then, the impurity 14 such as aluminum oxide, aluminum hydroxide or the like can be removed without corroding the wiring layer 12. By this setup, the performance of an element can be enhanced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a surface treatment method for removing impurities from the surface of a substrate to be treated, and in particular to a method for treating metal wiring used in semiconductor integrated circuit elements. The present invention relates to a surface treatment method for removing oxides etc. remaining on the surface.

(Prior Art) Conventionally, in the manufacturing process of semiconductor integrated circuit elements, the following process is used to form wiring between elements. That is, after depositing a metal thin film such as aluminum, a resist pattern is formed thereon.

Next, reactive ion etching (
After the pattern is transferred to the metal thin film by microfabrication using RIE) or the like, the resist is removed by plasma ashing.

When observing the surface after removing the resist, there may be residues standing vertically from the edges of the remaining metal thin film. This is due to aluminum sputtered due to ion bombardment during RIE re-attaching to the side walls of the resist.
It reacts with carbon in the resist and oxygen in the atmospheric gas during plasma ashing to form stable compounds such as aluminum oxide and aluminum hydroxide. Since such residue is brittle and easily peeled off, it becomes dust that re-adheres to the entire wafer as the process progresses, significantly deteriorating the characteristics of the integrated circuit elements.

On the other hand, in the multilayer wiring process, after forming a first layer wiring made of aluminum or the like, silicon oxide or the like is deposited as an interlayer insulating film, a contact hole is opened in this, and a second layer wiring material is deposited. At this time, a natural oxide film existing on the surface of aluminum, which is the underlying first layer wiring, becomes a factor that increases the wiring resistance.

Therefore, these oxides and carbides must be removed by some kind of cleaning process. Conventionally, the method used to remove it is to dissolve it using a dilute aqueous hydrofluoric acid solution. However, since aluminum itself is more easily dissolved in acid than oxides or carbides, there is a problem in that part of it is corroded during the cleaning process. Furthermore, recently, alloys such as aluminum-silicon-copper are sometimes used as aluminum alloys for wiring. Addition of copper has the effect of preventing electromigration, in which aluminum atoms move with electric current, and improves the reliability of wiring. However, in an electrolyte aqueous solution such as a hydrofluoric acid aqueous solution, there is a large difference in redox potential between aluminum and copper, which causes a problem in that batteries are formed locally and the dissolution of aluminum progresses extremely quickly.

Additionally, attempts have been made to remove etching residues and natural oxide films by sputtering using an inert gas such as argon, but since a strong electric field is applied to the underlying element, for example, M
There is a problem of deterioration of characteristics, such as dielectric breakdown of the dielectric films of OS transistors and MOS capacitors.

(Problem to be solved by the invention) As described above, with conventional surface treatment methods, it is difficult to remove oxides and carbides attached to the surface without damaging metal wiring such as aluminum, which is highly reactive and prone to corrosion. Met.

The present invention was made in consideration of the above circumstances, and its purpose is to be able to remove oxides and carbides attached to the surface without damaging the metal wiring, and to be suitable for cleaning treatment after dry etching. The objective is to provide a suitable surface treatment method.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to use an etching solution that does not attack metals such as aluminum and selectively dissolves oxides and carbides.

That is, in the present invention, a substrate to be processed, which has been processed by dry etching or the like and has a wiring layer of a metal (for example, aluminum) or a metal alloy (for example, an aluminum alloy) on the surface of which impurities containing metal have adhered, is immersed in an etching solution. In the surface treatment method for removing impurities, the etching solution contains at least one of hydrogen fluoride, ammonium fluoride, and silicofluoric acid and a weakly acidic nonaqueous solvent (for example, an organic fatty acid such as glacial acetic acid or phenol), Preferably, the method uses an etching solution having a water content of 20% or less by volume.

(Function) Aluminum oxide (AN 203 ) or aluminum hydroxide (An) (OH) 3 ), which is the main component of the residue generated after dry etching aluminum, contains hydrogen fluoride, ammonium fluoride, silicofluoric acid, etc. For example, according to the following reaction formula, 8Ω20. +12HF→2H3AρF6 +3H208Ω(OH)3 + 6 HF -H3AgF2 +3
Make H20 aluminum, hydrofluoric acid or its hydrate. This compound has the property of being soluble in polar solvents such as water and organic carboxylic acids.

On the other hand, metal aluminum does not react with molecular hydrogen fluoride, but reacts with hydrogen ions in the solution and dissolves.

1) +3H+ →AΩ ”+ (3/2)H2↑Also, when a metal with a higher electrode potential than Ag, such as A,1)-3i-Cu, coexists, a local battery is formed in the electrolyte solution. Since the potential of Ag becomes high, the reaction Ap -> A, Q"+3e- is promoted, and at the same time as the dissolution of AI progresses, hydrogen is generated on the Cu surface by the reaction 2H"+2e-=H2↑.

