JP2009004675A - Etching method and device for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for etching silicon wafer which can reduce variation of etching depth. <P>SOLUTION: In the etching method for soaking a silicon wafer into an etchant for etching, before etching, the silicon wafer is so heated that the temperature of the silicon wafer becomes the same as the temperature of the etchant or the temperature in a predetermined temperature range from the etchant temperature, and then the heated silicon wafer is soaked into the etchant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silicon wafer etching method and apparatus for removing processing strain generated in a silicon wafer manufacturing process such as a slicing process, a chamfering process, and a lapping process.

  Conventionally, silicon wafers used for integrated circuits such as ICs and LSIs and individual semiconductor elements such as transistors and diodes were obtained by the Czochralski method (CZ method) or the float zone method (FZ method). After cutting the single crystal with a wire saw, chamfering the periphery, and lapping the main surface with loose abrasive grains or grinding with fixed abrasive grains to improve flatness, In order to remove the processing strain applied to the wafer, wet etching is performed, and then mirror polishing is performed.

  For example, wet etching for removing the processing strain includes acid etching using a mixed acid composed of hydrofluoric acid, nitric acid, and acetic acid, and alkali etching using an alkali such as sodium hydroxide or potassium hydroxide.

  In the above acid etching, it is possible to control the etching rate and the surface state after etching by changing the ratio of the components constituting the mixed acid. However, the etching rate is generally high, and the flatness of the wafer improved by lapping. There is a problem that it is difficult to maintain the degree.

  On the other hand, the alkali etching has an advantage that a wafer having good flatness after etching can be obtained because of a low etching rate. In the manufacture of silicon wafers in recent years, very high flatness is required. Therefore, this alkali etching has been widely used because of its advantages.

  When polishing the wafer after this etching, the subsequent mirror polishing is performed by, for example, a single wafer type apparatus for polishing one by one or a batch type apparatus for simultaneously polishing a plurality of wafers. In addition, there are a method of polishing the front and back of the wafer simultaneously, a method of polishing one surface at a time, and the like.

  When manufacturing a wafer with high flatness that has been required in recent years, in addition to the ability of the polishing process, how to put a stable raw material into the polishing process is a problem. For example, in the case of a batch-type polishing apparatus that simultaneously polishes a plurality of wafer front and back surfaces, thickness variation after etching becomes a major issue.

  Usually, in an etching process, a wafer having a constant thickness in a lapping process or the like is subjected to an etching process for a fixed time, and processing distortion is removed with a fixed etching allowance (removed thickness). Therefore, the thickness variation after etching is affected by the variation in the machining allowance and the thickness before etching, for example, the thickness variation after being processed by lapping or grinding.

  Therefore, it is important to reduce the variation in the etching allowance in the etching process as much as possible.

  The present invention has been made in view of such a problem, and a main object of the present invention is to provide a silicon wafer etching method and apparatus capable of reducing variation in the machining allowance due to etching.

  The method for etching a silicon wafer according to the present invention is an etching method in which a silicon wafer is immersed in an etching solution to perform etching, and the temperature of the silicon wafer is within a predetermined temperature range from the temperature of the etching solution before performing the etching. The silicon wafer is heated so that the temperature becomes the temperature, and the heated silicon wafer is immersed in the etching solution.

  Thus, by making the temperature of the silicon wafer substantially the same as the temperature of the etching solution, the change in the chemical temperature at the start of etching can be moderated. As a result, the temperature control of the etchant during the etching process can be stabilized, and the etching allowance can also be stabilized.

  Therefore, as a result, the thickness variation after etching can be reduced, and a wafer with high flatness can be processed in the subsequent polishing process.

  In particular, before performing the etching, it is preferable to perform etching after heating the wafer so that the wafer temperature is within ± 5 ° C. of the etching solution. Although it is necessary to set the optimum temperature range depending on the type of etching apparatus (tank size, heater capacity, temperature control method, etc.), the temperature difference between the wafer temperature and the etching solution is at least within ± 5 ° C. It is effective to perform etching after heating in this manner. More preferably, the wafer temperature is preferably set to a temperature in the range of −1 ° C. to 0 ° C. that is slightly lower than the etching solution in consideration of the temperature rise due to the reaction heat between the etching solution and the wafer.

