JPH11279777A - Method for management of etchant and etchant management system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for management of an etchant capable of a homogeneously etching a silicon wafer and an etchant management system. SOLUTION: This method for management of the etchant consists in previously incorporating silicon into the initial etchant in such a manner that the silicon concn. in the etchant used to execute etching of the silicon wafer by immersing the silicon wafer into the etchant is maintained within a prescribed range and occasionally exchanging part of the etchant under use with the etchant not contg. the silicon or the etchant contg. the silicon and having the silicon concn. lower than the silicon concn. of the initial etchant to allow the continual use thereof. The etchant management system embodies such management method and the concn. in the prescribed range is preferably 5 to 20 g/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing an etching solution so as to control the etching solution so that the silicon concentration in the etching solution is within a predetermined range, and an etching method capable of suitably realizing the management method. It relates to a liquid management system.

[0002]

2. Description of the Related Art Generally, a silicon wafer is etched by putting an etching solution, which is a mixed acid containing hydrofluoric acid, nitric acid, etc., into an etching bath and cutting and lapping the silicon wafer. This is performed by dipping.

[0003]

By the way, it has been found that this etchant causes various problems on the silicon wafer.

[0004] For example, when a silicon wafer is immersed in a new etching solution, an excessive reaction of silicon and mixed acid occurs, and when viewed as a whole wafer, the central portion has a concave shape, and as shown in FIG. Has small irregularities.

On the other hand, when a silicon wafer is immersed in an etching solution repeatedly used many times, locally deep pits (hereinafter, referred to as local pits) are generated in the etched silicon wafer. These local pits are defects caused by scratches generated by lapping. FIG.
Fig. 2 schematically shows the appearance of local pits. When particles such as alumina and silicon carbide contained as abrasive particles in the lapping liquid at the time of lapping enter the silicon wafer, they are damaged as shown in FIG. When cleaning (lap cleaning) is performed after lapping, the damage further increases (FIG. 5B), and when the silicon wafer in this state is immersed in an etching solution and etched, the silicon wafer in FIG.
(C) As shown in FIG.
Occurs. The local pits become deeper as the etching liquid is used more frequently.

Further, when etching is performed with such an etchant used repeatedly, the surface roughness (Roughness) of the entire silicon wafer after etching is increased, and the surface brightness of the wafer is also reduced. If the local pits are deep or the surface roughness is large, problems such as a large polishing allowance must be taken in the polishing step after etching.

[0007] As a result, it is difficult to etch a silicon wafer in a good condition, even if it is a new etching solution or an etching solution used several times repeatedly. However, it was difficult to obtain a uniform silicon wafer. Therefore, it has been desired to control the etching solution, but conventionally, after repeated use,
Simply replacing the entire etching solution could not only suppress the occurrence of the above problem, but also inferior work efficiency.

[0008] In view of the above problems, an object of the present invention is to provide a method for managing an etching solution and an etching solution management system capable of uniformly etching a silicon wafer.

[0009]

As a result of diligent studies on the above-mentioned problems, the present inventors have found that the above-mentioned excessive reaction of the mixed acid with the silicon wafer and the problem of local pits are caused by the silicon concentration. Was. Then, in order to solve the above problems, the invention described in claim 1 of the present invention is:
Used when etching the silicon wafer by immersing the silicon wafer, so that the silicon concentration in the etching solution is maintained within a predetermined range, silicon is initially contained in the etching solution, and used. Part of the etchant in the, silicon-free etchant, or contains silicon, and,
The method of managing an etchant is characterized in that the etchant is replaced with an etchant having a lower silicon concentration than the initial etchant and used continuously.

