Decapping and Chip-Documentation - Howto

[Noopy]

10x should almost be enough for my 60D. But with a little more I can be sure that the magnification factor isn't the bottleneck.


Pictures with 100mm<=>10mm(r) show a similar "quality" than pictures with "distance"<=>10mm(r).

The resolution of the 100mm<=>10mm(r) seems to be a little better

BUT I have problems with the overall sharpness of the pictures. I have to do some more tests to check if it's a alignment problem or a lens problem or a handling problem.
The lower magnification makes it more difficult to find the focus.

[magic]

If one or two opposite sides are out of focus - that's alignment.
If all sides are soft but the center is sharp - that's the lenses not working very well together.

I have seen a mix of both effects on my PowerShot with webcam lens. Mostly the former, because small size and a rather amateur construction made it very difficult to align everything.

I used AF to fine-tune focus after it was roughly adjusted by tweaking distance.

[magic]

If anyone ever wondered what a SO8 package looks like inside, I found some old pictures from my experiments with blueskull's acid + saltpeter formula.

I'm not sure if I was supposed to make a saturated solution of saltpeter in acid or mix a saturated solution of saltpeter in water with acid; maybe the latter would have eliminated crystallization of salts on the chip and sped up the process, but dunno about corrosion OTOH.

Anyway, the junk covering the die on the first picture is just some salt from the process, nothing that came from the factory
The next two pictures were taken after cleanup and some mechanical separation.

[Noopy]

I have bought Armour Etch! 
I wanted to strip the metal layers of a ADR1000 and because of that I had to remove the SiO2. Unfortunately you need HF to remove SiO2 and HF is scary as shit. It´s corrosive, it´s toxic, in lower concentrations you don´t recognise it on your skin but it travels very fast in deeper regions of your body. Some gloves are no protection. => You don´t want to mess around with HF.
Armour Etch is a paste with ammonium bifluoride that generates HF. That´s also dangerous but you don´t have to handle large quantities of HF.






Here you see the die before etching. There are two metal layers.




Some Armour Etch on the die. 




After 6 minutes of HF you can spot some changes at the sides of the upper metal lanes.




5 minutes of 18% HCL dissolves the upper metal layer completely and removes a lot of the lower metal layer too. The SiO2 on top of the lower metal layer is still intact but the HCL takes it´s way through the SiO2 corridors. In the inner circle there is a small part of the metal left.
Where the upper metal layer is dissolved you can see the leftovers of the SiO2. Where the lower metal layer is dissolved you can see the SiO2 corridors.




6 more minutes of HF dissolves the SiO2 on top of the lower metal layer / the empty corridors. The metal leftover is still intact because the HF doesn´t dissolve the metal (Al).
The dark particles look like leftovers of the SiO2.




5 more minutes of HCL remove the metal completely.
There is still a non transparent yellowish layer where the lower metal was. HCL can´t dissolve the yellow layer. I assume that is a SiAl-complex.








More HF and you get rid of the yellow layer and the dark particles.
Unfortunately on this die the layers don´t show the nice colors we have seen with other dies. Nevertheless you can spot the different areas and conclude how the areas interact with each other.
Now you can do some analysis: https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3733504/#msg3733504








before and after the treatment 


https://www.richis-lab.de/Howto_Decap_HF.htm

 

[magic]

Looks good.

At one point I tried NaOH solution (less toxic and attacks both glass and aluminium) but it was unusably slow. Boiling should help because everybody says that hot NaOH eats laboratory glassware, but I didn't try.
NaOH is fairly effective against aluminium spills from overheating (a matter of minutes).

Unfortunately on this die the layers don´t show the nice colors we have seen with other dies.

Yep, because it was the glass

There are some tricks to stain doped areas, but it looks like nasty stuff.
https://siliconpr0n.org/wiki/doku.php?id=delayer:wet#staining

[Noopy]

Unfortunately on this die the layers don´t show the nice colors we have seen with other dies.

Yep, because it was the glass

I had the hope there is still some ... ... resonance ... ... refraction ... ... whatever. 

[RoGeorge]

AFAIK the color is given by the nanostructures being (multiple of) half wavelength, and the incident and reflected wave interfering with each other, somewhere in the middle of this video it is explained with a few more details:



Assuming the refraction index is the same, and the metal or semiconductor layers are glossy (no nano "bumps" on the surface to turn them into a metamaterial), I guess it should be possible to calculate the glass thickness by measuring the reflected spectrum.

