KR101086966B1 - Semiconductor Wafer Polishing Method - Google Patents

Abstract

The present invention relates to a method for polishing a semiconductor wafer, and more particularly, a lapping process of polishing a wafer by simultaneously applying a polishing liquid in which an aluminum oxide slurry is mixed together with a polishing liquid in which a diamond slurry is mixed, onto the semiconductor wafer. A semiconductor wafer polishing method comprising polishing a wrapped wafer surface with a diamond slurry. In the process of lapping a difficult-to-cut wafer such as a sapphire substrate or a brittle wafer such as gallium nitride (GaN), the aluminum oxide (Al ₂ O ₃ ) slurry is simultaneously added together with the diamond slurry as described above. When used, the scratches are smoothed and the by-products discharged smoothly, and plate distortion and wafer damage or cracking are minimized.

Semiconductor, Wafer, Lapping Process

Description

Grinding Process of Semiconductor Wafer

1 is a flowchart illustrating a semiconductor wafer manufacturing process according to the prior art.

2 is a flowchart illustrating a lapping process using a diamond slurry according to the prior art.

3 is a flowchart illustrating a lapping process using a diamond slurry and an aluminum oxide slurry simultaneously in accordance with the present invention.

4 is a flowchart illustrating a semiconductor wafer polishing process according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a semiconductor wafer. In the semiconductor wafer lapping process, a wafer is polished by simultaneously applying a polishing liquid in which an aluminum oxide slurry is mixed together with a polishing liquid in which a diamond slurry is mixed, to polish the wafer. The present invention relates to a method of polishing a semiconductor wafer capable of minimizing or alleviating the problem to minimize problems such as cracking of the wafer.

Silicon wafers (silicon wafers), which are widely used as materials for manufacturing semiconductor devices, are crystalline silicon thin films made of polycrystalline silicon as a raw material. The silicon is generally silicon oxide (SIO ₂ ), and is present in the form of sand, rock, minerals, and the like, and they constitute about one third of the earth's crust, and thus are very abundant on the earth. Therefore, silicon is not only a material that can be supplied very stably to the semiconductor industry, but also has no toxicity and is an environmentally excellent material.

In addition, since the silicon wafer made of silicon has a wide energy band gap (1.2 eV), the device can be operated even at a relatively high temperature (up to about 200 ° C.). Because of these advantages, silicon wafers are used in the semiconductor industry to make various types of semiconductor devices such as DRAM, ASIC, TR, CMOS, ROM, and EPROM. These devices are used in all industries such as computers, electronics, industrial machines, and satellites. Are indispensable parts.

Silicon wafers are classified into polished wafers (polished wafers), epitaxial wafers (epitaxial wafers), SOI wafers (silicon on insulator wafers), diffused wafers (diffused wafers), and high wafers (HI wafers). Are distinguished. Among them, polysilicon wafers are the most common wafers, which include a slicing process for thinly cutting single crystal silicon ingots into wafer forms, a lapping process for improving flatness while polishing to a desired thickness of the wafer, and damage to the inside of the wafer. (Damage) A semiconductor wafer produced as a wafer for a device through an etching process for removing a layer, a polishing process for improving surface mirroring and flatness, and a subsequent cleaning process.

