Patent Application
20050166848
The present invention relates to wafer holders employed in semiconductor manufacturing operations such as plasma-assisted CVD, low-pressure CVD, low-k film baking, plasma etching and dielectric-film CVD, and to semiconductor manufacturing apparatuses furnished with the wafer holders.
A variety of semiconductor manufacturing apparatuses for implementing on semiconductor wafers processes such as film-deposition and etching has been proposed to date. Such semiconductor manufacturing apparatuses are in their reaction chambers provided with wafer holders furnished with a resistive heating element, and carry out various processes on wafers while the wafers are retained and heated on the wafer holders.
A semiconductor wafer-heating device proposed in Japanese Unexamined Pat. App. Pub. No. H04-78138, for example, includes: a heater part made of ceramic, in which a resistive heating element is embedded, and that is provided with a wafer-heating side and is installed within a reaction chamber; a columnar support part provided on the side of the heater part other than its wafer-heating side and that forms a gastight seal between it and the reaction chamber, and electrode elements connected to the resistive heating element and leading out to the reaction chamber exterior so as substantially not to be exposed to the reaction-chamber interior space.
In another example, a structure in which a plurality of tubular pieces is joined to a ceramic susceptor (wafer holder) to support the susceptor is proposed in Japanese Unexamined Pat. App. Pub. No. H05-9740. This structure, which is an improvement on the ceramic wafer-heating device set forth in the abovementioned Pat. App. Pub. No. H04-78138, is one in which at least one of the electrode elements furnished in the ceramic susceptor is surrounded by a tubular piece made from an inert insulating material, and in which one end of the tubular piece is joined airtightly onto the ceramic susceptor, while the other end thereof is inserted through a through-hole provided in the reaction chamber, where it is sealed airtight.
What with a columnar support part attached to the ceramic susceptor in the wafer-heating device set forth in the abovementioned Pat. App. Pub. No. H04-78138, the columnar support part itself in order to support the ceramic susceptor ends up being of relatively large heat capacity, wherein a drawback has been that consequently the amount of heat escaping from the ceramic susceptor is large, spoiling the temperature uniformity of the wafer-heating face.
In the wafer-heating device of the abovementioned Pat. App. Pub. No. H05-9740, the fact that a plurality of tubular pieces is joined fast to the ceramic susceptor has meant that the stress acting on the tubular pieces during heating processes is great, such that the danger has been that in worst-case scenarios the tubular pieces have been destroyed. In particular, when the temperature of the ceramic susceptor has been elevated to a constant level, the distance between the tubular pieces affixed to the susceptor grows larger due to thermal expansion of the susceptor. Meanwhile, with heat from the ceramic susceptor and tubular pieces being transmitted to the reaction chamber, through which the other ends of the tubular pieces are inserted, the chamber also expands. Under these circumstances, in some cases the difference in extent of thermal expansion between the ceramic susceptor and the reaction chamber has been so significant that the stress acting on the tubular pieces grows large enough to damage them.
Especially with the transition to silicon wafers of larger diametric span moving forward in recent years have been calls for uniform heating of 12-inch silicon wafers. Because accompanying this transition has been a scaling-up of the ceramic susceptors that heat the wafers, thermal stress acting on the tubular pieces while the ceramic susceptors are heating has grown greater, which has made damage to the affixed tubular pieces all the more likely to occur.
The scaling up of ceramic susceptors has in turn meant that heating of the susceptors is carried out with the susceptor temperature divided into a number of blocks (zones), along with which the number of temperature-measuring probes for measuring the temperature of the susceptor, and the number of electrode terminals and lead lines for supplying power to the susceptor have thus grown. Consequently, because the number of hollow tubular pieces that house these components has also increased, and because in some instances solid columnar pieces are installed on susceptors, the risk that the tubular pieces and columnar pieces will be damaged has also grown all the greater.
An object of the present invention, in view of such circumstances to date, is to make available a wafer holder in which when the ceramic susceptor therein is in the process of heating, thermal-stress damage to the plurality of tubular pieces and/or columnar pieces affixed to the susceptor can be prevented, and to make available a high-reliability semiconductor manufacturing apparatus utilizing the wafer holder.
