JPH0722489A - Wafer fork - Google Patents

Abstract

PURPOSE:To provide a wafer fork which causes less wafer contamination due to impurities such as dust, less plastic deformation such as warpage and less breakage due to wafer warpage or collision. CONSTITUTION:A wafer fork 1 is permitted to hold and successively carry semiconductor wafers 8 in semiconductor manufacturing processes. At least the part which makes contact with the semiconductor wafer 8 is formed of ceramics and the surface roughness of the contact part is set at the center line average roughness (Ra) of 0.2-0.5mum. The ceramic material is constituted of at least one of the following: Si3N4, Si-Al-O-N, SiC and Al2O3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer fork used for transferring and transporting semiconductor wafers in a semiconductor manufacturing process, and in particular, contamination of the wafer by impurities such as dust is small and damage caused by slipping or collision of the wafer. The present invention relates to a wafer fork that has few occurrences, high strength, and high dimensional accuracy.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor wafer heat treatment process or a transfer line in a semiconductor manufacturing process, a large number of semiconductor wafers obtained by slicing single crystal silicon are sequentially processed.
Various holders such as a wafer fork and a wafer chuck are used for transferring and conveying. The wafer fork is formed by forming a shallow recess into which a semiconductor wafer is fitted in the central portion of a flat plate-shaped body, while the wafer chuck is a holder that holds and holds the wafer by vacuum suction or electrostatic action.

The above-mentioned wafer fork is fixed to, for example, the tip of an arm of a transfer robot, is inserted through a minute gap into a gap between cartridges or carriers for storing wafers in multiple stages, and the wafer is picked up and held in a concave portion.
It is transported to the processing section of the next process.

Conventionally, as the above-mentioned wafer fork, one in which a stainless steel plate is cut into a predetermined shape and then the processed surface is coated with a fluororesin film or the like, or one in which the entire fork is made of quartz glass is mainly used.

[0005]

However, in a wafer fork whose surface is coated with resin on a stainless steel surface, the coating layer is broken in a short period of time, and impurities such as iron and alkali salts are easily transferred to the wafer side, which easily causes contamination. There is. Further, the stainless steel forming the main body is likely to be plastically deformed, which often makes it difficult to carry out a highly accurate conveying operation. On the other hand, since the stainless steel itself has a high toughness, if the transfer device itself malfunctions, the wafer fork may damage peripheral equipment such as an expensive robot and stop the manufacturing process.

In addition, a wafer chuck type holder for sucking and holding a wafer by vacuum suction or electrostatic action has a drawback that it is easy to suck fine dust floating around, and dust is not attached to a wafer to be handled. There is a drawback that the amount of impurities increases and the ratio of impurity contamination is high.

On the other hand, a wafer fork made of quartz glass is less likely to be contaminated with impurities even when a coating layer is not formed, and is thermally stable, while it has a slightly low strength and rigidity, so it can be used repeatedly. There was a difficulty in using it as a structure that does. Especially in recent years
Cartridges and carriers that store multiple wafers are required to be loaded with more wafers in response to automation of semiconductor manufacturing processes, and the gap between adjacent wafers tends to be narrowed. There is an increasing demand for a thinner wafer fork to be inserted into the gap. However, as the device becomes thinner, its rigidity and mechanical strength also become smaller, so that it tends to bend in a short period of time, resulting in a problem of shortening the life.

As a means for solving the above problems, a purity of 9
A wafer fork formed by polishing an alumina (Al ₂ O ₃ ) sintered body of 9.0% or more is also used in part.

However, in the conventional wafer fork including the above-mentioned Al ₂ O ₃ wafer fork, the wafer may become slippery on the upper surface of the fork when the semiconductor wafer is transferred, and the slipped wafer may come to the inner edge corner of the wafer fork. There is a problem in that the wafer may collide and be damaged, which may hinder the subsequent transportation, and that the yield of the wafer itself may be reduced. Further, there is a problem that dust is easily generated due to the sliding of the wafer on the upper surface of the fork, and the contamination of the wafer with impurities is increased.

Further, in the Al ₂ O ₃ wafer fork, depending on the temperature condition and the atmospheric gas in the semiconductor manufacturing process,
There is a drawback that strength characteristics and durability are greatly different and uniform reliability cannot be obtained. On the other hand, as the degree of integration of semiconductor substrates has rapidly increased from 1 Mbit to 4 Mbit, the allowable limit of impurities such as dust on semiconductor wafers has become stricter, and conventional Al ₂ O ₃ wafer forks cannot handle this. It is becoming a state.

