JP5967710B2 - End point detection method of plasma etching - Google Patents

Description

  The present invention relates to a method for detecting an end point of plasma etching, and more particularly to a method for detecting an end point of plasma etching for forming a hole, a column, a groove or the like having a high aspect ratio in a silicon layer.

As a method for forming a vertical hole structure or a column structure with a high aspect ratio on a silicon substrate (Si substrate) by plasma etching, an etching process for etching the Si substrate using SF ₆ gas as an etching gas, and a hole formed in the etching process. A Bosch process is known in which a protective film forming step for forming a protective film on the surface is repeated. In Patent Document 1, the Si substrate etching by the Bosch process reaches the lower layer film (end point) in a work in which a lower layer film made of a material that is harder to etch than the Si substrate is provided under the Si substrate. A method for detecting the end point of plasma etching for detecting this is described. In this end point detection method, etching products (SiF ₄ and its dissociation species SiF _x (x = 0 to 3)) generated when etching the Si substrate react with the plasma (mainly electrons in the plasma). The intensity of light generated by doing so is detected. When the etching is performed up to the lower layer film, the amount of the etching product generated is reduced, so that the emission intensity by the etching product is reduced. The end point of etching is detected from the change in the emission intensity.

On the other hand, in order to increase the etching rate in the Bosch process, it is preferable to increase the supply amount of SF ₆ gas to generate a large amount of radicals and ions. However, when a large amount of such radicals and ions are generated, the movement of the etching product is hindered and it is difficult to reach the plasma. Therefore, the light emission intensity due to the etching product is lowered, and the end point detection accuracy is lowered. In addition, when a vertical hole structure or a column structure with a high aspect ratio is formed by plasma etching, it is necessary to increase the perpendicularity of ions in the plasma and make it incident on the Si substrate, and the distance between the high-frequency coil and the Si substrate is larger than usual. Is also performed (for example, FIG. 1 of Patent Document 1). In such a case, the etching products generated in the vicinity of the silicon substrate cannot react with each other unless they move a long distance to the plasma generated in the vicinity of the high frequency coil. When produced in large quantities, the amount of etching products that can reach the plasma is very small.
Si So, in the above end point detection method, an etching process, and a large amount supply step of supplying a large amount of SF ₆ gas, is divided into two steps of the small-amount supply step of supplying a small amount of SF ₆ gas, in the amount supply step After the etching of the layer is performed at a high speed, the end point of the etching is detected while the etching of the Si layer is performed at a low speed in the small amount supply step. When the supply amount of SF ₆ gas is small, radicals and etching products are generated little, but their movement is not hindered, so that strong luminescence can be observed.

JP 2008-053678 A

“Bosch Process”, [online], Samco Corporation, [searched on September 28, 2012], Internet <URL: http: //www.samco.co.jp/products/tech/03_bosch.php>

  In the end point detection method of Patent Document 1, a small amount supply step is provided to detect the end point.

  On the other hand, Non-Patent Document 1 discloses an isotropic etching process for isotropically etching a Si layer with an F-based radical, and a protective film for forming a protective film on the surface of the hole formed in the isotropic etching process. A Bosch process consisting of three steps is described in which a formation step and a bottom etching step for selectively removing a protective film formed on the bottom surface of the hole by irradiation with F-based ions are repeated. In the Bosch process described in Non-Patent Document 1, since the protective film on the bottom surface is selectively removed in the bottom surface etching step, the bottom surface side is easily etched in the isotropic etching step. Thereby, it becomes possible to form a vertical hole structure or a column structure having higher perpendicularity to the substrate surface than the Bosch process described in Patent Document 1.

  When the end point detection method described in Patent Document 1 is applied to the Bosch process of Non-Patent Document 1, a small amount supply step for performing end point detection is provided in the isotropic etching process for etching the Si layer. It will be. This is not preferable because the etching rate of the entire process is reduced.

  The present invention can detect the end point of etching without reducing the etching rate of the whole plasma etching in plasma etching having three steps of an isotropic etching step, a protective film forming step, and a bottom surface etching step. Is to provide a method.

The end point detection method of plasma etching according to the present invention made to solve the above problems,
An isotropic etching step for performing isotropic etching on the etching target layer of a workpiece having a layer to be etched and a lower layer film provided on the lower surface of the layer to be etched, and a portion etched in the isotropic etching step ions and the protective film forming step, while a higher degree of vacuum than the isotropic etching process, the protective film which the protective film is formed on the formed surface sac Chi bottom surface of the surface forming a protective film In the plasma etching having a bottom surface etching process selectively removed by irradiation of
The intensity of the light generated by the etching products formed by etching the etching target layer at the bottom surface etching step reacts with the plasma was measured in the bottom etching step, the light measured at the bottom surface etching step It is characterized by determining whether or not the etching reaches the lower layer film from the change in intensity.