  It is preferable that the temperature of the etching solution is in the range of 65 ° C to 85 ° C. The method of the present invention is particularly effective when etching is performed so that the silicon removal thickness (etching allowance) by etching is within the range of 10 to 40 μm on both sides.

  As the etching solution, an alkaline aqueous solution containing an alkali component is preferably used, and the concentration of the alkali component is preferably in the range of 48.0 to 55.0% by weight, and the alkali component is preferably sodium hydroxide. .

  When performing an etching process using such a high temperature etching solution (chemical solution) of 65 ° C. to 85 ° C., the etching solution is particularly susceptible to the temperature of the wafer to be introduced. Further, when processing is performed under the etching conditions as described above, there is an advantage that the processing distortion in the previous process can be sufficiently removed, the roughness of the wafer surface can be reduced as much as possible, and the burden on the polishing process can be reduced.

  The silicon wafer etching apparatus according to the present invention is an etching apparatus for performing etching by immersing a silicon wafer in an etching solution, and the temperature of the silicon wafer is set to a temperature of the etching solution before the etching tank for performing the etching. And a heating means for heating the silicon wafer so as to reach a temperature within a predetermined temperature range from the liquid temperature.

  The heating means is not particularly limited, but may be a hot water tank, or a furnace having heating means such as warm air or a heater may be installed.

  By using an etching apparatus equipped with a heating means as described above, the temperature of the silicon wafer can be made substantially the same as that of the etching solution before the silicon wafer is immersed in the etching solution. A small etching process is possible.

  According to the present invention, the temperature change of the etchant at the start of etching can be moderated, and the temperature control of the etchant during the etching process can be stabilized. As a result, the etching allowance of the silicon wafer can be stabilized. Therefore, the thickness variation after etching of the silicon wafer can be reduced, and an effect that a silicon wafer with high flatness can be processed in the subsequent polishing process is achieved.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to these. FIG. 1 is a schematic side view illustrating one embodiment of an etching apparatus according to the present invention.

  In FIG. 1, reference numeral 10 denotes an etching apparatus according to the present invention. The etching apparatus 10 is provided with a heating unit 12 including a hot water tank 12A which is a heating means. As the hot water tank 12A, for example, a hot pure water tank or the like is used. Reference numeral 14 denotes an etching unit including an etching tank 14A, which etches the heated silicon wafer W. An alkaline etching tank is preferably used as the etching tank 14A. Reference numeral 16 denotes a rinsing section including a rinsing tank 16A, which is installed for cleaning the etched silicon wafer W or the like. Reference numeral 18 denotes a drying section provided with a drying means 18A such as hot water pulling or suction, for drying the cleaned silicon wafer W.

  Reference numeral 20 denotes a loader unit for loading the silicon wafer W into the etching apparatus 10 and is provided at the front of the etching apparatus 10. Reference numeral 22 denotes an unloader for discharging the silicon wafer W from the etching apparatus 10 and is provided at the rear part of the etching apparatus 10. Reference numeral 24 denotes a transfer robot, which is movably provided above the heating unit 12, the etching unit 14, the rinsing unit 16 and the drying unit 18, and holds the silicon wafer W so as to connect the units 12, 14, 16, and 18 to each other. Transport and take-out operation from each part 12, 14, 16, 18 is performed.

  In addition, although the structure of tanks, such as the number of rinse tanks 16A, is arbitrary, in the etching apparatus of this invention, the heating part 12 containing the hot water tank 12A which is a heating means can be installed as a front | former stage of the etching tank 14A. is necessary. The number and form of the transfer robots 24 are also arbitrary.

  In the etching apparatus 10 of the present invention, the heating means constituting the heating unit 12 is not particularly limited, but may be constituted by warm air, a heater, or the like in addition to the hot water tank 12A.

  Here, a general method for manufacturing a silicon wafer will be described. FIG. 2 is a flowchart showing a general silicon wafer manufacturing process. The silicon ingot grown by the Czochralski method or the float zone method is first cut into a wafer shape by an inner peripheral slicer or a wire saw in a slicing step (step 100 in FIG. 2). Next, a chamfering process is performed in a chamfering process (step 102 in FIG. 2) in order to prevent the wafer side surface from being chipped. Further, lapping is performed in a lapping process (step 104 in FIG. 2) for flattening. In the subsequent etching process (step 106 in FIG. 2), etching is performed in order to remove processing strain generated by the processing applied up to the lapping process. After the etching step, a mirror surface silicon wafer is manufactured through a mirror polishing step (step 108 in FIG. 2) in which one or both of the main surfaces are mirror polished.