According to the method of controlling an etching solution according to the first aspect, the silicon concentration in the etching solution used when etching the silicon wafer by immersing the silicon wafer is maintained within a predetermined range. As described above, silicon is initially contained in the etching solution in advance, and a part of the etching solution in use is an etching solution containing no silicon, or contains silicon, and is more silicon than the initial etching solution. The silicon concentration of the etching solution can be easily changed, since the etching solution is replaced with a low-concentration etching solution as needed and used continuously.
It is possible to maintain the temperature within the predetermined range, and it is possible to uniformly etch the silicon wafer. In addition, since there is no need to perform a large-scale operation such as replacing the entire etching solution, the operation efficiency is improved as compared with the related art.

In the first aspect, the "predetermined range"
This is a range of silicon concentration that can be etched in a good state with respect to a silicon wafer, and depends on specific etching conditions.
When the amount is in the range of g / l (liter) to 20 g / l (liter), a favorable etching solution can be obtained in which the excessive reaction of the silicon wafer and the local pits described above are suppressed. Further, since "the silicon concentration is maintained within the predetermined range", the liquid may be exchanged for each etching. However, if the silicon concentration does not change so much by one etching, The liquid may be exchanged after repeating the etching several times.

Further, the invention according to claim 3 is characterized in that the etching solution contains an etching solution containing silicon in a predetermined concentration in an acidic aqueous solution in advance, and the etching bath contains the etching solution. A discharge means for discharging the liquid, and a supply means for supplying the acidic aqueous solution or the acidic aqueous solution containing silicon to the etching tank, and immersing the silicon wafer in the etching liquid in the etching tank for etching. Then, according to the silicon concentration after the etching, a part of the etching solution is discharged from the etching bath by the discharging means, and the discharged etching is performed so as to maintain the silicon concentration within the predetermined range. The acidic aqueous solution containing the same volume as the liquid or the acidic aqueous solution containing silicon is previously supplied by the supply means. The etching bath, an etching liquid management system and supplying.

[0013] According to the etching solution management system of the third aspect, the etching bath in which the etching solution containing silicon in a predetermined range of concentration is stored in advance.
When the silicon wafer is immersed and etched, a part of the etching solution is discharged from the etching bath by a discharging unit according to the silicon concentration after the etching so as to maintain the silicon concentration within the predetermined range. And the acidic aqueous solution containing the same volume of the acidic aqueous solution or silicon as the etching liquid to be discharged is supplied to the etching tank by the supply means.
The silicon concentration of the etchant can be easily maintained within a predetermined range, and the silicon wafer can be uniformly etched. In addition, since there is no need to perform a large-scale operation such as replacing the entire etching solution, the operation efficiency is improved as compared with the related art.

Further, since the discharge amount and the supply amount are the same, the amount of the solution in the etching tank can be kept constant, and further, the new solution can be obtained while controlling the silicon concentration within a predetermined range. Is added, the ratio of the acid in the etching solution or, when a plurality of types of acids are mixed, the ratio is close to the ratio of the original acidic aqueous solution, so that it is easy to maintain the etching conditions. , Easier to maintain.

According to a fourth aspect of the present invention, in the etching solution management system according to the third aspect, a partition wall having a height lower than an outer wall forming the outer periphery of the etching tank inside the etching tank. Is provided, and the etching tank has a storage tank filled with the etching liquid, which is partitioned by the partition wall, and an adjacent tank adjacent to the storage tank and the partition wall via the partition wall. Thereby, the acidic aqueous solution or the acidic aqueous solution containing silicon is supplied to the storage tank, an etchant overflowing from the etchant in the storage tank is injected into the adjacent portion, and the discharge unit is configured to discharge the adjacent solution. It is characterized by being provided in a part.

According to the etchant management system of the present invention, since the etchant is stored in the storage tank in a full state, if the supply means supplies the acidic aqueous solution to the storage tank, the supply amount is reduced. Since the same volume of liquid overflows from the storage tank and is injected into the adjacent part and is discharged from there through the discharge means, the discharge means is provided with a mere discharge port, and only the supply amount on the supply means side is provided. By monitoring, the supply amount and the discharge amount can be made equal, and the system of the present invention can be configured more easily.