  Note that “lower” here is for convenience, and does not mean “lower” as the direction of gravity. The lower layer film is a layer made of a material different from that of the layer to be etched. For the lower layer film, it is desirable to use a material in which the etching product is less likely to be generated than the etching target layer.

The plasma etching end point detection method according to the present invention is characterized in that the etching end point detection based on a change in plasma emission intensity is performed in the bottom surface etching step. The bottom surface etching process is performed in a state where the supply amount of SF ₆ gas is smaller and the degree of vacuum is higher than in the isotropic etching process so that the incidence of ions is not hindered by other floating particles such as radicals. Therefore, after the bottom protective film is removed, an etching product generated by ions etching the etching target layer easily reaches the plasma, and light emission is likely to occur due to the reaction between the plasma and the etching product. Therefore, it is possible to observe the change in the light emission intensity of the plasma with high sensitivity without reducing the etching rate in the bottom surface etching step.

In the plasma etching end point detection method according to the present invention, in order to observe the change in the emission intensity of the plasma in the bottom surface etching step where the supply amount of SF ₆ gas is originally lower than that of the isotropic etching step and the degree of vacuum is high, Can be detected with high accuracy. Further, since it is not necessary to reduce the supply amount of SF ₆ gas for end point detection, the etching rate of the entire plasma etching does not decrease.

The principal part block diagram of the inductively coupled reactive ion etching apparatus used in order to apply one Example of the plasma etching end point detection method concerning this invention. Schematic diagram for explaining the isotropic etching process of the Bosch process (a), schematic diagram for explaining the protective film forming process (b), schematic diagram for explaining the bottom surface etching process (c), finally FIG. 4D is a schematic diagram showing the shape of the etching hole obtained in (d). The graph which shows the time change of the emitted light intensity in the end point detection method of the plasma etching of a present Example. The table | surface which shows the etching conditions in the end point detection method of the plasma etching of a present Example and Comparative Examples 1-4. The graph which shows the time change of the emitted light intensity in the end point detection method of the plasma etching of the comparative example 1. FIG. The graph which shows the time change of the emitted light intensity in the end point detection method of the plasma etching of the comparative example 2. FIG. The graph which shows the time change of the emitted light intensity in the end point detection method of the plasma etching of the comparative example 3. FIG. The graph which shows the time change of the emitted light intensity in the end point detection method of the plasma etching of the comparative example 4. The table | surface which shows the etching arrival time and emission intensity ratio of the end point detection method of the plasma etching of a present Example and Comparative Examples 1-4.

  Hereinafter, an embodiment of a plasma etching method according to the present invention will be described with reference to the drawings. FIG. 1 shows the essentials of an inductively coupled reactive ion etching apparatus (ICP-RIE, product name: RIE-800iPB, manufactured by Samco Corporation, hereinafter referred to as “plasma etching apparatus”) used in the plasma etching method of this embodiment. FIG.

The plasma etching apparatus of FIG. 1 has a reaction chamber 10 for performing plasma etching. A flat lower electrode (cathode) 12 on which a work 11 is placed is provided at the bottom of the reaction chamber 10, and the lower electrode 12 is connected to a first high-frequency power source 18 via a blocking capacitor 16 and a first matching unit 17. It is connected to the. The lower electrode 12 is provided with a cooling gas passage (not shown) through which a cooling gas (He gas) for keeping the workpiece 11 at a predetermined temperature is circulated. Further, on the side wall of the reaction chamber 10, a gas introduction port 14 for introducing an etching gas or a film forming gas for forming a protective film, a gas exhaust port 15 for exhausting the inside of the reaction chamber 10 by a vacuum pump 26, and the inside of the reaction chamber 10 Is provided with an observation window 27 made of quartz glass or the like. A first gas supply source 22 and a second gas supply source 23 are connected to the gas inlet 14 via a first mass flow controller (MFC) 24 and a second MFC 25, respectively. SF ₆ gas is introduced into the reaction chamber 10 from the first gas supply source 22 as an etching gas, and C ₄ F ₈ gas is introduced into the reaction chamber 10 from the second gas supply source 23 as a film forming gas. In addition, a light detection unit 28 that detects the emission intensity of light having a predetermined wavelength in the plasma observed from the observation window 27 is provided outside the reaction chamber 10 with the observation window 27 interposed therebetween. A spiral coil 19 is provided above the reaction chamber 10 via a dielectric window 13. One end of the coil 19 is connected to the second high-frequency power source 21 via the second matching unit 20, and the other end is directly connected to the second high-frequency power source 21. The plasma etching apparatus of FIG. 1 also has a control unit 29 that controls each part of the apparatus. The control unit 29 operates the first high-frequency power source 18, the second high-frequency power source 21, the vacuum pump, the first MFC, and the second MFC based on preset conditions and the detection signal acquired from the light detection unit 28. Thereby, an isotropic etching process, a protective film forming process, and a bottom surface etching process described below are sequentially performed.

