MODIFIED COPPER SURFACE, HETEROAROMATIC SILANE COMPOUNDS AND THEIR USAGE FOR INCREASING ADHESION STRENGTH BETWEEN COPPER AND AN ORGANIC MATERIAL AND REDUCING HALO AND WEDGE VOID FORMATION

Abstract

The present invention relates to a method for increasing adhesion strength between a surface of a copper, a copper alloy or a copper oxide and a surface of an organic material.

Claims

1. A method for increasing adhesion strength and/or improved wedge void behavior between a surface of copper, a copper alloy or a copper oxide and a surface of an organic material comprising (i) providing a substrate, comprising the copper, copper alloy or copper oxide on at least one side of the substrate, followed by at least one of the steps of (i-c) treating the substrate yielding a substrate comprising copper oxide on at least one side of the substrate, wherein the copper oxide comprises copper (I) and copper (II) in a ratio of 90:10 or higher (mol/mol), preferably in a ratio of 95:5 or higher (mol/mol), even more preferably in a ratio of 98:2 or higher (mol/mol), most preferably the copper oxide essentially consists of copper (I) oxide; and/or (ii) contacting at least one section of the substrate with (a) at least one silane compound of formula (I); ##STR00052## wherein the ring structure ##STR00053## is selected from the group consisting of ##STR00054## and mixtures thereof; X and Y are independently selected from the group consisting of NH.sub.2, NH(NH.sub.2), NH(CH.sub.2).sub.oNH.sub.2, SH, SCH.sub.3, and OCH.sub.3; E is selected from the group consisting of S, NH and NH(CH.sub.2).sub.mNH; A is selected from the group consisting of NH, N(NH.sub.2) and S; Z is selected from the group consisting of ##STR00055## m is an integer in the range from 2 to 12, n is an integer in the range from 1 to 12, o is an integer in the range from 2 to 12, R independently denotes (CH.sub.2CH.sub.2O).sub.p-T, wherein independently p is 0, 1, 2, 3, or 4, and T denotes H or C1 to C5 alkyl; or (b) at least one amino acid; or a mixture of (a) and (b), wherein, if both steps (i-c) and (ii) are performed, step (1-c-) is performed prior to step (ii); (iii) applying the organic material, with the proviso that, if the ring structure ##STR00056## in the silane compound of formula (I) is ##STR00057## both steps (i-c) and (ii) are performed.

2. The method according to claim 1, wherein step (i-c) comprises contacting at least one section of said copper, copper alloy or copper oxide with an aqueous alkaline solution comprising at least one complexing agent.

3. The method according to claim 2, wherein the aqueous alkaline solution in step (i-c) has a pH in the range of from 7.5 to 14.0.

4. The method according to claim 2, wherein step (i-c) is applied as dip application and the contact time is 40 s or longer.

5. The method according to claim 2, wherein step (i-c) is applied as spray application and the contact time is 10 s or longer.

6. The method according to claim 1, comprising the step of (ii) contacting at least one section of the substrate with (a) at least one silane compound of formula (I); ##STR00058## wherein the ring structure ##STR00059## is selected from the group consisting of ##STR00060## and mixtures thereof; X and Y are independently selected from the group consisting of NH.sub.2, NH(NH.sub.2), NH(CH.sub.2).sub.oNH.sub.2, SH, SCH.sub.3, and OCH.sub.3; E is selected from the group consisting of S, NH and NH(CH.sub.2).sub.mNH; Z is selected from the group consisting of ##STR00061## m is an integer in the range from 2 to 12, n is an integer in the range from 1 to 12, o is an integer in the range from 2 to 12, R independently denotes (CH.sub.2CH.sub.2O).sub.p-T, wherein independently p is 0, 1, 2, 3, or 4, and T denotes H or C1 to C5 alkyl; or (b) at least one amino acid; or a mixture of (a) and (b).

