New Technology To Improve Etching Performance Using Shiny .
As originally published in the IPC Proceedings.New Technology to Improve Etching Performance Using Shiny Side SurfaceTreatment for HDIKeisuke YamanishiNippon Mining & Metals.Co., Ltd.3-3-1 Shirogane-cho, Hitachi City, Ibaraki, JapanTelephone No.: stractThis paper discusses a new technology to improve etching performance using shiny side surface treatment on copper foil.Until now, a lot of electro-deposited copper foils (ED foil) with very low profile on matte side have been introduced to themarket to obtain fine line products such as HDI. In addition to copper foil thickness, roughness of matte side is thought tobe a key factor to improve etching performance. However, our new technology is quite unique and different from othermethods to obtain narrow traces. Using new technology, 30 micron pitch circuits could be obtained using 9 micron copperfoil.Experimental(1) Sample preparation flow and test conditionCopper foil was laminated onto coverlay to make FCCL(flexible copper clad laminate). The flow of the sample preparationwas shown below.Copper foil Æ Coverlay press Æ resist spin coating Æ UV exposure Æ Development Æ resist baking Æ Etching*Mask pattern: 30 micron pitch (Line/space 25/5)40 micron pitch (Line/space 25/15)50 micron pitch (Line/space 33/17)*Etching solution conditionFeCl3 37wt%Temp. 50CBaume scale 40 BeSpray 0.15Mpa(2) Copper foil samplesIn order to verify the effect of surface roughness of copper foil, different type foils were chosen for the test shown in Table 1.Two foils were chosen from RA (rolled copper foil) and two foils from ED.Table 1 Type of copper foil used for etching test.Copper foil sample Type of copper foilSurface treatmentBHYARA (Rolled foil)Smooth typeBHYRA (Rolled foil)Regular treatment for RASpecial EDED (Flat type)Regular treatment on Flat type EDStandard EDED (Standard)Regular treatment on Regular ED(3) Etching performance evaluationSurface morphology was investigated by SEM on the matte side of the samples shown in Figure 1. It is clear that roughnessof ED was quit bigger than that of RA. The difference between BHY and BHYA was relatively small compared to ED.After etching, line width and the length only for the tail along the circuit was measured to obtain etching factor. Etchingfactor was defined as shown in Figure 3.From the etching test results, etching factor improved when matte side surface roughness decreased. Flatter foil seemed to bebetter to create narrower traces. So, flatter and thinner copper foil has been used to make narrower traces for such as COFapplication and packaging materials. Recently it was found that 30 micron pitch seemed to be the limitation for thesubtractive method, especially for COF industry. Thus, new technology should be investigated soon to overcome thelimitation.
As originally published in the IPC Proceedings.Low magnification1μmBHYABHYSpecial ED typeStandard ED typeRz 1.3μmRz 1.7μmRz 3.4μmRz 8.3μmFigure 1 Comparison among various copper foils with regards to different surface roughness.BHYABHYSpecial EDStandard EDｘ 6000resinCutoptopCuresinFigure 2 the effect of surface roughness on matte side of the copper foil on etching performance.(60 micron pitch pattern)T : width of the trace on topR: width of resistt: thickness of copper foilB: width of the trace on bottomEtching factor 2t/(B-T)Figure 3 the definition of etching factor.
As originally published in the IPC Proceedings.y 0.5982x 1.8015R2 0.9891866Etching factorTail length (micron)7y 7.135x-0.5487543543221100024681002Surface roughness (micron)46810Surface roughness (micron)BHYA (RA) BHY(RA) Special ED Standard EDEtching factor5.85.73.72.2Etching tail length (micron)2.62.64.16.7Surface roughness (micron)1.31.73.48.7Figure 4 the results of etching factor using different foils.(5) Effect of etching solution, direction of copper foil, and grain structure on etching performanceIn order to develop etching performance, three factors were investigated to affect on etching factor. Type of etching solution,circuit direction, and grain structure of copper foil were determined. 30 micron patter mask and 9 micron RA copper foilwere used for the test. Generally, new etching which was told to have anisotropic etching property was the best, second wasferric chloride, the last was cupric chloride. However, we could not see any difference on etching performance. In thesame way, the effect of circuit direction was determined. It was not found any difference on the etching performance withregards to direction of the circuit. The last one was effect of grain structure. There were two copper foil chosen for the test.One was HA foil which had very large re-crystalized grains, the other was HS foil which had layered structure related torolling process. Even though the grain structure was so different, the etching factor for each did not have any difference.1.6MD1.4Etching factor451.2EF1TD0.8HA foil (RA)0.60.4HS foil CupricMDchloride chloride45 45TDTDHAHAMGFHSFigure 5 The effect of various factors on etching factor.
