JP2918871B1 - Silicon semiconductor wafer etching method - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To make uniform "speed" and "movement distance" with respect to an etching liquid, which are basic requirements for etching processing, at each point of a rotating wafer, and to secure a good flatness. An etching method is provided. SOLUTION: An etching solution is supplied to a plurality of wafers W positioned in an upper part in an etching tank 3 from a lower part or a side part of the tank, and the rotation of the wafer group is separated from the rotation center of the wafer group by a center of the rotation. The flow rate of the etchant in the direction opposite to the rotation direction is adjusted to be smaller than the flow rate of the etchant on the side along the rotation direction, and the processing is performed in the etching fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method in which a wafer is immersed in an etching solution composed of a mixed acid for a required time while being rotated while rotating the wafer, and more particularly to an etching method for ensuring a good flatness. Related to the supply method.

[0002]

2. Description of the Related Art In a conventional etching method, for example, as shown in FIG. 1, a plurality of etching liquid flows from a lower part of an etching liquid tank 1 through a liquid inlet 6 and a rectifying porous plate 2 (arrows). The wafer is tens of r by a rotating jig composed of a noise shaft 4 for rotating the wafer 3 and a holding shaft 5 (three).
While rotating at pm, immersed in the liquid at a stretch from above the etching liquid tank, removed from the liquid after a lapse of the required time to remove the target etching allowance, immersed in cleaning water and removed the etching liquid to perform the etching process. Had finished. At this time, the etching solution is usually a mixed acid (nitric acid, hydrofluoric acid, acetic acid, diluting water), but reacts very vigorously with silicon and generates heat, so that the temperature of the etching solution (reaction temperature) does not rise. A constant amount of the etching solution adjusted to a constant temperature as described above is constantly flowed from the lower portion of the liquid tank to perform the etching process, and the etching solution overflowing from the liquid tank is collected and collected through the collecting port 7 of the receiver, and cooled. It is used cyclically. In the above example, the flow of the etching liquid is directed upward. However, a rectifying porous plate may be provided on the side surface of the liquid tank, and the etching liquid may flow horizontally toward the wafer.

[0003]

Assuming that the etching liquid in the etching bath is a stationary liquid in which the etching liquid does not flow at all, the relative speed of the wafer with respect to the etching liquid is maximum at the peripheral portion of the wafer and zero at the central portion of the wafer. This difference causes a difference in the cooling effect of the wafer, and the temperature of the central portion of the wafer, which is difficult to cool, increases, and the reaction proceeds at a high speed in the central portion of the wafer. It will be finished, and above all, when performing the etching process continuously, it becomes difficult to adjust the etching margin due to the rise in the liquid temperature.

Therefore, as described in the prior art, an etching solution adjusted to a constant temperature is supplied during etching, but the main purpose is to prevent the solution temperature from rising due to reaction heat. When converted to the flow velocity per sectional area of the liquid tank, it is usually about a fraction of the rotational speed of the outer periphery of the wafer. In such a case (for example, the ratio between the outer peripheral speed of the rotating wafer and the flow rate of the etching liquid is 4: 1), the relative velocity to the etching liquid at an arbitrary point of the wafer (select three points of the outer circumference, r / 2, and the center) is shown. It is shown in FIG. FIG. 2 shows the relative speed with respect to the etching liquid when the above-mentioned arbitrary point is rotated by the rotation angle θ, where A is the outer circumference (point r), B is r / 2 (r is the wafer radius), C indicates the center of the wafer (dotted line). The center is always at a constant speed and its value is small. Perimeter and r
At the / 2 point, the value of the relative speed fluctuates greatly in both cases. The horizontal axis indicates the rotation angle, but considering that the rotation speed is constant and therefore also the time axis, the area between each curve or straight line and the horizontal axis is exactly the same as when the wafer makes one rotation. The difference in the moving distance of the point with respect to the etching solution is also shown. It is. This also shows the difference in the cooling effect on the wafer during the etching, which is an exothermic reaction. The cooling effect decreases at the center, and the reaction proceeds at a higher reaction temperature, and the reaction progresses faster and becomes thinner at the center. That is, the fact that the flatness is deteriorated is supported.

[0005] The present invention has been made in view of the problem conventional etching method described above has, keep each point of the rotating wafer, "speed"及beauty "movement relative to the etchant is a basic requirement of etching It is an object of the present invention to provide a wet etching method in which the distance is made more uniform and good flatness can be secured.