Further, in the etching liquid management system according to the third or fourth aspect, the etching liquid overflowing from the storage tank is returned to the storage tank without being discharged to the outside as in the invention according to the fifth aspect. If the circulation means is provided, when it is not necessary to adjust the silicon concentration, when the etching solution overflows from the storage tank, or when it is configured to always overflow, if the circulation means, the circulation means, Since it is returned, the amount of the etching solution can be kept constant. Also, the etchant is not wasted,
Process costs can be saved.

In addition, in the etchant management system according to any one of claims 3 to 5, the "predetermined range" is a range of a silicon concentration at which a silicon wafer can be etched in a satisfactory state. Although it depends on the etching conditions, if the amount is 5 g / l (liter) to 20 g / l (liter), the excessive reaction of the silicon wafer and local pits as described above are suppressed. As a result, an etchant capable of satisfactorily etching the silicon wafer is obtained.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an example of the etchant management system of the present invention. The etching management system 1 includes an etching tank 2, a circulation path 50 including a stirring tank 3, a pump 4, a filter 5, a new liquid circulation line 6, and a new liquid connecting the circulation path 50 and the new liquid circulation line 6. It is composed of a supply line 11 and the like.

The circulation path (circulation means) 50 is a single closed system when the drain valve 10 and the supply valve 12 to be described later are closed.

A partition wall 2a is formed inside the etching tank 2, and the partition wall 2a
The inside of the etching tank 2 is divided into two chambers, a storage tank 8 and a discharge tank (adjacent tank) 9. The storage tank 8 contains 20
0 liter of the etching solution is filled up to the very height of the partition wall 2a. This etching solution is composed of hydrofluoric acid (concentration 50%), nitric acid (concentration 70%), and acetic acid (concentration 99.9%) in a volume ratio of 1: 2: 2 or 1: 2: 1.
Is an acidic aqueous solution mixed at a ratio of In this etching liquid, silicon is always dissolved at a concentration of 5 to 20 g / l (liter), particularly preferably 10 to 15 g / l. If the amount is less than 5 g / l, the silicon wafer is excessively etched when etching, and flatness of the surface cannot be obtained. When the concentration is higher than 20 g / l, as shown in the graphs of FIGS. 2 and 3, the depth of the local pit and the surface roughness are undesirably large due to the post-etching process. turn into. In order to always etch the silicon wafer within the above concentration range, silicon is dissolved from the beginning so as to have the above concentration in an etching solution in which the silicon wafer is not immersed at all.

A circulating line 7a is connected to the storage tank 8, so that the liquid passing through the circulating line 7a is supplied. The line extending from the circulation line 7a reaches the lower part of the storage tank 8, and the liquid having passed through the circulation line 7a is first injected into the lower part of the storage tank 8.

The discharge tank 9 is adjacent to the storage tank 8 via the partition wall 2a, and is poured into the discharge tank 9 when the upper portion of the etching liquid in the storage tank 8 overflows. . A circulation line 7b is connected to the discharge tank 9. The circulation line 7b is branched in the middle, and a drain valve (discharge means) 10 having a flow rate measuring device (not shown) is provided in the branched line.
Therefore, the etching solution poured into the discharge tank 9
When the drain valve 10 is closed, it flows through the circulation line 7b toward the stirring tank 3, and when the drain valve 10 is open, it is discharged outside. The opening and closing of the drain valve 10 is controlled by a control unit described later, and the flow rate measuring device is monitored by the control unit.

The new liquid supply line 11 is connected to the circulation line 7b.
The new liquid supply line 11 is provided with a supply valve 12 provided with a second flow meter (not shown). The new liquid supply line 11 is connected to a new liquid circulation line 6, and the new liquid circulation line 6 is connected to a new liquid tank (not shown) in which the above-mentioned acidic aqueous solution is stored. The acidic aqueous solution circulates inside. Therefore, when the supply valve 12 is opened, an acidic aqueous solution containing no silicon is supplied to the circulation line 7b through the new liquid supply line 11. The opening and closing of the supply valve 12 is controlled by a control unit described later, and the second flow rate measuring device is monitored by the control unit.