1 is a flow chart showing a semiconductor wafer manufacturing process according to the prior art. In the semiconductor wafer manufacturing method according to the related art, first, in the first step S11, a rod-shaped single crystal ingot having a predetermined diameter is sliced into several wafers, and the cut wafer is cleaned and cut. Removes particles or contaminants In the above, the wafer may be cut into single sheets of single crystal ingots by inner or outer blades one by one or by several pieces simultaneously by piano wires. In the second step S12, the edge of the cut wafer is ground with an edge grinder to make a curved surface. Grinding the edges of the cut wafers as described above eliminates defects occurring at the edges during the cutting process, and also makes the wafer edges curved to prevent the edges from being broken or causing defects during subsequent processing. . In a third step S13, both sides of the cut wafer are simultaneously wrapped and the wafer is cleaned. By wrapping the wafer in the above, the thickness uniformity and the flatness of the surface are improved, and the processing defect layer generated during cutting is removed to improve the surface roughness. In the fourth step S14, the both surfaces of the wafer are chemically etched to remove the defect layer generated in the lapping and to clean, thereby removing the etching solution. Chemical etching improves surface roughness by removing defects generated during wafer cutting and lapping. In the chemical etching process, a plurality of wafers, that is, 25 or 50 wafers, are simultaneously immersed in an etching bath containing an etching solution. In a fifth step S15, heat electrons are removed to remove hot electrons in the wafer. The heat treatment in the above proceeds to a temperature of about 400 ~ 700 ℃ in a heat treatment furnace (furnace). In the sixth step S16, the edge of the wafer is mirror polished to make a mirror surface. Then, the wafer is cleaned to remove abrasives and particles generated during edge mirror polishing. In the seventh step S17, the front surface of the wafer on which the semiconductor circuit is to be formed is polished to form a mirror surface. Therefore, the wafer is improved in flatness and precisely controlled to a predetermined thickness. Then, the wafer is cleaned to remove the abrasive and particles generated during the mirror polishing of the front surface to complete the manufacture of the semiconductor wafer.

However, the semiconductor wafer manufacturing method according to the related art does not uniformly etch from the front surface because several wafers are simultaneously etched when chemically etching the wafer, and the flatness is lowered. It is difficult to have a problem that the quality of the semiconductor wafer is degraded or the polishing time is increased.

On the other hand, as semiconductor wafers have increased integration degree of semiconductor devices and thus, a multi-layered wiring process has been put to practical use, various products capable of high integration and high speed operation are required in semiconductors in order to secure a margin of a photographic process and minimize wiring length. Accordingly, high quality products such as high cleanliness and high flatness are required for semiconductor wafers.

At present, methods for planarizing the underlying structure include boron-phospho-silicate glass (BPSG) reflow process, aluminum (Al) flow process, and spin-on glass. SOG) etch-back process and chemical mechanical planarization (CMP) process.

Among these, the CMP process has emerged as a prominent planarization technology in next-generation semiconductor devices because of the advantages of achieving global and low temperature planarization in a large space area which cannot be achieved by a reflow process or an etch back process. The CMP process is a process of removing the surface of the wafer to a predetermined thickness by mechanical friction and chemical action by supplying a slurry (slurry) to these interfaces while pressing the wafer held in the carrier on the polishing pad. ) Is proportional to pressure and time, and the technique of pressurizing the wafer to the polishing pad is very important because the removal thickness is required to be very precise in the hundreds to thousands of micrometers. The defects of the CMP process can be largely classified into particles, micro scratches, and discolors.

The particles are formed by the aggregation of slurry, and various CMP follow-up cleaning methods have been developed to remove below the oxide level, and the discolor is generated by the difference in the thickness of the optical image. It is removed while passing through and does not affect the device.

However, once the microscratch occurs in the CMP process, its size is further increased by a subsequent wet process, causing pattern bridge, pattern deformation, and stringer in a subsequent step. Done. For example, the CMP process for forming shallow trench isolation (STI) may damage the active region. Such microscratches are generally generated by a slurry used in a CMP process, in which colloidal aqueous solution or colloidal suspension of silica particles is mainly used as a slurry. That is, the silica particles have an average diameter in the range of 50-200 nm depending on the manufacturing company, and especially among the silica particles, there are so-called large particles that are well above the average diameter, which is the main cause of micro scratches in the CMP process. .

Here, materials such as gallium arsenide (GaAs) or InP are known for lapping, polishing, and CMP techniques for substrate processing, and thus, high-quality substrates for fabricating optical devices may be manufactured. However, for difficult-to-cut wafers such as sapphire substrates and brittle wafers such as gallium nitride (GaN), polishing or CMP techniques have not yet been established, and in particular, slurry used in CMP processes. Echant has not been developed yet. So, until recently, after fine polishing on gallium nitride, surface damaged parts are removed through an etching process such as reactive ion etching (RIE) or chemically assisted ion beam etching (CAIBE). The etching process has a problem in that a high quality gallium nitride substrate surface cannot be obtained due to damage of the gallium nitride surface or process by-products that may occur during the process.

Therefore, when cutting soft materials such as gallium arsenide (GaAs), the lapping process is performed by treating with aluminum oxide (Al ₂ O ₃ ) and glycerin (Glycerine) according to a conventional method to form a uniform plane of 2 μm or less. Although it is not possible to process difficult aluminum wafers such as sapphire substrates and brittle wafers such as gallium nitride (GaN), which are not easily cut into aluminum oxide slurry, the thickness is controlled by a grinder and diamond ( Diamond) The slurry has been used to finish the surface by gradually reducing the particle size such as 6㎛ → 3㎛ → 1㎛. However, when only the diamond slurry is applied, the larger the particle size, the better the cutting force. In particular, particles having a size of 6 µm or more have a deeper scratch and a plate distortion, which causes problems such as cracking of the wafer.

In addition, difficult-to-cut wafers such as sapphire substrates and brittle wafers such as gallium nitride (GaN) are more difficult to cut than softer wafers such as gallium arsenide (GaAs). And a lot of process by-products such as wax debris may be generated, resulting in lower cutting force and wafer damage. Therefore, especially in the cutting process step using a diamond slurry to which particles of 6 μm or more are applied, it is possible to minimize or mitigate scratches to solve problems such as cracking of wafers and to improve problems such as process by-products such as wax residue generated by heat. New processes were needed.

The present invention has been made to solve the above problems, in the lapping process using only the diamond slurry during the conventional semiconductor wafer polishing process, in addition to the use of the diamond slurry Facing operation to planarize the plate distortion By using the aluminum oxide slurry used in parallel to try to improve the problems and processing difficulties in the polishing process as described above.

As such, the present invention minimizes or mitigates scratches in the polishing process step using a diamond slurry to solve problems such as cracking of wafers, and process by-products such as wax residue caused by heat generation and wafer damage and cutting force reduction. It is an object of the present invention to improve such problems.

The present invention relates to a method of polishing a semiconductor wafer, and more particularly, in a step of lapping a semiconductor wafer, a polishing liquid in which an aluminum oxide slurry is mixed together with a polishing liquid in which a diamond slurry is mixed is applied simultaneously onto an upper portion of a semiconductor wafer. It is characterized by grinding a wafer.

In the method of polishing a semiconductor wafer according to the present invention, a method of polishing a semiconductor wafer includes: (a) polishing a wafer by simultaneously applying a polishing liquid in which an aluminum oxide slurry is mixed together with a polishing liquid in which a diamond slurry is mixed; Lapping and (b) polishing the wrapped wafer surface with a diamond slurry. Specifically, the diamond slurry used in the lapping process relates to a polishing method of a semiconductor wafer, characterized in that it has a particle size in the range of 6 ~ 10㎛.

Another feature according to an embodiment of the present invention includes a step of pacing a plate with an aluminum oxide slurry prior to the lapping process of simultaneously applying a polishing liquid mixed with a diamond slurry and an aluminum oxide slurry. That is, (a) a step of raising the semiconductor wafer on a chemical mechanical planarization (CMP) apparatus and applying wax, and then adjusting the thickness deviation of the processing area by using a press or a spring jig; (b) a grinding process of cutting the wafer having the thickness deviation adjusted to a desired thickness; (c) pacing the plate with an aluminum oxide (Al ₂ O ₃ ) slurry; (d) a lapping step of polishing the wafer by simultaneously applying the polishing liquid containing the aluminum oxide slurry together with the polishing liquid containing the diamond slurry in the range of 6 µm to 10 µm; (e) polishing the wrapped wafer with a polishing liquid mixed with a diamond slurry in the range of 1 to 3 μm; And (f) removing impurities from the polished wafer and drying the semiconductor wafer. Specifically, in the semiconductor wafer polishing method according to the present invention, between the (d) lapping step and (e) the polishing step, the wafer which has undergone the first lapping step with a polishing liquid containing a diamond slurry of 3 to 6 μm is mixed. It is also possible to have a form that further includes the process of lapping with tea. That is, the lapping step (d) may further include an additional lapping step of polishing the wafer polished by the lapping step with a polishing liquid containing a diamond slurry of 3-6 μm.

