JP3020910B2 - Rotational etching method for silicon semiconductor wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for etching a silicon semiconductor wafer. More specifically, the present invention relates to a wet etching method capable of securing good flatness even when a silicon semiconductor wafer has a large diameter.

[0002]

2. Description of the Related Art Generally, a silicon semiconductor wafer (hereinafter, referred to as a wafer) is subjected to mechanical processing such as slicing and lapping, and then to etching by a chemical action. This etching process is performed for the purpose of removing the processing strain caused by the mechanical processing in the above-mentioned previous process, and at the same time, in order to ensure the accuracy in the subsequent polishing process, even if the etched wafer has its appearance and flatness. A certain standard is required for surface roughness and the like.

As a conventional method of etching a wafer, as shown in FIG. 1, a carrier is vertically inserted at a required pitch into a flow of an etching solution at a constant flow rate through an entrance 2 at a lower portion of an etching tank 1, a current plate 3 and the like. A plurality of held wafers 4 are immersed in the drive shaft 5 which also has a wafer holding function.
The wafer is reacted while simultaneously rotating (rotating) in the same direction by the driven shaft 6 (holding shaft) and taken out of the etching tank after a required etching time has elapsed, and quickly immersed in water to remove the etching solution, thereby performing the etching process. The process was finished.

The etching solution used for this etching reaction is a diluted mixed acid (nitric acid, hydrofluoric acid, acetic acid), but reacts violently with silicon and generates heat. Since the reaction proceeds further due to the temperature rise due to heat generation, uniformity of the temperature distribution of the etching solution in the etching tank, that is, uniformity of the reaction between the wafer and the etching solution is important in order to improve the etching quality of the wafer. In addition, the rotation of the wafer in the liquid or the circulating supply for maintaining the liquid temperature as described above has been conventionally devised.

[0005]

However, with the recent increase in the diameter of the wafer, the conventional etching method as described above is not sufficient in quality maintenance (particularly, flatness).
The following problems occurred. The multiple wafers immersed in the etching solution inside the etching tank and held by the carrier at the required pitch immediately start reacting violently with the etching solution, but simultaneously generate heat and the heat stays between the narrow wafers and rises with the nearby temperature rise. Further, the reaction is accelerated.
The reaction heat tends to stay at the center of the wafer, and as a result, the reaction in that portion proceeds from the outer periphery of the wafer, and after the etching process, the wafer tends to have a concave cross-sectional shape.

To prevent this, as described above, the wafer has been rotated in the liquid or a temperature-adjusted etching solution has been flowed between the wafers. However, the area of the reaction surface becomes large, and the uniformity of the temperature distribution inside the wafer is largely destroyed with the rapid increase in the amount of heat generated. In the conventional method, it is impossible to maintain the uniformity of the reaction for securing the wafer flatness. It was becoming very difficult.

[0007] The present invention has been made in view of the above-mentioned problems of the conventional technology.
An object of the present invention is to provide an etching method capable of maintaining uniformity of a reaction between a wafer and an etchant for securing flatness of the wafer even for a large-diameter wafer.

[0008]

The present invention employs the following means to achieve the above object. According to a first aspect of the present invention, a plurality of silicon semiconductor wafers vertically held in a carrier at a required pitch are immersed in an etching tank in which an etching solution composed of a required mixed acid is circulated and supplied for a required time, and a required etching is performed. An etching method for removing a margin is characterized in that a wafer held vertically on a carrier is etched (rotated) in a direction opposite to each other while maintaining uniformity of a reaction.

According to a second aspect of the present invention, the flow of the etching solution circulating into the etching tank is controlled by the flow of the etching solution under the etching tank.
It is characterized in that the flow rate of the etchant is circulated and supplied in the direction of the carrier upward from the portion at a central portion of the wafer at a maximum and a flow rate distribution decreasing from the central portion toward the outer periphery.

The following effects are obtained by employing the means according to claim 1 described above. The rotation of the wafer in the conventional etching method employs a method of rotating all the wafers held vertically on the carrier in the same direction. Therefore, in this method, the etchant between the adjacent wafers is dragged by the wafer due to its viscosity,
A movement is made to rotate together with the wafer in the same direction. Generally, the peripheral velocity in the tangential direction of the outer periphery of the wafer due to the rotation of the wafer is 4 to 5 times the liquid flow velocity due to the circulation in the etching tank. Since it acts so as to be repelled and does not easily enter between the wafers and the liquid exchange on the reaction surface is not performed smoothly, the temperature becomes higher near the center of the wafer due to heat generation, and the uniformity of the reaction is impaired.

Therefore, the above-mentioned phenomenon is alleviated by rotating the adjacent wafers in opposite directions.
Although the etchant between the wafers is dragged by the wafer due to its viscosity on the surface of each wafer as in the past, the rotation of the wafers is opposite to each other because the rotations of the wafers are opposite to each other. At the center between the wafers, the "dragging speed" becomes zero. As a result, the circulating liquid in the etching tank passes between the wafers much more smoothly than in the past, eliminating the build-up of heat of reaction and extending the flatness even with a large diameter due to a uniform reaction. Is obtained.