The inside of the stirring tank 3 is filled with an etching solution, and is constantly stirred by a stirring member (not shown). In the initial state, the etching solution in the stirring tank 3 is one in which silicon is dissolved in an acidic aqueous solution, just like the storage tank 8. The acidic aqueous solution that has passed through the new liquid supply line 11 and the circulation line 7b enters the stirring tank 3, where it becomes substantially uniform with the etching solution in the stirring tank 3.

The pump 4 pumps the etching solution in the stirring tank 3 so that the amount of liquid in the stirring tank 3 is substantially constant.
To the circulation line 7c. The filter 5 removes dust, silicon fragments, and the like mixed in the liquid flowing through the circulation line 7c. In the filter 5, the filtered etchant enters the storage tank 8 of the etching tank 2 through the circulation line 7a.

That is, in the etching management system 1, a new acidic aqueous solution is supplied to the stirring tank 3 via the supply valve 12 and the new liquid supply line 11, whereby the silicon-containing liquid flowing out of the stirring tank 3 is discharged. , And is supplied to the storage tank 8 of the etching tank 2 through the circulation lines 7c and 7a.

It should be noted that, even when a new liquid is not being supplied, in this system 1, the etching liquid always overflows from the storage tank 8, and the overflowing liquid flows through the discharge tank 9 and the circulation line 7b. Then, the liquid is sent to the stirring tank 3 and the liquid is finally returned to the storage tank 8 via the pump 4.

The etching liquid management system 1 includes a control unit (not shown). When etching a silicon wafer, the diameter of the wafer, the etching allowance (thickness to be etched), and the control of the wafer immersed in the etching tank at one time are performed. Based on the number of sheets, the silicon concentration of the entire circulation path 50 after the etching is obtained, and in order to return the concentration to the original silicon concentration, the amount of a new acidic aqueous solution to be supplied and the amount of the etching solution in the storage tank 8 to be discharged are determined. Then, the supply valve 12 and the drain valve 10 are automatically opened in accordance with the result of obtaining the same capacity.
When the control unit detects that a predetermined amount of the etching liquid has been discharged from the drain valve 10, the control unit closes the drain valve 10 and detects that the required amount of new liquid has been supplied to the circulation path 50. Then, the supply valve 12 is closed. In addition, as a control part, a personal computer or a sequencer is mentioned, for example.

In the etching liquid management system 1 having the above-described configuration, for example, 50 silicon wafers are immersed in the storage tank 8 for a predetermined time and etched to a predetermined thickness. Thereby, the silicon concentration in the storage tank 8, that is, in the entire circulation path 50 increases. When inputting various data such as the diameter, the thickness to be etched, and the number of immersed silicon wafers to be etched into the control unit, the control unit returns the increased silicon concentration to the state before the etching. And the volume of liquid to be discharged and supplied. Then, the control unit controls the discharge valve 1
Opening 0, the discharge valve 10 is closed when the obtained amount of the etchant has been discharged. On the other hand, the control unit opens the supply valve 12 and monitors the flow rate with a second flow rate measuring device (not shown). close.

The supply amount and the discharge amount are the same as those of the etching tank 2 having the highest silicon concentration.
Since the etching solution is discharged from the
The amount is calculated to be smaller at a fixed rate than the amount calculated based on the entire silicon concentration.