In order to achieve the foregoing objective, a wafer holder of the present invention is for retaining and processing a semiconductor wafer on the holder's ceramic susceptor supported within a reaction chamber by tubular pieces, wherein at least two of the tubular pieces are anchored tubular pieces in which one end is affixed onto the ceramic susceptor and the other end is fixed into the reaction chamber, and is characterized in that letting
Another wafer holder that the present invention affords is for retaining and processing a semiconductor wafer on the holder's ceramic susceptor supported within a reaction chamber by tubular pieces and/or support pieces, wherein at least two of the tubular pieces and/or support pieces are anchored tubular pieces and/or support pieces in which one end is affixed onto the ceramic susceptor and the other end is fixed into the reaction chamber, and is characterized in that letting
Preferably in the above-characterized wafer holder of the present invention the thermal expansion coefficient of the ceramic susceptor is 8.0×10−6/K or less, while the thermal expansion coefficient of the reaction chamber is 15×10−6/K or more. Likewise, the thermal expansion coefficient of the ceramic susceptor more preferably is 6.0×10−6/K or less, while the thermal expansion coefficient of the reaction chamber more preferably is 20×10−6/K or more.
Also preferable in the foregoing wafer holder of the present invention is that the length of the anchored tubular pieces and/or the anchored support pieces from the ceramic susceptor to the reaction chamber be 320 mm or less. It is further preferable that the length of the anchored tubular pieces and/or the anchored support pieces from the ceramic susceptor to the reaction chamber be 150 mm or less, and that the thermal conductivity of the anchored tubular pieces and/or anchored support pieces be 30 W/mK or less.
In the above-described wafer holder of the present invention, the reaction chamber preferably is not water-cooled. In addition in the foregoing wafer holder of the present invention a reflection plate for reflecting heat from the ceramic susceptor preferably is furnished in between the reaction chamber and the ceramic susceptor.
In the foregoing wafer holder of the present invention, it is preferable that the parallelism of each of the anchored tubular pieces and/or the anchored support pieces, the respective ends of which are anchored along the reaction chamber and along the ceramic susceptor, be within 1.0 mm, and more preferable that the parallelism of each of the anchored tubular pieces and/or the anchored support pieces be within 0.2 mm.
In the wafer holder described above of the present invention, an O-ring fixed in the reaction chamber and being for maintaining gastightness against the reaction chamber exterior is preferably provided, wherein the microroughness in the vicinity of where the face of the tubular pieces and/or the support pieces abuts on the O-ring is 5.0 μm or less (Ra). The microroughness in the vicinity of where the face of the tubular pieces and/or the support pieces abuts on the O-ring is more preferably 1.0 μm or less (Ra), and is especially preferably 0.3 μm or less (Ra).
In the aforementioned wafer holder of the present invention, an O-ring fixed in the reaction chamber and being for maintaining gastightness against the reaction chamber exterior is preferably provided, wherein the size of surface defects present in the vicinity of where the face of the tubular pieces and/or the support pieces abuts on the O-ring is 1 mm or less in diameter. The size of surface defects present in the vicinity of where the face of the tubular pieces and/or the support pieces abuts on the O-ring is more preferably 0.3 mm or less in diameter, and is especially preferably 0.05 mm or less.
Likewise, in the above-described wafer holder of the present invention, it is preferable that the thickness uniformity (parallelism) of the ceramic susceptor and the reaction chamber bottom be 1.0 mm or less; that the parallelism of the ceramic susceptor and the reaction chamber bottom be 0.2 mm or less is more preferable still.
Also preferable in the foregoing wafer holder of the present invention is that the anchored tubular pieces and/or the anchored support pieces be 150 mm or less in length to the reaction chamber, and that the thermal conductivity of the anchored tubular pieces and/or the anchored support pieces be 30 W/mK or less. Additionally preferable is that the reaction chamber not be water-cooled.
Preferable in the foregoing wafer holder of the present invention is that the principal component of the ceramic susceptor be whichever of alumina, silicon nitride, aluminum nitride or silicon carbide. Likewise, the principal component of the ceramic susceptor more preferably is aluminum nitride, the principal component of the reaction chamber more preferably is either aluminum or an aluminum alloy, and the principal component of the anchored tubular pieces and/or the anchored support pieces more preferably is either mullite or a mullite-alumina composite.
The present invention also affords semiconductor manufacturing apparatus characterized in being outfitted with an above-described wafer holder. The semiconductor manufacturing apparatus is preferably one that is employed in low-k film baking.
A wafer holder 1 involving the present invention, as illustrated in
As another embodiment, furthermore, as illustrated in
Thus the ceramic susceptor 2 of the wafer holder 1 may be supported by tubular pieces that can contain an electrode terminal/lead 7, or a temperature-measuring probe 8 such as a thermocouple, and may be provided with support members apart from the tubular pieces—with solid support pieces for example. Moreover, employing tubular pieces and/or support pieces that are not anchored to the ceramic susceptor 2 and/or the reaction chamber 4 is also possible. It should be understood that even in these cases, what the subject matter of the present invention is relates to tubular pieces and support pieces that are anchored to ceramic susceptors and reaction chambers.
