IMPLEMENTATION IN MATERIALSSEMICONDUCTOR COMPONENTS122828

GROEP 2JASPER DIEPHUIS S0090743STEFAN VEENHOF S0139246

SUPERVISORS:JOOST MELAIGIULIA PICCOLO

TABLE OF CONTENTS

INTRODUCTION

For the course implementation in materials several different topic where available. Four diverse topics were presented to choose from, we made the choice to investigate photodiodes. The first sessions was a simply safety course through the MESA+ labs and after this several session in the MESA+ followed. In these sessions in the clean room 3 wafers were made which contained several simply photodiodes and some other structures. After the completion of the wafers the next phase of the course was involved doing several measurements on the wafers. Several characteristics of the photodiodes and wafers were measured and can be found in this report. In short the contents of this report are as follows: Firstly the theory behind photodiodes and their production will be discussed. In this section the questions from the manual will also be answered. Secondly the actual creation of the photodiodes and other structures is described as we went through this process. Lastly the measurements will be discussed and some conclusions will be drawn.

THEORY AND PROBLEM DEFINITION

THE PHOTODIODE

A photodiode consists of a couple of layers. Firstly there is a n-type layer and a p-type layer. In between these two layer is the depletion layer. Because of the transportation of holes from the p-type to the n-type layer and the transportation of electrons from the n-type to the p-type layer a electric field is created in the depletion layer. This field will oppose the transportation of the electrons and the holes and a state of equilibrium will be created.

When light is absorbed by the photodiode, a photon and its energy can create a free electron-hole pair by colliding with one of the silicon atoms. The electric field of the depletion layer will separate this pair (if the pair is in the depletion layer). These separated carriers will than contribute to the photocurrent.

QUESTIONS

Q1 (p16): For the standard photodiode with oxide you can also use mask 1 and 3. Mask 2 on the other hand has to be changed, in what way do you think it must be changed?

On the contrary of what is said in chapter 3 of the manual, the displayed masks will create a photodiode with oxide layer. As can be seen, mask 2 in figure 3.1 of the manual ensures that the oxide layer of the photodiode is not etched away. When a photodiode without an oxide is to be made, mask 2 can be disregarded.

Q2 (p18): Explain for the structures in figures 3.4 and 3.5 where the channel is. What are the channel width and length, and where are the source, drain and gate?

The channel can be seen clearly in the first masks of both figures as it is the n-type area between the two p-type areas. The width of the channel of figure 3.4 is given as e1 and is 100 µm the length is equal to e2, 600 µm. For the second type of MOSFET as shown in figure 3.5 the width of the channel is given as f1 and is 20 µm. The length of the second channel is f2, 4240µm. The aluminum strip that is placed over the channel is called the gate with both MOSFETs. The other two aluminum strips (on the sides) with both MOSFETs are the drain and source.

Q3 (p36): Describe the two physical processes that are responsible for the breakthrough of diodes.

The first process is called the avalanche breakdown. This process occurs when a high reverse voltage is applied which creates a large electric field across the depletion layer. The carriers in the depletion layer are accelerated by the field. When the carriers gain enough energy they are able to ionize silicon atom they collide with. This creates a new hole-electron pair wish will cause even further collisions and ionization. This works quite like an avalanche which is why it has acquired the name avalanche breakdown.

The second process is called the Zener breakdown. This effect occurs with heavily doped junctions which have narrow depletion layers. If a reverse voltage is applied and the depletion region is too narrow for avalanche breakdown (because carriers can not reach high enough energies over the small distance

traveled) the electric field will grow. The electric field can eventually become strong enough to pull electrons directly from the valance band to the conduction band.

Q4 (p36): Why is the breakthrough voltage an important parameter in the characterization of a pn-junction and how can it be increased?

The breakdown voltage is mainly depend on the size of the depletion layer and so on the doping of the pn-junction. To adjust the breakdown voltage the doping can be increased or decreased. The reason the breakdown voltage is an important parameter is because, depending on the application, it is a very desirable or undesirable effect. For instance some devices might not be able to handle the large current that is created at the breakdown voltage and for these devices it is important to know the limit of the reverse voltage that can be used. Other devices use the effect of the breakdown voltage for specific purposes, for these devices the breakdown is exactly what is wanted.

