JP5531795B2 - Circuit board manufacturing method and wet etching apparatus - Google Patents

Description

  The present invention relates to a circuit board manufacturing method.

  In general, an electronic device uses a circuit board having a via plug and a wiring pattern for mounting an electronic component. In a conventional circuit board, copper (Cu) having a low resistivity is used as a material for a via plug and a wiring pattern.

  On the other hand, in recent years, extremely high performance is required for electronic devices, and on the other hand, miniaturization is also required. As a result, the mounting density of electronic components on a circuit board is steadily increasing.

  As a circuit board manufacturing method that enables such high-density mounting at a low cost using Cu wiring, a so-called semi-additive circuit board manufacturing method is known.

  1A to 1E are views for explaining a method for forming a Cu wiring pattern on a circuit board by a semi-additive method.

  Referring to FIG. 1A, a Cu seed layer 13 is typically formed by sputtering on a substrate 11 made of resin, glass, silicon, or the like via an adhesion layer 12 such as Ti. In the step B), a resist film 14 having a resist opening 14A corresponding to a desired wiring pattern is formed thereon.

  Further, in the step of FIG. 1C, the Cu seed layer 13 is used as an electrode, and a Cu pattern 15 is formed in the resist opening 14A by electrolytic plating.

  Further, after removing the resist pattern 12 in the step of FIG. 1D, the Cu seed layer 13 is removed by wet etching in the step of FIG. As a result of such wet etching, the width W of the obtained Cu wiring pattern becomes smaller than the width W ′ of the initial resist opening.

Japanese Patent Laid-Open No. 9-33482 Japanese Patent No. 3188822

  However, in such a method for forming a Cu wiring pattern by the semi-additive method, the width W of the Cu wiring pattern in the process of FIG. 1 (E) is controlled by the width W of 5 μm, 2 μm or less. When shrinking to width, it becomes very difficult.

  For example, in order to reliably perform such wet etching so that no etching residue is generated, it is possible to inspect the state of the wiring pattern after the wet etching with a microscope and perform re-etching as necessary. Such a process is out of the question because it increases the cost of manufacturing the circuit board.

  In addition, in anticipation of the generation of etching residues, it may be possible to use a so-called over-etching technique in which the wet etching is performed in the process of FIG. Since it differs depending on the pattern width and pattern density, when wiring patterns are formed with different widths on the same circuit board, or when wiring patterns are formed with different wiring densities. It becomes very difficult to obtain the wiring pattern width as designed.

  Thus, there is provided an etching management method capable of detecting the disappearance of the etching residue so that no etching residue is generated and excessive over-etching is generated, and a circuit board manufacturing method using the etching management method. It has been demanded.

According to a first aspect, a method for manufacturing a circuit board includes a second metal material different from the first metal material via a first metal layer made of at least a first metal material on the substrate. A step of forming a second metal layer, a step of forming a metal wiring pattern made of a third metal material on the second metal layer, and a step of forming the metal wiring pattern, etching the second metal layer by wet etching in the etching solution, wherein the etching step of selectively removing said second metal layer to the first metal layer, before disappeared etching step Includes a step of measuring the time change of the immersion potential of the second metal layer in the etching solution, the immersion potential once decreases and then increases, and then the time change rate of the immersion potential further decreases. Is detected If, terminating the wet etching process.

According to the second aspect, a wet etching apparatus includes: a container that holds an etching solution; a holding device that holds a substrate to be processed and is immersed in the etching solution; an electrode that is immersed in the etching solution; A measurement unit that measures a time change in electromotive force between the substrate to be processed in the holding device and the electrode; and a control unit that determines an end point of etching from the time change in the electromotive force. the electromotive force once turned upward after lowering, then further, the time rate of the electromotive force is reduced to finish et etching process when it is detected.

  According to the first and second aspects, the end point of the wet etching for forming a fine pattern on the substrate can be determined appropriately, the etching residue accompanying the under-etching can be surely removed, and the excess over Etching can be avoided and the width of a fine pattern can be managed accurately.

