CN101379607A - Electrostatic chuck - Google Patents

Abstract

To provide an electrostatic chuck that, even after exposure to plasma, can maintain a smooth surface and consequently can suppress contamination of a material to be adsorbed, such as a silicon wafer, with particles, is excellent in adsorption and desorption properties of an adsorbent material, and can easily be prepared by low-temperature firing. An electrostatic chuck comprising a dielectric material for an electrostatic chuck. The dielectric material comprises not less than 99.4% by weight of alumina, more than 0.2% by weight and not more than 0.6% by weight of titanium oxide, has a volume resistivity at room temperature of 10<8> to 10<11> omega cm, and has a structure in which titanium oxide is segregated at the boundary of alumina particles.

Description

Electrostatic chuck

Technical field

The present invention relates to adsorb fixedly semiconductor wafer and FPD with the electrostatic chuck of the absorbate of glass substrate etc. with electrostatic force.

Background technology

The electrostatic chuck ceramic electrical amboceptor in past is to be that purpose constitutes (for example, with reference to Japanese documentation 1) to control this electric characteristic.

In this case, the pottery tissue exposes the situation under plasma environment to the open air, tissue suffers erosion, surface roughness meeting variation, this result has: the contact condition between electrostatic chuck surface and the wafer changes, cause in time to change (variation with time) or particle comes off from sintered body and becomes the dust of particle, cause causing the situation of reason of the wiring closet short circuit etc. of LSI.

In addition, also having particle diameter is the example (for example, with reference to Japanese documentation 2) that alumina ceramic material below the 2 μ m, relative density 99.9%, that make the plasma resistant raising is used for electrostatic chuck.But this situation though good plasma resistant is arranged about the not record of its electric rerum natura, can't make the basic function of so-called Claes Johanson-La Baike (Johnsen-Rahbek) type electrostatic chuck that manifests very big absorption affinity bring into play.

In addition, for the titanium oxide that contains 0.1～1wt%, specific insulation is 10 ⁰～10 ⁴The aluminium oxide ceramics of Ω cm (for example, with reference to Japanese documentation 3) on the books.But this situation can't obtain to make the characteristic of the electricity of electrostatic chuck performance function.

In addition, for the titanium oxide that in aluminium oxide ceramics, adds 0.5～2wt%, so that the electrostatic chuck (for example, with reference to Japanese documentation 4) on the books that the specific insulation of dielectric reduces.For this situation, interpolation is lower than 0.5wt%, and resistance can not descend, and adds more than the 2wt%, and electric current meeting excess flow is on the books.Also for titanium oxide can precipitate into aluminium oxide ceramics the grain circle also on the books.Specific insulation is reduced, will add the above additive of 0.5wt% at least, the electrostatic chuck of strict restriction is arranged then is too many additive for sneaking into impurity in the absorbate.

In addition, for aluminium oxide be more than 99%, average grain diameter be 1～3 μ m, 300～500 ℃ down these specific insulations become 10 ⁸～10 ¹¹The electrostatic chuck of Ω cm (for example, with reference to Japanese documentation 5) on the books.But, about the then not record of rerum natura of in addition temperature, the necessary dielectric of electrostatic chuck that for example uses under the lower temperature below 100 ℃.

Patent documentation 1: No. 3084869 communique of Japan Patent

Patent documentation 2: the 10-No. 279349 communique of Japanese patent laid-open

Patent documentation 3: the 2004-No. 18296 communique of Japanese patent laid-open

Patent documentation 4: special fair the 6-No. 97675 communique of Japan Patent

Patent documentation 5: the 11-No. 312729 communique of Japanese patent laid-open

Summary of the invention

The problem that invention will solve

The invention provides a kind of electrostatic chuck, this electrostatic chuck exposes to the open air after plasma, still can keep level and smooth face, consequently can suppress the pollution for the particulate that absorbate causes of silicon chip etc., and excellent absorption is arranged, break away from the characteristic that is adsorbed body, make easily with easy fired.

In order to solve the means of problem

In order to reach above-mentioned purpose, the present invention is a kind of electrostatic chuck, possess the electrostatic chuck dielectric arranged, described electrostatic chuck with the structure of dielectric be that aluminium oxide is that 99.4wt% is above, titanium oxide is for specific insulation is 10 greater than 0.2wt% and below the 0.6wt%, in the room temperature ⁸～10 ¹¹Ω cm and titanium oxide are segregated to the grain circle of aluminium oxide particles.This result can highly and deposit the plasma resistant of raising electrostatic chuck dielectric and the basic function of electrostatic chuck, and can be with making at a low price.

