1

The effect of hydrogen peroxide on polishing removal rate in CMP with various

abrasives

R. Manivannana, S. Ramanathan

a,*

aParticle Science and Polymer Laboratory

Department of Chemical Engineering,

Indian Institute of Technology Madras,

Chennai 600036,

India.

* Corresponding Author. Tel: +91 44 2257 4171, Fax: +91 44 2257 0509. Email: srinivar@iitm.ac.in.

2

Abstract

The effect of hydrogen peroxide in chemical mechanical planarization slurries for shallow trench

isolation was investigated. The various abrasives used in this study were ceria, silica, alumina,

zirconia, titania, silicon carbide, and silicon nitride. Hydrogen peroxide suppresses the

polishing of silicon dioxide and silicon nitride surfaces by ceria abrasives. The polishing

performances of other abrasives were either unaffected or enhanced slightly with the addition of

hydrogen peroxide. The ceria abrasives were treated with hydrogen peroxide, and the polishing

of the work surfaces with the treated abrasive shows that the inhibiting action of hydrogen

peroxide is reversible. It was found that the effect of hydrogen peroxide as an additive is a strong

function of the nature of the abrasive particle.

PACS: 81.65.Ps; 85.40.Ls

Keywords: Chemical mechanical planarization; shallow trench isolation; selectivity; abrasives;

additives

3

1. Introduction

Chemical Mechanical Planarization (CMP) is a key process in microelectronic chip fabrication

[1,2]. CMP is the process of smoothing and planarizing a surface by the chemical and

mechanical forces. Shallow trench isolation (STI) is the current method of electrically isolating

transistors [3]. Silicon dioxide is used as an insulator between devices to prevent the short

circuiting of the transistors. CMP is an important step in the STI integration scheme. STI shows

a high degree of planarity and a dramatic reduction in the chip area required for isolation [1].

STI allows scaling down device dimensions and denser packing [2]. In the process flow, silicno

dioxide is deposited over the trenches and the excess silicon dioxide has to be removed by CMP.

Once the silicon dioxide is brought to the desired level, the polishing is arrested using a silicon

nitride film as a stopping layer. This requires that the polishing process removes silicon dioxide

but not silicon nitride (selective removal).

Ceria and silica are the abrasives of choice for CMP slurries used for STI polishing [4]. Ceria

abrasives polish silicon dioxide and silicon nitride films very well, even though ceria is softer

than both silicon dioxide and silicon nitride [5,6]. The mechanism of silicon dioxide polishing by

ceria abrasives is believed to involve chemical interactions between the abrasive and the work

surface [5]. Various hypotheses have been proposed to explain the unusually high silicon dioxide

polish rate with ceria slurries [5,7-10]. Most of them propose chemical interaction between the

ceria abrasive and the silicon dioxide surface[5,7-9], while in situ frictional force measurement

seem to indicate that the effect may be mainly mechanical [10]. Various additives have been

used in ceria based slurries to suppress the silicon nitride polish rate and maintain a high or

moderate silicon dioxide polish rate, thus enhancing the selectivity [11-13]. The mechanism of

4

action of these high selective slurries is not understood well. Adsorption of the additive onto the

silicon nitride surface was proposed as a possible mechanism [11, 14-16], but it was determined

that adsorption is not the key mechanism of selectivity enhancement for at least certain amino

acids used as additives [17].

Hydrogen peroxide is commonly used as oxidizer in copper CMP slurries [18-21]. However, it is

rarely used in silicon dioxide polishing [22]. While it is unlikely to modify the silicon dioxide

surface significantly, it may enhance the silicon nitride hydrolysis which is the first step in

silicon nitride polishing. It may also modify the surface states of the ceria abrasives and thus

interfere with the chemical interaction between the abrasive and the work surfaces. In this study,

the effect of hydrogen peroxide as an additive in STI CMP slurries is reported. In order to

understand the effect of pH, the polishing was conducted at various pH values of slurries

containing ceria and silica abrasives. The effect of hydrogen peroxide on the STI CMP using

slurries containing other abrasives was also characterized. Ceria based slurries showed

interesting behavior with the addition of hydrogen peroxide. In order to determine if the effect

was permanent, ceria abrasives were treated with hydrogen peroxide, and a set of CMP

experiments were also conducted using the treated ceria abrasives.