  The etching apparatus 10 of the present invention is used in the etching process in the above-described silicon wafer manufacturing method, and its operation will be described below.

  First, the temperature of the etching solution in the etching tank 14A is set to a predetermined optimum liquid temperature according to the processing conditions of the silicon wafer W to be processed. Next, for example, the silicon wafer W that has undergone the lapping process of FIG. 2 is immersed in the hot water tank 12 </ b> A via the loader unit 20 to perform a heating process. In the hot water tank 12A, the silicon wafer W is heated to substantially the same temperature as the set temperature of the etching solution.

  The silicon wafer W heated to the predetermined temperature is transported to the next etching tank 14A by the transport robot 24, immersed therein, and subjected to an etching process. By this etching process, the silicon wafer W is removed from both surfaces by a predetermined amount of etching allowance.

  The etched silicon wafer W is transported to the next rinsing tank 16A by the transport robot 24 and cleaned in the rinsing tank 16A. Further, the cleaned silicon wafer W is transported to the next drying unit 18 by the transport robot 24 and dried by the drying unit 18. The dried silicon wafer W is discharged from the etching apparatus 10 via the unloader unit 22.

  Next, the silicon wafer etching method of the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing an example of the order of steps of the silicon wafer etching method of the present invention. First, the temperature of the etching solution used in the etching process is set to a predetermined temperature. Next, the silicon wafer that has undergone the lapping process is heated to approximately the same temperature as the etching solution in the heating process (step 200 in FIG. 3). Etching is performed by immersing the silicon wafer heated to the predetermined temperature in an etching solution heated to the predetermined temperature for a predetermined time (step 202 in FIG. 3). By this etching process, the silicon wafer is removed from both surfaces of the silicon wafer by a predetermined amount of etching allowance. The etched silicon wafer is cleaned by rinsing (step 204 in FIG. 3), and the cleaned silicon wafer is further dried in a drying process (step 206 in FIG. 3).

  The etching solution used in the etching method of the present invention is not particularly limited as long as silicon can be etched, but an alkaline etching solution containing an alkali component is preferable in terms of etching ability. The alkali component is preferably an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.

  Moreover, as an etching solution used in the present invention, the above-mentioned alkali component may be used alone, or a plurality of alkali components may be mixed and used. For example, sodium hydroxide and potassium hydroxide may be mixed and used, or sodium hydroxide may be used alone.

  Here, the temperature of the etching solution is not particularly limited as long as etching is possible, but it is preferably 65 ° C. to 85 ° C. If the temperature of the etching solution is less than 65 ° C., the etching rate is slow, which is not preferable from the viewpoint of productivity. Also, if the temperature of the etchant exceeds 85 ° C, there are equipment problems such as the risk of boiling the etchant and the risk of handling chemicals, and if the temperature exceeds 85 ° C, the reaction rate increases rapidly. This is not preferable because problems such as the point that selective chemical etching property becomes remarkable occur.

  Further, the etching allowance of the silicon wafer etched away by the etching method of the present invention is a minimum thickness that can remove the processing strain received in the process before the etching process (slicing process, chamfering process, lapping process, grinding process). Although there is no particular limitation as long as there is variation in the penetration depth of the processing strain that needs to be removed, the thickness is within the range of 10 μm to 40 μm on both sides of the silicon wafer.

  The removal thickness of the silicon wafer is controlled mainly by adjusting the time (etching time) in which the silicon wafer is immersed in the etching solution. Conversely, the immersion time of the silicon wafer is set in accordance with the relationship between the etching allowance and the concentration of the etching solution, and is preferably set to a time during which the etching allowance falls within the range of 10 μm to 40 μm. Usually, the etching time is about 5 to 20 minutes.

  In the present invention, when a silicon wafer is immersed in an etching solution, a conventional method such as rocking the wafer so that the silicon wafer is uniformly etched or applying ultrasonic waves to the etching solution is used in the present invention. Is also optional.

  The eye of the method of the present invention is that when etching is performed under the above-described etching conditions, the temperature of the silicon wafer immersed in the etching solution is previously heated to substantially the same temperature as the etching solution.