The anchored tubular pieces 5 and/or support pieces 5a affixed to the ceramic susceptor 2 become heated by heat applied to the ceramic susceptor 2 when a wafer is being processed, and this heat, transmitted to anchored tubular pieces 5 and/or support pieces 5a, is in turn transmitted to the reaction chamber 4. Moreover, heat is also transmitted to the reaction chamber 4 due to the emanation or radiation and convection of heat from the ceramic susceptor 2. The ceramic susceptor 2 and the reaction chamber 4 therefore expand thermally. In that situation, anchored tubular pieces 5 and/or support pieces 5a undergo stress corresponding to the difference in the amounts by which the ceramic susceptor 2 and the reaction chamber 4 expand thermally; in cases where the stress is great enough, damage occurs.
As a result of investigating in detail the relationship between the amount of thermal expansion by the ceramic susceptor and the reaction chamber, and damage to the anchored tubular pieces and/or support pieces, it was understood that if the difference between the two in thermal-expansion extent exceeded 0.7 mm, the anchored tubular pieces and/or support pieces would be damaged by stress. Therefore, in a wafer holder of the present invention the difference on the ceramic susceptor and on the reaction chamber in longest inter-piece distance among the plurality of anchored tubular pieces and/or support pieces when the maximum susceptor temperature has been attained is predetermined so as to be 0.7 mm or less.
Namely, as illustrated exemplarily in
Furthermore, in the present invention as illustrated in
the relational formula |(T1×α1×L1)−(T2×α2×L2)|≦0.7 mm,
L1 and L2 are predetermined.
Herein, the inter-piece distances among the anchored tubular pieces and/or anchored support pieces (including—identically hereinafter—the inter-piece distances among the anchored tubular pieces in
Because in general the tubular pieces and/or support pieces are anchored so as each to be orthogonal with respect to the ceramic susceptor and the reaction chamber, the inter-piece distance on the susceptor end and on the chamber end between two anchored tubular pieces and/or anchored support pieces will ordinarily be the same. But even such being the case, due to such factors as the difference in thermal expansion coefficient between the susceptor and the reaction chamber while the ceramic susceptor is heating, the longest inter-piece distance among the plurality of anchored tubular pieces and/or anchored support pieces will as a matter of course come to differ on the susceptor end and on the chamber end.
Given these circumstances, in accordance with the present invention, in instances like
In addition, the present invention is also applicable to cases in which the ceramic susceptor is not supported on tubular pieces only—for example, to cases, as illustrated in
Another problematic circumstance has been that due to thermal expansion of the ceramic susceptor and reaction chamber while the susceptor is heating, the positions of the plurality of anchored tubular pieces and/or anchored support pieces relative to one another vary. This runs the risk that in general the O-rings, which are made of rubber, installed between t the anchored tubular pieces and/or anchored support pieces and the reaction chamber will deform, degrading the gastightness of the reaction chamber interior.
In this situation, nevertheless, preconfiguring the discrepancy in the longest separation between the anchored tubular pieces and/or anchored support pieces in the foregoing relational formula to be 0.3 mm or less—i.e. |(T2×α1×L1)−(T2×α2×L2)|≦0.3 mm—will nearly eliminate degradation in gastightness and thus be that much more beneficial. Specifically, with the just-noted discrepancy in the longest separation between the anchored tubular pieces and/or anchored support pieces being 0.3 mm or less, a gastightness of 10−9 Pam3/s or less given as helium leak rate may be secured. Moreover, it is possible to ensure a value of 10−7 Pam3/s or less even if the discrepancy in the longest separation between the anchored tubular pieces and/or anchored support pieces is as much as 0.7 mm. It should be understood that in drawing the reaction chamber interior down to a vacuum at normal temperatures there are generally no problems at all with gastightness.
In the present invention the shape of the tubular pieces, which can house leads/electrode terminals for supplying electricity to the temperature-measuring probes and the resistive heating element, does not matter as long as it is tubular. On the other hand, the support pieces in the present invention are not particularly limited as to their geometry—circularly or quadrangularly columnar, tubular, etc.—as long as they can support the ceramic susceptor. Also, the tubular pieces and support pieces do not have to be affixed to the ceramic susceptor and to the reaction chamber; the tubular pieces and support pieces in such cases would not come under the applicability of the present invention. And as far as the way in which the ceramic susceptor and the anchored tubular pieces and/or anchored support pieces are fixed is concerned, as long as the anchoring method is such that the separation between the anchored tubular pieces and/or anchored support pieces varies along with the thermal expansion of the susceptor, all anchoring methods are applicable.