Further, the following effects are produced by employing the means according to the second aspect. The uniformity of the reaction within the wafer surface is improved by adopting the means according to claim 1 and smoothing the passage of the etching solution between adjacent wafers. By applying a liquid flow having a smaller velocity distribution to the wafer at the maximum toward the outer periphery, even if a large difference occurs in the heat accumulation in the plane due to the reaction due to the reaction in the etching of a large-diameter wafer (the center is more confined). ), The amount of circulating liquid corresponding to the amount of generated heat acts on the wafer, and acts to make the temperature distribution on the wafer reaction surface uniform.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the etching method of the present invention will be described. [Example 1] The diameter of the wafer to be etched is 150φ
The embodiment at the time of (1) will be described below. Basic conditions include: Etching solution: Standard mixed acid (nitric acid, hydrofluoric acid, acetic acid, dilution water) Supply temperature: 37 ° C Circulation method Wafer rotation speed: 30 rpm (3.14 rad / sec) Number of wafers filled: 100 Wafer gap: 4 mm It is. The present invention uses the apparatus (carrier) of FIG. 2 to rotate adjacent wafers in opposite directions in an etching bath.

To explain this, a plurality of (three in the drawing) side plates 11 arranged evenly in the longitudinal direction of the carrier are fixed by connecting rods 12 and positioned inside the connecting rods 12 to serve also as wafer holding. Two drive shafts 13 and one driven shaft (wafer holding shaft) 14 are arranged in parallel through the side plate. Small gears 15A and 15B are fixed to the side ends of the two drive shafts 13A and 13B, respectively. The small gear 15A of one drive shaft 13A is meshed with a large gear 16 driven and rotated by a bevel gear or the like. One drive shaft 13
The B small gear 15B is driven via the large gear 16 and the intermediate gear 17. Thereby, the two drive shafts 13
A and 13B rotate in opposite directions. The large gear 16 is configured to be driven by another drive source.

The two drive shafts 13A, 13B
A drive roller 18 fixed to a shaft and a driven roller 19 that freely rotates around the shaft are alternately mounted on the first wafer W1. The first wafer W1 is held by the drive roller 18 on the left and the driven roller 19 on the right. The adjacent second wafer W2 is held by a driven roller 19 on the left side and by a drive roller 18 on the right side, and the two types of rollers are alternately arranged in the following manner.

A driven roller which is freely rotated with respect to the driven shaft 14 is attached to the driven shaft 14 so as not to hinder the rotation of the wafer. And this driven shaft 14
In order to fill the carrier with the wafer, the carrier is movably supported along an arc-shaped long hole 20 of each side plate 11.
Grooves are formed in the drive roller 18 and the driven roller 19 provided on the drive shaft 13 and the driven shaft 14, so that the wafer supported at these three points can rotate smoothly. Filling the carrier of the above structure in this way,
With the plurality of wafers set, adjacent wafers rotate in the etching bath in opposite directions to each other, so that processing of a wafer having good flatness can be achieved.

[Embodiment 2] An embodiment in which the diameter of a wafer to be etched is 300φ will be described below. Basic conditions include: Etching solution: Standard mixed acid (nitric acid, hydrofluoric acid, acetic acid, diluting water) Supply temperature: 37 ° C. Circulation method Wafer rotation speed: 15 rpm (1.57 rad / sec) Number of wafers filled: 26 Wafer gap: 8 mm It is. FIG. 3 shows a state in which a wafer W is filled in a carrier 30 having the above-described wafer rotating mechanism, and the carrier 30 is immersed in an etching tank 31 to perform an etching process.

The circulated etching solution flows from a supply port 32 at the bottom of the etching tank into a front tank 33 in the tank. Front tank 33
Then, the processing tank 34 in which the carrier 30 is immersed is partitioned by a partition plate 35, and a plurality of rectifying plates 36 are attached to the partition plate 35 vertically below the carrier 30 so as to be directly below the carrier 30. Have been. In the center of the the partition plate 35 divided by the rectifying plate 36 is apertured rectangular holes 37 along their respective rectification plate, the opening area of the maximum wafer center beneath is, radially outer peripheral from the center It is configured to become smaller as going to. In this embodiment, eight rectifying plates are provided, and seven opening portions between the rectifying plates are arranged from the outer periphery toward the center of the wafer at two positions:
The area ratio was 3: 4: 5. As a result, the rate distribution shown in FIG. 3
Is obtained and the object is achieved.

[0019]

According to the etching method of the present invention, the circulating liquid in the etching tank passes between the wafers much more smoothly than in the prior art by the structure according to the first aspect. Is eliminated, and an etching process with excellent flatness can be performed by a uniform reaction. Further, according to the configuration of the present invention, even if a difference occurs in the heat retention in the plane due to the reaction in a large-diameter wafer, the amount of the circulating liquid corresponding to the generated heat acts on the wafer and the wafer reaction surface. Temperature distribution can be made uniform.

[Brief description of the drawings]

FIG. 1 is a sectional view of an etching tank showing a conventional etching method.

2A and 2B show a carrier used to carry out the etching method of the present invention, wherein FIG. 2A is a plan view and FIG. 2B is a front view.

FIG. 3 is a cross-sectional view showing an etching tank equipped with the carrier of FIG.

[Explanation of symbols]

 W: Wafer 30: Carrier 31: Etching tank

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21 / 304,21 / 306

Claims (2)

(57) [Claims] 1. An etching method for immersing a plurality of silicon semiconductor wafers vertically held in a carrier in an etching tank for circulating and supplying an etching solution composed of a required mixed acid for a required time to remove a required etching allowance. ,
A method for etching a silicon semiconductor wafer, comprising etching a wafer held vertically in a carrier while rotating adjacent wafers in opposite directions. 2. The flow of an etching solution circulating in the etching bath is directed from the lower portion of the etching bath to the upper carrier direction, and the flow rate of the etching solution is maximized at the center of the wafer and reduced from the center to the outer periphery. 2. The method for etching a silicon semiconductor wafer according to claim 1, wherein: