WO2020064282A1

WO2020064282A1 - Method for polishing a semiconductor wafer

Info

Publication number: WO2020064282A1
Application number: PCT/EP2019/073535
Authority: WO
Inventors: Klaus Röttger; Alexander Heilmaier
Original assignee: Siltronic Ag
Priority date: 2018-09-25
Filing date: 2019-09-04
Publication date: 2020-04-02
Also published as: TW202013487A; DE102018216304A1; TWI711081B

Abstract

The invention relates to a method for polishing a semiconductor wafer in that at least one side of the semiconductor wafer is pressed against a polishing pad secured to a rotating polishing disc in the presence of a polishing agent. The polishing pad has a surface interrupted by channels. The invention is characterized in that the polishing pad is secured to the polishing disc in that the polishing pad is adhered to the polishing disc and is pressed against the polishing disc in the region of the channels by means of a suitable tool.

Description

Process for polishing a semiconductor wafer

The invention relates to a method for polishing a semiconductor wafer.

The CMP (chemical mechanical polish is a one-sided polish, which is usually used to reduce the roughness of the front side of a semiconductor wafer. It is therefore also called "mirror polishing"). During the CMP, the semiconductor wafer with the side to be polished pressed by a rotating polishing head against a rotating polishing cloth and in

The presence of a polishing agent supplied is smoothed. This is described for example in US 5,916,016.

Double-side polishing (DSP) is a process from the group of chemical-mechanical processing steps. According to one embodiment described in the patent specification EP 0208315 B1, semiconductor wafers in rotor disks made of metal or plastic, which have suitably dimensioned recesses, are placed between two rotating polishing plates covered with a polishing cloth, a working gap being formed between the polishing plates in the presence of a

Polishing agent is moved on a path predetermined by the machines and process parameters and thereby polished.

With the DSP, the working layers are in the form of polishing cloths, and these are attached to the working disks in an adhesive, magnetic, form-fitting manner (for example using a Velcro fastener) or by vacuum, which are also referred to as so-called polishing plates in the DSP. Both polishing plates of a DSP system are included

Glued polishing cloths. To ensure high quality processing by DSP, both polishing cloths should be glued without bubbles. It is important that the polishing cloth adheres evenly over the entire polishing plate. In order to achieve the necessary adhesion of glue, the polishing plates are pressurized for a certain time after polishing cloths are glued on

moved together. This process is also called cloth presses. The adhesive flows through the pressing and adheres better. Corresponding procedures for Cloth presses are known for example from EP 1 775 068 A1 and from US 2008/0248728 A1.

US 2001/0014570 A1 discloses a method for producing a semiconductor wafer with a front side and a rear side and a polished edge, comprising a simultaneous polishing of the front side and the rear side of the

Semiconductor wafer with a continuous supply of an alkaline polishing agent between two rotating lower and upper polishing plates, both of which are covered with a polishing cloth, both polishing cloths essentially consisting of a porous, homogeneous, fiber-free polymer foam and the polishing cloth of the lower polishing plate having a smooth surface and the polishing cloth of upper

Polishing plates shows a surface interrupted by channels.

The polishing cloth adhering to the upper polishing plate is interspersed with a network of channels, while the polishing cloth adhering to the lower polishing plate does not have such a texturing but a smooth surface. Through this texturing, an improved distribution of the polishing agent used is achieved, which is a

Has an influence on the quality of the polished disc edges. The channels can be applied to the polishing cloth, for example, by a material removal milling process. The upper polishing cloth preferably has one

regular checkerboard arrangement of channels with a segment size of 5 mm x 5 mm to 50 mm ^c 50 mm and a channel width of 0.5 to 2 mm. Polishing cloths can consist of a thermoplastic or thermosetting polymer. A large number of materials can be considered as the material for foamed polishing cloths (foamed pads), for example polyurethanes, polycarbonate, polyamide, polyacrylate, polyester, etc. A polishing cloth produced from a polymer is disclosed, for example, in US 2008/0102741 A1.

But polishing cloths can also be made from foamed sheets or felt or

Fiber substrates that are impregnated with polymers exist (non-woven cloth, non-woven pad). Such a cloth is described for example in US 5,510,175 A. According to US 2014/0206261 A1, when the polishing cloths are glued on, it can be advantageous to heat the polishing plates, since the viscosity of the adhesive film increases while the polishing plates are heated, while at the same time improving the adhesiveness of the

Adhesive film reduced. The polishing plate covered with the polishing cloth is then cooled from the temperature set for the gluing to the desired process temperature over a period of at least 3 hours, the polishing cloth being pressed against the opposite polishing plate with a pressure of at least 10,000 Pa during the entire cooling process becomes.

In particular, when using hard, less compressible polishing cloths, there is the problem that after the conventional cloth pressing, the polishing cloths often do not adhere evenly to the polishing plates. This is due to the fact that there is a polishing gap of up to 300 pm between the upper and lower polishing plate, which results from the respective distance between the upper and lower polishing cloth. The non-uniform adhesion of the polishing cloths is also noticeable in the quality of the polished semiconductor wafers without countermeasures.

WO 2018/086912 A1 describes a method for polishing a surface on both sides

Semiconductor wafer known, polishing cloths with a hardness at room temperature of at least 80 ° according to Shore A and with a compressibility at room temperature of less than 3% are fastened on the upper and lower polishing plate, a semiconductor wafer being polished on both sides between the upper and lower polishing cloth, characterized in that that to fix the polishing cloths on the upper and lower polishing plates, the polishing cloths are glued to the upper and lower polishing plates, a cloth with a compressibility at room temperature of at least 3% is positioned between the two glued-on polishing cloths and then the two polishing cloths with the one between them Cloth pressed against each other for a certain period of time. However, it has been shown that when using a polishing cloth interspersed with channels according to US 2001/0014570 A1 and using the cloth press known from WO 2018/086912 A1, the geometry of the polished disk is worse than when using a smooth polishing cloth.

The task of the invention arose from this problem,

The object is achieved by a method for polishing a semiconductor wafer by pressing at least one side of the semiconductor wafer in the presence of a polishing agent against a polishing cloth fastened on a rotating polishing plate, the polishing cloth having a surface interrupted by channels, characterized in that the polishing cloth is attached to the polishing plate by gluing the polishing cloth onto the polishing plate and pressing it onto the polishing plate in the region of the channels using a suitable tool.

In one embodiment, it is a one-sided polish, e.g. a CMP process.

In another embodiment, it is a DSP polish, that is, a simultaneous polishing of the front and the back of a semiconductor wafer with the continuous supply of an alkaline polishing agent between two rotating lower and upper polishing plates.

With DSP both polishing plates are covered with a polishing cloth, one in

Embodiment, the polishing cloth of the lower polishing plate has a smooth surface and the polishing cloth of the upper polishing plate has a surface interrupted by channels.

To fix the polishing cloths on the upper and lower polishing plates, the polishing cloths are glued to the upper and lower polishing plates, the polishing cloth of the upper polishing plate being pressed onto the upper polishing plate in the region of the channels using a suitable tool. In another embodiment, the polishing cloth of the upper polishing plate has a smooth surface and the polishing cloth of the lower polishing plate has a surface interrupted by channels. In a further embodiment, both polishing cloths have a surface interrupted by channels.

The invention is based on the observation that a uniform pressing of polishing cloths with a surface interrupted by channels is difficult because the pressure is only exerted on the cloth surface and not in the channels. This can be seen in part after a used polishing cloth has been removed in the form of a pattern on the polishing plate. As a result, the polishing cloth is not pressed on exactly at the positions of the channels, which has the consequence that the flatness of the polishing cloth surface deteriorates slightly.

With double-sided polishing, this means that the geometry of the polished semiconductor wafer deteriorates slightly. In particular, the difference

front-related ZDD (= double derivation of the fleas perpendicular from the median plane to the front of the semiconductor wafer) and back-related ZDD is slightly deteriorated. The ZDD describes the mean curvature of a surface of the semiconductor wafer near the edge and is defined in SEMI M68-1015.

The invention counteracts this in that the channels are pressed separately.