7. The method according to claim 1, wherein the organic material applied in step (iii) is an organic polymer.

8. The method according to claim 1, wherein the organic material is applied in step (iii) by laminating the organic material onto at least the contacted section of the copper, copper alloy or copper oxide.

9. The method according to claim 1, if a step (ii) is performed, additionally comprising the following step before conducting step (ii): (i-a) contacting the at least one section of said copper, copper alloy or copper oxide with an etch-cleaning solution.

10. The method according to claim 1, if a step (ii) is performed, additionally comprising the following step before conducting step (ii): (i-b) contacting the at least one section of said copper, copper alloy or copper oxide with a (preferably second) etch-cleaning solution.

11. The method according to claim 1, wherein after step (ii), after step (i-a), after step (i-b) and/or after step (i-c), a rinsing of the at least one section of the copper, copper alloy or copper oxide is performed.

12. The method according to claim 1, wherein after step (ii), after step (i-a), after step (i-b) and/or after step (i-c), a drying of the at least one section of copper, copper alloy or copper oxide is performed.

13. The method according to claim 1, wherein after step (ii), no baking of the at least one section of copper, copper alloy or copper oxide is performed.

14. The method according to claim 1, comprising after step (iii) the additional step: (iv) subjecting the substrate and the organic material to a heat treatment with a temperature in the range from 142? C. to 420? C.

15. The method according to claim 1, wherein after step (ii), after step (i-a), after step (i-b) and/or after step (i-c), a rinsing of the at least one section of the copper, copper alloy or copper oxide is performed.

16. The method according to claim 3, wherein step (i-c) is applied as dip application and the contact time is 40 s or longer.

17. The method according to claim 3, wherein step (i-c) is applied as spray application and the contact time is 10 s or longer.

Description

FIGURES

[0337] FIG. 1: Top view SEM images (at different magnifications 2500? and 5000?) of copper foils treated after different immersion time in the alkaline treatment solution.

[0338] FIG. 2: Ra and RSAI values obtained from AFM investigations of the copper foils after different process steps: initial, after Differential Etch DE, after alkaline treatment and after alkaline treatment+Silane coating.

[0339] FIG. 3: Determined copper oxide thickness in nm formed on copper foils after different alkaline treatment time by integration of respective potential ranges with DSCV.

[0340] FIG. 4: FTIR grazing incidence measurement-Peak integration of Cu.sub.2O signal by alkaline surface treatment time on copper foil. Integration performed over 683-616 cm.sup.?1.

[0341] FIG. 5: STEM image of Cu panel treated with an alkaline solution (300 s dip) and coated with Silane. a) EDS analysis of oxide particles performed at three different areas. The small amounts of some elements are coming from the microscope: Mo.fwdarw.TEM-sample holder; Al, Zr.fwdarw.EDX detector, Pt, Ga.fwdarw.FIB Preparation, Fe, Co, Pb.fwdarw.TEM column. [0342] b) STEM images at 200 mV, Nano-beam diffraction (NBD) line scan.

[0343] FIG. 6: Example of halo measurement

[0344] The invention is further explained by the following non-limiting examples.

EXAMPLES

Synthesis of Tetrazole Silane Compound of Formula (IV)

[0345] Synthesis of tetrazole silane compound of formula (IV-a):

##STR00042##

4.92 g (57.8 mmol) 2H-tetrazol-5-amine were suspended in 84.3 ml diethylene glycol monobutyl ether (DEGBE). This suspension was heated to 80? C. At that temperature 13.67 g (57.8 mmol) 3-glycidoxypropyltrimethoxysilane were added. The reaction mixture was kept at 80? C. for 15 hrs.

[0346] Afterwards, a reaction product with a concentration of approximately 20 wt.-% in DEGBE was obtained. The thus obtained product was utilized without further purification.

[0347] ESI-MS confirms the formation of a compound comprising three methoxy groups connected to the silicon atom. In addition, compounds comprising one, two, or three DEGBE moieties instead of respective methoxy groups also have been identified.

Sample Preparation

[0348] Samples (each comprising several identical specimens) were prepared as follows.

