JP2726804B2 - Method for etching copper-containing devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device having a metallized region, and more particularly to a device having a copper metallized region.

[0002]

BACKGROUND OF THE INVENTION Many devices, such as multichip modules, printed wiring boards and hybrid integrated circuits, contain patterned copper areas. There is a clear trend in the fabrication of such devices to use increasingly finer patterns. That is, the thickness of the metallized line and the distance between the lines gradually decrease. At present, typical tips and spacings for integrated circuit substrates are 150 microns, 50-100 microns for ceramic substrates for multichip modules, and on the order of microns on silicon devices. The smaller the line thickness and spacing, the higher the density of components and active elements.

The manufacture of devices with copper-containing electrical interconnects, such as multi-chip modules and printed wiring boards, is described in G. K. Messner et al. Are the International Society for Hy
"The Thin-Film Multi-Chip Module", published in BridMicroelectronics, Reston, Virginia, 1992; Clark's Integrated Circuit Handbook, Van Nostrand Rei
nhold, New York, 1985, respectively. For certain substrates, such as silicon and ceramics, continuous deposition of an adhesion promoting metal or diffusion barrier metal to form a multilayer metallization is necessary for the interconnect to function as a whole. One approach to forming such devices is to deposit one or more continuous metal layers, place a mask such as a patterned polymer mask on the (these) layers, and expose the metal exposed through the mask openings. There is a method of removing a region by etching. Various etchants are used in this etching process. For example, hydrogen fluoride water is used for etching a titanium layer that is generally used as a lower adhesive layer, and hydrochloric acid or ammonia is used for etching a thicker copper layer, which is a part that mainly participates in carrying current. Or a solution of cupric chloride containing mainly the latter.

[0004]

Although these solutions are widely used, there are still problems in use as the spacing between the lines is reduced. Generally, these etchants remove material rapidly parallel to the substrate at a speed comparable to the desired direction that is perpendicular to the surface of the substrate.
The starting situation is shown in FIG. 1, where 2 indicates the mask material, 3 indicates the metal and 1 indicates the substrate. The etchant removes this material quickly in the direction of the substrate, but also etches underneath the masking material due to lateral etching. As a result, a shape as shown in FIG. 2 is obtained. Obviously, the greater the lateral etch, the greater the minimum linewidth obtained, which is disadvantageous. Further, as a result of the high etch rate, reproducibility is greatly reduced and line width control becomes more difficult. Therefore, it is generally desirable to create an etch process that has tighter control and less undercut.

[0005] This becomes even more critical when the metal structure to be etched includes multiple layers of different compositions. For example, metal patterns used in multi-chip modules to connect devices often use a copper upper layer with a lower metal layer such as a titanium layer, a palladium-doped titanium layer, or a continuous layer of palladium and titanium. I have. Even though sufficient etchants are obtained for each of the layers, etchants for one metal generally etch the other metal at a substantially different rate, resulting in less than entirely desirable results. . In addition, residue of one or more metals is often found in such situations. Palladium sandwiched between titanium and copper in the form of a metal or in the form of a titanium-palladium alloy is not removed by HF or by an ammoniacal copper etchant.

For example, in a metallized region having an upper copper layer 13 (FIG. 3) and a lower titanium layer 12 and masked by a material 14, an ammoniacal cupric chloride solution is used to etch said copper. Hydrogen fluoride aqueous etchant is used for etching the titanium. Etching of titanium with aqueous hydrogen fluoride after copper has been completely removed by the cupric chloride solution typically results in a large undercut of the titanium layer. The causes of this undercut are: 1) Since each metal is not sensitive to the etchant of the other metal, over-etching is required to complete the removal in each step; and 2)
The formation and retention of the passivated oxide by the copper etchant on the surface of the titanium requires an induction period to remove this layer, followed by a rapid etch-through and associated titanium undercut. One is given. As a result, the shape obtained after copper etching is as shown in FIG. 4 and the shape after titanium etching is as shown in FIG. The large undercut that occurs in this metal double layer is of course not desirable,
This limits line patterning density and module usefulness.