In one embodiment, this is done by means of a metal or plastic pin, which has a round tip that is adapted to the width of the channels, and with which the channels are moved in order to press the polishing cloth against the polishing plate in this way. Ideally, the diameter of the tip of the pin corresponds to the channel width. Even with this manual method, there is a noticeable improvement in the ZDD difference of the polished semiconductor wafers. In another embodiment, a template is used as the tool

Insert that has webs on one side that are dimensioned so that they can be taken up by the channels of the polishing cloth. The width of the webs ideally corresponds to the width of the channels. The height of the webs ideally corresponds to the channel depth or is somewhat larger.

In one embodiment, the second side of the template is smooth. This ensures that with DSP the smooth polishing cloth is not damaged if the polishing plates are moved together with the template positioned between them and a contact pressure is exerted in order to press the polishing cloth in the area of the channels.

In one embodiment, the polishing cloths are additionally pressed onto the polishing plates. This can be done before or after the previously described pressing of the polishing cloth in the area of the channels.

For one-sided polishing, this is preferably done by rolling.

In one embodiment, a polishing cloth with a hardness at room temperature of at least 60 ° according to Shore A and with a compressibility at room temperature of less than 7% is used.

In one embodiment, it is a DSP, polishing cloths having a hardness at room temperature of at least 70 ° according to Shore A and having a compressibility at room temperature of less than 3% being attached to the upper and lower polishing plates. The compressibility of a material describes which all-round pressure change is necessary to cause a certain change in volume. The compressibility is determined analogously to J IS L-1096 (Testing Methods for Woven Fabrics). The compressibilities mentioned here and elsewhere are to be determined at room temperature (23 ° C ± 2 ° C).

In one embodiment, polishing cloths with a hardness of 70 to 95 ° according to Shore A (DIN EN ISO 868) are used at room temperature (23 ° C ± 2 ° C). To press cloth between the two glued polishing cloths as

Liner a cloth with a compressibility at room temperature of

be positioned at least 3%. Then the two polishing cloths with the cloth between them for a certain period of time

pressed together.

In a further embodiment, the intermediate layer has in the area of

An increase in the amount of polish.

The blanket used as an intermediate layer is only used for blanket pressing. After pressing the cloth, it is removed from the polishing system. The same naturally applies to the template for pressing the polishing cloth in the area of its channels.

In one embodiment, the cloth used as an intermediate layer consists of felt or a fiber substrate, that is to say of a non-woven textile.

In one embodiment, it is felt made from PU elastomer fibers.

The thickness of the intermediate layer can be 0.5 to 3.0 mm. In one embodiment, the thickness of the intermediate layer is 1.5 to 2.6 mm. In a preferred one

Embodiment comprises the cloth used as an intermediate layer two or more layers of cloth that are glued together.

In one embodiment, the intermediate layer is in the region of the

Polishing agent feedthroughs increased by 200 - 300 μm. This can be achieved by additional layers of cloth or foils glued in these areas.

In one embodiment, the intermediate layer comprises one or more annular cloth layers or foils, which are each glued around the polish feedthroughs. In one embodiment, the annular cloth layers are made of felt, made of PU elastomer fibers.

In one embodiment, the annular foils are made of PE.

In one embodiment, the intermediate layer is aligned before the polishing plates move together, so that positions of the elevations correspond to the positions of the polishing agent feedthroughs. Due to the elevations in the areas of the polish feedthroughs, a particularly high adhesive adhesion is achieved in these areas, which prevents the polish from penetrating under the cloth.

In one embodiment, the compressibility is as an intermediate layer

used cloth 3-10%. A compressibility of the cloth used as an intermediate layer of 3.2-7.6% is very particularly preferred.

Before the cloth pressing process, the polishing cloths are glued to the respective polishing plate of the polishing machine.