Examples include, as illustrated in
On the other hand, the configuration between the tubular pieces and/or the support pieces and the reaction chamber uses O-rings or another means to keep the reaction chamber interior airtight, in order to maintain a vacuum or otherwise low-pressure state within the reaction chamber while the ceramic susceptor is heating (during wafer processing).
A preferable thermal expansion coefficient for of the ceramic susceptor is 8.0×10−6/K or less; a preferable thermal expansion coefficient for the reaction chamber is 15×10−6/K or more. The thermal expansion coefficient of the reaction chamber is made larger than that of the ceramic susceptor in order to hold down the amount by which the ceramic susceptor expands thermally, and conversely to increase the amount by which the reaction chamber expands thermally, to match the thermal expansions of the two, because when the susceptor is heating the temperature of the susceptor is relatively higher than that of the reaction chamber. Moreover, having the thermal expansion coefficient of the ceramic susceptor be 6.0×10−6/K or less, and the thermal expansion coefficient of the reaction chamber be 20×10−6/K or more, is especially beneficial in that it lessens restrictions on the viable temperature range for the ceramic and on the locations where the anchored tubular pieces and/or anchored support pieces can be attached.
As regards the reaction chamber, demands for scaled-down versions have been intense in recent years. For that reason the thermal conductivity of the tubular pieces and support pieces ideally should be 200 W/mK or less because then it is possible to have the length from the ceramic susceptor to the reaction chamber be 320 mm or less. Conversely, the thermal conductivity of the tubular pieces and support pieces being in excess of 200 W/mK is undesirable because the heat generated in the susceptor and transmitted through the tubular pieces and support pieces elevates the reaction chamber temperature such that it surpasses the O-ring's level of heat resistance, compromising the gastight integrity of the reaction chamber interior.
In addition, the reaction chamber structure preferably is one that is not water-cooled because, as stands to reason, attaching a water-cooling device to the chamber complicates the apparatus. It is also preferable that the length (distance) of the anchored tubular pieces and/or anchored support pieces from the ceramic susceptor to the reaction chamber be 150 mm or less, because the longer the length of anchored tubular pieces and/or anchored support pieces is, the larger the scale of the reaction chamber itself will have to be.
In order for the just-noted length of anchored tubular pieces and/or anchored support pieces to be established at 150 mm or less without the reaction chamber being water-cooled, conduction of heat from anchored tubular pieces and/or anchored support pieces to the reaction chamber must be restrained. For this reason, the thermal conductivity of anchored tubular pieces and/or anchored support pieces preferably is 30 W/mK or less. Making the thermal conductivity of anchored tubular pieces and/or anchored support pieces 30 W/mK or less also lessens the amount of heat that escapes from the ceramic susceptor to anchored tubular pieces and/or anchored support pieces, which enhances temperature uniformity in the wafer-heating face of the ceramic susceptor.
From a temperature uniformity point of view, alumina, mullite, and composites of alumina and mullite, as well as stainless steels are employable as a specific material for anchored tubular pieces and/or anchored support pieces. Using such materials affords a semiconductor manufacturing apparatus in which—with the length of anchored tubular pieces and/or anchored support pieces to the reaction chamber being within 150 mm, and with the structure, in not using water cooling in the reaction chamber, being simple—reduction of scale is enabled, and in which temperature uniformity in the susceptor wafer-heating face is outstanding.
Here, what may be housed inside the tubular pieces is, to give examples, leads for supplying power to a resistive heating element within the ceramic susceptor, RF electrodes for generating plasma, and leads for supplying power to electrostatic chuck electrodes that are for anchoring wafers. In addition, temperature-measuring probes for gauging the temperature of the ceramic may also be contained therein.
In addition, placing a reflection plate that reflects heat from the ceramic susceptor in between the reaction chamber and the susceptor is also possible. The power consumed by the susceptor can be reduced by installing a reflection plate, because heat from the susceptor is reflected back. Although in this case there are no particular restrictions as to where the reflection plate is installed, nearer the ceramic susceptor than the midpoint between the bottom of the reaction chamber and the susceptor is preferable because that way allows heat to be reflected efficiently.
The microroughness of the reflection plate preferably is 1.0 μm or less (Ra). For the reflection plate to be of microroughness greater than this would be disadvantageous because of the higher proportion, within the heat reflected from the ceramic susceptor, of heat absorbed by the reflection plate. Especially preferable is that the surface be in mirror-like condition—that is, 0.1 μm or less roughness average (Ra). As to further properties of the reflection plate, there are no particular restrictions as to its substance as long as it is inert with respect to the gases employed within the reaction chamber, and, against the temperatures at which the ceramic susceptor is employed, has the level of heat resistance at which deformations will not arise. Examples that may be mentioned include metals such as aluminum, stainless steel and nickel; and ceramics such as alumina, silicon carbide, silicon nitride and alum nitride.