According to the etching liquid management system 1 described above, the silicon concentration of the etching liquid can be reduced without performing a large-scale operation of replacing the entire etching liquid.
5 g / l to 20 that can perform good etching
g / l. The discharge amount of the etching liquid and the supply amount of the new liquid are the same, and the liquid overflowing from the storage tank 8 except during the supply of the new liquid returns to the storage tank 8 through the circulation path 50. Therefore, the amount of liquid in the storage tank 8 can always be kept constant,
Etching can be performed with the same amount of liquid each time, and etching can be performed under stable conditions. In addition, storage tank 8
Since the etching solution overflowing from is not wasted, the process cost can be saved. Further, since a new acidic aqueous solution is added while controlling the silicon concentration within a predetermined range, the ratio of the acid in the etching solution is a value close to the ratio of the original acidic aqueous solution, and it is easy to maintain, and the etching conditions are stabilized. . In addition, since the silicon concentration of the etching solution in the storage tank 8 is controlled within the range of 5 g / l to 20 g / l, excessive reaction of the silicon wafer and local pits are suppressed, and the silicon wafer is favorably etched. Will be able to do it.

In the above description, the flow rate measuring device may not be provided in the discharge valve 10 portion. In this case, when the supply valve 12 is opened, the discharge valve 10 is opened and the discharge section 9 is opened. The accumulated etchant may be discharged. With such a configuration, the amount of the new liquid to be supplied to the storage tank 8 and the amount of the etching liquid to be discharged can be equalized with a simpler configuration.

In the above embodiment, the etching liquid management system 1 shows a state in which only one circulation path 50 is connected to the new liquid circulation line 6, but the present invention is not limited to this. A plurality of circulation paths each having an etching tank may be connected to the new liquid circulation line 6, and in this case, the management described above is performed on the plurality of etching tanks. Further, in the above embodiment, the etching liquid is discharged and the new liquid is supplied after one etching, but the silicon concentration in the storage tank 8 is 5 to 15 g / l.
Within the range, the discharge and supply may be performed after etching is performed several times. Furthermore, the mixing ratio of each acid in the acidic aqueous solution may be different from that in the above embodiment, and the type of acid used is not limited to hydrofluoric acid, nitric acid, and acetic acid, and other acids may be used.

[0035]

According to the first aspect of the present invention, the silicon concentration of the etching solution can be easily maintained within a predetermined range, and the quality of the silicon wafer after etching is uniform. Becomes In addition, since there is no need to perform a large-scale operation such as replacing the entire etching solution, the operation efficiency is improved as compared with the related art. Also, if the amount of liquid to be taken out and the amount of liquid to be newly added at the time of replacement are the same, the amount of etching liquid can be kept constant, and the etching can be performed with the same amount of liquid every time.
It becomes easy to maintain the etching conditions.

According to the invention described in claim 2, according to claim 1
In addition to the effects of the invention described in (1), excessive reaction of the silicon wafer, local pits and the like are suppressed, and the silicon wafer can be favorably etched.

According to the third aspect of the invention, the silicon concentration of the etching solution can be easily maintained within a predetermined range, and the silicon wafer can be uniformly etched. Also, since there is no need to perform large-scale work such as replacing the entire etching solution,
The work efficiency is improved as compared with the related art. In addition, since the amount to be discharged and the amount to be supplied are the same, the amount of liquid in the etching tank can be kept constant, and further, it is necessary to add a new liquid while controlling the silicon concentration within a predetermined range. Therefore, the ratio of the acid in the etching solution and, if a plurality of types of acids are mixed, the ratio is close to the ratio of the original acidic aqueous solution, and it is easy to maintain the etching conditions. It will be easier.

According to the invention set forth in claim 4, according to claim 3,
In addition to the effects of the invention described in the above, the system of the present invention can be configured more easily.

According to the invention set forth in claim 5, according to claim 3,
Or in addition to the effect of the invention described in 4 above, when the etching solution overflows or when it is configured to always overflow, it is returned to the storage tank by the circulating means. Can be kept constant.

According to the invention described in claim 6, according to claim 3,
In addition to the effects of the inventions described in (1) to (5), excessive reaction of the silicon wafer and local pits are suppressed, and the silicon wafer can be favorably etched.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration as an example of an etchant management system of the present invention.