The most preferred embodiment of the present invention is characterized in that the semiconductor wafer is a difficult wafer, such as a sapphire substrate, or a brittle wafer, such as gallium nitride (GaN), which is not easily cut.

Hereinafter, with reference to the accompanying drawings, a semiconductor wafer polishing method and a specific manufacturing process of the present invention having the above characteristics will be described in detail.

In general, the lapping process in semiconductor wafer production is a process to reduce the thickness of the sliced wafer from the single crystal ingot, to remove surface damage caused in the previous process, and to make the facing surfaces of each wafer flat and parallel. In order to increase the efficiency of the lapping process, the wafer surface should be uniformly polished in a short time when lapping, the scratches on the wafer surface should be prevented, impurities must be completely removed after the lapping process, and the corrosion of the lapping machine should be avoided. Should be prevented. For this purpose, it is very important to control the properties of the lapping slurry used in the lapping process. In general, the lapping slurry is prepared by diluting and mixing the abrasive and the dispersant with water. Here, the physical properties of the dispersant will determine most of the properties of the lapping slurry, thus playing an important role in determining the efficiency of the lapping process. The components of the dispersant may be classified into thickening components, dispersing components, rust-preventing components, lubricating components, etc., and exhibit various characteristics due to changes in the type and composition of these components.

Lapping slurry components generally well known in the art are aluminum oxide (Al ₂ O ₃ ) and glycerin (Glycerine) when polishing soft materials such as gallium arsenide (GaAs). The particle size of the aluminum oxide contained in the lapping slurry may vary depending on the time allotted for lapping, the amount of wafer removed, and the degree of lapping damage, but generally has a size between 7 μm and 15 μm. However, for difficult-to-cut wafers such as sapphire substrates and brittle wafers such as gallium nitride (GaN), which are fragile, they are not processed with aluminum oxide slurry. Furnace has been used to finish the surface by gradually reducing the particle size such as 6㎛ → 3㎛ → 1㎛. That is, after the pacing process to flatten the plate with an aluminum oxide slurry as shown in Figure 2, after the first lapping with a 6㎛ diamond slurry and the second lapping with a 3㎛ diamond slurry, the pad with a 1㎛ diamond slurry The method of polishing was used while rotating the plate slowly. However, as described above, the lapping process using only the diamond slurry has a problem that the scratches become sharp and the process by-products such as wax residues are not easily removed, resulting in damage or breakage of the wafer.

Accordingly, as shown in FIG. 3, the present invention is characterized by a lapping process in which a polishing liquid in which an aluminum oxide slurry is mixed together with a polishing liquid in which a diamond slurry is mixed is applied to a semiconductor wafer to polish the wafer. In the present invention, the lapping process is performed to polish the single or both sides of the wafer, to remove the single crystal internal damage layer generated in the slicing process, and to obtain a uniform thickness and flatness of the wafer. Here, the lapping process is a process of polishing both sides of the wafer by the movement of the polishing liquid and micro fracture cutting while applying pressure by flowing the polishing liquid mixed with the abrasive powder, deionized water and the floating agent between the upper and lower platen and the wafer. It is an important process to control wafer flatness and shape. In the present invention, by applying aluminum oxide slurry in addition to the diamond slurry during the lapping process, by smoothing the sharp edge of the scratch and increasing the fluidity, by-products from the process such as wax residue caused by a lot of heat generated during difficult grinding and smoothly discharged Now.

The present invention is particularly useful when applying a diamond grain size of 6 µm or more with good cutting force. This is because when the particle size is 6 µm or more, problems such as cracking of the wafer may occur remarkably due to deep scratches and easy distortion of the plate. In such an embodiment of the present invention, a semiconductor wafer polishing method is preferable in which the lapping process is applied to a difficult-to-cut wafer such as a sapphire substrate or a brittle wafer such as gallium nitride (GaN).