As to specifics of the anchored tubular pieces and/or anchored support pieces the respective ends of which are affixed along the reaction chamber and along the ceramic susceptor, they preferably have a parallelism that is within 1.0 mm. Parallelism greater than this is undesirable because in mounting the wafer holder in the reaction chamber, stress excessive enough to be damaging would be applied to the anchored tubular pieces and/or anchored support pieces affixed to the susceptor. Such damage can be prevented if the parallelism of the anchored tubular pieces and/or anchored support pieces affixed to the susceptor is within 1.0 mm, because then the capacity of the hermetically sealing O-rings to deform will alleviate stress produced between the ceramic susceptor and the anchored tubular pieces and/or anchored support pieces. In particular, it is especially preferable that the parallelism be within 0.3 mm, because then the O-ring-effected gastight seal can be made to be—given as helium leak rate—10−9 Pam3/s or less.
Again, O-rings are employed for a gastight seal between the reaction chamber and the tubular pieces and/or support pieces. Therein the microroughness in the vicinity of where on the face of the tubular pieces and/or support pieces the O-ring abuts is preferably Ra≦5.0 μm. For the face to have a microroughness above this level would be undesirable because achieving a vacuum of 10−7 Pam3/s or less would be exceedingly difficult, even if vacuum grease is used on the face of the tubular pieces and/or support pieces in the vicinity O-ring abutment. With the microroughness being Ra≦5.0 μm, and if vacuum grease is employed, then a vacuum of 10−7 Pam3/s or less can be achieved. Likewise, if the microroughness of the abutment surface is Ra≦1.0 μm, then a vacuum of 10−7 Pam3/s or less can be achieved even if vacuum grease is not used. Moreover, the microroughness being Ra≦0.3 μm is particularly ideal, because then a vacuum of 10−9 Pam3/s or less can be achieved even if vacuum grease is not used.
And again, the size of surface defects in the vicinity of where on the face of the tubular pieces and/or support pieces the O-ring abuts preferably is 1 mm or less in diameter. For defects of magnitude greater than that to be present in the vicinity of the abutment area would be detrimental because achieving a vacuum of 10−7 Pam3/s or less would be exceedingly difficult, even if vacuum grease is used. By the same token, with the magnitude of the defects being 1.0 mm or less in diameter a vacuum of 10−7 Pam3/s or less can be achieved by employing vacuum grease. Furthermore, if the magnitude of defects present in the vicinity of the abutment area is 0.3 mm or less in diameter, then a vacuum of 10−7 Pam3/s or less can be achieved even if vacuum grease is not used. Still further, the defect magnitude being 0.05 mm or less in diameter is particularly ideal, because then a vacuum of 10−9 Pam3/s or less can be achieved even if vacuum grease is not used.
The thickness uniformity of the ceramic susceptor and the reaction chamber bottom preferably is within 1.0 mm. Thickness uniformity in excess of this is undesirable because it can lead to wafer drop-off when wafers are mounted onto and demounted from the wafer holder. In particular, when the wafer is set onto the wafer holder, lift pins—3 ordinarily being present—support the wafer in the space over the ceramic susceptor. Therein, the positions of the lift-pin tips are preset so that the plane they form is parallel to the reaction chamber. Then by the lowering of the three lift pins the wafer is installed on the wafer-carrying side of susceptor.
If, however, in this situation the thickness uniformity of the ceramic susceptor and reaction chamber exceeds 1.0 mm, in the interval until the lift pins have descended the wafer will end up coming into contact with the susceptor. This means that the wafer will be put into a state in which it is supported by two of the lift pins and the susceptor wafer-carrying side; and when the lift pins have descended, the wafer, being at an incline, will at times drop off or will end up slipping out of the wafer-carrying location. With the parallelism of the ceramic susceptor and reaction chamber being 1.0 mm or less danger of drop-off is eliminated; moreover, a parallelism of 0.2 mm or less is advantageous because such displacement as to become a hindrance to wafer processing will not arise. It should be noted that “wafer displacement” means, for example, the riding up of a wafer on the rim of the wafer pocket formed in the susceptor wafer-carrying side.
Although it does not particularly matter what the material for the ceramic susceptor employed in the present invention is, preferable is one in which the chief component is whichever of alumina, silicon nitride, aluminum nitride, and silicon carbide. Because demands for uniformization of temperature distribution in ceramic susceptors have grown intense in recent years, materials of high thermal conductivity—specifically, materials whose thermal conductivity exceeds 100 W/mK, such as aluminum nitride and silicon carbide—are preferable, with aluminum nitride being particularly preferable owing to the superiority of its corrosion resistance and insulating properties. Meanwhile silicon nitride, because the strength of the ceramic itself at elevated temperatures is high compared with other ceramics, is ideal particularly for susceptors employed at high temperatures. Another advantage of silicon nitride, aluminum nitride, and silicon carbide is their superior resistance to thermal shock, such that these ceramics are capable of rapid rise and fall in temperature. Alumina stands out meanwhile in that from a cost aspect it is superior compared with other ceramics. The choice as to which of these ceramics to use will as a matter of course depend on the application.