Gluing preferably comprises the following steps:

- Preparation of the polishing plate surface by appropriate cleaning

- Remove the protective film from the self-adhesive PSA layer on the cloth

- Bubble-free application of the polishing cloth to the polishing plate. In a further embodiment, the polishing plates are heated before the polishing cloths are glued on. For example, the polishing plates can be heated to a temperature of 40 - 50 ° C. This reduces the viscosity of the adhesive film while improving its liability. After the polishing cloths have been glued on, the polishing plates are cooled, if necessary. In one embodiment, the polishing plates are cooled to the desired polishing temperature, which is generally between 10 and 50 ° C. The heating and cooling of the polishing plates before and after the polishing cloths are stuck on is preferably carried out by means of an internal temperature control of the polishing plates.

In a preferred embodiment, the polishing plates are cooled over a period of one to several hours.

In a further embodiment, the polishing plates are cooled during the cloth pressing. In one embodiment, the pressing process is carried out by pressing the two less compressible polishing cloths together with the more compressible cloth between them for a certain period of time.

The cloth is preferably pressed at a pressure of at least 11,000 Pa. In one embodiment, the pressing process takes from about a minute to several hours. The pressing process is preferably carried out by the

Manufacturer of the polishing cloths recommended adhesive temperature. In a

Embodiment, the pressing process takes place at room temperature. With DSP, for example, you can do the following:

- sticking on the polishing cloths (top and bottom)

- Optional normal pressing of the two towels by moving the plates together, if necessary with an intermediate layer

- Insert a template (e.g. on the upper plate)

- Press both polishing plates together with the template inserted

- Remove the template - Optional normal pressing of the two cloths by moving the plates together, if necessary with an intermediate layer

The optional normal pressing of the polishing cloth can be done manually, with rollers or by pushing the polishing plates together in the case of a double-sided polishing system.

A template is pressed against the polishing cloth having channels in such a way that corresponding webs of the template lie in all channels. The back of the template is flat ..

The template is preferably about the same size as the polishing cloths and covers all channels.

In one embodiment, the template is made of metal (e.g. stainless steel) or plastic (e.g. PEEK, PFA, PVDF).

The webs preferably have the same width as the channels (e.g. 2 mm channel width corresponds to a web width of 2 mm); The web height is preferably the same or slightly larger than the channel depth.

In one embodiment, the channel depth is 0.5 mm, the web height of the template being 0.5 mm to 1 mm.

A web height of 0.5 mm - 0.7 mm is particularly preferred, very particularly preferably 0.5 mm - 0.6 mm. In one embodiment, the shape of the web tip is adapted to the channel shape, for example rectangular in the case of rectangular channels or round in the case of U-shaped channels.

The template can be in one or more parts.

In the case of a double-sided polishing system, the template is preferably pressed on by moving the two polishing plates together. In the case of double-sided polishing systems, pressing with the template can be used on both the upper and the lower plate.

The pressing can also be done by manually pressing the template onto the polishing plate or by applying a weight. The template is preferably pressed on for a period of 1 s to 5 min, particularly preferably between 20 s and 3 min.

In one embodiment, the polishing cloth is pre-pressed or re-pressed. This can be done manually, with rollers or by pushing the polishing plates together in the case of a double-sided polishing system. characters

Reference list

1 polishing plate

2 polishing cloth

3 channel

4 channel bottom

5 tools

6 Air trap between the polishing cloth and the channel base

1A shows a polishing plate 1 on which a polishing cloth 2 comprising channel 3 with channel base 4 is pressed. The channel is pressed by means of a tool 5, which is guided to channel 3, in order to close the polishing cloth 2 on channel base 4 against the polishing plate 1 Press and remove the air trap 6.

Fig. 1 B shows the state after pressing the channels 3 and additional

Cloth presses. There is no air inclusion. The polishing cloth 2 also adheres to the polishing plate 2 in the area of the channel base 4. Examples

example 1 Special manual pressing of the channels / polishing agent channels by tracing with a metal pin rounded off at the front (e.g. for channels 2 mm wide with a round tip of 2 mm diameter)

Example 2 The polishing cloth is a foamed cloth made of polyurethane with channels 2 mm wide and 4 mm deep.

DSP uses a 77 "diameter PEEK template to press the channels. The thickness of the template is 3 cm. The web height is 0.5 mm with a rounded tip. The two polishing plates with the template in between are made at 1000 dN Pressing force against each other for 3 min The side of the template that surrounds the webs is pressed against the upper polishing cloth, the smooth side against the lower polishing cloth.

