Lab #8 Help Document

Lab #8 Help Document

This help document will be structured as a walk-through of the lab. We will include instructions about how to write the report throughout this help document.

This lab will be completed in room260 CTB.

You will need to partner up in groups of two for this lab. Since there is only one metallurgical Microscope, each group will have to alternate in and out to get a turn using it.

This lab will require the use of the following pieces of equipment:

Metallurgical Microscope

IC samples

Computer

Digital ruler or Dial Caliper

Procedure

1. Using the material covered in class, study the pictures on the class website for this lab. Using them, determine the process resolution. Using one of the website pictures, or a chip of your choice, determine the process Cpk. (See * below) Also record other observations, such as the relative dimensions of a transistor.

For this part of the lab, you will need to access a computer and get onto the class website to view pictures for lab 8:

There should be 5 pictures. Look them over and find a picture with a feature that repeats completely (not partially cut off of the page) at least 3 times. You will need to include the picture that you choose in your lab report for this section.

The purpose of this part of the lab is to calculate the process Cpk for the part you have chosen to measure. The process Cpk is calculated using the following equation:

Cpk = |(χ – NSL) / 0.5 PW| , where:

χ = process mean

PW = process width = (Highest measured value) – (Lowest measured value)

NSL = nearest specification limit (to the mean). This is the measured value nearest to the mean.

(χ – NSL) = process resolution (you’ll need this to answer a question for part 1 of the lab).

Measure the width of at least 3 of the repeating features. To make a measurement, either use the dial calipers to measure the image features on the screen or paste the image into a paint page, then paste in the ruler provided in the help section for lab 8 on the class website.

When making a measurement, measure in the same place for each feature and make the same kind of measurement. The easiest measurements are the width and height of the feature. Pick either the width or the height as the type of measurement you will make.

Once you have determined how you will make your measurement, measure at least 3 of the features using your chosen method. The units are not relevant for part 1 of the lab since the process Cpk is a ratio and is therefore unitless so don’t worry about including units.

Now that you have your measurements, you can use them to find the components for calculating the process Cpk. Start by finding the process mean (χ). Do this by adding your 3 (or more) measurements together and dividing by 3 (if you do more than 3 measurements, divide by the number of measurements that you made.)

Now find the process width (PW). Do this by taking subtracting your lowest measurement from your highest one.

Now find the nearest specification limit (NSL). This will simply be the one measurement you took that is closest to your calculated process mean.

Now that you have all of the components, plug them into the equation to find Cpk .

Cpk = |(χ – NSL) / 0.5 PW|

This part of the lab also asks you to find the process resolution. The process resolution is equal to the process mean (χ) minus the NSL or in other words (χ-NSL).

For lab report: Include the picture whose features you measured. Identify which feature you measured on the picture. Indicate whether you measured width or height of the feature. Include your 3 or more measurements. Include your calculations and equations used for process mean, process width, and Cpk and specify which value you chose for your nearest specification limit. Also record any additional observations you wish to make about the image.

2. Observe any one of the sample IC chips on the metallurgical microscope. Measure the smallest dimension you can find (include the picture in your lab book). How many different areas do you see on this chip? Determine the area of a transistor. Assuming about 60% of the chip area to be transistors, calculate the number of transistors on the chip.

For this part of the lab, you will observe an IC chip sample using the metallurgical microscope. To operate the microscope, first turn on the power button located on the right side at the bottom.

There are two knobs on each side. The larger knob adjusts focus by a large amount while the smaller knob is used for fine focus adjustment. Make sure that the knobs are adjusted such that the tray that a sample is placed on is in its lowest position whenever starting to look at a sample.

There are two vertical knobs under the sample tray. The smaller lower one adjusts the tray’s left-right position while the larger upper knob controls the tray’s forward and backward position.

There are four objective lenses under the sample tray with magnifications of 5x, 10x, 20x, and 50x from the shortest to the largest. When starting a new sample observation, always adjust to the lowest magnification, find the focus, then increase magnification and find focus again until features are able to be clearly seen.

There are also some knobs and levers on the back of the microscope that change the lighting effect. Ignore these as they are not needed for this lab.

There are two samples that you can choose from for this part of the lab. These can be found in the top right-hand drawer of the desk on the back wall inside of a container labeled “Leadframe and Wafer pieces”.

To view a sample, place the surface to be viewed down over the hole in the sample tray.

Make adjustments by viewing the sample through the eyepieces first. Then use the Motic Image program on the computer next to the microscope to make measurements of the sample and take a picture.

Before making a measurement, use a calibration dot to scale the grid on the Motic Image viewer. Use that grid scale to measure the features asked for.

Now to take the measurements that the lab document asks for.

First, the operator will zoom in and identify the smallest dimension on the chip that can be measured and that measurement will be taken. The smallest dimension is basically the shortest straight line on the chip that you can identify. Measure that and record it in your lab report.

Next, identify the number of different areas that are seen on the chip. Not that the piece of silicone wafer is made of many different chips that have not been separated. Several areas will be stacked next to each other in a chip forming a pattern, so one area will be a section of circuit that is not repeated within itself. Record the number of areas on the chip in your lab report.

Measure the total area of the chip. Remember that this is not the total area of the wafer, but rather the area of one of the chips on the water.

Measure the area of a transistor. A transistor should be a smaller rectangular component such as the one identified in the image below.

Estimate the number of transistors by multiplying the total chip area by 0.6 and dividing that by the transistor area.

A picture like the one above needs to be taken and included in your report. You can take the picture using either a camera or screen capture.

NOTE: When done with the lab, TURN OFF the microscope. Leaving it on unused wastes energy and reduces the useful life expectancy of the microscope.

For lab report: Include a picture of the IC chip that was examined and indicate the smallest dimension that you measured on the picture. Include all measurements (the smallest dimension you could find, the number of areas on the chip, the area of a transistor, the area of the chip). Include your calculation and equation for finding the number of transistors on the chip.

3. Record other observations, such as dirt, irregularities, scratches, or other unusual findings.

This part is pretty self-explanatory. Just include the above mentioned observations in your lab report.

Equipment

Accu-Scope Metallurgical Microscope 0713234

Computer

Silicone wafer

Conclusion

Compare what you saw and determined to what you expected from what you learned in class and read in the book. Explain why typical yields in IC manufacturing are lower than 90%.

For lab report: Make the above mentioned comparison and also explain why IC yields are lower than 90% (hint: Think about the small scale that IC manufacturing occurs on. How easy is it to make a mistake when dealing with such small sizes on so many chips? Also, think about the CPk that you calculated earlier. Is this a good CPk?)