Of the foregoing ceramic-susceptor substances aluminum nitride and silicon carbide are, on account of the temperature uniformity demanded of wafer holders in recent years, preferable; while aluminum nitride, whose corrosion resistance against every sort of corrosive gas employed is high, is especially preferable. Concerning the amount of sintering additive contained in the aluminum nitride, 0.05 weight % or more, 3.0 weight % or less is especially preferable. An amount of sintering additive lower than this is unadvisable in that because inter-grain interstices will be present in the sintered aluminum nitride compact, leading to etching from the interstitial areas, particles will be generated. On the other hand, with components of the additive persisting along the grain boundaries of the aluminum nitride grains if the amount of sintering additive is in excess of 3.0 weight %, there will be etching from the additive components, in which case also particles will be produced.
There are no particular restrictions with regard to the reaction-chamber substance. With metals, for example, aluminum or aluminum alloys, nickel or nickel alloys, and stainless steels may be employed. Although there are no particular restrictions with ceramics either, substances such as alumina or cordierite may be employed.
Turning to what the substance of the tubular pieces is, given the fact that leads for supplying power to the resistive heating element, RF electrodes, and electrostatic-chuck electrodes are contained in them, they advisably are an insulator. This is because if electrical continuity is created in between the tubular piece and the leads, under low pressure and under a vacuum, problems such as sparks being generated between the electrodes and being conducted into the reaction chamber will arise. Inorganic materials such as ceramics are, to be specific, preferable.
A further consideration is that in cases in which among these tubular pieces, the anchored tubular pieces affixed to the ceramic susceptor are bonded with glass or a brazing material, the difference in thermal expansion coefficient between the anchored tubular piece and the susceptor should be small. In specific terms, it is preferable that the difference between the thermal expansion coefficient of the anchored tubular pieces at normal temperature, and the thermal expansion coefficient of the ceramic susceptor at normal temperature be 5.0×10−6/K or less. A thermal-expansion-coefficient discrepancy in excess of this existing between the two would be unadvisable because when being joined the ceramic susceptor and anchored tubular pieces would break, or would be subject to cracking. Nevertheless, this restriction does not apply in cases in which the tubular pieces are not joined directly to the ceramic susceptor, but are affixed to it by screw-fastening or the like.
Specifically, while for the tubular-piece substance it is possible to use the same substance as that of the ceramic susceptor, using mullite, alumina or sialon is also possible, as is using silicon nitride. These substances are preferable because with their thermal conductivity being comparatively low, they make for lowered heat transmission from the susceptor to the reaction chamber. It should be understood that even with tubular pieces there are no particular restrictions on what their substance is in cases in which they do not contain leads, etc.
Meanwhile there are no particular restrictions regarding the support-piece substance. The use of a variety of materials such as various ceramics and metals, or composites and the like of ceramics and metals is possible. In particular, the appropriate selection may be made depending on the environment in which the ceramic susceptor is employed.
With regard to the substance of anchored support pieces, which among the various support pieces are affixed to the ceramic susceptor, in cases in which they are joined on using glass or a brazing material, the difference in thermal expansion coefficient between the anchored support pieces and the susceptor should be small. To be specific, the difference in the thermal expansion coefficient of the anchored support pieces at normal temperature, and the thermal expansion coefficient of the ceramic susceptor at ordinary temperature preferably is 5.0×10−6/K or less. A thermal-expansion-coefficient discrepancy in excess of this, present between the two, would be detrimental because when being joined together, the ceramic susceptor or the tubular pieces would be damaged, or cracks would arise in them. Nevertheless, this restriction does not apply in cases in which the support pieces are not joined directly to the ceramic susceptor, but are affixed to it by screw-fastening or the like.
With regard to specific support-piece substances, although employing the same substance as that of the ceramic susceptor is possible, using mullite, alumina or sialon is also possible, as is using silicon nitride. These substances are preferable because with their thermal conductivity being comparatively low, they make for lowered heat transmission from the susceptor to the reaction chamber.
