DE69726278T2 - Semiconductor wafer carrier with CVD film coating made of silicon carbide - Google Patents

Description

BACKGROUND THE INVENTION

Field of the invention

This invention relates to a holder for the fixation of semiconductor wafers by means of suction and a method for making them.

description of the related art

There are different types of conventional ones Mounts for the application of a smooth surface to an object being held and holding said piece are designed, e.g. B. Devices used in the manufacturing process of semiconductor integrated circuits are used around wafers to transport and fix at predetermined positions. In exposure systems, that play a fundamental role in the lithographic process, become vacuum fixtures for fixing thin-film wafers within one level used.

It is known that anodized Aluminum alloys and alumina ceramics currently as materials for the Contact area with that held by the bracket of this type Object can be used. It is also known that for a bracket, whose contact area is made of an aluminum alloy, impossible is, the accuracy of their suction surface due to abrasion or the like over a longer Maintain period while a holder with a made of an alumina ceramic Contact area is also not easy, namely when using the Holder part is electrically charged, attracted dust particles, which are transferred to wafers and contaminate the suction accuracy of the held objects reduce.

As a result of micro miniaturization the past few years, it provided the integrated semiconductor circuits affected, it is necessary that the wafer exposure surface has a Completely two-dimensionally flat and ultra smooth surface. Accordingly it is required the surface accuracy the suction surface the holder (vacuum holder), the object to be held (Wafer) holds, has an ultra smooth finish.

If the contact surface of the Bracket is formed by tension, the aluminum alloy, although it is soft and easy to machine, it quickly deteriorates. Alumina ceramics tend to have fine holes and because of the existence electrical charge to absorb dust particles, with what another disadvantage of a big one Coefficient of thermal expansion connected is.

• (1) Hervorragende Abriebbeständigkeit, z. B. ein hoher Härtegrad;
• (2) keine Ansaugung von Staubpartikeln aufgrund der Existenz von feinen Löchern und elektrischer Aufladung;
• (3) kleiner Wärmeausdehnungskoeffizient;
• (4) ein geringes spezifisches Gewicht und eine hohe Härte; und
• (5) eine hervorragende Spanbarkeit.

As explained in the aforementioned prior art, the following properties of the bracket materials designed to hold the held objects in contact with the smooth surface of the bracket are required:

• (1) Excellent abrasion resistance, e.g. B. a high degree of hardness;
• (2) no suction of dust particles due to the existence of fine holes and electric charge;
• (3) small coefficient of thermal expansion;
• (4) low specific weight and high hardness; and
• (5) excellent machinability.

The previously mentioned properties will be described in detail below.

The contact surface between the bracket and the held object wears out and suffers from repetition damage to the holding process. Especially when a thin piece like such as a thin film wafer on a vacuum chuck is sucked in and held there, the surface of the Wafers, which is exposed to the suction, in terms of optimal Position for correct the exposure system for light generation, d. H. one if possible exact two-dimensional surface. Accordingly, high abrasion resistance and high hardness are the desired Textures of the contact surface between the bracket and the held object to a deformation of the piece, the is due to defects caused by abrasion of the contact surface, just like one due to the presence of tiny particles that generated by abrasion wear resulting from their contact to avoid conditional deformation of the piece. In the event of of wafers the deposition of tiny particles on the surface to break the wire and shorts when printing circuits.

Furthermore, in addition to the abrasion wear mentioned above, dust is attracted to the electrically charged holder, e.g. B. penetrates into the fine holes on the ceramic surface which leads to the same damage as mentioned before.

In the case of the vacuum holder of an exposure system due to the absorption of the Light is stored at the time of exposure to heat. As a result, a large coefficient of thermal expansion of the holder causes the actual holder to change in size, making it impossible to hold the wafer in a predetermined position in the state of being attracted by the suction and being fixed to the holder. Therefore, it is desirable that the coefficient of thermal expansion be as small as possible in order to suppress dimensional errors when printing circuits.

When a large held object is held must be increased the load on the holding components of the bracket, which is why a material with high mechanical hardness is required for the holder, taking this to an increase the material thickness would, so an increase the hardness runs counter to the effort to make the bracket easy.

The most time-consuming and labor-intensive Step in the material cutting process is the step of Abrading. Especially in the case of the vacuum chuck to hold wafers, the contact surface with the wafer must be because of the for the Achieving flatness during correction required for vacuum suction must be ultra smooth. Therefore the grindability of the bracket material becomes a critical factor.