The present invention has been made in order to solve the above-mentioned problems, and the contamination of the wafer by impurities such as dust is small, and the plastic deformation such as warpage is small, and the damage due to the slip or collision of the wafer is small. It is intended to provide a reduced number of wafer forks.

[0012]

In order to achieve the above object, the inventors of the present invention have investigated the cause of dust generation and the cause of wafer damage. In particular, the surface roughness of a wafer fork with which a semiconductor wafer contacts is large. I found out that it would affect me. That is, it has been found that by properly setting the surface roughness of the wafer fork, the slip and collision of the wafer on the upper surface of the wafer fork can be effectively prevented, and the amount of dust generated by the slip can be significantly reduced. The present invention has been completed based on the above findings.

That is, a wafer fork according to the present invention is a wafer fork that holds and sequentially conveys semiconductor wafers in a semiconductor manufacturing process, in which at least a portion in contact with the semiconductor wafer is formed of a ceramic material and the surface roughness of the contact portion is roughened. The roughness is set to 0.2 to 0.5 μm based on the center line average roughness (Ra).

Further, the wafer fork according to the present invention is such that when the semiconductor wafer is placed on the walk body made of a plate-shaped ceramics sintered body, the wafer fork is in contact with the peripheral portion of the wafer and holds the wafer at a predetermined position. A step and a recess that is not in contact with the wafer are formed by grinding or the like, and the peripheral step surface that comes into contact with the semiconductor wafer is given a predetermined surface by grinding with a grindstone or polishing using loose abrasive grains. Roughness, that is, the center line average roughness (Ra) is set in the range of 0.2 to 0.5 μm for manufacture.

When the surface roughness of the contact portion with the semiconductor wafer is less than 0.2 μmRa, the semiconductor wafer tends to slip on the surface of the fork, and the damage due to the collision between the wafer and the fork is likely to occur. On the other hand, when the surface roughness exceeds 0.5 μmRa, dust is likely to be generated. Therefore, it is desirable to set the surface roughness of the contact portion with the semiconductor wafer in the range of 0.2 to 0.5 μmRa. The surface roughness can be arbitrarily adjusted by changing the particle size of the abrasive grains used and the polishing time.

Particularly, as a method for efficiently manufacturing a so-called near net shape wafer fork close to the shape of the final product, a ceramic molded body as a material of the wafer fork is laser-processed to precisely cut the contour of the wafer fork. Then, after that, the processed ceramic molded body may be degreased and sintered, and the obtained sintered body may be ground and polished to form the peripheral stepped portion and the recessed portion.

The ceramic sintered body or the ceramic molded body which constitutes the wafer fork according to the present invention includes silicon nitride (Si ₃ N ₄ ) and sialon (Si-A).
l-O-N), at least one silicon carbide (SiC) and alumina (Al ₂ O ₃₎ is used. In particular, among the above various ceramic materials, Si ₃ N ₄ , Si-Al-
O-N and SiC are high-purity products with a low content of alkali metal elements or alkaline earth metal elements such as Na and Ca, which are contaminants (contamination) substances to semiconductor wafers, and thus have little impurity contamination. This is preferable because a wafer fork can be formed. Further, both silicon nitride and sialon have high strength values such as rigidity and toughness and environmental resistance characteristics as compared with other ceramics, and have sufficient durability even when formed thin such as a wafer fork, Since it has excellent thermal shock resistance, it can be used under all process conditions of the semiconductor manufacturing process.

In particular, the wafer fork formed of the above-mentioned silicon nitride sintered body can be used as it is, but by further forming a contamination prevention layer such as a fluorine resin coating on the surface of the sintered body, the contamination of the wafer is more effective. Can be prevented.

The wafer fork is manufactured by the following procedure, for example. First, a raw material mixture is prepared by adding various sintering aids to at least one raw material powder of silicon nitride powder, sialon powder, and silicon carbide powder, and uniformly mixing the raw material powder. Is pressure-molded by a die press or the like to obtain a rectangular ceramic molded body having a uniform thickness. Next, the obtained ceramic formed body is cut by laser processing to form a wafer fork formed body having a predetermined contour. Next, this wafer fork compact is degreased under predetermined conditions and further sintered, and the obtained wafer sintered compact is ground to form a peripheral step and a concave portion, and then the peripheral edge is polished by using loose abrasive grains. It is manufactured by polishing the surface of the step portion and adjusting the surface roughness to 0.2 to 0.5 μmRa. Further, the surface of the wafer fork can be coated with a fluororesin coating or the like for preventing contamination to prevent impurity contamination.