[0349] Table 1 gives an overview on the reaction steps which are then described in more detail thereafter.

TABLE-US-00001 TABLE 1 Typical step process make up Temp dwell time remarks (i) Providing copper substrate Annealing 160? C. Air ventilated (optional) oven, 1 h (i-a) Differential 25 ml/l Hyperflash 25 30? C. Depending Target etch depth is Etch 50 ml/l H.sub.2SO.sub.4 50% on etch 0.5 ?m & 1 ?m 65 ml/l H.sub.2O.sub.2 35% rate Triple cascade water Rinse Dry (optional) Up to dry (i-b) H.sub.2SO.sub.4 5% 130 ml/l H.sub.2SO.sub.4 50% ambient 30 s Triple cascade water ambient 20 s Rinse (i-c) aqueous alkaline pH 14 50? C. 30-600 s solution Rinse Water ambient 20 s Dry (optional) Up to dry Hot air dryer, e.g. air gun, hair dryer (ii) Adhesion Diff. Silanes ambient 60 s See table with APs Promoter Triple cascade water Ambient 30 s each rinse Dry Up to dry Hot air dryer, e.g. air gun, hair dryer (ii-a) Baking (optional) 130 30 min Air ventilated oven (iii) Lamination See Table 2

Step (i):

[0350] Copper foils having a copper surface (150 mm?75 mm?35 ?m, plated in house) were used. Under simplified laboratory conditions, copper foils without substrates are used for the examples.

[0351] For wedge void and or halo investigation plated copper panels were used.

[0352] The preparation conditions are as follows:

[0353] Electrolytically plated Copper type: [0354] foil (adhesion test) [0355] panels (wedge void)

[0356] Electrolyte: [0357] Cupracid AC

[0358] Plating Parameters: [0359] 103 min [0360] 1.5 A/dm.sup.2=35 ?m plated Copper thickness
Step (i-a):

[0361] The copper surfaces of the copper foils were treated by 25 ml/l Hyperflash 25, 50 ml/l H.sub.2SO.sub.4 50% and 65 ml/l H.sub.2O.sub.2 35% at 30? C. to achieve 0.5 or 1 ?m etch depth. After the etch-cleaning the etch-cleaned copper surfaces were rinsed with water for approximately 30 seconds and optionally dried. As a result, etch-cleaned and rinsed copper surfaces were obtained.

Step (i-b):

[0362] The copper surfaces of the copper foils were cleaned at room temperature for 20-30 seconds by using a 5 vol % sulfuric acid.

Step (i-c):

[0363] The copper surfaces of the substrates were treated with aqueous alkaline solution (50? C., dipping, 300 sec or 50? C., spraying, 30 sec). After the treatment the treated copper surfaces of all copper foils were rinsed with cold water for approximately 30 seconds.

Step (ii):

[0364] Copper surfaces of the substrates were immersed for 60 sec at 25? C. into a coating solution containing a triazine silane compound and solvents. If water is present, the pH of the coating solution was 7 (triazole and tetrazole silanes) (adjusted with sulfuric acid, if needed) or up to 13.5 (triazine silanes). Details are given in Table 2.

[0365] Afterwards the resulting copper surfaces of all copper foils were rinsed with water for approximately 30 seconds and dried. As a result, silanized and dried copper surfaces of the copper foils were obtained.

Step (ii-a):

[0366] Copper foils were then annealed for 30 minutes at 130? C. to remove remaining moisture from the surface. Note: this thermal treatment step is also known as baking. These substrates containing copper surfaces were subsequently subjected to laminating a build-up film (see text below).

Step (iii):

[0367] In a laminating step, an insulating film (see Table 2) was vacuum laminated onto the copper foils of all samples in a clean room with a room temperature in the range from 20 to 25? C. and with a relative humidity of 50 to 60% by using a vacuum laminator.

[0368] The conditions for vacuum lamination were as follows: 100? C., vacuum: 30 sec. at 3 hPa, pressure: 30 sec at 0.5 MPa.