FIG. 2 is a graph showing a relationship between a silicon concentration in an acidic aqueous solution similar to the etchant used in the etchant management system of FIG. 1 and a local pit depth after etching; Nitric acid: acetic acid concentration 1: 2:
2 shows a case, and (b) similarly shows a case of 1: 2: 1.

3 is a graph showing the relationship between the silicon concentration in an acidic aqueous solution similar to the etchant used in the etchant management system of FIG. 1 and the surface roughness after etching, wherein (a) is hydrofluoric acid: nitric acid : Acetic acid concentration of 1: 2: 2, and (b) shows a case of 1: 2: 1.

4A and 4B show a state of a surface after etching a silicon wafer W in an etching solution having a low silicon concentration, wherein FIG. 4A is a perspective view of the silicon wafer W, and FIG. FIG. 4 is an enlarged sectional view of a portion B of FIG.

FIGS. 5A and 5B are cross-sectional views schematically showing a mechanism of local pit generation, wherein FIG. 5A shows a flaw in a portion where abrasive grains have entered a silicon wafer W by lapping, and FIG. 5B shows a flaw (a). (Dotted line) shows a state of growing to the point indicated by the solid line by lapping and washing, and (c) shows a state in which the scratched part (dotted line) of (b) remained as a concave part A as shown by the solid line by etching. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Etching liquid management system 2 Etching tank 2a Partition wall 3 Stirring tank 4 Pump 5 Filter 6 New liquid circulation line 8 Storage tank 9 Drain tank (adjacent tank) 10 Drain valve (discharge means) 11 New liquid supply line 12 Supply valve 50 Circulation route (circulation means)

Claims (6)

[Claims] An etching solution containing silicon in advance so that the silicon concentration in the etching solution used when etching the silicon wafer by immersing the silicon wafer is maintained within a predetermined range. Aside from this, a part of the etchant in use is replaced with an etchant containing no silicon or an etchant containing silicon and having a lower silicon concentration than the initial etchant, as needed. An etchant management method characterized by being used continuously. 2. The method according to claim 1, wherein the concentration in the predetermined range is 5 g / l to 2 g / l.
2. The method according to claim 1, wherein the amount is 0 g / l. 3. An etching tank in which an etching solution containing silicon in a predetermined range of concentration in an acidic aqueous solution is stored in advance, and a discharge unit for discharging the etching solution from the etching bath; Supply means for supplying the acidic aqueous solution or the acidic aqueous solution containing silicon to the etching tank, wherein when the silicon wafer is immersed in the etching solution in the etching tank and etched, the silicon concentration is adjusted to the predetermined value. According to the silicon concentration after the etching, a part of the etching solution is discharged from the etching tank by the discharging means, and the acidic aqueous solution having the same volume as the discharged etching solution is maintained in the range. Supplying the etching solution to the etching tank by the supplying means. Stem. 4. An etching solution, wherein a partition wall having a height lower than an outer wall forming an outer periphery of the etching tank is provided inside the etching tank, and the etching tank is partitioned by the partition wall. And a storage tank that is adjacent to the storage tank and the storage tank that is adjacent to the storage tank via the partition wall. The supply unit supplies the storage tank with the acidic aqueous solution or the acid containing silicon. The etching solution according to claim 3, wherein an aqueous solution is supplied, an etching solution overflowing from the etching solution in the storage tank is injected into the adjacent portion, and the discharge unit is provided in the adjacent portion. Management system. 5. The etching liquid management system according to claim 3, further comprising a circulation unit for returning the etching liquid overflowing from the storage tank to the storage tank without discharging the etching liquid to the outside. 6. The concentration in the predetermined range is from 5 g / l to 2 g / l.
The etching liquid management system according to any one of claims 3 to 5, wherein the amount is 0 g / l.