As described above, by performing laser cutting processing on the ceramic molded body at the stage of the molded body to form a wafer fork molded body having a predetermined shape, the ceramic sintered body is significantly processed as compared with grinding. The number of steps can be reduced. That is, in the case where a ceramic compact is irradiated with a fine laser beam to perform a cutting process (green process), the laser beam is finely focused by the condenser lens of the optical system, and the laser beam is focused on the contour line of the wafer fork to be formed. The corresponding position is irradiated. The irradiated laser light heats the irradiated part of the molded body to a high temperature, and volatilizes the ceramic components and the like of the part in an instant. As a result, a fine wafer fork compact having high dimensional accuracy can be efficiently formed.

When the ceramic molded body is cut by laser processing at the stage of the molded body as described above, since the impact force due to cutting is extremely small, the processing influence is small, and even a soft molded body is deformed or deformed. It is possible to efficiently form a fork molded body with high dimensional accuracy that is extremely close to the shape of the final product without the risk of cracking.

[0022]

According to the wafer fork having the above-mentioned structure, since the contact portion with the semiconductor wafer is formed of the ceramic material, the plastic deformation such as warpage is small. Further, since the surface roughness of the contact portion is set to 0.2 to 0.5 μmRa, even when the semiconductor wafer is transferred to the wafer fork, the semiconductor wafer rarely slides and slides on the fork surface. Therefore, it is possible to prevent the wafer from colliding against the fork and being damaged due to the slip, and the product yield of the semiconductor wafer can be significantly increased. In addition, the amount of dust generated by the slipping of the wafer can be reduced, and the impurity contamination of the semiconductor wafer can be effectively prevented.

[0023]

The present invention will now be described more specifically with reference to the following examples and drawings.

Example 1 Al ₂ O ₃ powder was 4% by weight with respect to silicon nitride powder,
3% by weight of AlN powder and 5% by weight of Y ₂ O ₃ powder were uniformly added to prepare a mixed powder, which was press-molded under a pressure of 80 MPa to obtain a ceramic molded body having a thickness of 5 mm. The fork compact is cut by machining to form a fork compact, and the obtained fork compact is degreased in a nitrogen gas atmosphere at a temperature of 700 ° C. for 3 hours, and subsequently sintered in a nitrogen gas atmosphere at a temperature of 1750 ° C. for 6 hours. Then, a wafer fork sintered body 5 was prepared.

Next, in the obtained wafer fork sintered body, the portion to be ground corresponding to the recess 3 is ground by a flat grindstone to form the recess 3 having a depth of 0.9 mm as shown in FIG. The portion to be ground corresponding to the peripheral step portions 2 and 2 is ground by a cup grindstone to form the peripheral step portions 2 and 2 having a width of 4.25 mm and a depth of 0.8 mm as shown in FIG.
Further, by adjusting the surface roughness of the upper surfaces of the peripheral stepped portions 2 and 2 to 0.2 to 0.5 μmRa by polishing using loose abrasive grains, a vertical length of 60 mm × as shown in FIG. 1 is finally obtained.
A large number of wafer forks 1 according to Example 1 having dimensions of 193 mm in width and 1.6 mm in thickness were manufactured.

The obtained wafer fork 1 has an average bending strength of 600 MPa and a fracture toughness value of 5 to 6 MPa /
m ^1/2 , Young's modulus of 290 GPa, thermal shock temperature difference of 60
The temperature is 0 ° C., and a conventional wafer fork made of quartz glass (Young's modulus 68 to 72 GPa) and a wafer fork made of stainless steel (tensile strength 520 MPa, Young's modulus 200)
It was found to be superior in strength and thermal shock resistance as compared with GPa).

Example 2 100 parts by weight of Al ₂ O ₃ powder having a purity of 99.5% was added to 80M.
The die is press-molded at a pressure of Pa, the obtained ceramic molded body with a thickness of 5 mm is cut by machining to form a fork molded body, and the obtained fork molded body is heated in the air at a temperature of 700 ° C. for 1 hour. After degreasing, continue in the atmosphere at a temperature of 1
Sintering was performed at 700 ° C. for 2 hours, the obtained wafer fork sintered body was ground to the same size as in Example 1, and further polished so that the surface roughness of the peripheral step was 0.3 to 0.5 μmRa. The wafer fork according to the second embodiment is processed to 5
One sheet was manufactured.