Q5 (p36): Which factors influence the efficiency of the diode?

The most important factor is the lifetime of the electron-hole pairs. The longer the lifetime the higher the chances of carriers, that were originally generated in the neutral region, of reaching the depletion layer. If these carriers reach the depletion layer they will be separated by the electric field and contribute to the photocurrent. Another factor is the recombination of holes at the surface, preventing this also increases the efficiency. Lastly the reflection at the surface of the diode is an important factor. The lower the reflection the more efficient the diode will be.

Q6 (p36): How can the efficiency be increased?

The lifetime of the electron-hole pairs depends on the impurities in the crystal and can be improved by the application of special temperature steps during processing. To prevent recombination of holes at the surface a layer of for instance SiO2 can be added on the surface and the dimensions of the metal contact can be reduced. Minimizing the reflection can be done by added a special top layer (for instance S iO or Al2O3) that reduces the reflection coefficient.

Q7 (p36): For which color of light is the photodiode most sensitive and why?

For this answer see the picture below, in which it is shown which wavelengths of light are reflected the least. As can be easily seen light with a wavelength of around 0,6 µm is reflected the least. This wavelength correspond with orange (perhaps even slightly red) light. The reasons the photodiode is the most sensitive to this color are simply that if less light is reflectived more is absorbed and used.

Q8 (p36): In which way can the color sensitivity be shifted to the blue/ violet region and which problems occur if you do this?

Applying top layers can reduce the reflection of a broader spectrum allowing the absorption of even blue and violet light. A single top layer however only works only for a limited bandwidth. It is also possible to use multiple top layer but applying these can be a difficult task.

Q9 (p36): Why is the curve factor always less than one?

Firstly the equation for the curve factor:

CF=V MP ∙ IMP

V OC ∙ I S C

This formula can also been seen as the maximum power divided by the ideal power. Now consider the following figure:

In practice the VOC is always higher than Vmp and Isc always higher (more negative) than Imp. This result in the fact that the product of VOC and Isc will always be larger than the product of Vmp and Imp. Now look back at the formula for the curve factor and it will be easy to realize that the curve factor can never be more than (or equal to) one.

Q10 (p38): What causes the contact resistance and why is it so important?

The contact resistance is caused by the resistance between the aluminum and the p+-layer and also by the p+-layer itself. The contact resistance act as a series resistance in the model of the diode. The effect of this resistance can be seen in the figure below:

As can be seen the contact resistance has a large influence on the V-I characteristic of the diode. The higher the contact resistance the lower the maximum power will be. This makes the contact resistance very important, since it has a direct influence on the maximum power and efficiency of the diode.

Q11(p38): Why is the voltage being measured with separate probes?

…… don’t know. Perhaps because the voltage meter has to have a very high resistance to ensure no current goes through it.

Q12 (p38): Where does the accuracy of the calculated values of R and RC depend upon?

The accuracy depends on the contact resistance of the aluminum contacts with the probe and off course the accuracy of the measurement device.

DETAILS OF THE PROCESSING

INTRODUCTION

The fabrication process of photodiodes is described in the following paragraphs. 3 wafers with several photodiodes, Greek Cross structures, Long diffusion areas and MOSFETs were created in the cleanroom. All these structures were realized on a n-type silicon wafer on which a layer of SiO3 with a high boron concentration was deposited. When the wafer is heated the boron will diffuse into the silicon and create a p-type region. This is the process which allows for the creation of the required structures. The entire process will now be discussed in detail.

DAY 1: CREATING P-TYPE REGIONS

The first thing done to the wafers was a thorough cleaning process to ensure there were no contaminations of any kind on the wafer. This standard cleaning process will be described once, but was in fact used many times. The wafers are first deposited in fuming pure HNO3. There are to beakers the first is for the worst dirt and the second for the little that remains after the first. This ensures the second beaker is always somewhat clean. The wafer spend 5 minutes in the first and than 5 minutes in the second beaker to clean off all organic material. After this the wafer are rinsed in water. The wafer the proceed into a beaker with a boiling (95°) 69% HNO3 solution. The wafer spend 10 minutes in this solution to clean off any metals. After this the wafers a rinsed once again and dried using a spinner and some nitrogen to remove the last drops.