(A)-(E) are sectional drawings explaining the formation method of the circuit pattern by a semi-additive system. It is sectional drawing which shows the etching apparatus used in one Embodiment. It is a figure which shows the graph and electron micrograph which show the time change of the immersion potential by 1st Embodiment. It is sectional drawing which expands and shows a part of sample substrate used with the etching apparatus of FIG. It is a top view explaining the outline | summary of mounting | wearing of the sample substrate to the etching apparatus of FIG. It is sectional drawing explaining the detail of mounting | wearing of the sample substrate to the etching apparatus of FIG. (A)-(D) are sectional drawings which show the state change of the wiring pattern produced corresponding to the process of FIG. It is a graph which shows the time change of the immersion potential at the time of using another etching liquid. It is a graph which shows the time change of the immersion potential at the time of using another etching liquid. It is a graph which shows the time change of the immersion potential at the time of changing a pattern density. It is sectional drawing which shows the example of application to the multilayer laminated structure of a metal film. It is a cross-sectional view showing the application of the Ti film on the TiO ₂ film. It is a graph which shows the time change of the immersion potential in 2nd Embodiment. It is a block diagram which shows the structure of the etching apparatus by 3rd Embodiment. It is sectional drawing which shows the structure of the holder by 4th Embodiment.

[First Embodiment]
First, a wet etching apparatus 1 used in the present invention will be described with reference to FIG.

  Referring to FIG. 2, the wet etching apparatus 1 has a container 3 for holding an etching solution 2. In the etching solution 2, a silicon wafer 4 carrying a metal layer 4A on its surface is a holder. 5 and is immersed as a sample.

  A space 5A into which the etching solution 2 does not enter is formed in the holder 5. In the space 5A, the electrode terminal 5a is in contact with the metal layer 4A on the surface of the wafer 4.

  Further, in the container 3, a reference electrode 6 such as Ag / AgCl is provided soaked in the etching solution 2, and an electromotive force generated between the electrode terminal 5a and the reference electrode 6 is It is measured in the measurement unit 7 as an immersion potential.

  FIG. 3 is a graph showing the time change of the immersion potential observed when the metal film 4A on the surface of the wafer 4 is wet etched in the wet etching apparatus 1 of FIG. 2, and an electron micrograph corresponding thereto. However, a line and space pattern which will be described later with reference to FIG. 4 is formed on the metal film 4A by the semi-additive method, which is in the state of FIG. As the etchant 2, a 5-fold diluted aqueous solution of a potassium sulfate etchant (for example, CU3930 manufactured by Meltex) is used.

  Referring to the graph on the left side in FIG. 3, the potential with respect to the standard hydrogen electrode (SHE) is set to 255 to about 62 seconds after the wafer 4 is immersed in the etching solution 2 and wet etching is started. Although an immersion potential of 250 mV has been observed, it can be seen that this immersion potential starts to drop rapidly when the time exceeds 62 seconds, and reaches a minimum value after about 81 seconds from the start of etching.

  Thereafter, the immersion voltage starts to rise rapidly, and after about 100 seconds from the start of etching, it turns out that it shifts to a steady state again between 260V and 265V.

  Therefore, the first period from the start of wet etching to the start of the drop in immersion potential, the second period from the start of the drop until the immersion potential reaches the minimum value, and the third period from the lowest value to the steady state again. After returning to the state, if the subsequent period is named as the fourth period, as shown in the leftmost photograph showing the state 90 seconds after the start of etching in the scanning electron micrograph on the right side in FIG. Until now, it can be seen that there is an etching residue in the pattern, whereas there is no etching residue in the fourth period as shown in the rightmost photograph showing the state after 130 seconds from the start of etching. However, in the fourth period, the pattern width narrows, and it can be seen that overetching and the accompanying etching shift have occurred.

  On the other hand, in the state 100 seconds after the start of wet etching, that is, where the transition from the third period to the fourth period is completed, there is no etching residue and the pattern has a desired width, and an optimum etching is obtained. You can see that

  In each photo on the right side of FIG. 3, the lower photo shows the state before the etching start corresponding to FIG. 1D, and the upper photo shows the state after the etching corresponding to FIG. The state is shown on the same scale as the lower picture.

  4 is an enlarged cross-sectional view showing a part of the sample used in the experiment of FIG. 3, FIG. 5 is a plan view showing a 6-inch silicon wafer 4 used as the sample, and FIG. 2 is a cross-sectional view showing in detail a holder 5 used to hold the silicon wafer 4 in the etching apparatus 1 in a state where the silicon wafer 4 is held. FIG.

  Referring to FIG. 4, a thermal oxide film 42 having a thickness of, for example, 300 nm is formed on the silicon wafer 4, and a Ti film 43 as an adhesion film is formed on the thermal oxide film 42 by a sputtering method, for example, 5 nm. The thickness is formed. Further, a Cu film 44 is formed as a seed layer on the Ti film 43, for example, with a thickness of 50 nm. Further, a Cu line and space pattern 45 having a height of 2 μm and a width of 2 μm is formed on the Cu film 44 by the semi-additive method described above with reference to FIG. However, in the state of FIG. 4, in preparation for wet etching of the Cu seed layer 44, each Cu pattern constituting the line and space pattern 45 has a value W ′ slightly larger than the design value W of 2 μm. It is formed to have. Here, the portion from the Ti adhesion film 43 to the Cu line and space pattern 45 corresponds to the metal layer 4A.

  Next, referring to FIGS. 5 and 6, an outer peripheral portion 4 a having a width of 5 mm, for example, shown by a broken line in FIG. 5 in the silicon wafer 4 is held by the holder 5, and a main portion 4 b inside the broken line. Further, the Cu line and space pattern 45 of FIG. 4 is formed. At that time, as shown in FIG. 6, the holder 5 holds the silicon wafer 4 via a seal member 5b so that the etching solution does not enter the inner space 5A, and the inner space 5A is made of Pt. Alternatively, the Pt-coated electrode terminal 5a contacts the Cu seed layer 44 at the outer peripheral portion 4a. In the outer peripheral portion 4a, the Cu seed layer 44 is not formed with a Cu pattern 45, and the Cu seed layer 44 continuously extends in a ring shape surrounding the main body portion 4b in the outer peripheral portion 4a. To do. With such a configuration, the problem that the etching solution 2 contacts the electrode terminal 5a in the space 5A of the holder 5 during the measurement of the immersion potential and the measurement of the immersion potential is disturbed by the resulting contact potential is avoided. The

  In the configuration of FIG. 6, the electrode terminal 5a is connected to a measuring unit 81 described later in the embodiment of FIG.

When the wafer 4 in the state of FIG. 6 is immersed in the etching solution 2 in the container 3, Cu is dissolved at the interface between the Cu pattern 45 and the Cu seed layer 44 and the etching solution 2, and the reaction Cu → Cu ²⁺ + 2e. ↑ (Formula 1)
As a result, electrons are released into the etching solution 2, and an electromotive force is generated between the etching solution 2 and the Cu seed layer 44 in contact with the electrode terminal 5a.

  Therefore, the immersion potential on the silicon wafer 4 is measured by comparing this electromotive force with the electromotive force between the Ag / AgCl reference electrode 6 and the etching solution 2. In the example of FIG. 3, a commercially available Cu etching solution (for example, Cu3930 manufactured by Meltex) is used as the etching solution.

  Hereinafter, the results shown in the graph of FIG. 3 will be described with reference to FIGS.

  FIG. 7A shows the same sample as FIG. 4, but when this is immersed in the etching solution 2 in the step of FIG. 7B, the Cu line and space pattern 45 and the Cu seed layer are shown. The surface portion 44 is dissolved in the etching solution 2 according to the formula (1), and an immersion potential of about 260 mV is generated between the reference electrode 6 and the surface portion. This corresponds to the first period of FIG.

On the other hand, when the etching of the Cu line and space pattern 45 and the Cu seed layer 44 is further advanced, an opening for exposing the Ti adhesion layer 43 therebelow is formed in the Cu seed layer 44 as shown in FIG. It begins to be done. The Ti film 43 does not dissolve in the etching solution 2, but as the exposed Ti adhesion film 43 comes into contact with the etching solution 2 and the area of the exposed Ti film gradually increases, the equation (1) the reaction, from the reaction ^{(Cu → Cu 2+ + 2e- ↑} on Cu) on the Cu seed layer 44 as in the first phase, the reaction on the Ti adhesion film ^{43 (Cu → Cu 2+ + 2e-} ↑ on Ti), the immersion potential changes from that in the first period, and starts to decrease. This corresponds to the second period in FIG. This is because when the Ti adhesion film 23 is not exposed at the contact portion with the exposed Ti adhesion film 23, the thermodynamic activity or activity of Cu in the metallic state constituting the Cu seed layer 23. It is none other than to decrease.

As the etching further proceeds, the exposed area of the Ti adhesion layer 43 increases with time, and eventually the seed layer 44 is substantially completely removed as shown in FIG. The transition from the state of FIG. 7C to the state of FIG. 7D corresponds to the third period in FIG. In the state of FIG. 7D, the reaction on the Ti adhesion film 43 (Cu → Cu ²⁺ + 2e− ↑ on Ti) itself continues, but the exposed area of the Ti adhesion layer 43 increases. The immersion potential is mainly reflected on the effect of the electrode reaction between Ti and the etchant species on the Ti adhesion film 43. For this reason, the observed immersion potential increases rapidly as the etching residue of the Cu seed layer 44 shrinks and disappears. The immersion potential of the Ti film itself was 274 mV.

  Even after the state shown in FIG. 7D, the Cu pattern on the Ti adhesion film 43 is gradually dissolved in the etching solution 2, and the immersion potential is also in the fourth period of the graph of FIG. As shown, the voltage gradually rises toward the potential of 274 mV. In this state, the Cu seed layer 43 has already disappeared, and a large amount of the isolated thick Cu line and space pattern is gradually dissolved. Therefore, the temporal change rate of the immersion potential decreases rapidly, and as shown in the graph of FIG. 3, a clear shoulder or bending occurs in the temporal change of the immersion potential at the boundary between the third period and the fourth period.

  Since the bending of the graph corresponds to the state of FIG. 7D, when the bending is detected (“etching end-point” in the graph of FIG. 3), the etching is terminated. A structure corresponding to the state (D) can be obtained, and almost ideal etching management can be performed. Actually, the result of electron microscope observation of the line and space pattern obtained in this way is the figure indicated by the label “100 sec” at the center of the electron micrograph on the right side of FIG. No residue is observed, and the pattern width of the line and space pattern is controlled to a predetermined value, which is the same as that of the third stage (under-etching) electron micrograph labeled “90 sec” on the left side. I can see that However, in the third stage, etching residue is generated. In the electron micrograph of FIG. 3, in the fourth stage (over-etching) indicated by the label “130 sec” on the right side, the width of each Cu pattern constituting the line and space pattern is reduced after etching. It can be seen that it deviates from the predetermined value.

  Note that the change in the immersion potential shown in the graph of FIG. 3, that is, the immersion potential once suddenly decreases with time and then rapidly increases, then transitions to a gentle change. The tendency of bending was observed in the same manner even when the etching solution was changed.

  For example, FIG. 8 shows an example in which the stock solution of the etching solution used in the experiment of the graph of FIG. 3 and the electron micrograph is used without dilution. The etching can be accurately managed by terminating the etching at the shoulder portion of the potential change with time or at the bending point.

  FIG. 9 shows the change in the immersion potential over time when a deterioration solution that has been used for a long time is used as the etching solution 2. As in the previous example, the shoulder or weave clearly shows the advantage. Can be detected. In the experiment of FIG. 9, the etching solution 2 is the same as the etching solution used in the experiment of FIG. 3 and the etching solution after processing 30 wafers.

  Further, the inventor of this embodiment performed etching while changing the density of the Cu line and space pattern 45 in the sample of the cross-sectional view of FIG. 4, and measured the immersion potential. The result is shown in the graph of FIG. However, in the graph of FIG. 10, the curve indicated by “Pattern A” shows the result when the pattern density representing the area ratio of the Cu pattern on the wafer is 14%, and “Pattern B”. The curve indicated by “” shows the result when the pattern density is 11%.

  Referring to the graph of FIG. 10, in any case, the shoulder or bending of the time change rate of the immersion potential can be clearly detected, and when this is detected, the etching is stopped and the same as in the previous embodiment. In addition, accurate etching management that avoids overetching and underetching becomes possible.

  As described above, this embodiment is effective for detecting the etching end point not only for the samples having the specific pattern density described above but also for samples having various other pattern densities. It is useful. In addition, the target pattern in this embodiment is not limited to the line and space pattern.

  Further, in the sample shown in the cross-sectional view of FIG. 4, the seed layer 44 does not have to be Cu, and may be a metal material other than Cu, such as a Ni film, Co, or Cr film. Also in this case, the thermodynamic activity or activity of the seed layer 44 rapidly decreases when the underlying Ti adhesion film 43 is exposed, and the immersion potential decreases once, but the Ti adhesion film 43 As the exposed area increases, the immersion potential increases rapidly and changes gradually when the etching residue disappears. Therefore, it is possible to accurately determine the end point of etching by detecting the appearance of the shoulder or the bending point of the time change rate of the immersion potential.

  The present embodiment is also useful for detecting the end point of etching in the patterning of a multilayered structure of metal films as shown in the cross-sectional view of FIG.

In the example of the cross-sectional view of FIG. 11, the metal films 62 _{1 to} 62 _n are stacked on the silicon wafer 4 via the thermal oxide film 42 and the metal film 61. When the lower metal film, for example, the metal film 62 _n-1 is exposed, the thermodynamic activity or activity of the upper metal film 62 _n that is etched changes abruptly. The immersion potential decreases rapidly and then increases rapidly. Further, when the etching of the lower metal film 62 _n-1 is completed and the etching residue disappears, the temporal change of the immersion potential becomes gentle, and similarly, the appearance of the shoulder or the bending point of the temporal change rate of the immersion potential. By detecting it, it becomes possible to accurately determine the end point of etching. In the configuration of FIG. 11, it is desirable that the lowermost metal film 61 does not dissolve in the etching solution so that the immersion potential can be detected.

  In the present embodiment, the adhesion layer 43 is not limited to Ti, and Ta, W, Zr, and compounds thereof can be used.

[Second Embodiment]
Furthermore, the present invention is effective not only for the detection of the etching end point of the Cu film as described in the previous embodiment, but also for the detection of the etching end point of another metal film such as a Ti film.

12 shows a structure in which a Ti film 72 is formed on a silicon wafer 4 with a thermal oxide film 41 and a TiO ₂ film 71 interposed therebetween. FIG. 13 shows a pattern in which the Ti film 72 in FIG. It is sectional drawing and a graph which respectively show the time change of the immersion potential at the time of forming a space pattern. However, in the examples of FIGS. 12 and 13, Ti3991 manufactured by Meltex was used as the etchant _{2 so} that the TiO ₂ film 71 was not etched.

  Referring to FIG. 13, also in this case, the immersion potential first gradually decreases with time corresponding to the first period of FIG. 3, and when about 85 seconds have passed after the start of immersion, the second period of FIG. 3 and then rapidly increases corresponding to the third period of FIG. 3, and stabilizes corresponding to the fourth period of FIG. 3 approximately 105 seconds after the start of immersion. Where the transition from the third period to the fourth period occurs, a shoulder or bend occurs in the time change of the immersion potential, and the etching can be accurately controlled by ending the etching in response to the bend. Become.

  As described above, the present invention can be generally used as long as it is a process for removing a metal film by immersion wet etching in an etching solution. However, it is preferable that a non-etched conductive film or member exists below the metal film to be etched so that the immersion potential can be measured.

[Third Embodiment]
FIG. 14 is a block diagram showing a configuration of an etching apparatus 1A according to the third embodiment configured based on the above knowledge. However, in FIG. 14, the same reference numerals are given to the parts described above, and the description thereof is omitted.

  Referring to FIG. 14, in the container 3, a silicon wafer 4 is held in a holding tool 5 and immersed in an upright state in the etching solution 2, and the electrode terminal 5 a is stored in the holding tool 5. Is in contact with the metal layer 4A formed on the surface of the wafer 4.

  Further, in the present embodiment, a driving unit 5B is provided that is coupled to the holder 5 and immerses the silicon wafer 4 together with the holder 5 in the etching solution 2 and pulls it up.

  Therefore, the potential of the metal film 4A detected at the electrode terminal 5a is supplied to the measuring unit 81 corresponding to the measuring unit 7 of FIG. 2 together with the reference potential detected by the reference electrode 6, and the measuring unit 81 From this value, the immersion potential of the metal film 4A is calculated, and a signal representing this is supplied to the controller 82.