  Usually, in an etching apparatus, an etching solution is set at a constant temperature, for example, 80 ° C., and this temperature is controlled by a heater or the like. The temperature control is generally performed by PID (proportional integral derivative) control or the like.

  The temperature of the etchant is reduced by natural radiation, or a silicon wafer having a temperature much lower than the etchant temperature (for example, about 20 ° C. to 25 ° C.) is introduced into the etchant. The liquid temperature decreases. When the liquid temperature of such an etching solution decreases, the output of a heater or the like works to try to keep the liquid temperature at a constant temperature.

  The problem here is that the temperature of the etching solution is lowered by introducing the silicon wafer, but the temperature of the etching solution immediately rises due to reaction heat. At this time, the heater output is increased, and the reaction heat generated by the reaction between the silicon wafer and the etching solution is added, so that the temperature of the etching solution rises rapidly and tends to be higher than the set temperature of the etching solution.

  In general, the factor of PID control is often set by auto-tuning in a state where a product or the like is not put in, and the temperature control often does not follow a rapid temperature change when the product is put in. In addition, PID control may be set in consideration of the state when the product is entered. However, when the number of processed products changes, the temperature control may be similarly unstable.

  In the method of the present invention, before etching, the temperature of the silicon wafer is heated to substantially the same temperature as the liquid temperature of the etchant, and then etched with an etchant (preferably an alkaline etchant). Thus, the temperature change of the etching solution can be stably controlled even by PID control set by auto-tuning.

  In the above description, the temperature control of the etching solution in the method of the present invention is based on PID control. However, the same description can be applied to other control means, for example, only proportional control or ON / OFF control. Is.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated, it cannot be overemphasized that these Examples are shown by illustration and should not be interpreted limitedly.

(Example 1)
First, a p-type silicon single crystal ingot having a diameter of 300 mm and a resistivity of about 10 Ω · cm was obtained by the Czochralski method. The obtained ingot was cut with a wire saw by a process as shown in FIG. 2 and the peripheral part was chamfered, and then lapped to obtain a wrapped silicon wafer.

  As the etching solution, a 51.0% sodium hydroxide aqueous solution was prepared. The aqueous sodium hydroxide solution was filled in an etching tank and heated to 80 ° C.

  After the temperature increase, the 20 lapped silicon wafers subjected to the lapping process were etched in an etching tank maintained at 80 ° C. At this time, using an etching apparatus as shown in FIG. 1, a hot water bath at 80 ° C. was prepared in the previous stage, immersed in the hot water bath for about 2 minutes, and then put into an etching bath set at 80 ° C. FIG. 4 shows the temperature change and heater power change at that time.

  The silicon wafer was etched for 11 minutes, and the etching allowance of the subsequent silicon wafer was measured. This etching allowance was calculated by measuring the thickness before and after etching. The etching allowance of the silicon wafer at this time was 20.0 μm on average on both sides.

  Similarly, a plurality of batches of silicon wafers were continuously processed, but the variation in the etching allowance after the etching of these silicon wafers was within about 20.0 ± 0.6 μm.

(Comparative Example 1)
The 20 lapped silicon wafers subjected to the lapping process were directly put into an etching solution in an etching tank maintained at 80 ° C. Changes in temperature and heater power at this time are shown in FIG. The temperature of the silicon wafer before charging was about 25 ° C. By introducing a low temperature silicon wafer, the temperature of the etching solution rapidly decreases from 80 ° C., and the heater output also changes abruptly. After that, even after 80 ° C., the heater output worked by PID control and did not immediately return to the set value of 80 ° C. During this time, a predetermined etching time (11 minutes) was completed, and the etching allowance of the silicon wafer was an average of 20.9 μm on both sides.

  Similarly, a plurality of batches of silicon wafers were processed successively, but the variation in etching allowance after etching of these silicon wafers was as large as about 20.5 ± 1.5 μm.

(Example 2)
As the etching solution, an aqueous sodium hydroxide solution having a concentration of 48.0% was prepared. The aqueous sodium hydroxide solution was filled in the etching tank and heated to 65 ° C.

  After the temperature increase, the wrapped silicon wafer after the lapping was performed in an etching bath maintained at 65 ° C. was etched. At this time, using an etching apparatus as shown in FIG. 1, a 60 ° C. hot water tank was prepared in the previous stage, immersed in the hot water tank for about 2 minutes, and then poured into an etching tank set at 65 ° C. The silicon wafer was etched for an arbitrary time.