The next step is to apply a photo resist to the wafer. Before applying the actual photo resist, a layer of HDMS (hexamethyldisilazane) is applied to the wafer. This makes it easier for the resist to attach to the wafer. The HDMS replaces the OH groups at the surface of the wafer with CH3 groups. A few drops of HDMS are applied and the wafer spins for 20 seconds to ensure an even distribution of the solution. After that a few drops of resist 907/17 are applied and the wafer spins again to distribute it evenly. Now the resist is applied and the wafer is baked for 5 minutes at 95° to remove the solvent.

Next is the actual lithography and the first mask was applied on the wafer. Since a positive resist was used any areas touched by UV light will eventually be etched away. Only those areas that are not subjected to UV light will retain their boron layer and only these areas will become p-type regions after heating. After correctly positioning the mask the wafer is exposed to UV light for several seconds. Then the wafers are baked for 60 second at 120°. The wafer are then put into a developing solution called TMAH (tetramethylammoniumhydroxide) which removed the photo resist only in those areas exposed to UV light. The wafer are baked once again after this step for 5-10 minutes at 120° (hard bake). The etching is

done with a HF solution which is buffered with NH4F.

HF+H 2O↔H3O+¿+F−¿¿¿

SiO2+6HF→ [H 2 ] [ Si F6 ]+2 H2O

Using the standard cleaning procedure described earlier the wafer are cleaned and the remaining resist stripped from the wafers. After this the wafers are baked at 1100° in nitrogen for 30 minutes, during which the p-type regions with boron doping are created.

2B2O3+3S i→3S iO2+4 B

Followed by a bake of 1100° in oxygen for 30 minutes to oxidize then entire wafer.

DAY 2: DEFINING THE CONTACT POINTS

The day started by measuring the thickness of the oxide layer using a elipsometer. Using two lasers (one of 632 nm and one of 1550 nm) the thickness is measured by looking at the change in polarization of the laser when it is reflected.

n=1n=0 A t632=88,67±n ∙281,50nm

B t 1550=370,22±n∙699,69nmt A=370,17tB=370,22

Thickness of the layer that was not etched.

n=0n=0 A t632=117,94 ±n ∙281,50nm

B t 1550=118,81±n ∙699,69nmt A=117,94tB=118,81

Thickness of the layer that was etched.

Once again a layer of photo resist is applied and then the second mask has be applied to the wafer. This time careful alignment was needed, using a microscope and the arrows and crosses available on the wafers and mask. Once the mask was properly aligned the wafers were exposed to UV light and baked afterwards.

The etching process is once again done with a HF solution but in the dark. This is to prevent pitting and staining. Light would generate charge in the photodiode (see the equation below) and this process combined with the HF solution would create holes on the wafers.

Contineus cycle ¿

After cleaning the sheet resistance of the wafers is measured using a 4-point probe. This method is explained in more detail in the measurement section and will not be discussed now. The results of the measurement were a bit inconsistent between the two machines that were used. However the sheet resistance was around 10 Ohms.

DAY 3: ETCHING THE ALUMINUM

A layer of aluminum was applied to the wafers and as a result the third step of the cleaning process was omitted. The boiling HNO3 solution would have cleaned off all the aluminum, which is why this was not done when cleaning the wafers. Using the MAXIMUS machine the resist was applied (without HDMS, because the resist doesn’t need to attach to silicon but aluminum) and the wafers were baked. After that the third mask was aligned and the wafers exposed to UV light. The MAXIMUS machine was once again used to develop the resist after which the wafers were hard baked. To etch the aluminum PES is used. After etching the wafers are cleaned again (without boiling HNO3 off course).

After this a aluminum layer is deposited on the backside of the wafers, this is done to simplify contact between the wafers and ground during measurements. The last step is called sintering, in this step the wafers are baked at 400° inside a wet nitrogen (N + a little H2O) atmosphere for 10 minutes. In this time

free H+ attach to free Si connections, this is done to ensure that these free connections do not interfere in later stages.