From the above, aluminum nitride is especially preferable as a ceramic-susceptor substance, and for the substance of the anchored tubular pieces and/or anchored support pieces that are attached to it, mullite and mullite-alumina composites are especially preferable in that their thermal expansion coefficients matche that of aluminum nitride, and also for their low thermal conductivity. In turn, aluminum or aluminum alloys are especially preferable as a reaction-chamber substance for their matching of thermal expansion coefficient in terms of the combined assembly. In actual apparatuses, corrosive gases will sometimes be employed depending on the situation, and therefore the selection of substances corresponding to the application will of course be critical.
Then, utilizing a wafer holder in the present invention makes available a highly reliable semiconductor manufacturing apparatus in which there is no damage to the anchored tubular pieces that serve to contain electrode terminals/leads for the ceramic susceptor and to contain temperature gauging probes as well, nor to anchored tubular pieces and/or anchored support pieces that simply support the susceptor. In particular, among the variety of semiconductor manufacturing apparatuses that there are, this will be especially suitable as an apparatus for low-k film baking, in which the restrictions on the materials that may be introduced into the reaction chamber are few.
Slurries were prepared by putting a predetermined amount of sintering additive in the ceramic powders set forth in Table I below, furthermore adding a solvent or the like and blending the mixture together with a ball mill. Granules were prepared from the slurry by spray-drying it, and the obtained granules were press-molded using dies of predetermined form. The molded objects thus produced were degreased and then sintered at respective predetermined temperatures into sintered ceramic compacts. The thermal expansion coefficient and thermal conductivity of each of the sintered ceramic compacts obtained were measured, and together are set forth in Table I.
Using a screen-printing technique, a resistive heating element was formed and, according to requirements, RF electrodes and electrostatic-chuck electrodes were fashioned, onto substrates respectively constituted from the sintered ceramic materials noted above. Each printed substrate was baked under predetermined conditions, and a ceramic plate was bonded over it in order to protect the resistive heating element, RF electrodes, and electrostatic-chuck electrodes printed as needed. A wafer pocket for carrying a wafer was formed by a machining operation, and then electrode terminals and leads for connecting to electrical circuits were installed, into the ceramic susceptors thus produced.
Anchored tubular pieces and/or anchored support pieces constituted from the substances set forth in Table II below were attached and anchored to the surface on the side (back side) of each ceramic susceptor opposite its wafer-heating side. Utilized as anchoring methods were: bonding by means of glass, represented in
Herein, the parallelism of each of the tubular pieces and/or support pieces attached to the ceramic susceptor was measured, wherein it was within 0.1 mm in every case. Likewise, the microroughness in the vicinity of the O-ring abutment area of the attached tubular pieces and/or support pieces was in each instance Ra≦0.3 μm, and as a result of observing the surface under an optical microscope, that there were no defects exceeding 0.05 mm was verified.
For the wafer holders thus fabricated, reaction chambers of predetermined configuration, constituted from the substances set forth in Table III below, were readied. The wafer holders were installed within the reaction chambers, and were sealed gastight by means of an O-ring made of rubber in between the tubular pieces and/or support pieces and the chamber. Therein, the parallelism of the wafer-carrying side of the ceramic susceptor and the reaction chamber was 0.15 mm or less in every case. Following that, power was supplied to the ceramic susceptors to raise their temperature to a predetermined level, the temperature of the ceramic susceptors and of the reaction chambers was measured with the thermocouple, and then the temperature uniformity of the ceramic susceptor was found. The temperature was then lowered to the normal level, and the tubular pieces and/or support pieces were checked for damage.
The results obtained are set forth, by ceramic-susceptor (heater) and anchored-tubular-piece and/or anchored-support-piece substance, in the following Tables IV-XLV, divided into test conditions and test results. In the tests, the atmosphere within the reaction chamber while the ceramic susceptors were heating was made a vacuum. The temperature uniformity of the susceptors was measured using a wafer-temperature gauge. Also, gastightness between the reaction chamber, and the tubular pieces and/or support pieces is indicated in the tables as “V. good” where the leak rate was 10−9 Pam3/s or less while the temperature was high, and as “Good” where it was 10−7 Pam3/s or less.
The Sample 3-1 wafer holder employed in Embodiment 1 was readied. To this a reflection plate made of stainless steel was attached, and with the temperature of the ceramic susceptor raised to 500° C. the susceptor power consumption was measured. Holes 12 mm in diameter were drilled in the reflection plate so as to allow the tubular pieces and/or support pieces to pass through. Power-consumption measurements were also made at different installment separations between the reflection plate and the ceramic susceptor. The stainless steel plate therein was of 0.5 mm thickness, 330 mm diameter, and Ra=0.05 μm microroughness. The results are set forth in the following Table XLVI.
