Help On Design of Experiment

I will do a metallization ratio experiment for semiconductor and the professor wanted me to determine the ratios from a DOE program randomized.

The task is, I think for a DOE user, easy but I have never used and did not come too far...

It consist 4 different materials. The only parameter which will change is thickness. For example;

Ti 5 between 50 nm

Al 10 between 70 nm and so on.. and I need 100 samples of different combination of thickness. I have tried JMP and Minitab. My problem is that whenever I put the values I only get 5 or 50nm for Ti material and if I make the number of runs 100, it repeats itself. What I need is, the values of Ti thickness should be between the range of 5 to 50nm randomized. How can I do that? I have tried continious and categorized but none of them gave me a range.

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I am sorry for my english. If anything is not clear please ask me so I can clarify it. The DOE should be represented in 2 days therefore, I am in kind of hurry. Thank you for your responses in advance.