As the materials that of the above have met the above-mentioned requirement, ceramic Materials developed. Nevertheless, the existing ceramic ones require Materials that are generally very hard are considerable Degree of Machining as well as grinding energy to grind up the surface to a degree of ultra smoothness, as previously described. The intensification of grinding leads to, that the polished surface damaged becomes, and therefore makes it difficult to have a smooth and level surface higher precision to obtain.

US 5 258 047 relates to a holding device for holding an object by an electrostatic force, including a body made of a low resistance dielectric such as SiC with a CVD-SiC film thereon, and an electrode provided on the surface facing away from a holder surface, so that a potential difference between the object and the holder surface is generated.

JP 09-142996 discloses a sintered SiC mask substrate with a ( 220 ) CVD-SiC film, which has good polishability with the aim of improving the exposure accuracy during the production of the mask.

Taking into account the above statements it is the object of the present invention to provide a vacuum chuck for holding a semiconductor wafer that is excellent Holding properties and good workability, where he a great one Hardness and has good abrasion resistance.

The invention solves this problem by Vacuum clamping holder according to claim 1 and the method according to claim 5. Advantageous further developments are provided by the features of the subclaims.

The electrical discharge chip process is usually applied to the difficulty of machining overcome conventional ceramic materials. Still points Area subjected to the electrical discharge voltage mostly the formation of recesses and tiny holes, so for making a smooth contact surface with the object being held there is no other approach but to step by step Grinding is the most difficult step in machining ceramic Represents materials to leave. It is preferred that for the vacuum holder for the The semiconductor wafer of the present invention is a sintered silicon carbide substrate first shaped and then their surface is coated with a CVD silicon carbide film, thereby making them is facilitated.

The vacuum holder is also used for semiconductor wafers of the present invention, the sintered silicon carbide for the contact area not directly to the held object, but it becomes the CVD silicon carbide film on the surface applied, thereby grinding the excess of the bracket with respect the most critical property, e.g. B. the machinability of the contact surface object, relieved to an ultra smooth and flat surface becomes.

In addition, the present Invention through an improvement in the difficulty of Sanding the surface due to the lack of alignment of the crystal planes on the surface of the usual Silicon carbide material characterized by orientation the crystal planes of the silicon carbide vapor deposition film and The orientation of the fissile planes enables the surfaces to ultra smooth and flat surfaces be ground with less grinding energy, while the Formation of damage as far as possible is prevented.

It is preferable that the electrical resistance of the sintered silicon carbide mixture material used for the present invention is below 10 ⁶ Ω · cm. This property is a so-called mixture-inherent conductivity. In other words, in addition to the properties of the high rigidity, the low weight and the high hardness of the sintered ceramics, the vacuum holder for semiconductor wafers according to the present invention has a conductivity which is suitable for existing Al ₂ O ₃ -Ke ramiken is so far unreachable. Accordingly, their abrasion resistance has increased and the formation of a static charge at the contact area with the held object is prevented, thereby reducing the separation of dust.

The one used for the invention CVD silicon carbide film according to this Invention is of such a dense structure that the film is free of fine holes that occur in normal ceramic surfaces. Hence the Contact area between the semiconductor wafer holder and the held object free from any deposition of foreign objects in the fine holes, and if there is any deposit, the deposit can easily cleaned and removed.

The one in the present invention CVD silicon carbide film used can be manufactured in such a way that he has many types of film structures with the orientation mentioned above dependent from the vapor deposition condition. According to that The method of the present invention becomes the CVD silicon carbide film produced by means of the CVD at reduced pressure in a non-acidic atmosphere.

As long as the semiconductor wafer vacuum chuck of the present invention a mode for holding the held Object due to its smooth and flat surface, there are no specific restrictions for their Applications for the promotion and keeping wafers for the semiconductor substrates, e.g. B. vacuum clamps (vacuum clamps, which the wafers in one plane of the exposure system of the lithographic Process, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

Other features regarding structure, Handling and advantage of the present invention will become apparent to those skilled in the art clear from the following description when combined is read with the accompanying drawings, of which:

1 10 is a plan view of a vacuum chuck according to an embodiment of a semiconductor wafer holder of the present invention;

2 is a schematic sectional view of the vacuum chuck of 1 is;

3 a partially enlarged view of the schematic sectional view of the vacuum chuck from 2 is.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First, referring to Test examples the effects of the present invention in the following described in detail.