In another aspect of the present invention, the lapping process of simultaneously polishing a wafer by simultaneously applying a polishing liquid in which an aluminum oxide slurry is mixed together with the polishing liquid in which a diamond slurry is mixed is performed by using a aluminum oxide (Al ₂ O ₃ ) slurry. It is applied after the pacing process. And prior to this, the present invention can be applied to the step after adjusting the thickness in the grinding (grinding) process. That is, as shown in Figure 4 (b) the grinding step of cutting the wafer with the thickness deviation adjusted to the desired thickness, (c) the step of pacing the plate with aluminum oxide (Al ₂ O ₃ ) slurry and (d) 6 ~ And a lapping process for simultaneously polishing the wafer by simultaneously applying the polishing liquid mixed with the aluminum oxide slurry together with the polishing liquid mixed with the diamond slurry in the range of 10 μm. Here, applying the polishing liquid mixed with the aluminum oxide slurry together with the diamond slurry means maintaining the aluminum oxide slurry supply state used in the plate facing process so that the aluminum oxide slurry is applied together with the diamond slurry on the surface.

When polishing a semiconductor wafer by a general polishing process, that is, a single-side polishing process, only the upper surface is polished using a polishing pad while the opposite side of the surface to be polished is fixed to the support plate using vacuum or wax. At this time, in the process of fixing to the support plate, a slight deformation of the semiconductor wafer is made, and polishing is performed in this state. In other words, the shape deformation generated during the fixing of the semiconductor wafer by vacuum is reflected to the upper surface polishing as it is, and if the processing is continued by the grinding process of adjusting the wafer thickness, not only the upper polishing pad but also the plate fixed to the support plate may be distorted. Accordingly, the present invention includes a step of pacing the plate with an aluminum oxide slurry prior to the lapping process, in order to satisfy the strict surface flatness, which means that the aluminum oxide slurry used in the plate facing process is maintained in the feeding state even in the lapping process. Made it possible.

The present invention as described above includes a step of lapping the wafer subjected to the lapping step with a polishing liquid mixed with a diamond slurry of 3 ~ 6㎛ in the step between (d) lapping process and (e) polishing process It is also possible to form, and this lapping process is preferably applied to difficult-to-cut wafers, such as sapphire substrate, or brittle wafers such as gallium nitride (GaN).

Hereinafter, another preferred embodiment of the present invention is presented. However, the following examples are only one preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Step 1: Wafer Mounting

In order to polish the semiconductor wafer according to the present invention, the semiconductor wafer was placed on a chemical mechanical planarization (CMP) apparatus in one step, and wafer mounting fixing was performed to control thickness variations of the processing area. This is a process of adjusting the thickness deviation by applying wax to the wafer and then pressing and cooling it using a press or a spring jig.

First, the wafer, the glass plate, and the metal block were cleaned and dried. This is because when dust, granules, etc. are included, it becomes a bad factor. Then, the metal block was heated and wax was applied. Wax used soft type that melts at around 65 ℃ because hard type is disadvantageous in terms of shock absorption during processing. Afterwards, when the wax melts, the glass plate is rotated to the left or right and the wax is evenly applied. Then, pressing and cooling were performed using a press or a spring jig. Using a precision measuring instrument, it was confirmed that there was no thickness deviation in the processing area. If there is a deviation, the process of melting the wax again is repeated. Subsequently, the metal block to which the glass plate was pre-bonded was heated again. After wax application, the wafer is positioned with the working surface facing out. The wafer was rotated left and right or evenly so as to apply wax, and the glass guide was placed on the outside of the wafer and pressed and cooled using a press or a spring jig. Use a precision measuring instrument to check that there is no thickness variation in the processing area. If any deviations exist, repeat the process of melting the wax again. If there is no deviation, it was charged into the machine and the cutting process was carried out.

Step 2: Grinding

In the second step, a grinding process was performed to cut the wafer having the thickness deviation adjusted to a desired thickness. First, the grinding wheel was polished using a dressing block, and the cutting was performed by the desired thickness with the initial thickness as the origin. If the processing amount is insufficient, measure the thickness and finish by additional processing.

