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Diversionary Method

| On 01, Apr 1998

Gregory Frenklach
gregoryf@avx.co.il

Do you remember this joke: “If everything is OK with your system – Don’t worry – It will not last for a long time”? Different methods like FMEA, for example, were developed in order to predict future system failures. The aim of the FMEA-like methods is to answer to the question: “What might be wrong with a system?” But these methods don’t answer to the other very important question: “How might it occur?”

For more than ten years in TRIZ there has been an approach which enables us to know ” in advance” and to prevent system failures and/or harmful effects. According to this approach instead of asking the question: “What might be wrong with a system?” we ask another question: “How could one make the system fail?” or “How one could make the system cause the maximum harm?” This transformation of questions “why” or “what” in the FMEA-like methods into question “how” enables us to use all TRIZ instruments.

Such an approach was realized in the method which was developed by B. Zlotin and A. Zusman. This method (which at the very beginning was called “Diversionary Method” or “Diversionary Analysis” now is called “Anticipatory Failure Determination” abbreviated as AFD) enables us to predict the appearance of harmful effects in our system or its failures and prevent them before they occur. The weak point of this method is the connection to the TRIZ instruments. It is not so clear which instruments have to be chosen in order to resolve the “transformed problem”, because there isn’t classification of “diversionary” problems and clear rules of their transformation into the fit inventive situation .

The aim of this work is to increase efficiency of the AFD by means of clear classification of the “diversionary” problems and connection of the TRIZ instruments.

The “Diversionary” Method (I prefer the old name) could be divided into four main stages:

I. The possible harmful effects (“diversionary” problem synthesis)

In order to expose all possible harmful effects and system’s failures the functional analysis is made. Possible harmful effects creation or intensifying are considered for every element of each functional group: function carrier, function, function object. This is done for every stage of the analyzed system’s life cycle. (This reminds us of solving diagnostic problems of the second type—see the March issue of The TRIZ Journal.)

For example: Let’s take as our system a device for shadow termination in sputtering machine. The function of this device is to press a metal mask to a wafer.

The device consist of a base plate 1, bridges 2, press-strips 3 and a metal mask 4. The mask is pressed to the wafer 6 with help of screws 5 and the press-strips 3. The device is made of stainless steel. The bridges are welded to base plate. Every bridge has two slots . The press-strips are inserted into these slots and can move upwards and downwards inside them.

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The wafer looks like sandwich which consist of alumina strips which are stuck with special glue to a glass carrier.

The worker put the mask upon the wafer and then insert this “sandwich” into the device. Then he performs alignment of mask position under a microscope and then presses the mask to the wafer with help of press-strips and screws. Then a number of devices are put upon pallet and are loaded into the sputtering machine.

In the machine under condition of deep vacuum and temperature about 300oC the parts of the wafer, which are uncovered by the mask, are coated with Cr. and then with Cu. The principle of work of this sputtering machine is based on plasma bombing of the Cr., Al or Cu targets. The atoms “bombed out” from the targets of these metals fall down and coat the uncovered parts of the wafer. Then the wafers are taken out of devices and the devices are cleaned from Cr. and Cu in special chemical solutions.

Let’s perform, first of all, short functional analysis of our system (it is simple enough) and then for every “function group” let’s “invent” harmful effects which could appear at every stage of life cycle of the analyzed device:

  • manufacture
  • using (work)
  • maintenance
  • storage

We will consider for every element of a functional group the harm which could be caused by the element to other elements of the system or environment at every stage of the system life cycle or the harm which could be caused by other elements of the system or environment to the analyzed element. Four types of possible “diversionary” problems will be taken into account:

  1. harm (connected with changing of parameters or properties of the analyzed element) creation
  2. creation harm (connected with wrong measurement)
  3. intensifying of harm, which already exists
  4. useful interactions’ elimination

1. The function of the base plate is to hold the wafer.

Functional group:
plate – holds – wafer;

2. The functions of the bridges are:

a. to hold and direct the press-strips.
Functional groups:
bridge – holds – strip;
bridge – direct – strip;

b. to press press-strip to mask (together with screws).
Functional groups:
bridge – presses – press-strip to mask;
screw – presses – press-strip to mask;

3. The function of the press-strip is to press the mask to the wafer (together with base plate).

Functional groups:
press-strip – presses – mask to wafer;
plate – presses – wafer to mask;

4. The function of welding is to join the bridge and the base plate.

Functional group:
welding – joins – bridge and plate.
Let’s take, for example, the functional group: press-strip — presses — mask to wafer. We will consider this group on different stages of life cycle of the device in order to invent possible failures and harmful effects which are connected with this group.

Stage of manufacture:

Press-strip can be deformed;
Mask can be deformed;
Wafer might have dirty surface;
Surface of wafer can be wavy;
Glass carrier can be cracked;
And so on.

Stage of storage:

Press-strip can be deformed;
Mask can be deformed;
Wafer might have dirty surface;
Glass carrier can be cracked;
And so on.

Stage of work:

Press-strip can be deformed;
Mask can be deformed;
Glass carrier can be cracked;
Nearly all of these harmful effects either don’t exist or can be explained on the basis of common sense except for mask deformation on “work stage” (the analyzed system is real and it works very well). Moreover the effect of thermal extension of the mask in the sputtering machine was taken into account. That’s why the mask was made of kovar instead of stainless steel Thus one of our “diversionary” problems is the mask deformation (which will cause harmful effect – metal coating under the mask) inside of sputtering machine.

II. Transformation of every “diversionary” problem into inventive one. (This is similar to the diagnostic problem of the first type).

The “diversionary” problems can be divided into four types:

  1. Finding the ways to perform the action, which causes the harmful effect connected with changing parameters or properties.

  2. Finding the ways to perform the action which causes the harmful effect connected with wrong measurement.

  3. Finding the ways of intensifying of the action which causes the harmful effect.

  4. Finding the ways of elimination of the useful effect, function or interaction.

For example: Our problem belongs to the first type.

These problems then can be transformed into two types of the inventive situations:

  1. One has to perform some function in order to get the harmful result which further is considered as useful; (points 1 and 2)

  2. One has to eliminate an undesirable effect (useful interaction, which further is considered as harmful, or low efficiency of a harmful action, which further is considered as useful); ( points 3 and 4)

For example: We can transform our problem into the inventive situation of the first type. We have to find a technical facility, which will perform the function: to deform the mask.

Then we transit from these situations to problems according to the rules of such a transition:

For a) we define:

the function;
the object of the function;
the known method (facility) of the function’s performing;
the UDE (undesirable effect) which arises if we use this known method;

For b) we define:

the UDE;
the element connected with this UDE;
the function of this element;
the object of the function;

For example:

the function – to deform mask
the object of the function – mask
the known method of the function’s performance – heating the mask (the mask is pressed by press-strips to the wafer, thus thermal expansion can deform it)

UDE – the thermal expansion is too small and it isn’t enough to deform the mask.

Then we choose the possible directions in order to resolve the problems.

There are two possible directions:

  1. performance of the function without using of known method (facility);

  2. elimination of the UDE which is connected with usage of known method (facility);

Theoretically, the choice of the right direction depends on the condition: “To use only resources of the system in order to find the solution”, but in real life the two directions have to be checked…

For example: We choose the second direction.

The problems can be solved with help of the Adapted Algorithm for the Diagnostic Problems’ Solving (see article “Classifying of the Diagnostic Problems in the March, 1998, issue of The TRIZ Journal).

Using this algorithm You easy will come to following solution: “To use mask coating by other metal in order to cause its deformation”

III. The invented harmful effect “realization” check in the real system.

Here are the possible questions to be answered:

  1. Is the effect realized in the system ?
    For example: From one hand it is. The mask is coated by Cr. and then by Cu so we have thermal expansion effect of the ” bi-metal sandwich”. But on the other hand it isn’t, because we don’t see it.

  2. If it isn’t – What are the possible conditions in which it could be realized?

For example: The effect will be realized if:

  1. The layer of metal coating on the mask will be thick;

  2. The mask will be thin (by the way, we are going to use more thin masks for smaller electronic elements);

IV. Elimination of the harmful effect and/or conditions in which it could be realized.

At this stage we have to solve “usual ” inventive or routine problems.

For example: We can easy solve the first problem. The routine solution is to clean the masks from Cr. and Cu after number of cycles in sputtering machine. But the second problem is “inventive”. Let’s describe it in brief:

Metal coating of the mask in the sputtering machine together with high temperature cause mask deformation. This causes appearance of a metal on the wafer surfaces which have to be protected by the mask from metal coating. What can be done?

Try to solve this problem using TRIZ tools, which you already know. Good Luck!

Bibliography

  1. G. Altshuller. Creativity as an Exact Science. NY. Gordon & Breach Science Publishers, 1984.

  2. G. Altshuller, B. Zlotin, A. Zusman Filatov. Search of the New Ideas: From Inspiration to Technology. Kishinev. Karta Moldovenyaske, 1989 (in Russian)