[Noopy]

I agree with you. 
Nevertheless I had the hope... 

[XantheFIN]

If anyone ever wondered what a SO8 package looks like inside, I found some old pictures from my experiments with blueskull's acid + saltpeter formula.

I'm not sure if I was supposed to make a saturated solution of saltpeter in acid or mix a saturated solution of saltpeter in water with acid; maybe the latter would have eliminated crystallization of salts on the chip and sped up the process, but dunno about corrosion OTOH.

Anyway, the junk covering the die on the first picture is just some salt from the process, nothing that came from the factory
The next two pictures were taken after cleanup and some mechanical separation.

Hi what is this formula you used in process? "blueskull's acid + saltpeter formula"?

[magic]

You can find it quoted here, the guy who posted it quit the forum and nuked most of his content.
https://www.eevblog.com/forum/projects/decapping-and-chip-documentation-howto/msg2875340/#msg2875340

It's a messy process and I'm not sure if I have done it the same way blueskull did or differently. At any rate:
- I now know that nitric acid evaporates from mixtures with concentrated H₂SO₄ quickly starting at ~80°C (this technique is used for distilling anhydrous HNO₃) so the whole process seems somewhat inefficient/wasteful
- I needed high temperature for anything to happen, it fumed quite a lot, I recirculated some vapor by putting a cap on top so it condensed (but don't pressurize the test tube)
- it took a few hours
- those HNO₃ and NO₂ fumes are toxic, just so you know
- maybe I was supposed to add water to the reaction (use a solution of KNO₃ instead of dropping dry salt into H₂SO₄) but not sure
- too much water means corrosion of bonding pads and/or bond wires

Generally, you should only bother with that if you want to preserve everything intact, including wires and pads.
For just a bare die, it's much easier to use:
- ordinary 65% nitric acid ~120°C in 5ml beaker with watch glass cover (don't sniff the fumes)
- 2ml sulphuric acid at 200~250°C - less toxic, more danger of burns, it bubbles, eye protection advised
- electric heater 400~600°C (needs a few tries to get it right)
- fire (Russian roulette)
- boiling rosin at who know what °C - some people say it works, I never succeeded

This source claims that pure concentrated sulphuric acid may work without corrosion, but it didn't work like that for me. Maybe I haven't used enough and the concentration dropped as water was produced in reactions.
http://www.stockly.com/forums/showthread.php?p=2239

See also
http://siliconpr0n.org/wiki/doku.php?id=decap:epoxy_acid

Have fun

[XantheFIN]

Thanks for answer  Sorry i did read full topic but missed the user name.

I can't have fun as hard to get any good stuff (sulfuric acid, hydroflouric acid, Nitric Acid) after all wanna be muham**** manufacturing explosions so very limited in EU. 

[Noopy]

Heat works quite well for me... 
1-5% failures is ok since I don´t have to work with nasty chemicals and I can do 25 parts per hour. 

[XantheFIN]

With only partial decapping and bond wires survives?...  I am looking to save chip in as whole and keep operational but just make it visible physically.

[Noopy]

Well no...

[magic]

Heh, I missed your flag. Yes, sulphuric acid has been banned by EUnuchs literally this year
I happen to have a "friendly" business which stocks some good stuff so I can occasionally play with it.

If you can't find anything like that or register your own company just for this purpose you are going to have problems.

For the record, it is possible to produce nitric acid from atmospheric nitrogen by electric discharge and concentrate it by distillation (even to fuming concentration with magnesium nitrate, if that thing isn't banned too). Information is easy to find, but both steps are PITA for a complete amateur and need some glassware. Efficiency isn't great, either.

You could try that rosin thing as alternative. This guy's results look somewhat encouraging:
https://www.eevblog.com/forum/projects/whats-inside-the-cheapest-and-fakest-jellybean-opamps/msg3545907/#msg3545907
My advice: use identical glass bottle and the same gas burner and the same colophony because I have tried similar things a few times and never got good results.

[Noopy]

I have an update for the Howto (https://www.richis-lab.de/Howto.htm). I will show you how I do panorama pictures.




To get good pictures for a panorama you have to move the die in X and Y while keeping it in the focus plane of the camera. The best way to do this is to use a micro positioning tool. I have such a tool which allows moving X and Y and tilting around the X- and Y-axis. The tilting is important to get the whole die into the focus plane.




I have a metal block on which I can screw the micro positioning tool. With the help of two locking screws I can move the tool up and down.