A multi-part template, e.g. comprising four equal segments.

For polishing, the semiconductor wafers are dimensioned appropriately

Cutout of a rotor disc. A liquid is preferably fed into the working gap formed between the working layers of the polishing cloths during the polishing. This liquid is preferably a polishing agent suspension. It is particularly preferred to use colloidally disperse silicic acid, if appropriate with additives such as sodium carbonate (Na ₂ CO 3),

Potassium carbonate (K ₂ CO3), sodium hydroxide (NaOH), potassium hydroxide (KOH),

Ammonium hydroxide (NH ₄ OH), tetramethylammonium hydroxide (TMAH), as a polishing agent suspension. With simultaneous polishing of the front and the back of the semiconductor wafer, a surface removal of 3 μm to 9 μm per side is preferably carried out. Unless otherwise stated, all of the aforementioned parameters were determined at a pressure of the surrounding atmosphere, that is at about 1000 hPa, and at a relative humidity of 50%. Shore A hardness is determined in accordance with DIN EN ISO 868. It comes in

Type A durometer for use (Zwick 3130 hardness tester). The tip of the hardened steel rod presses into the material. The indentation depth is measured on a scale from 0 - 100. The steel pin has the shape of a truncated cone. Five measurements are taken, of which the median value is given. The measuring time is 15 s, the material to be tested was stored for 1 h in a standard climate (23 ° C, 50% humidity). The pressure weight of the durometer is 12.5 N ± 0.5.

The regarding the above-mentioned embodiments of the

Features specified according to the inventive method can be implemented either separately or in combination as embodiments of the invention.

Furthermore, they can describe advantageous designs that can be protected independently.

Claims

1. A method for polishing a semiconductor wafer by pressing at least one side of the semiconductor wafer in the presence of a polishing agent against a polishing cloth fastened on a rotating polishing plate, the polishing cloth having a surface interrupted by channels, characterized in that the polishing cloth is glued to the polishing plate and is pressed onto the polishing plate in the area of the channels using a suitable tool.

2. The method according to claim 1, wherein by means of a metal or plastic pin, which has a round, adapted to the width of the channels, the channels are traced to the polishing cloth in this way to the

To press polishing plates.

3. The method of claim 1, wherein as a tool a template is used, which has on one side webs that are dimensioned so that they can be received by the channels of the polishing cloth and wherein

The template is pressed manually or by means of weights or pressure with that side against the polishing cloth.

4. The method according to any one of claims 1 to 3, wherein it is a CMP polish and before or after the processing of the channels manually or under

Using a roller, the polishing cloth is additionally pressed onto the polishing plate.

5. The method according to any one of claims 1 to 4, wherein the polishing cloth has a hardness at room temperature of at least 60 ° according to Shore A and a compressibility at room temperature of less than 7%.

6. The method according to any one of claims 1 to 3, wherein it is a simultaneous

Polishing the front and the back of the semiconductor wafer between two rotating polishing plates, wherein the polishing cloth glued on one polishing plate has a smooth surface and the polishing cloth glued on the other polishing plate has a surface interrupted by channels.

7. The method according to claim 6, wherein a template is used as a tool, which has on one side webs which are dimensioned such that they can be received by the channels of the polishing cloth, the other side of the template being smooth, the Template is placed between the upper and lower polishing plate so that the webs of the template are taken up by the channels of the polishing cloth, the polishing plates are moved together and a contact pressure is exerted to press the polishing cloth in the area of the channels.

8. The method according to claim 7, wherein before or after the pressing of the polishing cloth in the area of the channels between the two glued-on polishing cloths, a cloth with a compressibility at room temperature of at least 3% is positioned as an intermediate layer and then the two polishing cloths with the cloth between them for a certain period of time

be pressed together

9. The method according to claim 8, wherein the intermediate layer in the region of

Polish feedthroughs has an increase.

10. The method according to any one of claims 6 to 9, wherein on the upper and lower

Polishing pad polishing cloths with a hardness at room temperature of at least 70 ° according to Shore A and with a compressibility at room temperature of less than 3% are stuck on.