[0369] After lamination, laminated copper surfaces were obtained.

TABLE-US-00002 TABLE 2 Overview Conditions Step (i-c) Time Step (ii) Time Sample [no/dip/spray] [s] [yes/no] silane [s] C1 no n/a No n/a n/a (comparative) 1a dip 30 No n/a n/a 1b Spray 30 No n/a n/a 2a dip 60 No n/a n/a 2b Spray 60 No n/a n/a 3a dip 120 No n/a n/a 3b Spray 120 No n/a n/a 4a dip 300 No n/a n/a 4b Spray 300 No n/a n/a 5 dip 30 Yes (IVa) 60 s 6 dip 60 Yes (IVa) 60 s 7 dip 120 Yes (IVa) 60 s 8 dip 300 yes (IVa) 60 s 9 dip 300 yes (Vb) 60 s 10 dip 300 yes (Ila) 60 s [00043][00044][00045]

Surface Morphology

[0370] The surface morphology was measured by means of Field Emission Scanning Electron Microscopy (FESEM). FEI NOVA Nanolab 600 and FEI Helios Nanolab 660 Microscopes were used to investigate surface as well as FIB prepared cross-sections.

SEM

[0371] Scanning Electron Microscopy (SEM) images show the change in the surface structure after step (i-c) at different times (FIG. 1). At 30 s oxide particles formed on the surface (Sample 1). With longer treatment according to step (i-c) the Cu surface gets flattened caused by oxide particle growth.

AFM

[0372] Atomic Force Microscopy (AFM) was used to measure the surface roughness: for each sample, the surface was imaged on 5 measuring windows of 20 ?m?20 ?m The average roughness R.sub.A, and the relative surface area increase RSAI were calculated. FIG. 2 depicts how the roughness increases by alkaline treatment and remains unchanged after application of silane.

Characterization of Copper Oxide

DSCV

[0373] The characterization of copper oxide was performed by means of Double-Sweep-Cyclic-Voltammetry (DSCV). Applied method used for Cu oxide quantification. During the first scan, cupric and cuprous oxides are reduced to Cu providing corresponding cathodic currents. Background currents are measured during the third scan in the same cathodic directions as the first scan. They are subtracted from the cathodic currents of the first scan in order to calculate the quantity of electrical charge required for the reduction of corresponding Cu oxide species. Experiments were performed it LiCl (4 M) solution at RT, potential range: ?0.5 to ?1.6 V (vs Ag/AgCl (3M KCl), Scan rates 100 mV/s, # of scans 3. [0374] For scan rate 100 mV/s: [0375] CuO: ?0.5 to ?1.08 V (vs Ag/AgCl (3M KCl)) [0376] Cu.sub.2O: ?1.08 to ?1.3 V (vs Ag/AgCl (3M KCl)) [0377] Oxide layer thickness (d) nm was calculated using Faraday law:

[00001]$d=\frac{Q.Math.M}{z.Math.F.Math.A.Math.?}$ [0378] A=0.95 cm.sup.2 [0379] M(CuO)=79.59 g/mol [0380] M(Cu.sub.2O)=143.19 g/mol [0381] ?(CuO)=6.31 g/cm.sup.3 [0382] ?(Cu.sub.2O)=6.00 g/cm.sup.3 [0383] z=2 [0384] F=96485 C/mol

[0385] The measurement shows that Cu(II) oxide remains at the zero level for the whole time. In contrast; Cu(I) oxide increased (FIG. 3).

FTIR

[0386] Fourier-transform infrared spectroscopy (FTIR) with Grazing Incidence unit was used to characterize the substrate surface. The surface oxide state change during the alkaline treatment was evaluated. (FIG. 4)

EDS

[0387] Elemental analysis of samples was carried out using Energy-dispersive X-ray spectroscopy (EDS). A lamella prepared for scanning transmission electron microscopy (STEM), and further used for the EDX measurements. Details are given in FIGS. 5a) to c) and respective description.