As originally published in the IPC Proceedings.(4) Idea of the new etching technologyFrom our results, the assumed major factors (etching solution, direction of circuit, and grain structure) for etching did notaffect on the actual etching performance. Thus new approach should be considered to overcome this situation. Thefollowings are the idea of our new technology to improve etching performance.Usually, etching proceeds evenly to side wall and to the bottom. In the case of narrow traces, side etching creates a bigproblem. The width of top circuit cannot be kept due to the side etching. In order to refrain this side etching behavior,special coating on shiny side was thought. If this special coating was not easy to dissolve in the enchant compared to copper,this layer may be able to protect side etching or somehow reduce side etching speed. From now, this special coating is called“EF treatment” which enhances etching performance.9micron RA foil, 30 micron pitch pattern were used for the etching test to determine the effect of the EF treatment.Surprisingly, the etching factor of EF treatment improved twice compared to that without EF treatment shown in Figure 6.The width of top circuit was almost the same as 10 micron, but the width of the bottom was different. If this sample wasetched longer, the top width should be much shorter. This is the reason why the subtractive method has fine line limitation.a) EF treatment (New technology)b) without EF treatment (Conventional case)Figure 5 Image of the cross section during etching process.a) With EF treatmentb) Without EF treatment10μmEtching factor : 2.7Etching tail length : 3.3 micronEtching factor : 1.2Etching tail length : 7.8 micronFigure 6 The cross sectional observation on the etching test using EF treatment.(30 micron pitch patterns, 9 micron RA foil were used.)
As originally published in the IPC Proceedings.In Figure 7, comparison was made between 9 micron RA with EF treatment and 9 micron flat type ED. Due to the roughersurface on matte side, some circuit shorted area was found on ED foil, while no irregular was found on RA with EFtreatment.In Figure 8, cross sectional analysis was done to verify the difference between EF treatment and without EF treatment. Atthe beginning of the etching, the width of the opening did not change at all. However, the difference of the opening widthbecame larger when the etching continued. When etching stopped at almost the middle of the copper foil thickness, there was6 micron difference between EF and without EF. In addition, overhang at the top edge attached to resist could be found inthe case of EF, while there was not overhang on without EF. Thus it was found that EF treatment actually could refrain sideetching.Figure 9 showed the potential of the EF treatment making very narrow traces. Using 18 micron RA, 40 micron pitch tracecould be produced by EF treatment, while top width disappeared in the case of ED foil. Even for the thicker foil, stillnarrower traces can be made using EF treatment.In addition, Figure 10 showed the result of EF using COF material, which was 2 layer sputtering type FCCL. EF treatmentcould improve etching factor almost triple compared to that without EF. Using EF treatment, it could be assumed that itmay be able to make narrower trace less than 30 micron pitch using regular subtractive method.a) With EF treatment on 9 micron RAb) Without EF treatment on 9 micron flat type EDFigure 7 the comparison between RA with EF treatment and flat type ED without EF treatment.(30 micron pitch pattern, 9 micron copper foils were used. Red circle marked circuit short area.)
