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Friday, October 27, 2017

Metal Layer Stack (Nomenclature) Part 2

In the last part we have discussed about the Metal Stack. The way foundry provide data, different restrictions and available options. Now it's time to understand the very next step - how to communicate the complex Metal Stack information across the design team or groups or companies. For this Foundry also provide Nomenclature of metal stack.

If you remember in the last article we have discussed that there are different metal wires like Mx, My, Mz, Mr , Mu, etc (in XYZ Foundry). Below diagram can help you to remind this very well.

Now, lets suppose you want to use Stack type 7 and same you want to communicate to other user, then there is a standard way for this. (You might be thinking that I will communicate directly that you are referring Stack type 7. But if we do this - every time user has to refer this table to understand different metal layer optons. :) ).

If you will check closely the Stack Type 7, you will find below information.
  • There are Total 6 metal layers.
  • Metal 1 is of M1 type.
  • Metal 2, 3, 4 are of Mx type. Means next 3 Metal layers (After M1) are of Mx type.
  • Metal 5 is of My type. Means next 1 metal layer (after Mx) is of is of My type.
  • Metal 6 is of Mz type. Means next 1 metal layer (after My) is of is of Mz type.

Now, if I combine all this information and write something like this.

M1_3Mx_My_Mz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.

Between 2 metal layers (e.g M1 and M2) - we will use VIA as per upper metal layer type (e.g Vx type)
The way I have defined the sequence also help to understand the sequence of Metal layer.

Any one can now interpret that :
Metal 1 = M1
Metal 2 = Mx1 (Mx Type)
Metal 3 = Mx2 (Mx Type)
Metal 4 = Mx3 (Mx Type)
Metal 5 = My1 (My Type)
Metal 6 = Mz1 (Mz Type)

VIA 1 = Vx1 (Vx type)
VIA 2 = Vx1 (Vx type)
VIA 3 = Vx1 (Vx type)
VIA 4 = Vx1 (Vy type)
VIA 5 = Vx1 (Vz type)
Remember, number of VIAs are always 1 less then the number of Metal layers. :)

Different companies uses different way to understand this. Like following are few examples.
  1. M1_3Mx_My_Mz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.
  2. 3Mx_My_Mz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.
  3. 3MxMyMz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.
  4. 6M_3MxMyMz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.
  5. 1P6M_3MxMyMz : 1 (M1 Type) + 3 (Mx type) + 1 (My Type) + 1 (Mz Type) = 6 Metal layer.

  • In the 2nd, 3rd, 4th and 5th option, First Metal layer M1 is considered by default.
  • In the 4th option, It was mentioned explicitly that stack has 6 metal layer (6M).
  • In the 5th option, It was mentioned explicitly that stack has 1 Poly layer (1P) and 6 metal layer (6M).

For the above figure, I have added all the nomenclature as per 5th option. Also for your easiness, I have mentioned Stack name at the Top and Bottom (both places same information). I am sure, after this there will be no confusion. :)

In the last, I just wanted to highlight that above nomenclature and metal stack options is for 1 foundry. But different Foundries may have different ways to provide and representation their information. With in the companies or group or team, they can also decide their own way to represent Metal Stack but when they communicate with outside world, either they have to use certain standard or they have to provide details of their nomenclature (which is very common).


  1. Thank you for sharing! This is what I want to find.

  2. Thank you for sharing.
    I have a question?

    As you mentioned there are so many metal option by foundry.

    How can I select appropriate metal option for my design?
    Is there priority or check point to select metal option by design?

    1. may that is given by fabrication people in .tf file
      plz correct if I`m wrong


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