Several proposals have been made for etching a metallized region including two or more metal layers. For example, K. K. of August 24, 1982. L. No. 4,345,969 to James et al. And September 2, 1980.
Date M. A. US Patent No. 4,220,70 to Spack
As described in No. 6, concentrated inorganic acids having a strong oxidizing action are used in combination. However, such a combination places great restrictions on the composition of the substrate and the resist. There is a need for an etchant that can form copper lines with higher resolution and facilitates control of the etching of multilayer metal areas. It is also environmentally desirable to provide an etchant that can recover copper and recycle used etchants and that minimizes waste disposed of.

[0008]

By using an aqueous solution of cupric chloride containing an acid such as hydrofluoric acid and a chloride salt such as potassium chloride, copper-titanium and copper-palladium-titanium multilayer structures can be obtained. The improvement of the copper etching resolution and the reproducible control with respect to the etching of the multi-layered metal region become possible. As already mentioned, this result is quite surprising, given that HF etchants or cupric chloride etchants alone produce unsatisfactory results.

Therefore, by using the mixed solution, the etching rate of copper and titanium is set to a very close level,
It can be controlled, and a multi-layer metallization pattern can be formed with almost vertical side walls with good reproducibility even for a combined multi-metal structure.
There are no unacceptable residues such as palladium, which often occur in multilayer metals. Furthermore, the etchant solution can be easily recycled.

[0010]

DETAILED DESCRIPTION OF THE INVENTION As previously mentioned, an aqueous solution of cupric chloride containing an acid such as hydrofluoric acid in addition to cupric chloride, as well as chloride salts, can be used to etch multi-layer copper structures without undesirable undercuts. To form a fine-wire copper structure. The copper pattern is formed by various etching techniques as described in Clark's introduction above. The etching process of the present invention can generally be performed according to these techniques. Typically, the layer of copper material is formed by conventional techniques such as sputtering or electrodeposition. In a multi-layer structure, usually the lower layer (the lower layer, which in the present invention indicates the layer closer to the substrate) is first deposited by conventional techniques, and then the copper upper layer described above is formed. You. In order to etch the pattern, the material layer to be etched is covered with an energy-sensitive material such as a photoresist, the energy-sensitive material is patterned, an etch mask having a desired pattern is formed, and then the etch mask is contacted. Etching is performed.

In such an etching process, an aqueous solution is used as an etchant. The etchant is introduced by conventional techniques such as immersing the substrate with the etch mask in the etchant while spreading, or by spraying the substrate with the etchant or other means utilizing convection. Usually 5 layers are etched
Processed with an etchant for seconds to 10 minutes. In general, processing times greater than 10 minutes are undesirable because they can cause non-uniform results and slow process flow.
On the other hand, if the processing time is 5 seconds or less, various problems such as incomplete etching, poor reproducibility, and excessive undercut occur.

[0012] The composition of the etching solution must be controlled. The aqueous solution must contain cupric chloride. Usually cupric chloride in a concentration in the range of 0.2 to 2M is used. The etching rate of copper depends on the concentration of the cupric species, the concentration of the chloride and the concentration of the acid. Chloride salts (eg, NH ₄ Cl, NaCl,
KCl and LiCl) must be soluble in the etchant mixture and must not chemically react with the etchant components. The chloride salt concentration in the aqueous etchant must be in the range of 1 to 5M. Concentrations above 5M cause solubility problems and concentrations below 1M slow down the rate of etching. Usually, chloride salts such as potassium chloride and sodium chloride are used. The molar ratio of chloride salt to cupric chloride must be in the range of 1: 1 to 10: 1.

The titanium layer is etched with a hydrofluoric acid component typically used at a hydrofluoric acid concentration of 0.5 to 10% by weight. The exact composition used must be adjusted by adjusting the relative concentrations of the components so that no more than two orders of magnitude change occurs in the etch rate of each layer being etched.

After etching, it is usually desirable to rinse away any residual etchant with water. Although such rinsing is usually performed with caution, using the method of the present invention, no residue, such as a palladium-containing residue, is present after etching, which allows for an advantageous and clean process. .