As originally published in the IPC Proceedings.a) EF treatmentb) Without EF treatment16.4μ m16.2μ m19.2μ m20μ m23.4μ m29.7μ mFigure 8 the cross section analysis to compare between EF treatment and without EF treatment on RA during etchingprocess. (30 micron pitch pattern, 9 micron copper foil was used.)a) EF treatmentb) Without EF treatment50 micron50 micronFigure 9 The comparison between RA with EF treatment and flat type ED without EF treatment.(40 micron pitch pattern, 18 micron copper foil were used)
As originally published in the IPC Proceedings.a) EF treatmentEF 5.8b) Without EF treatmentEF 1.410μmFigure 10 the comparison between EF and without EF treatment on 2 layer sputtering type FCCL.(30 micron pitch pattern, 8 micron copper thickness)In Figure 11, our latest surface treatment for shiny side was “Cliff treatment”. The Cliff treatment was laboratory base madeusing vacuum metallization process. The element used for the treatment was different from the EF treatment. Bothelements were not easy to dissolve in etchant compared to copper. It was very interesting that the Cliff treatment couldimprove etching factor much more compared to that of EF. Without EF treatment, etching factor was 1.6 for EF foil. Inthe case of EF treatment on RA foil, etching factor was 3.3 similar to the previous results. On the other hand, surprisingly,etching factor of the Cliff treatment was 7.2.
As originally published in the IPC Proceedings.Thus, it was found the possibility to improve etching performance by shiny side surface treatment.a) Cliff treatmentEF 7.2b) EF treatment(vacuum metalized)EF 3.3c) Flat type ED without EFEF 1.6Figure 11 the comparison among Cliff treatment, EF treatment on RA foil and flat type ED without EF treatment.(30 micron pitch pattern, 9 micron copper foil was used)ConclusionRecent high-end electronic products need the printed circuit board with HDI. For instance, cellular phone is going to havemulti-function in the same size. Flat panel display is going to become much more high density type which needs morecircuit traces in the same space. Thus circuits seem to be much narrower than before. Now we are facing the limitationusing conventional subtractive etching method. In this paper, new etching technology, EF treatment was introduced andshowed its possibility to overcome the limitation. EF treatment is ready to supply samples to customer, and more trials is tobe completed for the Cliff treatment.
After etching, line width and the length only for the tail along the circuit was measured to obtain etching factor. Etching factor was defined as shown in Figure 3. From the etching test results, etching factor improved when matte side surface roughness decreased. Flatter foil seemed to be better to create narrower traces.
Etching is a process of removing material from the substrate’s surface. In general, there are two categories that etching can be divided into dry etching, and wet etching. The focus of this section will be solely on dry etching. Wet etching, a process where the substrate is submerged
etching is usually faster than the rates for many dry etching processes and can easily be changed by varying temperature or the concentration of active species. Wet Etch Synonyms: chemical etching, liquid etching Definition: Wet etching is a material removal process that uses liquid chemicals or etchants to remove materials from a wafer.
Plasma Etching Page 2 OUTLINE Introduction Plasma Etching Metrics – Isotropic, Anisotropic, Selectivity, Aspect Ratio, Etch Bias Plasma and Wet Etch Summary The Plasma State - Plasma composition, DC & RF Plasma Plasma Etching Processes - The principle of plasma etching, Etching Si and SiO2 with CF4
Al etching start and thus to diff erent etching depths or times (Fig. 118). The formation of hydrogen in the etching reaction is also problematic for a homogeneous etching result. The constantly produced H 2 bubbles stick to the surface and block the etching process through a sup
different etching cycle time. With longer etching cycle time, the etching rate is higher and sidewall roughness is better, but sidewall perpendicularity becomes worse at the same time. At etching cycle time of 16 seconds, the inclined angle is 89.5 , etching rate is 2.8 m/min, and sidewall roughness is 50 nm, as shown in Fig. 4(c).
Dry plasma etching has become the dominant patterning technique for the group-III nitrides, due to the shortcom-ings in wet chemical etching. Plasma etching proceeds by either physical sputtering, chemical reaction, or a combination of the two often referred to as ion-assisted plasma etching, Physical sputtering is dominated by the
Plasma Etching Plasma etching involves physical bombardment of the substrate by an ion which is nominally inert. – Ar is the most common gas used for this. The impact (momentum transfer) from accelerated Ar ions knocks loose substrate ions, called sputter etching or simply plasma etching.
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