[0006]

Means for solving the above-mentioned problems according to the present invention, which the present invention has taken to solve the above-mentioned problems, is that a plurality of silicon semiconductor wafers are rotated to form an etching solution comprising a mixed acid in a required mixing ratio. when immersed in the etching process relates supply of the etching liquid to the rectangular cross section of the liquid tank, the plurality of wafers in the etchant bath, the etching solution is supplied so as to be directed vertically upward or horizontal direction
Occasionally, the rotating wafer group is located at the bottom or side of the tank.
Adjustment of the flow rate of the etching solution supplied to the wafer
Avoid etching space and introduce etching solution just before
The partition plate to be installed is arranged perpendicular to the rotation plane of the wafer,
Adjust the amount of liquid that flows into each section of the liquid separated by the cutting plate
Adopt a method to do. Further, the means according to claim 2 includes:
For each introduction part of the liquid divided by the partition plate of the etching liquid tank,
The temperature of the supplied liquid is adjusted.

The operation according to claim 1 will be described below. As can be seen from FIG.
The moving speed (except for the center point) and the moving distance of the point (outer circumference, r / 2 point, rotation center point) per rotation are not constant, and this causes a difference in the cooling effect of the wafer and causes the etching in the radial direction. As described above, the difference in the reaction progress rate is considered to be the first cause of the deterioration of the flatness of the wafer. However, it is conceivable to increase the liquid flow velocity relatively to the velocity due to the rotation of the outer periphery of the wafer so as to reduce the influence of the rotation, but theoretically an infinite flow velocity is required. There are, of course, practical limitations.

Therefore, under a normal etching flow rate,
As shown in FIG. 2, when the rotation of the wafer is 0 °, the rotation direction of the wafer and the flow direction of the etchant are completely the same (cocurrent).
At 180 °, the direction is completely opposite (countercurrent), so that on the “left half” side of the wafer, both velocities (the speed of the liquid and the speed of the wafer itself due to rotation) are so-called “positive”. Although it can be said that they act so as to be synthesized, the "right half" of the wafer can be said to be the opposite relationship, so when the wafer is rotated leftward, the flow rate of the etchant on the "left half" side of the wafer is changed to " When the wafer is rotating clockwise toward the right, the flow rate of the etchant on the “left half” side of the wafer is set to be larger than that of the “right half” .
Avoid the space where the wafer rotates in the direction perpendicular to the rotation plane.
A partition plate for introducing the etching solution until just before
And let the liquid separated by the partition plate flow into each introduction part.
The amount of liquid is adjusted by opening the flow control valve directly connected, or
Easy adjustment by adjusting the displacement setting of the variable displacement pump
Good and flatness by controlling the flow rate (flow velocity)
Good processing can be performed. The above operation will be described in a specific example. FIG. 4 is a simplest example in which different flow rates are adopted on the left and right sides with respect to a vertical center line passing through the center of rotation of the wafer. The rotation speed of the section: the flow rate of the counter-current side etching liquid: the flow rate of the parallel-flow side etching liquid = 2: 1: 3. The moving distance (the area between the curve or the straight line and the horizontal axis) and the moving speed are not greatly changed, and are greatly improved as compared with the conventional example shown in FIG. 2, so that the etching process with good flatness can be performed.

According to a second aspect of the present invention, in addition to the adjustment of the flow rate of the etching solution for each section of the partition plate, the liquid temperature of each section is controlled independently of the adjustment of the flow rate. The movement distance per rotation of a point and the speed thereof are made uniform, and the problem of heat radiation of the wafer itself that becomes more apparent when the wafer to be processed has a large diameter, that is, the center portion of the wafer is originally smaller than the outer periphery. This is a solution to the problem that the etching is more difficult to be performed and the etching proceeds further, and the central portion of the wafer becomes thinner. The central portion acts to cool more.

[0010]

Embodiments of the present invention will be described below. Example 1 An example of a wafer having a diameter of 150φ will be described below. The etching conditions are as follows: etching solution: standard mixed acid (nitric acid, hydrofluoric acid, acetic acid, diluting water) supply liquid temperature: 37 ° C. circulating method wafer rotation speed: 30 rpm (ω = 3.14 rad / sec, outer peripheral portion speed: 0) .24 m / se
c) The present invention will be described with reference to FIG. Wafer W rotates 1
It is held between the drive shaft 1 and the three driven shafts 2 and dipped in the etching bath 3 while rotating, taken out after a lapse of a required time, dipped in a cleaning water bath, the etching solution is removed by the cleaning water, and the etching process is completed. .