On the other side of the tool there is a dish with some double sided adhesive tape on which I put the die.

The horizontal arrangement is favourable because the camera does a good job in this position.




If you have a die in a package or on a ceramic plate or in the middle of a wafer you can get problems with shadowing. In this case the lower parts of the die are darker than the upper part.




To compensate the shadowing you can use the automatic exposure of your camera but if the die is very inhomogeneous that can cause other problems. Pictures with brighter areas get too dark and darker areas get too bright. It is better to change the exposure time manually.




A lot of people use Hugin. In my view Hugin demands a lot of picture adjustment, arrangement and marking by the user.
I use Helicon Focus.




If you are able to move the die quite accurate Helicon Focus is probably able to merge the panorama by itself. If the alignment is not perfect you have to do some work by yourself.




Most of the time moving the pictures to the right place is no bigger problem.






You can adjust in which area Helicon Focus is looking for the right spot to merge pictures. The initial value is 0,1%. For my arrangement that puts out bad results too often. 0,3% is a good value for me.






Edge smoothing 0% is good to find bad picture alignments.






Edge smoothing 100% doesn´t give you the best pictures. 100% moves the edges of the other picture into the foreground.






50% edge smoothing is best for a nice picture.




Done!




Rotating and cutting edges, contrast adjustment and ready to go! 


https://www.richis-lab.de/Howto_Panorama.htm

 

[mawyatt]

Nice 

Lenses for use in panorama type macros need to have very little distortion for chip imaging, whereas for typical insect and flowers this doesn't matter much since the "edges" are easier to blend that chips orthogonal features. When you get into depth type panoramas for that 3D effect, then the lens system needs to be somewhat telecentric as well as have little distortion. As usual no free lunch, and driving up cost and complexity!!

Anyway, you've done the community a great service with all this wonderful chip images! Few appreciate with what's involved in doing so, know we do!!

So hat's off to you 

BTW haven't seen a dual axis tilt stage like that, the manual ones we have are based upon 40 or 60mm square, this looks smaller.

Best

[Noopy]

It seems like I was very lucky with my Canon EF-S 10-22mm f/3,5-4,5 arrangement. 

The next few days I will update the HowTo with some focus stacking experience. Stay tuned! 

Thanks for the compliments!
I´m always happy to get new high quality pictures of things I wasn´t able to see some years ago. I like the mixture of old and new, sophisticated and simple, expensive and cheap, big and small, famous and unknown semiconductors. 

I know that´s a really small micro positioning stage. It was a gift. I have no idea where it came from. For me that´s the perfect tool. 

Greetings!

[Noopy]

A small update regarding the focus stacking.
I have built a new computer and now I get pictures a lot faster! 




Helicon Focus contains a benchmark. My old i7-4770K working at 4,3GHz on all cores with 16GB of DDR3 handles just 104 Megapixel per second.




My new i9-12900K rises the conversion speed up to 423 Megapixel per second.




My GeForce RTX 3070 Ti gives the system a real boost rising the conversion speed to 1.212 Megapixel per second. 




With my old system this picture took me more than one minute to render. My new system does the job in 12 seconds.


https://www.richis-lab.de/Howto_Focus.htm#Upgrade

 


...


I just realised that I have put the initial focus stacking post into the MEMS topic. 
If you are just reading this topic please jump to:

https://www.eevblog.com/forum/projects/mems-nice-die-pictures/msg4009918/#msg4009918

 

[magic]

Well, I suppose you could "edit" the post, copy its contents here and delete the old one.

BTW, I have a question about those ICs after SiO₂ removal.
Are the isolation areas depressed below the level of transistors or are they raised above?
Supposedly they should be depressed because oxidation, oxide stripping and re-oxidation consumes silicon from the surface, but it's hard to tell form the pictures.
Same goes for the "shadows" of buried diffusions.

[Noopy]

Well, I suppose you could "edit" the post, copy its contents here and delete the old one.

But then the "first" focus post would be behind the second one. I think I will leave it like it is right now.

BTW, I have a question about those ICs after SiO₂ removal.
Are the isolation areas depressed below the level of transistors or are they raised above?
Supposedly they should be depressed because oxidation, oxide stripping and re-oxidation consumes silicon from the surface, but it's hard to tell form the pictures.
Same goes for the "shadows" of buried diffusions.

That´s an interesting point. Depending on the light inclination the areas look like being depressed or raised. It´s absolutely puzzling how the optical effect changes with the light.