MEASUREMENTS

INTRODUCTION

The second phase of the course was measuring and testing. In the following section it is described how the photodiodes and other structures where measured and tested. The results have partly been processed in tables but another part has been added as an appendix because some of the graphs are not digital. Further more the results be discussed in a short conclusion.

MEASUREMENT EQUIPMENT

Before the measurements and tests are described, the specification of the used equipment is discussed, so it doesn’t repeated elsewhere in the report. Two devices were used, a semiconductor parameter analyzer and a sort of DC analyzer.

HP-4145 Semiconductor Parameter Analyzer (SPA):

The most import specifications are given in the manual and have been copied into this report, see table x.x.x.

7.1 QUALITATIVE MEASUREMENTS

In the first measurement (M-1) 40 photodiodes divided over 3 wafers were measured and tested. From each diode the basic characteristics were measured: the short circuit current (I sc), the open circuit

voltage (V oc) and the breakdown voltage (V b). Beside these parameters, the photodiode is also classified in three states (M-2). Good, bad and defect.

METHOD

With a I-V curve that includes the breakdown voltage and a forward conduction is it easy to classify the photodiode. A bad photodiode shows the basic characteristics of a diode but with high a R s or/and low

Rp. A defect photodiode doesn’t show a characteristic that looks like a diode. Within this I-V curve the basic characteristics are also presented and so it can be used for both measurements. The photodiodes are measured evenly with and without oxide on top of the layer.

The measurement was done using the following construction. From the SPA there are two connections, one ground and one signal. In the figure x.x.x. a simplified version of this construction is shown.

Figure x.x.x.

RESULTS

Measurement one (M-1) and two (M-2) are both shown in a table in appendix x.x.x. With this table the difference between oxide and non-oxide involving the short-circuit current (I sc) can be placed in a histogram, see graph x.x.x. The numbers on the horizontal axis are the column number on the wafer. So the couples that can be seen, are on the wafer, right next together.

1 2 3 4 5 6 7 8 9 10 1 3 5 7 9 1 3 5 7 90

10

20

30

40

50

60

70

OxideNon-oxide

# diode

Isc (uA)

In this graph it is easy to see the difference between the oxide and the non-oxide photodiodes. This difference can be explained with the advantage of a top layer of SiO2. The most important advantage is that the lifetime of a electron hole pair will be extended so that the chance that the pair will reach the depletion region is higher. The lifetime is extended because the SiO2 on top of the upper neutral region prevents the recombination of the electron hole pair at the surface. The more pairs from the neutral regions reach the depletion region, the more reverse current will flow during closed circuit. Another reason is that the layer of SiO2 reduces the reflection of the photodiode. SiO2 is not the most useful substance, but it is better the silicon surface. More successful chemicals are: SiO, Si3N4 and Al2O2.

7.2 PLOTTING THE I-V AND P-V CURVE AND DETERMINING R S AND RP

In this measurement the I-V and P-V curves of different photodiodes were measured and as a reference a standard industry diode was also measured. In both measurements a controlled source of light will shine on the photodiode, so the amount of reverse current (I r) can be manipulated.

METHOD

The same construction as the previous measurement was used, only this time the light intensity will be the variable. In the first measurement (M-3) the I-V and P-V curves of the reference diode are measured with a I r of 50 µA and 100µA. This in combination with a constant voltage of -0,25 V across the diode.

In the second measurement (M-4) the I-V and P-V curves of the diodes on the wafer are to be measured. This time only with a I r of 100µA

In the third (M-5) and the fourth measurement (M-6) the resistances of two bad photodiodes with respectively a bad serial resistance or bad parallel resistance have to be determined. The parallel resistance can be found with one measurement with a reverse current of 100µA. The serial resistance can be found by doing two measurements using a different reverse current in each measurement. In the table x.x.x (grote tabel in 7.1) from the previous paragraph the photodiodes are listed with a classification, and based on these results diode number 20 from wafer 1 is chosen for the Rp measurement and diode

number 5 from wafer 2 is chosen for the R s measurement.

RESULTS

All the plotted curves are added to the appendix.

-M-3 appendix x.x.x.

-M-4 appendix x.x.x.

-M-5 appendix x.x.x.

-M-6 appendix x.x.x.