2. Experimental

Commercial grade ceria particles (DCP-73A, Sodiff Inc., Korea), fumed silica particles (Cab-o-

sil M5, Cabot Sanmar, India), and titania (DCW, India) were used to prepare slurries. Analytical

grade ceria, silicon nitride, silicon carbide, alumina and zirconia (all from Sigma-Aldrich, USA)

were also used to prepare slurries for characterizing the effect of abrasives. Ceria slurries

5

contained 0.25 wt % solids and silica slurries contained 5 wt % solids. All other slurries

contained 1 wt % solids. All the experiments were carried out at room temperature. The pH of

the slurry was adjusted by using KOH or HNO3 solution. MilliQ water (Millipore) was used for

preparing the slurries. The abrasives were continuously kept in suspension by using a magnetic

stirrer. The slurries were fed to the CMP equipment at a constant flow rate of 60 ml/min using a

peristaltic pump. The wafers were polished in bench-top Struers (Labopol - 5 & Laboforce – 3)

CMP equipment. LPCVD silicon nitride and thermal silicon dioxide coated wafers (Semi Wafer

Inc, Taiwan) were used for the polishing experiments. The wafers were cut into square pieces of

1” size and fixed to the polishing equipment. A force of 20 N was applied to the wafer, and a

rotational speed of 100 rpm and 250 rpm were maintained for the turntable and the wafer holder

respectively. Stacked polyurethane pads (SUBA IV, Rodel Inc) were used for all the

experiments. Initially, the pad was soaked in distilled water for 24 hours and conditioned with

dummy polish runs. After each polishing run, the pad was conditioned with a silicon carbide grit

paper and cleaned with a nylon brush to ensure consistent pad surface condition. After polishing,

the wafers were rinsed and cleaned with MilliQ water in an ultrasonication bath to remove any

abrasive particle. Subsequently, the wafers were dried with compressed air. The pre and post-

polish thicknesses of the silicon dioxide and silicon nitride films were measured using a

Filmetrics F20-UV thin film analyzer to determine the polish rate. The thickness was measured

at 5 locations and the average was taken as the representative thickness. The duration of each

experimental run was 1 min. The experiments were repeated at least 3 times, and the average

values of the polish rates along with the standard deviations are reported. Polishing experiments

using ceria and silica abrasives were carried out in the pH range of 7 – 10. For all other

abrasives, the polishing experiments were conducted at a slurry pH value of 9.

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3. Results and Discussion

3.1 Effect of hydrogen peroxide in silica based slurries

Fig. 1 shows the silicon dioxide polish rate as a function of pH for the silica based slurry with

and without hydrogen peroxide. When hydrogen peroxide is not present, in the pH range of 7 to

9, the silicon dioxide polish rate increases with pH. However, there is no significant change in

the polish rate when the pH was increased from 9 to 10. The solubility of silica is known to

increase with the pH, particularly after a pH value of 10 [23]. When silicon dioxide is exposed to

water, the top layer is modified, and the Si-(OH) bonds are formed on the surface. This layer

would be softer than the silicon dioxide, which facilitates its removal. It was reported that water

was found to be essential to for polishing silica [5]. The silicon dioxide polish rate decreased

when the water in the slurry was replaced by alcohols, and the polish rate dropped drastically

when organic solvents, which did not contain hydroxyl functional group, were used in the slurry

[5]. It is seen from Fig.1 that when hydrogen peroxide is added to the slurry, the polish rate does

not change except at the pH value of 10. At the pH value of 10, when hydrogen peroxide was

added to the slurry, the polish rate increased from 22 nm/min to 36 nm/min. Hydrogen peroxide

can act as a proton donor as well as a proton acceptor [24]. As proton acceptors, hydrogen

peroxide molecules are known to form stronger bonds with silicon dioxide than do water

molecules as proton donors [24]. The addition of hydrogen peroxide would provide some OH

radicals which may alter the surface of the hydrated silica. Since the surface nature of the silicon

dioxide itself changes with pH, this may lead to an enhanced silicon dioxide polish rate at the pH

value of 10 with the addition of hydrogen peroxide. It is to be noted that the silica abrasive

particles would also be modified by the hydrogen peroxide present in the slurry.