Specific insulation must have 10 ⁸～10 ¹¹Ω cm is to use the event of absorption affinity that Claes Johanson-La Baike effect is used as electrostatic chuck.Use Claes Johanson-La Baike effect and produce very powerful absorption affinity, this result is provided with protuberance by the surface at electrostatic chuck, just can make the contact area with absorbate, with respect to the area of adsorption plane, and minimizing 1～10%.

And then, the height that is arranged on the protuberance on surface is made as 5～15 μ m, even be touched portion thus, still can act on absorption affinity.This result is the area that can make protuberance, with respect to the area of adsorption plane, is more than 0.001% and does not reach 0.5%.The temperature of absorbate diminishes with the contact area of work protuberance, and heat can see through contact site and conduct, so even for example the tissue of protuberance is subjected to the plasma erosion, this influence also can diminish.Therefore, by improving the plasma resistance, and reduce with contacting extremely of absorbate, the result can realize changing in time seldom electrostatic chuck.

In addition, for the response characteristic that will make above-mentioned absorption affinity becomes good, must reduce the value of following formula.

Ts=1.731 * 10 ^-11* ρ (ε r+d/h) (second)

Herein, ts is 100% for the absorption affinity with the initial stage, and the time (second) till this absorption affinity is damaged to 2%, ρ is the specific insulation (Ω cm) of dielectric layer, and ε r is the dielectric constant of dielectric layer, and d is the thickness (m) of dielectric layer, and h is the height (m) of protuberance.The value of this formula be 0.001 to 0.6 and the height of protuberance be the words of 5～15 μ m, can make the area of protuberance, with respect to adsorption plane, become till 0.001～0.5%, and all good electrostatic chuck of response that can form the voltage that applies absorption affinity, remove for load.

Above-mentioned formula is to be calculated and derive (numerical expression 1)～(numerical expression 4) and obtain through parsing by the equivalent circuit among Fig. 1.Herein, q ₁Be charge density, S is an electrode area, and C is an electrostatic capacitance, and G is that electricity is led, and V is for applying voltage, and t is time (variable), and T is the voltage application time.

Numerical expression 1

$\begin{array}{cc}f=\frac{{q_1}^2}{{2\mathrm{\&epsiv;}}_0}& (q_1=\frac{Q_1}{S})\end{array}$

0≤t≤T

(1)

$q_c=C_1\frac{C_2}{C_1+C_2}V\&CenterDot;\exp (-\frac{G_2}{C_1+C_2}t)---\left(2\right)$

$q_j=C_1\frac{G_2}{G_1+G_2}V\&CenterDot;\{1-\exp (-\frac{G_2}{C_1+C_2}t)\}---\left(3\right)$

t>T

(4)

Numerical expression 2

$\mathrm{\&tau;}=\frac{2(C_1+C_2)}{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="A200780004585E00111.png,A200780004585E00121.png"\; state="\{\{state\}\}">G</figure-callout>}}_2}$

Numerical expression 3

$C_1={\mathrm{\&epsiv;}}_0\frac{S}{d}$

${\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A200780004585E00111.png,A200780004585E00121.png"\; state="\{\{state\}\}">C</figure-callout>}}_2={\mathrm{\&epsiv;}}_0{\mathrm{\&epsiv;}}_r\frac{S}{h}$

${\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="A200780004585E00111.png,A200780004585E00121.png"\; state="\{\{state\}\}">G</figure-callout>}}_2=\frac{1}{R_2}=\frac{S}{\mathrm{\&rho;d}}$

Numerical expression 4

t>T

$q_1=C_1\frac{C_1}{C_1+C_2}V\&CenterDot;\exp (-\frac{G_2}{C_1+C_2}(t-T))$

In addition, the electrostatic chuck of other example of the present invention is to possess to have: aluminium oxide is that 99.4t% is above, titanium oxide for greater than 0.2wt% and below the 0.6wt%, bulk density is 3.97g/cm ³More than, specific insulation is 10 in the room temperature ⁸～10 ¹¹1 Ω cm and titanium oxide are segregated to the electrostatic chuck dielectric of structure on the grain circle of aluminium oxide particles.This result is this electrostatic chuck, is that the porosity of this tissue is few, and the basic function that improves plasma resistant and electrostatic chuck can highly and be deposited, and can be with making at a low price.

In the preferred form of the present invention, selected the electrostatic chuck that in the low temperature below 100 ℃, uses for use.

In preferred configuration of the present invention, disclose as inventing each electrostatic chuck of putting down in writing in 1 to 4, it is characterized in that, constituted by having to be formed with a plurality of protuberances and will to be adsorbed the dielectric that body is positioned in this level and smooth surface above protuberance, the ratio of the area on total area above aforementioned a plurality of protuberance and aforementioned electric amboceptor surface is more than 0.001% and does not reach 0.5%, and the height of protuberance is 5～15 μ m.This result can make contact portion with absorbate be subjected to that plasma attack causes surperficial roughening and by the influence to the variation of the adsorbed state of absorbate that shaggy influence causes, drops to Min..At this moment, the ratio of contact area becomes below 0.001%, and the size of each protuberance will become excessively trickle, causes processing to have any problem.In addition, greater than 1%, then be subjected to the influence that plasma corrodes and just can't ignore with the face that is adsorbed the protuberance that body contacts.

The invention effect

According to the present invention, have: expose to the open air after plasma, still can keep level and smooth face, consequently can suppress pollution for the particulate that absorbate causes of silicon chip etc., and excellent absorption is arranged, break away from the characteristic that is adsorbed body, make with easy fired, be easy to just can make the effect of electrostatic chuck.

Description of drawings

Fig. 1 is the figure of expression electrostatic chuck of the present invention.

Fig. 2 is the figure of the equivalent circuit of expression electrostatic chuck of the present invention.

Fig. 3 is the enlarged drawing of the configuration of surface of electrostatic chuck of the present invention.

Fig. 4 is the electron micrograph of expression electrostatic chuck of the present invention with the structure of dielectric.

Embodiment

Raw material is aluminium oxide, titanium oxide, other transition metal oxide, carries out granulation with the allotment ratio shown in the table 1.Be ready for average grain diameter 0.1 μ m, the aluminium oxide of purity more than 99.99%.Use the titanium oxide of purity more than 98%.

(slurry allotment, granulation, original processing)

Above-mentioned raw materials is mixed with the allotment ratio shown in the table 1 and pulverized, add propylene and be adhesive after allotment, carry out granulation, make the particle powder with the spraying drying machine.After the particle powder is loaded in the rubber cast, implement CIP (pressure 1ton/cm ²), make ingot bar, be processed into the shape of regulation afterwards, make initial formed body.During mixing, use ion exchange water etc., do not sneak into impurity as far as possible.

(burning till)

Under the reduction atmosphere of nitrogen, hydrogen, burn till above-mentioned original processome.Firing temperature is set at 1150～1350 ℃, and firing time is set at 1～8 hour, selects the condition of bulk density maximum.At this moment, use humidified gases in order to want degreasing.Reduce that to burn till be because of will turning to purpose with the nonstoichiometric composition that carries out titanium oxide, and will with specific insulation be adjusted to purpose so.

(HIP processing)

Now carries out HIP to be handled.The HIP condition enactment is Ar gas 1500 air pressure, and temperature is set at identical with firing temperature or low 30 ℃ temperature.

(physical property measurement)

Via what above-mentioned HIP processing obtained be, utilize the bulk density of burning till, the SEM that organizes of sintered body to observe, average frictional force measuring, residence time mensuration in particle size determination, specific insulation mensuration, the vacuum.Frictional force measuring and residence time are measured and the thickness of ceramic electrical interlayer will be set as 1mm.Residence time mensuration is the absorption voltage that applies 200V, with dump, measures the decay of residual friction after voltage applies 1 minute.Absorbate is the silicon chip minute surface.Residence time then is that the frictional force behind the dump is decayed to time till 2% as the residence time.

In addition, the variation of the surface roughness (center line average roughness Ra) of also actual irradiation plasma and mensuration pottery.A-stage, surface roughness are below the Ra 0.05 μ m.Plasma is the active-ion-etch device, and etching gas is CF ₄+ O ₂, 1000W made plasma discharge 5 hours.

In addition, at the part of sample, to electrostatic chuck and adsorbing be adsorbed the pressure that applies He gas between the body after, the pressure (POPOFF absorption affinity) when being adsorbed body and breaking away from write down the practical absorption affinity of evaluation electrostatic chuck.The absorption voltage of this moment is 1000V.