The following example is provided to illustrate the present invention.

Example 1 Sufficient cupric chloride, potassium chloride and HF were added to water to produce a solution having a concentration of 0.66 M cupric chloride, 1 M potassium chloride, and 2.1 M hydrofluoric acid. 0.1
A 1 μm thick composite area of titanium and palladium was deposited over the entire major surface of the substrate. The top copper layer was deposited to a thickness of 2.5 μm (this substrate was all ceramic or all ceramic coated with a layer of dielectric polymer). , Exposed in a test pattern and developed by conventional techniques. Then, while maintaining the substrate in a vertical position, an etching solution was sprayed onto the patterned substrate for 35 seconds using a nozzle array to start etching. Next, the resist agent was removed using a standard resist stripper, and the formed pattern was inspected.

The copper undercut was calculated by subtracting the measured line width from the line width drawn in the photoresist.
m plus or minus 1.8 μm. (Line width was measured using an optical microscope.) This undercut was approximately equal to what is commonly observed in conventional processes.

The undercut of titanium was measured after first removing the upper copper layer with an alkaline copper etchant that did not act on the lower titanium layer. The undercut in the exposed titanium layer was calculated by subtracting this titanium linewidth measurement from the already measured copper linewidth, but the average of 69 or more measurements was essentially 0 or -0. 0.6 μm, plus or minus 0.8 μm. This undercut is 5.8 μm observed when the same process is performed using an ammoniacal copper chloride etchant for copper and then using an HF aqueous solution for titanium, and the values are ± 3.4 μm. Very good value. In addition, no residue was observed, and no leakage current was detected by the giga ohm meter.

[0019]

As described above, according to the present invention, by using a specific mixed solution as an etchant, it is possible to set and control the etching rate of copper and titanium to a very close level, and to obtain a multi-metal structure. However, the multilayer metallized pattern can be formed with almost vertical side walls with good reproducibility. There are no unacceptable residues, such as palladium, which often occur in multilayer metals, and the etchant solution can be easily recycled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a shape obtained by single-layer etching.

FIG. 2 is a diagram showing a shape obtained by single-layer etching.

FIG. 3 is a diagram showing a shape obtained by multilayer etching.

FIG. 4 is a diagram showing a shape obtained by multilayer etching.

FIG. 5 is a diagram showing a shape obtained by multilayer etching.

FIG. 6 shows the shapes and properties achieved in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Mask 3 Metal 11 Substrate 12 Titanium layer 13 Copper layer 14 Mask

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication H01L 21/308 H01L 21/306 F 21/3213 21/88 C (72) Inventor Barry Miller United States of America, 07974 New Jersey, Murray Hill, Fox Run 54 (72) Inventor Barbara Joyce Sapjeta United States of America, 07054 New Jersey, Parsippany, Redstone Drive 56 (72) Inventor Akshay Bajubhai Shah United States of America, 07922 New Jersey, Berkeley Heights, Killarney Drive 270 (72) Inventor Ken Matthew Takahashi United States, 07059 New Jersey, Warren, Old Sterling Road 24 (56) References JP Hei 7-283197 (JP, A)

Claims (7)

(57) [Claims] 1. A method of fabricating a substrate having a metal electrical interconnect, said interconnect comprising a first metal over a second metal, wherein said process comprises said second metal. Etching a region of the first layer of the first metal overlying a second layer of the metal, wherein the first and second layers are both A method for producing a substrate having a metal electrical interconnect, characterized by being etched using a solution containing HF, cupric chloride and chloride salts. 2. The method of claim 1 wherein said first metal comprises copper. 3. The method of claim 2 wherein said second metal comprises titanium. 4. The method according to claim 3, wherein said titanium oxide contains palladium. 5. The method of claim 1, wherein said second metal comprises titanium. 6. The method of claim 5, wherein said titanium comprises palladium. 7. The method according to claim 1, wherein the chloride salt is NaCl, KCl, L
iCl or method of claim 1, characterized in that it consists NH ₄ Cl,.