7

Fig. 2 shows the silicon nitride polish rate as a function of pH for the silica based slurry with and

without hydrogen peroxide. The silicon nitride polish rate is more or less the same in the pH

range investigated, and it varies only between 8 nm/min and 14 nm/min. The addition of

hydrogen peroxide to the silica based slurry does not affect the silicon nitride polish rate to a

significant extent. The silicon nitride polish is believed to occur by a two step mechanism [6,25].

In the first step, the silicon nitride is hydrolyzed to silicon dioxide and ammonia, and in the

second step, the silicon dioxide is removed by the polishing action. A comparison of Fig.1 and

Fig.2 shows that at the pH value of 8 and above, the silicon nitride polish rate is less than the

silicon dioxide polish rate. This indicates that the first step of hydrolysis is the rate limiting step

in this pH range. However, at the pH value of 7, the nitride polish rate is higher than the oxide

polish rate. This is contrary to the prediction of the two step mechanism. Accordign to the two

step mechanism, the silicon dioxide remoal rate will be the upper limit of the silicon nitride

removal rate. However, direct interaction between the abrasives and the silicon nitride surface

has also been proposed [6]. In that case, the abrasive would remove the top layer containing

silicon dioxide, as well the inner layer of silicon nitride. This will result in a higher polish rate

for silicon nitride film compared to silicon dioxide film. Thus the results indicate that at the pH

value of 7, direct removal of silicon nitride film also contributes to the overall polish rate.

3.2 Effect of hydrogen peroxide in ceria based slurries

Fig. 3 shows the silicon dioxide polish rate as a function of pH for ceria based slurries with and

without hydrogen peroxide. A comparison of Fig. 1 and Fig.3 shows that when hydrogen

peroxide was not present in the slurries, the polish rate of silicon dioxide surface in ceria slurries

8

is significantly higher than that obtained with silica based slurries. It is worth noting that the

ceria slurries contained only 0.25 wt % solids while the silica slurries contained 5 wt % solids.

This is similar to the reported behavior of STI CMP polishing [4]. Thus, mechanical action alone

is insufficient to explain the polish rates exhibited by ceria slurries. Ceria based slurries also

show higher polish rate at a pH value of 7 rather than at the pH value of 10. The point of zero

charge (pzc) of ceria is about 7 and the polish rate is expected to be high near the abrasive pzc

[26]. Above a pH value of 7, the polish rate does show a moderate increase with pH. Thus the

interaction between ceria abrasives and silicon dioxide surface is more significant than the

solubility change with pH, confirming that the abrasive-work surface interactions are the most

significant forces in ceria polishing of silicon dioxide.

Fig. 3 also shows that hydrogen peroxide suppresses the silicon dioxide polish rate to a great

extent. The polish rate does not vary significantly with pH, which indicates that the effect is not a

strong function of pH. However, since hydrogen peroxide does not inhibit the silicon dioxide

polishing by silica based slurries (Fig. 1), it is clear that the inhibition is not due to any

modification of the silica surface. Hence hydrogen peroxide must have changed the ceria

abrasive surface in such a way that the interaction between ceria and silicon dioxide would be

inhibited. Fig. 4 shows the silicon nitride polish rate as a function of pH for the ceria based slurry

with and without hydrogen peroxide. The nitride polish rates varied between 25 to 20 nm/min in

the pH range investigated, when hydrogen peroxide was not present in the slurry. The addition of

hydrogen peroxide to the ceria based slurry reduces the nitride polish rate significantly. In

particular, at the pH value of 10, the silicon nitride polish rate is almost completely suppressed.

A comparison of Fig. 2 and Fig. 4 indicates that hydrogen peroxide suppresses the nitride polish

9

rate only when ceria is the abrasive and not when silica is the abrasive in the slurry. This also

leads to the conclusion that the inhibition of silicon nitride polish rate by the addition of

hydrogen peroxide is due to the modification of the ceria abrasive surface by hydrogen peroxide.

3.3 Effect of hydrogen peroxide concentration in ceria based slurries

In order to determine the extent of polish rate suppression , the concentration of hydrogen

peroxide in the slurry was changed. Fig. 5 shows the effect of hydrogen peroxide concentration

on the polish rate of silicon dioxide and silicon nitride for ceria based slurry at a pH value of 9.

With the addition of 0.5 vol% of hydrogen peroxide, the silicon dioxide polish rate reduced to

about 13 nm/min. Further increase in the hydrogen peroxide concentration did not result in

further reduction of polish rate. Thus a small amount of hydrogen peroxide is sufficient to

modify the ceria surface and suppress the silicon dioxide polish rate. The silicon nitride polish

rate decreased gradually with the increase in hydrogen peroxide concentration, and it reached a

low value of 2 nm/min, when the concentration of hydrogen peroxide was 1.5 vol %. When

hydrogen peroxide is added to the ceria based slurry, it may modify the nitride surface as well as

the ceria surface. The conversion of silicon nitride surface to silicon dioxide may be enhanced by

the presence of hydrogen peroxide, while the modification of ceria surface by hydrogen peroxide

would also occur simultaneously. The combined effect would determine the trend of silicon

nitride polish rate vs hydrogen peroxide concentration. In Fig.5, at any given hydrogen peroxide

concentration the silicon nitride polish rate was always lower than the corresponding silicon

dioxide polish rate. This supports the hypothesis that the hydrolysis of nitride surface and

subsequent removal of surface oxide film is the main mechanism of nitride polishing at the pH

value of 9.

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3.4 Effect of hydrogen peroxide in slurries with other abrasives

Silicon dioxide and silicon nitride films were polished using slurries containing other abrasives

viz., ceria (Sigma-Aldrich), titania, zirconia, alumina, silicon carbide, and silicon nitride, with

and without hydrogen peroxide. The pH value was maintained at 9, and the results are

summarized in table 1. It was found that the hydrogen peroxide suppresses the silicon dioxide

and silicon nitride polishing by ceria abrasives, regardless of the source of ceria. Thus it is clear

that the suppression of polish rates with the addition of hydrogen peroxide is not due to the

possible presence of impurities in the commercial grade ceria (Sodiff Inc.). Zirconia showed a

moderate polish rate without hydrogen peroxide, and the addition of hydrogen peroxide

increased the silicon dioxide as well as silicon nitride polish rates. The titania based slurries did

not show any significant change in the polish rates, with the addition of peroxide. The polish rate

with alumina and silicon carbide based slurries were very low to begin with, and remained low

with the addition of hydrogen peroxide. Silicon nitride based slurries exhibited moderate polish

rate without hydrogen peroxide and an increased polished rate with the addition of hydrogen

peroxide. It is likely that the silicon nitride particle surfaces were hydrolyzed well in the presence

of hydrogen peroxide and the resulting silicon dioxide coating led to the higher polish rate.

Thus the suppression of oxide and nitride polish rate with the addition of hydrogen peroxide is

specific to ceria based slurries. This also supports the hypothesis that there is a significant

chemical interaction between ceria and silicon dioxide (or silicon nitride) surface during CMP.

3.5 Proposed mechanism of silica polish by ceria abrasives

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The surface of ceria particles are known to contain significantly more Ce3+

ions than the bulk

[26]. Electron energy loss spectroscopy (EELS) also showed that the impurities such as

lanthanum were found to be on the surface rather than in the bulk [27]. Ce4+

is

thermodynamically less stable than Ce3+

[28]. Thus, cerium in the tetravalent state is an

oxidizing agent which can be reduced to the trivalent state [7]. However, since hydrogen

peroxide is a strong oxidizing agent, it is likely that it would oxidize the Ce3+

to Ce4+

rather than

reduce the Ce4+

to Ce3+

. It has been proposed that the redox reaction due to Ce3+

/Ce4+

may

provide the assistance to break up the silicon dioxide lattice [7]. It was also proposed that cerium

hydroxide (Ce(OH)4) may react with the silica and form silicic acid (Si(OH)4). Cook proposed a

series of steps to explain the high removal rate of silica by ceria abrasives [5]. In that

mechanism, Si-O- sites would react with Ce-OH sites to form Si-O-Ce bond. During abrasion,

the bond between bulk silicon dioxide and the top atomic layer may rupture leading to removal

of silica [5]. This mechanism would lead to formation of Si(OH)4 molecules in the solution.

Hoshino et al. proposed that silica is removed as a lump rather than as monomer or oligomers of

Si(OH)4. In this mechanism, the breaking of Si-O-Si bond is controlled by chemical

depolymerization as well as mechanical tearing [8]. Thus all the mechanisms proposed to explain

the silica polish by ceria propose that a bond is formed between the ceria abrasive and silicon

dioxide work-surface in its hydrated form.