  The control unit includes a computer, and the immersion potential sent from the measurement unit is changed over time, or based on the rate of change in time, the immersion potential is once lowered and then increased, and then the immersion potential is further changed over time. Raise an alarm when the rate decreases.

  Further, the control unit 82 sends a control signal to the driving unit 5B simultaneously with the generation of the alarm, and lifts the silicon wafer 4 together with the holder 5 from the etching solution 2. Thereby, the etching of the metal layer 4A is completed.

  In the etching apparatus 1B of FIG. 14, in addition to the reference electrode 6, for example, a Pt-coated conductive plate or pin is inserted in the etching solution 2 as the reference electrode 6A. The change can also be performed by measuring a potential difference or an electromotive force generated between the reference electrode 6A and the metal film 4A using a reference electrode 6A other than the reference electrode 6. In this case, the absolute value of the immersion potential cannot be obtained as in the case where the Ag / AgCl reference electrode 6 is used. However, in the present invention, it is only necessary to obtain the change over time. Even when an easy reference electrode is used, the etching end point can be detected.

[Fourth Embodiment]
In the holder 5 shown in FIG. 6, the etching solution 2 does not enter the space 5A during the measurement of the immersion potential. However, in this configuration, the Cu wafer is cut along the outer peripheral portion 4a of the silicon wafer 4 after the etching. -The layer 44 will remain.

  Therefore, when it is preferable to remove the Cu seed layer 44, the silicon wafer 4 is lifted from the etching solution 2 and then the etching solution 2 is introduced into the space 5A as shown in FIG. Is also possible.

  For this reason, in the embodiment of FIG. 15, the holder 5 is provided with a port 5c for introducing the etching solution 2 into the space 5A and a port 5d for discharging it.

  As mentioned above, although this invention was described about preferable embodiment, this invention is not limited to this specific embodiment, A various deformation | transformation and change are possible within the summary described in the claim.

DESCRIPTION OF SYMBOLS 1,1A Wet etching apparatus 2 Etching liquid 3 Container 4 Silicon wafer 4A Metal layer 4a Outer peripheral part 4b Main part 5 Holder 5A Space 5B Drive part 5a Electrode terminal 5b Seal 5c, 5d Port 6 Standard electrode 6A Reference electrode 7, 81 Measurement Unit 42 Thermal oxide film 43 Ti adhesion layer 44 Cu seed layer 45 Cu line and space pattern 61, 62 _{1 to} 62 _n metal film 71 TiO ₂ film 72 Ti film 82 Control unit

Claims (4)

Forming a second metal layer made of a second metal material different from the first metal material on a substrate via at least a first metal layer made of the first metal material;
Forming a metal wiring pattern made of a third metal material on the second metal layer;
After the step of forming the metal wiring pattern, the second metal layer is etched by wet etching in an etching solution, and the second metal layer is selectively removed with respect to the first metal layer. Etching process;
Including
Before disappeared etching step includes the step of measuring the time variation of the immersion potential of the second metal layer in the etching solution,
The turned upward after the immersion potential is once lowered, it followed further wherein when the time rate of change of the immersion potential is reduced is detected, the manufacturing method of the circuit board, characterized in that to end the pre disappeared etching step .   The time change of the immersion potential is measured by measuring the time change of the electromotive force generated between the second metal layer and the reference electrode immersed in the etching solution. The method for manufacturing a circuit board according to claim 1.   The first metal material is selected from the group consisting of Ti, Ta, W, and Zr, the second metal material is selected from the group consisting of Cu, Ni, Co, and Cr, and the third metal material is Cu. The method for manufacturing a circuit board according to claim 1, wherein: A container for holding an etching solution;
A holding device for holding a substrate to be processed and dipping in the etching solution;
An electrode immersed in the etching solution;
A measuring unit for measuring a time change of electromotive force between the substrate to be processed and the electrode in the holding device;
A control unit for determining an etching end point from the time variation of the electromotive force;
With
Wherein the control unit, the turned upward after the electromotive force is temporarily lowered, followed further the wet etching apparatus, which comprises terminating the d etching process when the time rate of change of the electromotive force is detected that decreased .