Test example 1

Table 1 shows the physical Properties of vacuum chucks (also referred to below as "brackets"), where the silicon carbide films from each for conventional mounts used material by chemical vacuum deposition in non-acidic the atmosphere from an embodiment were formed. Every physical property of a metal, one Ceramics, materials and materials representing stainless steel of alumina are shown as comparable materials.

Table 1

The following information has been removed from Get Table 1. Like that when calculating property values the brackets that require flatness and the materials for the support devices, which is a small size and high capacity shows a comparison of the elastic modulus and the specific Weight in both cases, that the CVD silicon carbide blend material used in this invention the most wanted Values of a great Young's modulus and have a small specific weight. Of the three Materials, this material has the lowest coefficient of thermal expansion, causing small dimensional changes generated even when heat is over you longer Exposure time period is saved. It means that the use of such materials to manufacture a vacuum chuck ensures minor dimensional errors when printing circuits of a wafer fixed by suction be generated.

There are almost no fine holes the surface chemically separated from the steam or the contact surface the held object. Hence the chances of deposition of dust on the suction surface very low, resulting in a low probability of reducing the flatness of the held Object due to the presence of dust between the contact surface and leads to the held object. It is also advantageous that their high hardness makes it impossible to produce tiny particles due to abrasion wear and the deposition on the held object is effected.

The sintered α-silicon carbide used as the substrate shows an electrical resistance of approximately 10 ⁶ Ω · cm. Since the carbide is present as a mixture structure with the crystallized CVD silicon carbide film of the β structure, the carbide nevertheless has an electrical resistance below 10 ⁶ Ω · cm, which ensures excellent conductivity in ceramics, which is why there is no dust deposition caused by static charge is effected on the bracket. Even if some dust should be removed, such a deposit can be easily removed. Cleaning the bracket is therefore simplified.

Furthermore, the small coefficient of thermal expansion for one minor dimensional changes the bracket during of heat storage responsible at the time of exposure, etc. As a result, the dimensional errors of the wafer when the wafer is held and a highly sensitive Photoresist over used a long period of exposure at low intensity will be kept within tolerance.

Test example 2

A comparison was made between the vapor deposition film, which was determined by an arrangement for the orientation of the crystal planes in the ( 220 ) and ( 111 ) Levels were obtained in Miller indexes, and the vapor deposition film was performed with no orientation in terms of the grinding energy required for grinding and in terms of duration, and it was found that the oriented film was superior to the non-oriented film in that the oriented vapor deposition film had a much lower energy consumption as well as a clear difference in the polar state of the surface.

Test example 3

The crystal structures of both vapor deposition films formed under reduced pressure or atmospheric pressure were subjected to X-ray diffraction for comparison, with the result that the crystal structure of the film formed under reduced pressure atmosphere 220 ) Level about 52 times more common than the ( 111 ) Level in Miller indices, in contrast to the recording of about 32 times more frequently under a normal pressure atmosphere. Since it is more difficult to grind materials with a non-oriented crystal structure than materials with an oriented crystal structure, this means that the film formed under a reduced pressure atmosphere has a stronger orientation in the direction of the ( 220 ) Level ensures superior sandability.

embodiment

An embodiment of the semiconductor wafer holder according to the present Invention will now be described with reference to the accompanying figures described.

1 10 is a plan view showing a schematic construction of a vacuum fixture for wafer fixing, which is an embodiment of the semiconductor wafer holder according to this invention.

2 Fig. 3 is a sectional view, from the line AA 'in 1 ,

3 is a partially enlarged view of 2 ,

A wafer suction surface of the vacuum chuck WH according to this embodiment has a round shape with a slightly smaller diameter than the wafer W. A plurality of annular protrusions 1 (area holding the wafer W) and annular recesses 2 (Vacuum suction grilles), both concentric to the center of a holder WH, are formed as rings with a fixed distance on the wafer suction surface.

On every ring-shaped depression 2 is an inlet opening 3 designed for the vacuum suction radially, with each inlet opening 3 in connection with a sleeve-shaped opening 4 (Vacuum suction opening) extends radially into the interior of the bracket WH. The connection of the opening 4 with a negative pressure source with subsequent negative pressure generation creates a negative pressure in one of the back of the wafer W and each annular recess 2 surrounding space, so that the back of the wafer W of the surface edges of the plurality of annular projections 1 is corrected for leveling.