The inhibiting effect of hydrogen peroxide on the polishing of silicon dioxide and silicon nitride

surface by ceria slurries, as seen in the current work, indicates that oxidizable sites such as Ce3+

ions on the surface of ceria abrasives play a vital role in the CMP. It was reported that reducing

the concentration of ceria abrasives from 1 wt % to 0.25 wt % increases the relative

12

concentration of Ce3+

which leads to a better polish rate [29]. Based on the results shown in Fig.

2 and Fig.3 and the data in the published literature, the following hypothesis is proposed. The

oxidizable sites on the ceria surface may be considered as active sites. When the active surface

sites are available, silicon dioxide bonds with the ceria abrasive, and the monomer or oligomers

of Si(OH)4 are likely to be removed by the movement of the abrasive. It was reported that glass

samples polished with ceria abrasives show the best surface [5]. If the silicon dioxide removal

mechanism by ceria abrasives involve removal of lumps of SiO2, as proposed by [8], then the

surface is not likely to be smooth. Hence it is unlikely that SiO2 would be removed as lumps by

ceria slurries. When the active surface sites are oxidized by the hydrogen peroxide, the resulting

Ce4+

ions do not interact strongly with the silicon dioxide surface. Thus, in the presence of

hydrogen peroxide there is no chemical interaction between the ceria and silicon dioxide. Hence

the polishing would be purely mechanical and hence is expected to be low.

In order to determine if the changes in surface sites by the addition of hydrogen peroxide are

permanent, a few experiments were conducted with ceria abrasives treated with hydrogen

peroxide. Ceria (Sodiff Inc.) slurries of 0.25 wt % solids, with and without 1 vol % of hydrogen

peroxide, were prepared, and the pH values of the same were adjusted to 9. The slurries were

mixed for about 15 min using a magnetic stirrer. Then the slurries were filtered through a

vacuum filter setup. The precipitate was dried in an oven at 105 ºC for a period of 12 hours, to

remove the moisture content from the particles. The treated particles were re-suspended in water

and used for the polishing experiment. The resuspended slurry did not contain any additional

hydrogen peroxide. It is possible that some of the finer powders were not filtered effectively

during this treatment process. Hence, experiments were also conducted with ceria particles

13

treated by the same process mentioned above, but without the addition of hydrogen peroxide.

The results are shown in table 1. It is seen that the polish rate is reduced from 91 nm/min to 73

nm/min when the ceria particles were subjected to the filtration and drying treatment. However, a

comparison of the polish rates using abrasives which were treated with peroxide and abrasives

that were treated only with water shows that the effect of hydrogen peroxide is not permanent.

The slurry containing hydrogen peroxide treated ceria yielded a polish rat of 77 nm/min. The

slurry containing ceria abrasives treated with water yielded a polish rate of 73 nm/min. If

hydrogen peroxide were to permanently modify the surface sites, the treated abrasives would be

ineffective in polishing silicon dioxide and silicon nitride surface. However, the silicon dioxide

and silicon nitride polish rates were more or less the same for ceria abrasives treated with both

water and hydrogen peroxide.. Thus it can be concluded that the modification of the surface sites

on ceria by hydrogen peroxide is temporary and that they tend to return to their natural

equilibrium when hydrogen peroxide is not present.

4. Conclusions

The effect of hydrogen peroxide on STI CMP with slurries containing various abrasives was

characterized. Hydrogen peroxide does not alter the polishing behavior of silica based slurries.

For ceria based slurries, the addition of hydrogen peroxide suppressed the silicon dioxide and

silicon nitride polish rates over a pH range of 7 to 10. Silicon dioxide polish rate suppression

effect saturated at 0.5 vol % concentration of hydrogen peroxide, while silicon nitride polish rate

suppression was saturated at 1.5 vol % hydrogen peroxide concentration. The change is

reversible, since abrasives treated with hydrogen peroxide show good polishing behavior after

the peroxide is removed. The polish rates with zirconia and silicon nitride based slurries

14

increased with the addition of hydrogen peroxide, while the other abrasives showed low polish

rate with and without hydrogen peroxide.

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Acknowledgements

The authors would like to thank the Department of Science and Technology (DST), India for

financing this project (SR/S3/CE/57/2005-SERC-ENGG), Sodiff Inc, Korea for donating the

ceria abrasives and Molycorp. Inc, USA for providing the report on ceria.

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[8] T. Hoshino, Y. Kurata, Y. Terasaki, K. Susa, J. Non-cryst. Solids 283 (2001)129.

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18

Figure Captions

Fig. 1. Polish rate of silicon dioxide surface vs pH in 5 wt % silica slurry with and without 1 vol

% hydrogen peroxide.

Fig. 2. Polish rate of silicon nitride surface vs pH in 5 wt % silica slurry with and without 1 vol

% hydrogen peroxide.

Fig. 3. Polish rate of silicon dioxide surface vs pH in 0.25 wt % ceria slurry with and without 1

vol % hydrogen peroxide.

Fig. 4. Polish rate of silicon nitride surface vs pH in 0.25 wt % ceria slurry with and without 1

vol % hydrogen peroxide.

Fig. 5. Polish rate of silicon dioxide and silicon nitride surface vs hydrogen peroxide

concentration in 0.25 wt % ceria slurry.

Table Caption

Table 1. Polishing characteristics of slurries containing various abrasives at pH value of 9.

19

Fig. 1

0

10

20

30

40

50

7 7.5 8 8.5 9 9.5 10

pH

Ox

ide

po

lis

h r

ate

(n

m/m

in)

With Hydrogen Peroxide

Without Hydrogen Peroxide

20

Fig. 2

0

10

20

7 8 9 10

pH

Nit

rid

e p

oli

sh

ra

te (

nm

/min

) With Hydrogen Peroxide

Without Hydrogen Peroxide

21

Fig. 3

0

30

60

90

120

150

7 8 9 10

pH

Ox

ide

po

lis

h r

ate

(n

m/m

in)

With Hydrogen Peroxide

Without Hydrogen Peroxide

22

Fig. 4

0

5

10

15

20

25

30

35

40

7 8 9 10

pH

Nit

rid

e p

olish

ra

te (

nm

/min

)

With Hydrogen Peroxide

Without Hydrogen Peroxide

23

Fig. 5

0

50

100

150

0 0.5 1 1.5

H2O2 conc. (vol %)

Po

lish

rate

(n

m/m

in)

0

5

10

15

20

25

Silicon dioxide

Silicon nitride

24

Table 1.

Abrasive

Type

Abrasive

Concentration

(wt %)

Without hydrogen peroxide With 1 vol % hydrogen

peroxide

Oxide

polish Rate

(nm/min)

Nitride

polish Rate

(nm/min)

Oxide

polish Rate

(nm/min)

Nitride polish

Rate

(nm/min)

Ceria – Sodiff 0.25 91 22.9 9.4 7.6

Ceria Sodiff

(treated)

0.25 73.2 20.9 76.9 17.7

Ceria-Sigma

Aldrich

0.25 63.7 10.9 3.6 1.5

Alumina 1 3.7 1.7 1.4 0.2

Titania 1 21.2 7.9 20.3 8.8

Zirconia 1 51 30 130.2 41.3

Silica 5 23.1 8.3 24.6 10.6

Silicon

Nitride

1 26.6 15.5 44.3 25.9

Silicon

Carbide

1 2 1.4 1.8 1.3

25

Fig. 1 (B&W)

0

10

20

30

40

50

7 7.5 8 8.5 9 9.5 10

pH

Ox

ide p

oli

sh

ra

te (

nm

/min

)

With Hydrogen Peroxide

Without Hydrogen Peroxide

26

Fig. 2 (B&W)

0

10

20

7 8 9 10

pH

Nit

rid

e p

oli

sh

ra

te (

nm

/min

) With Hydrogen Peroxide

Without Hydrogen Peroxide

27

Fig. 3 (B&W)

0

30

60

90

120

150

7 8 9 10

pH

Ox

ide

po

lis

h r

ate

(n

m/m

in)

With Hydrogen Peroxide

Without Hydrogen Peroxide

28

Fig. 4 (B&W)

0

5

10

15

20

25

30

35

40

7 8 9 10

pH

Nit

rid

e p

olish

rate

(n

m/m

in)

With Hydrogen Peroxide

Without Hydrogen Peroxide

29

Fig. 5 (B&W)

0

50

100

150

0 0.5 1 1.5

H2O2 conc. (vol %)

Po

lish

rate

(n

m/m

in)

0

5

10

15

20

25

Silicon dioxide

Silicon nitride