[0388] EDS analysis was performed at three different areas of oxide particles

[0389] It has been found that, the ratio of Cu to O is 2 to 1, indicating that the oxide particles formed by alkaline solution are of Cu.sub.2O nature.

HRTEM

[0390] The nano-beam diffraction (NBD) measurements from high resolution transmission electron microscopy (HRTEM) mode is a most favorable technique for routine strain analysis (simple experimental set-up, nano-meter spatial resolution and high measurement sensitivity (std. dev. ?0.1%)).

[0391] The line scan was performed along the oxide particle height at nine positions. All obtained patterns are nearly identical.fwdarw.same quality oxide along the particle height is expected

Adhesion Evaluation Via Peel Strength Test

[0392] For selected samples obtained after the lamination, peel strength was determined: [0393] (1) Initial, [0394] (2) after 96 hours HAST (HAST conditions: 130? C., 85% rh, HAST chamber: EHS-221M). [0395] (3) after 12 cycles IR Reflow (thermal reliability, simulation of soldering process with temperature peak at 260? C.)

[0396] In order to determine the peel strength, several stripe-type fragments have been prepared from each specimen by adhering the respective copper foils to a rigid board (identical size as the copper foils) in such a way that the rigid board faced the insulating film. As a result, copper surfaces with structurally enforced insulating films were obtained.

[0397] The obtained copper surfaces with structurally enforced insulating films were then cured in an oven: copper surfaces with GL102 material at 200? C. for 90 minutes and copper surfaces with GX-T31 material at 190 C for 90 min.

[0398] Afterwards, each copper surfaces with structurally enforced insulating films was sliced into said strip-type fragments (10?100 mm, Bugard drilling/routing).

[0399] The strip-type fragments were subjected to a peel force measuring machine (RoeII Zwick Z010) to individually evaluate the peel strength (angle: 90?, speed: 50 mm/min) which is needed to delaminate the copper surface from its respective structurally enforced insulating films. Typically, the higher the peel strength needed to avoid delamination the better is the adhesion.

[0400] The peel strength of samples 1 to 15 are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Step (i-c) dipping Step Peel strength Peel strength [time (II) GX-T31 (N/cm) GL 102 (N/cm) in s] [silane] Initial HAST Reflow Initial HAST Reflow C1 n/a n/a 6.6 2.1 2.1 6.4 1.6 4.7 1a 30 n/a 9.3 3.7 5.0 7.5 2.2 5.6 2a 60 n/a 9.5 4.8 4.3 7.2 2.5 4.8 3a 120 n/a 9.7 5.6 4.5 7.6 2.7 5.2 4a 300 n/a 10.2 5.8 4.8 7.9 3.3 5.6 C2 n/a (Vb) 7.5 4.4 5 n/a (IVa) 5.8 2.8 3.0 7.2 2.4 6.3 6 n/a (IIa) 8.4 4.0 5.0 6.8 3.6 5.7 7 30 (IVa) 8.6 2.9 4.0 6.1 2.9 5.8 8 60 (IVa) 8.8 4.7 4.5 6.8 4.3 6.2 9 120 (IVa) 10.2 5.6 5.6 6.9 4.9 6.5 10 300 (IVa) 9.8 8.3 7.5 7.3 4.8 6.3 11 300 (Vb) 7.3 4.6 12 30 (IIa) 8.7 6.5 6.2 6.3 3.8 5.8 13 60 (IIa) 8.9 7.4 7.2 6.5 4.2 5.8 14 120 (IIa) 9.5 7.8 7.4 6.7 4.7 6.2 15 300 (IIa) 9.4 8.5 7.8 7.5 5.0 6.5 [00046][00047][00048]

[0401] The experiments show that the inventive examples exhibit a good adhesion strength, here expressed as peel strength.

Halo and Wedge Void Evaluation

Sample Preparation:

[0402] In order to evaluate the halo, the copper samples have been prepared by adhering the respective insulating films to copper panels. As a result, copper surfaces with structurally enforced insulating films were obtained.