In addition, power consumption was likewise measured with the position of the reflection plate being fixed at 15 mm from the ceramic susceptor, and with the microroughness of the reflection plate being varied. The results obtained are set forth in Table XLVII. From these results it will be understood that the power consumption may be reduced by employing a reflection plate whose microroughness is 1.0 μm or less (Ra), furthermore 0.1 μm or less, installed in a position near the ceramic susceptor.
One end of tubular pieces and support pieces made of mullite, similar to those of Embodiment 1, were by glass bonding attached to the aluminum nitride susceptor employed in Embodiment 1. In doing so, the parallelism was varied by polishing the tubular-piece and support-piece end faces for the susceptor bonding face to change the angle of their attachment to the susceptor. The other ends of the tubular pieces and support pieces were then mounted into a reaction chamber made of aluminum, and the reaction chamber interior was pumped down to assay its helium leak rate. The results are set forth in Table XLVIII. Here, the microroughness in the vicinity of the O-ring abutment area on the mullite tubular pieces and support pieces was Ra≦0.3 μm in every case, and as a result of observing the surface under an optical microscope, that there were no defects exceeding 0.05 mm was verified.
Next the microroughness in the vicinity of the O-ring abutment area of a plurality of mullite tubular pieces in being fitted into the reaction chamber was varied, and they were attached, by glass bonding, to the ceramic susceptor using the same technique as in Embodiment 1. After mounting the tubular pieces into the reaction chamber, the reaction chamber interior was pumped down to assay the helium leak rate of the seal areas. The results are set forth in Table XLIX.
The same tubular pieces made of mullite as in Embodiment 1 were readied for the aluminum nitride susceptor employed in Embodiment 1. From among them, mullite tubular pieces on which there were defects differing in size in the vicinity of the O-ring abutment area were selected out; these as well as tubular pieces having no defects were respectively glass-bonded to an aluminum nitride susceptor. Subsequently the remaining ends of the tubular pieces were mounted into the reaction chamber, and after pumping the chamber down, the helium leak rate where the O-rings abut on the face of the tubular pieces was assayed. The results are set forth in Table L.
Tubular pieces and support pieces made of mullite, similar to those of Embodiment 1, were by glass bonding attached to the aluminum nitride susceptor employed in Embodiment 1. In doing so, the parallelism of the ceramic susceptor and reaction chamber was varied by polishing the tubular-piece and support-piece end faces for the susceptor bonding face to change the angle of their attachment to the susceptor. These ceramic susceptors were installed in a reaction chamber made of aluminum, the reaction chamber interior was pumped down, and a wafer mounting/demounting test was carried out. The results are set forth in Table LI.
The anti-corrosive properties of the ceramic susceptors were compared, and in order to do so, the top face of each of the sintered ceramic compacts set forth in the foregoing Table I was polished. After being processed each of the sintered-compact samples was checked for usability by the following protocol.
At first a discoid heater was fashioned with a specially prepared aluminum-nitride ceramic as a matrix, into which a tungsten filament was embedded. Next, each of the sintered-compact samples in Table I was set on the susceptor, which was then arranged within the vacuum chamber of a plasma-generating apparatus using 13.56 MHz high RF power. The sintered-compact samples were each treated 5 hours at a 100° C. heating temperature under a CF4 gas environment having a plasma density of 1.4 W/cm2. After that the density of etch pits on the plasma-irradiated face was examined (number of pits whose maximum diametric span is at least 1 μm, present within a arbitrary surface visual field of 1000 μm2 when observed using a scanning electron micrograph); the counts are set forth in Table LII below.
It will be understood from the results noted above that aluminum nitride is superior in terms of anti-corrosiveness, and that the samples thereof where the amount of sintering additive was from 0.05 weight % to 1.0 weight % were especially favorable.
The wafer holders from Embodiment 1 that yielded excellent results were each introduced into a semiconductor manufacturing apparatus, and were run respectively in plasma-assisted CVD, low-pressure CVD, low-k film baking, plasma etching, and dielectric-film CVD operations. The result was that there were no incidents of damage to either the anchored tubular pieces and/or anchored support pieces with any of the holders while wafers were being processed. In the low-k film baking application in particular, especially homogeneous film quality was obtained.
Next various example structures will be discussed. These structures may variously be selected in accordance with each application, reaction-chamber configuration, etc. For example, as illustrated in
The present invention eliminates damage to the tubular pieces serving to house electrode terminals and leads for supplying power to a ceramic susceptor and to house temperature-measuring probes, as well as damage to support parts that support the ceramic susceptor—even with the housing/supporting components being anchored to the susceptor and its reaction chamber—thereby affording wafer holders realizing very significant improvement in reliability, and semiconductor manufacturing apparatuses in which the wafer holders are employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-282120 | Sep 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP03/12311 | 9/26/2003 | WO |