But I´m not sure about your conclusion. Oxidation consumes silicon, that´s right. But silicon oxide occupies more room than bare silicon, doesn´t it?

[magic]

If an image is confusing, you tend to assume that the light is coming from above or from the opposite side of you (rather than from you). That's why 3D user interface elements on computers are drawn as illuminated from top or top left.

Looking at the ADR1000 pictures you posted here, I see raised isolation at first but I can "force" myself to see it depressed with a bit of concentration. If I simply rotate the same image 180°, it works the opposite way.

I made a small experiment. This die is illuminated with a single LED from top left at a shallow angle. Another die is placed on top to confirm the direction of light. It looks to me like isolations, metal contact windows and likely P/N+ diffusions are all depressed. There are also four test structures ("B" letters) at the bottom. The outer ones (including metal) seem raised, the inner two appear depressed.

The reason for such structure is because at first silicon is consumed to make oxide, then the oxide is dissolved to expose silicon to doping, then more silicon is consumed to make new oxide for further masks. Thickness of silicon keeps decreasing with each processing step applied to given area and the oxide also isn't as thick as on areas where no processing has been done.

That's how I see it.

[Noopy]

That´s a good explanation for the look of the pictures. 

And you are right with the height of the areas. Of course every oxide layer that is removed due to processing deepens the area. 





Here a quick comparison how different the structures can look like.

[magic]

Perhaps nothing new for regular readers of this thread, but I will post it for completeness

https://zeptobars.com/en/read/National-LH0042CH-hybrid-opamp-FET-SEM
https://zeptobars.com/en/read/SEM-deep-dive-1
https://zeptobars.com/en/read/RCA-CA3019-BJT-transistor-array

These are SEM micrographs of ICs at Zeptobars which show what the 3D structure of the surface looks like.

[magic]

co lo pho ny


Well, yes. I found an article written by the CCC guys who popularized this technique a few years ago. Perhaps the most important part:

In "Präparationstechniken für die Fehleranalyse an integrierten Halbleiterschaltungen" von Friedrich Beck aus dem Jahr 1988 habe ich einen Hinweis auf die Entkapselung mittels Kolophonium gefunden. Kolophonium enthält Abietinsäure (etwa 40%). Beck schreibt: "Zum Öffnen wird das Bauteil im Drahtkörbchen in das auf 320 - 360 °C erwärmte Kolophonium getaucht, bis der Chip völlig freiliegt (5 - 10 Minuten); anschließend läßt sich mit trockenem Aceton das anhaftende Kolophonium entfernen." (S. 19, 20) Beck schreibt ferner, dass die Kolophoniumrückstände den Abzug versiffen und das schwer zu entfernen ist. Dies sei der Grund, warum das Verfahren selten angewandt wird.

As far as I understand, they say that the whole idea came from an old German book about semiconductor failure analysis, and according to the book, temperature of 320~360°C is required and it must be maintained for 5~10 minutes because that's how long the reaction takes. Also something about this technique rarely being used in practice because colophony messed up fume hoods

The rest of the article describes author's own experiments, and they were less happy because the process worked, but took an hour or two per chip. However, the author says nothing about any attempts at precise temperature control, he just used a spirit burner.


Well, I thought that I will be clever and perhaps manage to achieve reasonable speed by regulating temperature precisely in the recommended range. I loaded my old thimble cooker with colophony and two different SO8 chips, connected it to a variable DC power supply, shoved a thermocouple in it and adjusted power to reach and maintain progressively increasing temperatures above 300°C. (I tried 270°C for two hours previously, so it surely made no sense to bother with less than 300°C).

15 minutes at 320~330°C. There were small bubbles and some smoke coming, nothing terrible.
15 minutes at 330~340°C. Similar to above. Some colophony lost, but not a lot.
Then I refilled and tried to hit 350~360°C, but it ended up more like 360~380°C. Now, bubbling and smoking got much worse and colophony was disappearing faster.
After another 10~15 minutes, there was almost nothing left so I turned it off.


And the outcome? Almost nothing. Maybe the chips are a little smaller than initially, but surely not dissolved fully or even significantly. I have no patience to wait a few hours and see what happens.

This guy says it should be a few minutes. At this point I don't understand what's going on. At least I know that it isn't about temperature - less than 300°C is completely ineffective, and 400°C or more is lots of smoke and colophony gone.

Maybe there is something wrong with my colophony. I use some "activated" colophony for soldering. I will look if I can find unprocessed natural colophony somewhere. Other than that, no idea