[0403] The obtained copper surfaces with structurally enforced insulating films were then semi-cured in two steps in the ovens: copper surfaces with GL102 material at 130? C. for 30 minutes followed by 175? C. for 30 minutes; and copper surfaces with GX-T31 material at 100? C. for 30 minutes followed by 170? C. for 30 minutes.

[0404] After completing the lamination and semi-curing step, the copper panels were lasered with UV-laser to drill the blind micro vias (BMV). Thereafter, the substrates were subjected to the desmear and reduction condition steps. In particular, these included a sweller treatment under alkaline conditions with Securiganth MV Sweller (Atotech); a permanganate treatment under alkaline conditions with Securiganth MV Etch P (Atotech) and a reduction conditioner treatment under acidic conditions with Securiganth MV Reduction Conditioner (Atotech). After each step the sample were rinsed with water.

[0405] The lamination material exhibits a thickness of ca. 10 ?m for wedge void and halo and 35 ?m in case of adhesion investigations, respectively.

Measurements:

1) Halo Evaluation

[0406] The substrates were measured by light microscope (200? magnification; see Table 4). Pictures depicting the halo measurement can be found in FIG. 6.

[0407] The investigated test Blind Micro Via's (BMV) are manufactured as a test grid on surface treated and Ajinomoto Build up Film (ABF) laminated test vehicles by utilizing Laser Drilling technology. The halo data is obtainable after sending the prepared test vehicles through entire Desmear process (Sweller, Permanganate, Reduction Conditioner) as described above.

[0408] Halo measurement is performed by camera (CCD) supported light microscopy. Hereby, the microscope must be operated in epi-illumination mode. All image generation must be carried out by using Darkfield (DF) filter setting. A magnification factor of approx. 200? is typically used.

[0409] The fully processed test vehicles are firmly installed on the measurement table and the BMV capture pad must be set as optical focus. CCD exposure time must be adjusted to the maximum possible contrast of halo boundaries. Hereby, the capture pad should appear as bright as possible.

[0410] The visible diameter of the via hole (or clean capture pad), the inner (innermost) and the outer (outermost) appearing halo like boundaries are measured and recorded according to FIG. 6. The actual halo values can now be calculated by using following relations.

Outer Halo (?m)=(Outermost Diameter (?m)?Diameter of Via Hole (?m))/2 1.

Inner Halo (?m)=(Inner Diameter of Halo (?m)?Diameter of Via Hole (?m))/2 2.

[0411] Typically, this process is iterated at least three times at random test vias to enable minimal statistical statements.

TABLE-US-00004 TABLE 4 GL102 (?m halo size) GL102 Step (i-c) With baking (?m halo size) dipping Step (II) (130? C., 30 min) Without baking Sample [time in s] [silane] Inner Outer Inner Outer C1 n/a n/a 79.9 143 49.6 91.8 2a 60 n/a 61.9 104 39.7 71.2 4a 300 n/a 19.2 61.7 17.9 38.6 C2 n/a (Vb) 67.2 76.4 (comparative) 5 n/a (IVa) 65 85 15 41 6 n/a (IIa) 19.0 75 15 60 8 60 (IVa) 50 70 n/a n/a 10 300 (IVa) 23.1 68.7 19.5 42.0 11 300 (Vb) 22.5 74.8 12 300 (IIa) 20.0 25 [00049][00050][00051]

[0412] The best result is obtained for the combination of step (i-c) with step (ii) comprising T-E silane

[0413] The experiments show that the inventive examples exhibit a good behavior regarding avoidance of wedge void formation, here expressed as halo sizes.

2) Wedge Void Evaluation

[0414] In addition, substrates were subjected to Focused Ion Beam (FIB) cuts and subsequent Scanning Electron Microscopy (SEM) measurement. This method allows to analyze the copper adhesion in the vicinity of a blind micro via (BMV), also known as wedge void.