Step 3: Plate Facing

After adjusting the wafer thickness by grinding as described above, in order to improve the flatness of the plate, the plate was plated. An aluminum oxide slurry was used as a solution for pacing, and the solution was filled in an aluminum oxide supply apparatus and mixed well. The solution was then applied to the surface while the plate was slowly rotated. The solution is supplied with a Facing Block placed on top.

Step 4: Lapping

The lapping step is a process of polishing the wafer using the polishing liquid containing the slurry according to the present invention to improve the surface damage and flatness generated on the surface of the sliced wafer by the slicing step. The sample wafer was mounted on the jig of the CMP apparatus, the polishing liquid was filled in the diamond slurry spraying device, mixed well, and the polishing liquid was sprayed onto the surface while the plate was slowly rotated. The solution was sprayed with the jig up.

In the conventional lapping process, only the diamond slurry was sprayed, but in the present embodiment, the polishing liquid in which the diamond slurry was mixed on the surface was simultaneously applied while maintaining the aluminum oxide slurry supply state used at the time of pacing.

Subsequently, the diamond grain size was reduced to remove grinding traces and scratch damage of large grain size existing on the surface. The method according to the invention is most preferably applied when the diamond grain size is 6 μm or more. This is because when the diamond particle size is less than 3 µm, the wafer is rarely broken or damaged even by applying the conventional method.

Step 5: Polishing

In the polishing step, the wafer bonded to a predetermined block or the like is subjected to chemical mechanical polishing by a slurry and a pad. In this embodiment, the wrapped wafer is polished with a polishing liquid in which a diamond slurry of 1 µm is mixed.

First, the pad plate was polished using a facing block, and the jig was equipped with a wrapped sample wafer. After that, the solution was filled in the diamond slurry spraying device, mixed well, and the solution was sprayed onto the surface while the pad plate was slowly rotated. Then, the solution is sprayed with the jig put up.

Step 6: Demounting

The final step is a demounting process that removes the polished wafer, removes impurities and dries. The thickness of the polished wafer was recorded and peeled off in the heated solution. Finally, remove the impurities using a cleaning agent, and finish by drying.

Through the steps 1 to 6 as described above, the present invention is a polishing process using a diamond slurry and aluminum oxide together to smooth the scratch, minimize the distortion of the plate and the damage and crack of the wafer, a lot of heat Process byproducts such as wax debris that occur and the resulting cutting forces and problems such as wafer damage have been solved.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to the above-described embodiments, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the claims It belongs to the scope of the present invention.

According to the present invention, in the semiconductor wafer polishing step using a diamond slurry to which particles of 6 µm or more are applied, distortion of the plate becomes severe when only the diamond slurry is sprayed, thus maintaining the supply state of the aluminum oxide slurry used in the pacing process. By applying the two slurry solutions on the surface at the same time, the scratch is smooth and by-product discharge is smooth, it has the effect of minimizing plate distortion and wafer damage or cracking.

Claims (5)

delete delete (a) raising a semiconductor wafer on a chemical mechanical planarization (CMP) apparatus and applying wax, and then adjusting a thickness deviation of the processing area by using a press or a spring jig; (b) a grinding process of cutting the wafer having the thickness deviation adjusted to a desired thickness; (c) pacing the plate with an aluminum oxide (Al ₂ O ₃ ) slurry; (d) a lapping process of simultaneously polishing a wafer by applying a polishing liquid mixed with the aluminum oxide slurry together with a polishing liquid having a diamond slurry in a range of 6 µm to 10 µm; (e) polishing the wrapped wafer with a polishing liquid mixed with diamond slurry in the range of 1 to 3 μm, and (f) removing impurities from the polished wafer and drying Method of polishing a semiconductor wafer, characterized in that consisting of. The semiconductor wafer according to claim 3, wherein the lapping step (d) further comprises an additional lapping step of polishing the wafer polished by the lapping step with a polishing liquid containing a diamond slurry of 3 to 6 mu m. Polishing method. The method of claim 3 or 4, wherein the semiconductor wafer is a sapphire wafer or a gallium nitride (GaN) wafer.

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