  The etching process was performed by changing the number of processed sheets in one batch to 1, 5, 10, 15, and 20. Etching allowance at this time is as follows: 1 sheet processing: 20.2 μm, 5 sheet processing: average 20.4 μm, 10 sheet processing: average 20.3 μm, 15 sheet processing: average 20.5 μm, 20 sheet processing : The average was 20.6 μm, and even when the number of processed batches was different, it was within the range of 20.2 μm to 20.6 μm, and the variation was small.

(Comparative Example 2)
The wrapped silicon wafer after the lapping process was directly put into an etching solution in an etching tank maintained at 65 ° C. The temperature of the silicon wafer before charging was about 25 ° C. As in Example 2, the etching process was performed by changing the number of processed batches to 1, 5, 10, 15, and 20.

  Etching allowance at this time is 1 sheet processing: 19.0 μm, 5 sheets processing: average 19.8 μm, 10 sheets processing: average 20.6 μm, 15 sheets processing: average 20.0 μm, 20 sheets processing: The average was 20.9 μm, and the range of 19.0 μm to 20.9 μm and the variation became large.

  In this way, due to the difference in the number of wafers when a low-temperature silicon wafer is put into the etching solution, the temperature of the etching solution becomes unstable due to the difference in the temperature change of the etching solution and the variation in the heater output. Affected.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has the same configuration as the technical idea described in the scope of claims of the present invention, and any device that exhibits the same function and effect is the present invention. Are included in the technical scope.

  In particular, in the description of the present invention described above, as a scene of etching a silicon wafer, the description has been mainly focused on etching to remove processing distortion after the lapping process, but the present invention is not limited to such etching, The semiconductor silicon wafer is not particularly limited as long as it can be etched. For example, when etching the silicon wafer surface in a device process, etching a thin film on a silicon wafer, or etching other silicon wafers, the present invention is not limited to any etching as long as it is required to reduce the variation in the finished thickness. It is also applicable to and has an effect.

It is a side schematic explanatory drawing which shows one Embodiment of the etching apparatus of this invention. It is a flowchart which shows the manufacturing process of a general silicon wafer. It is a flowchart which shows an example of the process order of the etching method of this invention. It is the figure which showed the relationship between the liquid temperature of the etching liquid in Example 1, and a heater output. It is the figure which showed the relationship between the liquid temperature of the etching liquid in Comparative Example 1, and a heater output.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10: Etching apparatus, 12: Heating part, 12A: Hot water tank, 14: Etching part, 14A: Etching tank, 16: Rinse part, 16A: Rinse tank, 18: Drying part, 18A: Drying means, 20: Loader part 22: Unloader part, 24: Transfer robot, W: Silicon wafer.

Claims (8)

  In the etching method in which etching is performed by immersing a silicon wafer in an etching solution, the silicon wafer is tempered so that the temperature of the silicon wafer becomes a temperature within a predetermined temperature range from the temperature of the etching solution before performing the etching. A method of etching a silicon wafer, characterized by heating and immersing the heated silicon wafer in the etching solution.   2. The silicon wafer etching method according to claim 1, wherein the silicon wafer is heated so that the temperature of the silicon wafer is within ± 5 ° C. of the temperature of the etching solution.   3. The method for etching a silicon wafer according to claim 1, wherein a temperature of the etching solution is in a range of 65 [deg.] C. to 85 [deg.] C.   4. The silicon wafer according to claim 1, wherein the etching is performed so that a removal thickness of the silicon wafer by the etching is within a range of 10 to 40 μm on both surfaces of the silicon wafer. 5. Etching method.   5. The method for etching a silicon wafer according to claim 1, wherein the etching solution is an alkaline aqueous solution containing an alkali component.   6. The method for etching a silicon wafer according to claim 5, wherein the concentration of the alkali component is in the range of 48.0 to 55.0% by weight.   7. The method for etching a silicon wafer according to claim 5, wherein the alkali component is sodium hydroxide.   In an etching apparatus for performing etching by immersing a silicon wafer in an etching solution, the temperature of the silicon wafer is set to a temperature within a predetermined temperature range from the liquid temperature of the etching solution before the etching tank for performing the etching. An apparatus for etching a silicon wafer, comprising a heating means for heating the silicon wafer.