By avoiding the place where the wafer W is located in the etching tank 3, the space between the rotating surface and the vertical wall is divided by five partition plates 4 at a position below the wafer, and each of the divided inlets is divided. 6-1, 6-2, 6-3, 6-4, 6-5, 6
Assuming that the amount of liquid from each inlet is 6-6, 6-
The flow rates of each of the inlets 6-3, 6-2, and 6-1 are set to 0.3 m / sec so that the flow rate becomes 0.15 m / sec. With the control valve,
Alternatively, the flow is adjusted by directly connecting to the variable flow rate pump, and the flow of the inflowing etching liquid is made uniform by the porous rectifying plate 5. In addition, regarding the adjustment of the flow velocity,
On the 6, 6-5, 6-4 side, a perforated plate with a small opening ratio is used, and on the inflow ports 6-3, 6-2, 6-1 side, a perforated plate with a large opening ratio is used. Although it is possible to adjust the flow velocity or increase the speed by simultaneously blowing air or nitrogen gas on the right side of the wafer, which is a parallel flow, it is difficult to finely adjust the speed. In the example, the partition plate 4 extends to a position just before the wafer while avoiding the space where the wafer rotates, and in addition to the fact that the flow rate control can be easily performed, it is possible to reliably control at least immediately before the wafer. . The overflowing etchant is collected from a receiver outlet 6 into a liquid collection tank (not shown), cooled to a constant temperature (37 ° C.), and circulated.

[Embodiment 2] An embodiment of a wafer having a diameter of 300φ will be described below. The etching conditions are as follows: etching solution: standard mixed acid (nitric acid, hydrofluoric acid, acetic acid, diluting water) wafer rotation speed: 15 rpm (ω = 1.57 rad / sec wafer outer peripheral speed 0.24)
m / sec) The basic part of the etching method is the same as that of the first embodiment. In this case, the flow rate of the liquid to the center of the wafer is 0 at the inlets 6-6, 6-5, and 6-4. .15 m / se
c, 0.30 for inlets 6-3, 6-2, 6-1
m / sec. In the first embodiment, the liquid temperature of the etching solution for each inlet is all the same 37 ° C. However, in the present embodiment, the inlets 6-6, 6-5, and 6 are also considered in view of the large diameter.
Although the liquid temperature of −2 and 6-1 is 30 ° C., the liquid temperature of the inlets 6-4 and 6-3 is somewhat lowered (for example, 3 ° C.). As a specific method, the present invention can be carried out simply by branching off the liquid feed pipe of the etching solution cooled to a certain temperature in the liquid collecting tank and cooling it again. This cooling of the central part of the wafer is effective in solving the problem that the cooling effect originally has a gradient in the radial direction, and the central part of the wafer that becomes apparent when the diameter of the wafer becomes large becomes thinner. By adjusting the liquid temperature in addition to the flow rate adjustment according to the first aspect , an etching process with extremely good flatness can be performed.

[0013]

According to the etching method of the present invention, the speed and the moving distance with respect to the etching solution, which are the basic requirements for the etching process, at each point of the rotating wafer are made more uniform, and the flatness of the flatness is improved. Good etching can be performed. Further, according to the configuration of claim 2,
The center part of the wafer can be cooled more than the outer part.
As a result, the temperature distribution of the wafer can be made more uniform.
Therefore, it is possible to provide an etching method capable of securing good flatness even with a large-diameter wafer.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a relative speed with respect to an etching solution when arbitrary points (three points) on a rotating wafer are rotated in a conventional etching method.

FIG. 3 is a sectional view of an etching tank showing an embodiment of the etching method of the present invention.

FIG. 4 is an explanatory diagram showing a relative speed with respect to an etching solution when an arbitrary point on a rotating wafer is rotated in the etching method of the present invention.

[Explanation of symbols]

 W: Wafer 3: Etching tank 4: Partition plate

Continuation of front page (58) Fields investigated (Int.Cl. ⁶ , DB name) H01L 21/306 H01L 21/308 H01L 21/304 C23F 1/00-3/06

Claims (2)

(57) [Claims] 1. A method of supplying an etching solution by dipping a plurality of silicon semiconductor wafers in an etching solution composed of a mixed acid of the required mixing ratio of while rotating the wafer at the time of the etching process, the lower portion of the etching bath or Etchin supplied from the side
Adjust the flow rate of the solution to avoid the space where the wafer rotates.
Immediately before that, place the partition plate into which the etchant is
Arranged perpendicular to the rotating surface, the liquid separated by the partition plate
A method for etching a silicon semiconductor wafer, characterized in that the method is performed by adjusting the amount of liquid flowing into each introduction section . 2. The method according to claim 1, wherein the partition is divided by a partition plate at a lower portion of the etching tank.
2. The method for etching a silicon semiconductor wafer according to claim 1 , wherein the temperature of the liquid is adjusted for each of the introduction portions of the liquid .