(relatively product)

In addition, the aluminium oxide ceramics of illustration method for making acquisition in the past in order to compare.Relatively the aluminium oxide 98wt% that is allocated as average grain diameter 0.5 μ m, the titanium oxide 2wt% of product 1, relatively the allotment of product 2 then is aluminium oxide 99wt%, titanium oxide 1wt%, firing temperature is 1580 ℃.In addition, A-stage, relatively the surface roughness of product 1 is Ra 0.23 μ m.A-stage, relatively the surface roughness of product 2 is Ra 0.2 μ m.Relatively product then are not handle through HIP.

The result of above-mentioned test is presented in table 1, the table 2.As can be known: if the control firing temperature, the titanium oxide addition is greater than 0.2wt% and below the 0.6wt%, and bulk density is 3.97g/cm ³When above, can obtain the specific insulation of the function of electrostatic chuck.Learn: with the past particle diameter be that the amount that the situation more than the 50 μ m is added is made comparisons, just obtain equal effect with considerably less addition.The method for making in past is in order to make firing temperature bring up to 1580 ℃ and the titanium oxide and the aluminium oxide that add react, to become aluminium titanates (Al ₂TiO ₅) compound that waits, with respect to this, the present invention then is by using the alumina raw material of average grain diameter less than 0.2 μ m, the highly purified particulate of purity more than 99.9%, so that firing temperature is reduced to below 1300 ℃, the titanium oxide that adds does not react with aluminium oxide and titanium oxide is still preserved work, and this point utilizes X-ray diffraction to be proved.Know: the specific insulation of aluminium titanates is considered to than higher: for the specific insulation that will make aluminium oxide reduces, efficient can be also poorer than titanium oxide, must add more amount.Secondly, the microstructure of the dielectric that will use as electrostatic chuck of the present invention with the temperature with respect to low 80～150 ℃ of degree of firing temperature, carries out the SEM photo of the etched sample of hot type, is presented among Fig. 4.Know: titanium oxide (white partly on the photo) is segregated to the grain circle (black partly on the photo) of the following aluminium oxide particles of average grain diameter 2 μ m, forms the structure that continuity links.The network that is considered to utilize this titanium oxide to form makes specific insulation reduce effectively.By above result, make comparisons with dielectric with the electrostatic chuck in past, electrostatic chuck of the present invention can utilize the titanium oxide that adds trace that specific insulation is reduced with dielectric, be still not exist and titanium oxide is segregated to the grain circle of aluminium oxide particles with titanium oxide because of the titanium oxide that adds reacts with aluminium oxide, form structure that continuity links so.In addition, be considered to: titanium oxide burns till via reduction and becomes nonstoichiometric composition, and makes conductivity become good more.Be considered to: in this mode, can utilize the titanium oxide of trace to come CONTROL VOLUME resistivity, the chemical contamination that is caused for silicon chip etc. also can also will be suppressed more than the past again.

[table 1]

NO.	Aluminium oxide	Titanium oxide	Firing temperature ℃	The bulk density g/cm of sintered body 3
					1	100wt％	0wt％	1240	3.79
2	100wt％	0wt％	1270	3.88
					3	99.9wt％	0.1wt％	1300	3.78
4	99.9wt％	0.1wt％	1240	3.89
					5	99.8wt％	0.2wt％	1210	3.74
6	99.8wt％	0.2wt％	1240	3.89
					7	99.7wt％	0.3wt％	1180	3.23
8	99.7wt％	0.3wt％	1210	3.91
					9	99.6wt％	0.4wt％	1180	3.60
10	99.6wt％	0.4wt％	1210	3.92
					11	99.5wt％	0.5wt％	1150	3.60
12	99.5wt％	0.5wt％	1180	3.92
					13	99.4wt％	0.6wt％	1150	3.92
14	99.4wt％	0.6wt％	1180	3.92
					Compare thing 1	98wt％	2wt％	1580	3.75
Compare thing 2	99wt％	1wt％	1580	3.7

[table 2]

NO.	Bulk density g/cm behind the HIP 3	Sintered body average grain diameter μ m	HIP handles back specific insulation Ω cm	Frictional force gf/cm when 200V applies 2	Second residence time	Plasma treatment front surface rugosity Ra μ m	Plasma treatment rear surface rugosity Ra μ m
								2	3.98	0.9	>10 15	>400	>300	0.03	0.06
4	3.98	1.1	10 15	>400	>300	0.03	0.06
								6	3.98	1.3	10 12.7	>400	120	0.03	0.06
8 10	3.98 3.98	1.4 1.5	10 1010 9.3	>400 >400	8 4	0.03 0.03	0.06 0.07
								12	3.98	1.5	10 8.5	>400	1	0.03	0.07
14	3.97	1.7	10 8.3	>400	1	0.03	0.07
								Compare thing 1	-	80	10 10.3	>400	15	0.23	0.56
Compare thing 2	-	70	10 11	>400	30	0.2	0.6

The result of the evaluation of the characteristic of electricity learns: can be 10 ⁸～10 ¹⁶Ω cm on a large scale in, by titanium oxide separately or the adding proportion of titanium oxide+transition metal oxide control.

Use the situation of resist, consider this heat resisting temperature, preferably using electrostatic chuck below 100 ℃.

The characteristic of the desired electricity of dielectric that electrostatic chuck is used, preferably under the temperature of using electrostatic chuck, specific insulation is 10 ⁸～10 ¹¹Ω cm.Do not reach lower limit 10 ⁸Ω cm, the electric current that probably flow into wafer becomes excessively big and the damage device.Greater than higher limit 10 ¹¹Ω cm, the response that applies for absorption, the voltage of disengaging wafer then can reduce.The operation of the etching work procedure below 100 ℃ for example, preferably lower limit is 10 ⁹～10 ¹¹Ω cm degree.

Titanium oxide is greater than 0.6wt%, and specific insulation will become and do not reach 10 ⁸Ω cm, the electric current that probably flow into wafer becomes excessively big and the damage device.In addition, titanium oxide is below the 0.2wt%, and the effect of utilizing the interpolation titanium oxide to reduce specific insulation then can diminish.

If the energy of ions in the plasma is excessive, any material all can be etched, so plasma resistant is estimated with the variation of surface roughness.

This result, the ceramic electrical amboceptor among the present invention, also littler than the past of being changed significantly of surface roughness.This situation is presumably because of the very little event of dust granules.

Make: have and be formed with a plurality of protuberances and will be adsorbed body and be positioned in this level and smooth surface above protuberance, containing specific insulation is 10 ^9.3The electrostatic chuck of Ω cm is 0.089% electrostatic chuck with the ratio of the area on total area above the protuberance of the electrostatic chuck of dielectric and aforementioned electric amboceptor surface.At this moment, from the teeth outwards, it is outstanding to link to each other with each summit that is the equilateral triangle of 8mm on one side, disposes the protuberance of φ 0.25mm.The height of protuberance is 10 μ m.

This result, the surface roughness after the plasma irradiating with low uncertainty and overlapping with considerably less these two things of the contact area of absorbate can make the variations in temperature of silicon chip when handling as absorbate change in time seldom.

The record of POPOFF absorption affinity is that whole samples all has more than the 100torr.Promptly learn: when to adsorb silicon chip etc. be adsorbed body the time, can obtain fully practical power.

Claims (5)

1. electrostatic chuck is characterized by:

Possess the electrostatic chuck dielectric is arranged, described electrostatic chuck is that aluminium oxide is more than the 99.4wt% with the structure of dielectric, and titanium oxide is greater than 0.2wt% and below the 0.6wt%, and specific insulation is 10 in the room temperature ⁸～10 ¹¹Ω cm, and titanium oxide is segregated to the grain circle of aluminium oxide particles.

2. electrostatic chuck is characterized by:

Possess the electrostatic chuck dielectric is arranged, described electrostatic chuck is that aluminium oxide is more than the 99.4wt% with the structure of dielectric, and titanium oxide is greater than 0.2wt% and below the 0.6wt%, and bulk density is 3.97g/cm ³More than, specific insulation is 10 in the room temperature ⁸～10 ¹¹Ω cm, and titanium oxide is segregated to the grain circle of aluminium oxide particles.

3. as claim 1 or 2 electrostatic chucks of being put down in writing, it is characterized by, in the particle of aforementioned aluminium oxide particles,, do not have aluminium titanates (Al with the grain circle ₂TiO ₅).

4. as each electrostatic chuck of putting down in writing in the claim 1 to 3, it is characterized by: under the low temperature below 100 ℃, use.

5. as each electrostatic chuck of putting down in writing in the claim 1 to 4, it is characterized by, constituted by having to be formed with a plurality of protuberances and will to be adsorbed the dielectric that body is positioned in this level and smooth surface above protuberance, the ratio of the area on total area above aforementioned a plurality of protuberance and aforementioned electric amboceptor surface is more than 0.001% and does not reach 0.5%, and the height of protuberance is 5～15 μ m.

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