All of these corrosion reactions of metal aluminum are reactions with hydrogen ions in a solution. Therefore, if the ionization of hydrogen fluoride is suppressed, corrosion of aluminum can be suppressed. In a solution, hydrogen fluoride has an equilibrium relationship expressed by the following formula, %, but in an acidic solution, the equilibrium shifts to the left. That is, H, which is a non-aqueous polar solvent such as an organic carboxylic acid,
Dissociation of F, NH4F, and H2S i F6 is suppressed.

Therefore, according to the present invention, impurities such as aluminum oxide and aluminum hydroxide can be removed from aluminum by using at least one of hydrogen fluoride, ammonium fluoride, and silicic acid and a weakly acidic non-aqueous solvent as an etching solution. It is possible to remove the metal wiring without corrosion.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a cross-sectional view showing the process of forming aluminum interconnections using a method according to an embodiment of the present invention. First, Figure 1 (a
), Ag was deposited on a silicon wafer (not shown) on which a silicon oxide film 11 was previously formed as an insulating layer.
A thin film 12 of 1 μm thick made of -8i (1%) alloy is formed by sputter deposition. Thereafter, as shown in FIG. 1(b), a mask 13 corresponding to the wiring pattern is formed on the thin film 12 using a photoresist.

Next, as shown in FIG. 1(C), the thin film 12 is selectively etched by RIE. A parallel plate dry etching device was used for this etching, the gas used for etching was chlorine, the pressure inside the container was 5 Pa, and the density of the high frequency power (13.5 MHz) applied to the cathode was IW.
/c (.Next, the resist mask 13 was removed by plasma ashing in oxygen gas and observed with a scanning electron microscope. As shown in FIG. 1(d), the aluminum wiring (thin film 12 ) remnant 1 standing vertically from the edge of
It was confirmed that 4 remained.

Next, the present invention is applied to the sample to perform impurity cleaning treatment. First, a 49% aqueous solution of hydrogen fluoride (HF) with a purity of 9
Dissolved in 9.9% glacial acetic acid (CH3C00I+) and IF
A solution of CH3C0OH at a dilution rate of 40 times was prepared and used as an etching solution. The sample shown in FIG. 1(d) was immersed in this etching solution for 10 minutes, then washed with ethyl alcohol and alcohol, and then dried. As shown in FIG. 1(e), the residue 14 was completely removed, and no corrosion of the Aρ alloy thin film 12 itself was observed.

FIG. 2 is a characteristic diagram showing the relationship between the time required to remove the residue 14 using this etching solution, the corrosion rate of Ap itself, and the dilution rate with CH3C0OH. At a dilution rate of 10 times, the time required for removal is 1 minute. On the other hand, AI
The corrosion rate is 100 people/min, and only 100 people of All are corroded during removal. In addition, when the dilution rate is 640 times, it takes 100 minutes to remove the residue, but A
[Since the corrosion rate is as low as 3 people/min, the AJ
) is only 300 people, and corrosion can be virtually ignored.

On the other hand, FIG. 3 is a characteristic diagram showing the relationship between the dilution rate, the removal time of the residue 14, and the corrosion rate of Aj when an HF aqueous solution is used. For the same dilution rate, the removal time of the residue is approximately the same as for the Clh C00tl solution, but the corrosion rate of 1 is about 10 times greater, making the corrosion during removal not negligible.

FIG. 4 shows the relationship between the water content in the etching solution and the corrosion rate of A and Q. When the water content exceeds 20%, the corrosion rate increases rapidly. Therefore, the effectiveness of the present invention is exhibited when the water content is 20% or less. In addition, although the corrosion rate of Afi is plotted in FIGS. 2 to 4, it is approximately the same in the case of AΩ alloy.

Thus, according to this embodiment, A after being processed by RIE
A sample with a wiring layer made of 9 alloys was prepared using HF, CH, and C.
By processing with an etching solution containing 0OH, it is possible to reliably remove the residue adhering to the surface without causing corrosion of the wiring layer. Therefore, it is possible to improve the reliability of the wiring layer, and it is possible to contribute to improving the characteristics of semiconductor integrated circuit elements.

Next, we will discuss the fifth example of applying the present invention to multilayer wiring formation.
This will be explained using figures. First, as in the previous embodiment, a first layer wiring 52 of aluminum is formed on a silicon oxide film 51, as shown in FIG. 5(a). Next, as shown in FIG. 5(b), a silicon oxide film 53 is formed using the CVD method.
After depositing as an interlayer insulating film, a contact hole 54 is opened using the RIE method.

Next, before depositing the second layer wiring material, in order to remove the natural oxide film 55 present on the surface of the first layer wiring 52 made of aluminum, an acetic acid solution containing 5% silicic acid was used for 3 minutes. Soaked. Thereafter, after cleaning with ethanol, it was placed in a sputter deposition container, and a second layer of aluminum film 56 was deposited thereon. After drying, the sample was treated with dry nitrogen until it was introduced into the sputtering container in order to prevent the natural oxide film from growing again.