For this embodiment, the actual holder WH was produced by coating a sintered silicon carbide substrate with a silicon carbide film formed by CVD. First, an α-silicon carbide substrate 6 , shaped like it 1 and 2 show sintered. Because the sintered frame has already been designed so that it has annular projections 1 and recesses 2 (0.2 to 0.5 mm deep), the sintered support substrate has printed protrusions and depressions. The cutting was again carried out with annular projections 1 with a vertex distance of exactly 0.2 mm and the grinding was carried out thereon to produce a surface roughness of up to 0.01 mm.

The surface holding the wafer and the groove surface of the substrate were treated with simultaneous film formation, that is, both surfaces of the annular protrusions 1 and the annular depressions 2 have been subjected to chemical vapor deposition of high purity silicon carbide under two different vapor deposition conditions, resulting in the formation of a silicon carbide film in question 5 led. One was a vacuum vapor deposition in a non-acidic atmosphere with a vapor deposition temperature of 1300 ° C at a vapor deposition rate of 10 to several tens of μm / h, while the other was a normal pressure vapor deposition in a non-acidic atmosphere with the same vapor deposition temperature at the same vapor deposition rate.

The two surfaces of the Vacuum chucks were then machined with diamond powder for 5 hours polished, whereupon those obtained by vapor deposition under the aforementioned vacuum atmosphere film surface by grinding up to 8 Å (10 Å = 1 nm) rms and the other obtained by vapor deposition under a normal pressure atmosphere film surface up to 500 Å rms was completed.

Like the previous description has shown is what the manufacture of the semiconductor wafer holder this Invention relates to this simple. In addition, the sintered silicon carbide not directly for uses the contact area with the held object, but it becomes a CVD silicon carbide film that makes it easier to grind, for the surface used, which ensures excellent workability of the contact surface the held object as a smooth and flat surface the most critical factor is reached.

Furthermore, this invention enables that the surface of the CVD silicon carbide film using less grinding energy deposits smoothly and evenly while the formation of damage by orienting the crystal planes and aligning the fissile levels as much as possible is prevented. In particular, it is formed by coating the CVD silicon carbide film produced in a non-acidic atmosphere under reduced pressure Film a specific crystal structure, causing the formation of the ultra smooth and flat surface by means of grinding, which is the most difficult step in ceramic Represents materials, is facilitated.

The freedom of silicon carbide film from any fine holes and the property of conductivity of the semiconductor wafer holder according to this invention the deposition of dust due to the generation of a static Charging, which makes the bracket easy to clean.

Another beneficial effect arises from the use of sintered silicon carbide for the substrate: due to the properties of high hardness and low weight, the for Ceramics are characteristic, resulting toughness enables the held object to maintain and make corrections to keep a flat surface stable over a long period of time. Another characteristic is the high one Dimensional stability as a result a small coefficient of thermal expansion, which is beneficial when dimensional changes due to heat storage of heat pose a problem.

While now what has been described as the preferred embodiment of the invention, it is understood that many of them Modifications can be made in the area of Invention as in the pending claims is defined, fall.

Claims (5)

Vacuum clamping holder (WH) for holding a semiconductor wafer (W), the holder having a flat surface ( 1 ) to be contacted by the object, vacuum suction grooves ( 2 ) leading to the flat Are recessed, the holder being a sintered silicon carbide substrate ( 6 ) which has the flat surface and the vacuum suction grooves, the sintered silicon carbide substrate further comprising an inlet channel ( 3 . 4 ) for applying a vacuum suction to the vacuum suction grooves, the flat surface of the substrate and the surface of the vacuum suction grooves with a CVD silicon carbide film ( 5 ) are coated, whose crystal planes correspond to the ( 220 ) and the ( 111 ) Levels are oriented. Vacuum chuck according to claim 1, wherein the sintered silicon carbide substrate comprises α-silicon carbide or β-silicon carbide, wherein the CVD silicon carbide film β-silicon carbide is. A vacuum chuck according to claim 1 or claim 2, wherein the X-ray diffraction power of the ( 220 ) Crystal planes of the CVD silicon carbide film about 52 times that ( 111 ) Is crystal planes. Vacuum chuck according to claim 1 or claim 2, wherein the X-ray reference strength of the ( 220 ) Crystal planes of the CVD silicon carbide film approximately 32 times that of the ( 111 ) Is crystal planes. Method of making a vacuum chuck according to one of the claims 1 to 3, in which the CVD carbide film by CVD at reduced pressure in a non-acidic atmosphere is formed.