The results of measurement M-3 and M-4 are extracted from the graphs, I sc, V oc, Pmax and CF(Curve Factor) are given in de following table x.x.x

Task Wafer # Diode # Isc (uA) Voc (V) Pmax (uW) CF

M-3 NA VTB8440B -48,32 0,39 -13,6 0,72

2

NA VTB8440B -99,25 0,41 -29,20,71

8

M-4 1 3 -98,31 0,48 -37,30,79

0

1 4 -102,8 0,48 -39,40,79

8

1 9 -99,12 0,48 -37,50,78

8

1 10 -100,7 0,48 -38,10,78

8

3 1 -98,66 0,48 -37,30,78

8

3 2 -95,84 0,48 -36,10,78

5

3 9 -102,5 0,48 -39,60,80

5

3 10 -98,15 0,48 -37,80,80

2

Rp from a bad diode

To determine the Rp from a I-V curve the following method, shown in figure x.x.x from the manual, can be used.

With the printed graph in the appendix (appendix x.x.x.) the Rp is determined using a pencil and a ruler. The following parameters were found:

∆V=600mv

∆ I=6.25 µA

These parameters entered into the formula give:

Rp=∆V∆ I

=96kOhm

Because the measurement is done with a pencil and a ruler the accuracy is relatively low. The accuracy of the SPA can be neglected in comparison with that of the ruler. A approximation is that the maximum error is half a millimeter on the grid of the graph. With these numbers a maximum and minimum resistance can be calculated. The grid has a resolution of 3mV per half millimeter on the horizontal axis and roughly 0.5µA per half millimeter on the vertical axis. This gives a maximum and a minimum of the real Rp

Rpmax=105kOhmRpmin=88 kOhm

R s from a bad diode

From the manual, figure x.x.x gives the method needed to determine the R s.

The printed graph in the appendix (appendix x.x.x.) was also edited with a pencil and the data is acquired with a ruler. The following parameters were found:

∆V=25.5mv∆ I=4.62µA

These parameters entered into the formula give:

R s=∆V∆ I

=5.5kOhm

The possible error involved in this measurement can be compared with that of the Rp measurement but the scale is a bit different. The horizontal axis is the same, but the vertical axis is 1/3 µA per half millimeter and that gives a minimum and maximum as follows:

R smax=6.6 kOhmR smin=4.5 kOhm

7.3 MEASURING R USING THE FOUR–POINT METHOD

In this paragraph the sheet resistance of the large p+ diffusion area is measured. This is done with the four-point measurement method which will be explained in this paragraph.

METHOD

The four-point method is constructed as follows, see figure x.x.x.

A current is forced between the two outer contact points. With the two inner contact points the voltage is measured. The current and the voltage that can be measured give the sheet resistance. The current does not flow in a straight way but spreads over the sheet, therefore a factor necessary to compensate for this behavior. This factor is given in the manual as 4,53. With this the formula for the sheet resistance is as follows:

R=4,53∙ VI

For this measurement the current is set on 100µA. A HP mulitmeter is used for this measurement, the specification can be found be above. This multimeter also has a current source, so there is no other equipment needed for this measurement.

RESULTS

Six diodes were tested two from each of the three wafers, on each wafer the two big non-oxide diodes were tested. The results can be seen in table x.x.x. The results do not seem very reliable because the sheet resistance is very high. During the measurements it was noticeable that the more pressure on the wafer with the four point needles, the less the measured voltage was. During the measurement we thought that the needles were pushed against the wafer strongly enough but perhaps this was not the case. Luckily this is not the only sheet resistance measurement, in the following measurements the sheet resistance will be measured again, this will allow us to check these results.

Wafer # Voltage Set current (µA) R(Ohm)

1 1 0,32 100 14496

1 2 0,41 100 18573

2 1 0,35 100 15855

2 2 0,095 100 4303,5

3 1 0,24 100 10872

3 2 0,38 100 17214

7.4 THE SHEET- AND CONTACT RESISTANCE OF THE DIFFUSION AREA

When devices are created on a wafer there is always a point where it has to be connected to another device. For this connection little space is available and so the contact resistance ( Rc) might be significant. The contact resistance is the resistance from the aluminum contact holes to the diffusion area. On the wafers a special structure was implemented to check this resistance. With this structure the sheet resistance can also be measured.

METHOD

On the wafer the following structure was implemented:

The different lengths of diffusion areas (L1 and L2 ) make it possible to determine Rc and also the R. The formulas are from the manual and are as follows:

R=B

L2∙(c−1)∙ (R1−R2)

Rc=c ∙R2−R1

2 ∙(c−1)

With

c=L1

L2

The parameter B is the width/length of the contact holes. The parameters L1, L2 and B are determined

during the fabrication and are as follows: L1=200 µm

L2=2000 µm

B=60 µm

For this measurement the SPA is used but the way of measuring is a bit like the point-measurement. Two probes drive a current through the diffusion area and two other probes measure the voltage caused by the current. The measurement setup is shown in figure x.x.x.

RESULTS

Sheet resistance In table x.x.x the result of this measurement are given.

Wafer # # R1 (Ω) R2 (Ω) R(Ω) Rc(Ω)

1 3 116 1170 35,13 -0,56

1 4 112 1080 32,27 2,22

1 6 110 1030 30,67 3,89

1 8 110 1010 30,00 5,00

2 1 115 1020 30,17 7,22

2 3 115 1040 30,83 6,11

2 5 109 1030 30,70 3,33

2 7 102 1030 30,93 -0,56

The sheet resistance seems this time more reliable because the measured values are more stable and the technique used is also more reliable than the previous four point measurement. Looking at these results the previous results seem very unlikely. Putting the results of both R measurements in a histogram is not very helpful, since the results differ so greatly.

Contact resistanceA histogram of the contact resistance (Rc) can be found in graph x.x.x.

1--3 1--4 1--6 1--8 2--1 2--3 2--5 2--7-1.00

1.00

3.00

5.00

7.00

Contact Resistance

R_c

wafer # -- diode #

Rc (Ω)

The most remarkable observation is the fact that there are negative results. Negative resistances are not considered valid results and might be caused by a broken device on the wafer. Why these faults are so clear when the contact resistance is calculated is shown by the formula that is used. The formula used to determine the contact resistance contains the following factor:

c ∙R2−R1

c=0,1

The parameter should be R2 ¿10∙ R1 but it is very close to R2≈10∙ R1

And with a little error in the measurement a negative result is possible. There could be different reason for these errors. One could be that de measurement error is too large and the probe needles are perhaps not stable enough. Because the contact area is very small, a wrong contact is easily possible. This kind of error is however not likely, because the SPA has an accuracy that is much higher. Another reason could be that the devices are broken, not that a broken device can have a negative resistance, but it could lead to negative results.

Because the results were processed after the completion of the measurements , there possibility to perform the measurement again. Performing the measurement again could determine whether the device was broken or the measurement method had flaws.

7.5 MEASURING THE SHEET RESISTANCE USING THE GREEK CROSS STRUCTURE

Another test structure that can be used for easy determination of the sheet resistance is the Greek Cross structure, see figure x.x.x.

METHOD

Once again the SPA is used and just like in the previous measurement, four probes are used. Two probes are to set up a current and the other two probes measure the voltage.

With this special structure there is also a formula given which can determine the sheet resistance when the voltage and current are given. The formula is as follows:

R=π

ln 2∙ VI

RESULTS

In table x.x.x. are the results given

Wafer # Measured Voltage (mV) R (Ohm)

1 1 67,6 3064

1 5 62,6 2837

1 8 62 2810

2 1 60,9 2760

2 5 59,9 2715

2 8 59,5 2697

3 1 56,9 2579

3 5 53,8 2438

3 8 50,4 2284

This is the third measurement were the sheet resistance is measured, but it is also the third time that the result is completely different from the other results. A average of the results is roughly 2,5kOhm, this is lower than the measurement of 7.3 but it is still to high to be a sheet resistance. So this measurement most likely gone wrong somewhere. The error that has occurred must be a structural error because the results of the measurement are relatively close to each other. That leaves two possibilities, structural error in the measurement or a structural error in the design of the device. The last one is a bit unreal because that would stand for that all wafers ever made with this pattern would be faulty. On the other hand no real structural measurement error can be thought of , so that makes it difficult. A more unrealistic error would be that the given formula is wrong, but we look into in and we couldn’t find something.

A summarize of the three measurements a the great difference is given in this graph (x.x.x.) The fact that the vertical axis is logarithmic says enough over the abnormality.

10

100

1000

10000

100000

7.57.47.3

R (Ohm)

7.6 MEASURING THE JUNCTION DEPTH x j OF THE DIFFUSION AREA

The objective of last measurement is to determine the junction depth(x j) of the diffusion area. This can be done with a simple yet destructive method and for that reason the measurement was already done for us with another wafer.

METHOD

The method used for this measurement is the ball-grooving method. This method makes use of a steel ball (diameter of 4 cm) to grind a pit into the wafer. Once this pit is made, it has to be treated with a few drops of stain etch (200ml of HF plus a few drops of HNO3). Because the P+¿¿-type silicon oxidizes faster than the N−¿ ¿-type region the resulting pit can be seen as a circle with a dark edge under the microscope, see figure x.x.x.

When distance a and b are measured, the junction depth x j can be calculated.

x j=a ∙b2 ∙r

With r being the radius of the steel ball.

RESULTS

The measurement that was made for us had the following result, see figure x.x.x.

The parameters are already given in the picture:

a=184 µm

b=566.67µm

Using these parameters in the formula gives:

x j=a∙b2 ∙R

=2.61µm

FINAL CONCLUSIONS

APPENDICES

Appendix x.x.x

Measure results of 7.1

Wafer # Photodiode # Isc (µA) Voc Vb Classification Reason

1 1 -31,58 0,4-0,6 -77 + -

1 2 -21,51 0,4-0,6 -77,4 + -

1 3 -29,35 0,4-0,6 -78,6 + -

1 4 -21,32 0,4-0,6 -78,2 + -

1 5 -30,42 0,4-0,6 -79,8 + -

1 6 -22,1 0,4-0,6 -80,4 + -

1 7 -31,68 0,4-0,6 -80,6 + -

1 8 -23,72 0,4-0,6 -79 + -

1 9 -35,78 0,4-0,6 -80 + -

1 10 -27,43 0,4-0,6 -80 + -

1 11 -37,12 0,4-0,6 -80,6 + -

1 12 -30,88 0,4-0,6 -81 + -

1 13 -38,07 0,4-0,6 -80 + -

1 14 -30,6 0,4-0,6 -80 + -

1 15 -38,72 0,4-0,6 -80,8 + -

1 16 32,18 0,2-0,4 -80,2 - Rp

1 17 -57,28 0,4-0,6 -80,6 - Rp

1 18 -44,87 0,4-0,6 -81,2 - Rp

1 19 -65,38 0,4-0,6 -82 - Rp

1 20 -59,12 0,4-0,6 -81 - Rp/Rs

2 1 -30,03 0,4-0,6 -80,2 -- Rs

2 2 -22,85 0,4-0,6 -79,4 -- Rs

2 5 -30,48 0,4-0,6 -79,6 -- Rs

2 6 -23,07 0,4-0,6 -79,4 -- Rs

2 9 -30,89 0,4-0,6 -80 -- Rs

2 10 -22,82 0,4-0,6 -80,2 -- Rs

2 13 -30,12 0,4-0,6 -78,4 -- Rs

2 14 -22,01 0,4-0,6 -80,6 -- Rs

2 17 -32,12 0,4-0,6 -79,2 -- Rs

2 18 -23,89 0,4-0,6 -79,2 -- Rs

3 1 -28,69 0,4-0,6 -79,4 + -

3 2 -20,19 0,4-0,6 -78,6 + -

3 5 -29,41 0,4-0,6 -80 + -

3 6 -20,95 0,4-0,6 -80 + -

3 9 -31,16 0,4-0,6 -81,6 + -

3 10 -20,87 0,4-0,6 -82 + -

3 13 -29,21 0,4-0,6 79,8 + -

3 14 -21,41 0,4-0,6 81,2 + -

3 17 -30,32 0,4-0,6 80,6 + -

3 18 -22,43 0,4-0,6 81 + -