The resistance between the first and second layer wirings formed in this manner was measured. As a result, the contact resistance was 0.1Ω/μm2 or less. On the other hand, when the natural oxide film was not removed, the contact resistance was 2Ω/μm2, and it was confirmed that the contact resistance could be reduced to 1/20 or less by this treatment.

Here, the reason why silicofluoric acid is used in this embodiment is to prevent the vapor-phase grown 5i02 film used as the interlayer insulating film 53 from being etched. Silicic acid is HF and 5in2
Since it is a compound produced by the reaction, it hardly dissolves 5in2. Furthermore, washing with ethanol without using water after immersion in the etching solution has the effect of preventing corrosion due to hydrogen fluoride remaining during washing. The subsequent drying is
It is desirable to carry out the process in dry nitrogen at a temperature of 250° C. or higher for 30 minutes or longer.

Further, although aluminum is used as the second metal wiring layer in this embodiment, it is also effective when using tungsten or the like, for example. A tungsten thin film can be selectively grown on a metal using a CVD method using tungsten hexafluoride (WF6) gas, but a natural oxide film on aluminum hinders such selective growth. If the present invention is used to remove the native oxide film in advance and then such selective growth is performed, the effect is tremendous.

Note that the present invention is not limited to the methods of each embodiment described above. For example, as the etching agent, in addition to hydrogen fluoride and silicic acid, ammonium fluoride or a mixture thereof may be used. That is, any compound that contains F and H and becomes acidic in an aqueous solution may be used. Furthermore, as a solvent, CH3
In addition to COO11, organic acids such as phenol, carboxylic acids,
Various other non-hydroxy acidic solvents can be used. In addition, in this example, after etching aluminum, 02
Impurities are removed after the etching mask is removed using a plasma ashing method. This method is advantageous in that at least impurities attached to the side walls of the mask are dissolved from both the front and back sides.

However, impurities may harden further during plasma ashing and become difficult to dissolve. The order of these steps may be changed as appropriate depending on the dry etching conditions, the composition of the aluminum alloy, the material of the etching mask, etc. Also,
The wiring layer is not limited to aluminum or aluminum alloys, but can be applied to metals or alloys that are corroded by cleaning solutions such as dilute hydrofluoric acid aqueous solution for removing residual materials.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, thin metal oxides and carbides on the surface can be removed without corroding the metal itself. Therefore, if the present invention is applied to the manufacture of integrated circuit devices, the amount of dust generated will be reduced, the yield rate will be improved, and the resistance between interconnects in multilayer wiring will be reduced, improving the performance of the device.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the wiring forming process according to an embodiment of the present invention, FIG. Figure 3 is a characteristic diagram showing the removal time of deposits and the corrosion rate of Al when H2O is used as a solvent, and Figure 4 is a characteristic diagram showing the relationship between the water content in the etching solution and the corrosion rate of Ap. , and FIG. 5 are cross-sectional views showing a multilayer wiring forming process according to another embodiment of the present invention. 11.51.53...Silicon oxide film, 12...Aluminum alloy thin film, 13...Photoresist mask, 14...Residue, 52...Aluminum alloy thin film (first layer wiring), 54・・・Contact hole, 55・
...Natural oxide film, 56...Second layer wiring. Applicant's agent Patent attorney Takehiko Suzue 91 Figure 1 Figure 1 Get St! @ #1M? ! -Open (r)--Side wall Izushil t' left, Arro 1h agony (Zukeu-H20/(H2
0+CH3CO0H)('/Q)→Figure 4Figure 5

Claims (5)

[Claims] (1) A substrate to be processed having a metal or metal alloy wiring layer on which impurities containing metal elements have adhered is treated with at least one of hydrogen fluoride, ammonium fluoride, and silicofluoric acid and a weakly acidic non-aqueous solvent. A surface treatment method characterized by removing the impurities by immersion in an etching solution containing the impurities. (2) The surface treatment method according to claim 1, wherein the wiring layer is made of aluminum or an aluminum alloy. (3) The surface treatment method according to claim 1, wherein the etching solution has a water content of 20% or less by volume. (4) Claim 1 characterized in that an organic fatty acid such as glacial acetic acid or phenol is used as the weakly acidic non-aqueous solvent.
Surface treatment method described. (5) A substrate to be processed having a wiring layer of aluminum or aluminum alloy that has been selectively etched by dry etching using an etching mask and has impurities including aluminum attached to the surface is immersed in an etching solution to remove impurities on the surface. In the surface treatment method for removing, the etching solution contains at least one of hydrogen fluoride, ammonium fluoride, and silicic acid, and a weakly acidic nonaqueous solvent, and has a water content of 20% or less by volume. A surface treatment method characterized in that the substrate to be treated is immersed in the etching solution before or after removing the etching mask.