Comparative Examples 1 to 3 On the upper surface of the peripheral step portion of the wafer fork sintered body made of Si ₃ N ₄ prepared in Example 1, polishing was performed by changing the abrasive grain size, and the surface roughness of the peripheral step portion was changed. 0.05 to 0.1 μmRa and 0.8 to 1.2 μmR
a, adjusted to 1.4 to 1.6 μmRa, and five wafer forks according to Comparative Examples 1 to 3 were manufactured.

Comparative Example 4 The upper surface of the peripheral step portion of the Al ₂ O ₃ wafer fork sintered body prepared in Example 4 was subjected to polishing with increasing the size of the grindstone grains, and the surface roughness of the peripheral step portion was reduced. 1.
Five wafer forks according to Comparative Example 4 were manufactured by adjusting the pressure to be 2 to 1.6 μmRa.

Comparative Example 5 A 96% quartz glass plate was ground to prepare a quartz glass wafer fork of Comparative Example 5 having the same size and shape as those of Example 1 shown in FIGS. 1 and 2. The Young's modulus of the wafer fork according to Comparative Example 5 was 68 GPa, which was about 1/4 that of the fork of Example 1.

Comparative Example 6 A fork having the same size and shape as in Example 1 was manufactured by cutting a stainless steel (SUS304) plate, and a fluorine resin (Teflon) coating layer having a thickness of 20 μm was formed on the surface of the fork. A conventional wafer fork according to Example 6 was made. The tensile strength of the SUS304 wafer fork according to Comparative Example 6 was as high as 520 MPa, but the Young's modulus was 200 GPa, which was significantly lower than that of Example 1.

Further, five wafer forks according to each of Examples 1 and 2 and Comparative Examples 1 to 6 were subjected to a transportation test. That is, as shown in FIGS. 1 and 2, after fixing the robot arm 6 of the wafer transfer device through the fastening screw 7 and transferring the 6-inch semiconductor wafer 8 to the wafer fork 1 500 times, The number of impurity fine particles (dust) having a diameter of 0.2 μm or more attached to the wafer surface was counted, the average value thereof was calculated, and the stability during wafer transportation was evaluated. The stability during wafer transfer is indicated by a cross when the wafer or fork is damaged at least at one place, and is indicated by a double circle when there is no damage. The measurement evaluation results are shown in Table 1 below.

[0033]

[Table 1]

As is clear from the results shown in Table 1, according to the wafer forks according to Examples 1 and 2, the surface roughness of the contact surface with the semiconductor wafer is optimized, so that the slip of the wafer on the upper surface of the fork occurs. It is possible to reduce the amount of dust generated due to the sliding of the fork and the wafer. Also, it was proved that the damage due to the collision of the wafer was small and the product yield of the semiconductor wafer could be improved. On the other hand, if the surface roughness of the contact part (peripheral step) with the semiconductor wafer is excessively reduced, the amount of dust generated will be small, but damage due to slipping of the wafer will increase and stability during transportation will be impaired. It turned out to be Further, in the wafer forks shown in Comparative Examples 2 to 3 in which the surface roughness is set excessively,
Although the stability during transportation was good, it was confirmed that the dust generation amount increased and the impurity contamination of the wafer increased.

[0035]

As described above, according to the wafer fork of the present invention, since the contact portion with the semiconductor wafer is formed of the ceramic material, there is little plastic deformation such as warpage. Also, the surface roughness of the contact area is 0.2 to 0.5 μmR
Since it is set to a, even when the semiconductor wafer is transferred to the wafer fork, the semiconductor wafer rarely slides and slides on the surface of the fork. Therefore, it is possible to prevent the wafer from colliding against the fork and being damaged due to the slip, and the product yield of the semiconductor wafer can be significantly increased. In addition, the amount of dust generated by the slipping of the wafer can be reduced, and the impurity contamination of the semiconductor wafer can be effectively prevented.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a wafer fork according to the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG. 1 Wafer Fork 2 Edge Step 3 Recess 5 Wafer Fork Sintered Body 6 Robot Arm 7 Fastening Screw 8 Semiconductor Wafer

Claims (3)

[Claims] 1. In a wafer fork for sequentially holding and transferring semiconductor wafers in a semiconductor manufacturing process, at least a portion that comes into contact with the semiconductor wafer is formed of a ceramic material, and the surface roughness of the contact portion is a center line average roughness. A wafer fork characterized by being set to 0.2 to 0.5 μm on the basis of (Ra). 2. The ceramic material is Si ₃ N ₄ , Si-
Al-O-N, wafer fork according to claim 1, characterized in that it consists of at least one of SiC and Al ₂ O _3. 3. The wafer fork according to claim 1, wherein a contamination prevention layer such as a fluororesin coating is formed on the surface of the ceramic material.