Hereinafter, the method for detecting the end point of plasma etching according to this embodiment will be described. In this embodiment, a case where a vertical hole structure is formed in a Si substrate by a Bosch process having three processes, an isotropic etching process, a protective film forming process, and a bottom etching process, will be described with reference to FIGS. . Note that a SiO ₂ layer (lower layer film) 31 is formed on the lower surface of a Si substrate (etched layer) 30 to be etched on the workpiece 11 placed on the lower electrode 12 in the reaction chamber 10. A mask 32 is formed on the upper surface of the Si substrate 30 (FIG. 2).

The control unit 29 first evacuates the reaction chamber 10 by operating the vacuum pump 26 to reduce the internal pressure of the reaction chamber 10 to 10 Pa. Subsequently, the first MFC 24 is operated, and 1000 sccm of SF ₆ gas is introduced into the reaction chamber 10 from the first gas supply source 22. At this time as well, evacuation by the vacuum pump 26 is continued, and the internal pressure of the reaction chamber 10 is adjusted to maintain 10 Pa. Next, the control unit 29 causes the high-frequency power 3000 W having a frequency of 13.56 MHz to be input from the second high-frequency power source 21 to the coil 19. With the above operation, plasma is generated inside the reaction chamber 10. Thereafter, at least until the etching of the Si substrate 30 is completed, the high-frequency power is continuously supplied from the second high-frequency power source 21 to the coil 19.

[Isotropic etching process]
In this step, the control unit 29 introduces SF ₆ gas having a flow rate of 1000 sccm from the first gas supply source 22 into the reaction chamber 10 by the first MFC 24 and adjusts the pressure in the reaction chamber 10 to 10 Pa by the vacuum pump 26. . In this step, C ₄ F ₈ gas is not introduced from the second gas supply source 23 into the reaction chamber 10. Further, no high frequency power is supplied from the first high frequency power source 18 to the lower electrode 12.

The SF ₆ gas introduced into the reaction chamber 10 reacts with the plasma, and radicals, ions, and electrons are generated from the SF ₆ gas. Of these products, F-based radicals contribute to the etching in this step. The F radicals reach the Si substrate 30 of the workpiece 11 through the holes formed in the mask 32 and react with Si. Thereby, Si is etched from the Si substrate 30. At this time, SiF _x (x = 1 to 4) is generated as an etching product. Since the F radicals are isotropically incident on the Si substrate 30 by diffusion, the etching holes 33 formed in this step are etched not only in the vertical direction but also in the horizontal direction (FIG. 2A). ).

[Protective film formation process]
In this step, the control unit 29 stops the SF ₆ gas from the first gas supply source 22 to the reaction chamber 10 by the first MFC 24 and the C ₄ F ₈ gas having a flow rate of 400 sccm from the second gas supply source 23 by the second MFC 25 . It introduces into the reaction chamber 10. At the same time, the pressure in the reaction chamber 10 is adjusted to 4 Pa by the vacuum pump 26. Also in this step, high-frequency power is not supplied from the first high-frequency power source 18 to the lower electrode 12.

The C ₄ F ₈ gas introduced into the reaction chamber 10 is decomposed by plasma, and a CF polymer is polymerized. This is deposited in the etching hole 33 formed in the isotropic etching process, and a protective film 34 is formed on the side wall and the bottom surface of the etching hole 33 (FIG. 2B).

[Bottom etching process]
In this step, the control unit 29 stops the supply of C ₄ F ₈ gas from the second gas supply source 23 to the reaction chamber 10 by the second MFC 25, and SF ₆ having a flow rate of 400 sccm from the first gas supply source 22 by the first MFC 24. Gas is introduced into the reaction chamber 10. At the same time, the pressure in the reaction chamber 10 is kept at 4 Pa by the vacuum pump 26. Further, 100 W of high frequency power having a frequency of 13.56 MHz is input to the lower electrode 12 from the first high frequency power supply 18.

The SF ₆ gas introduced into the reaction chamber 10 reacts with the plasma, and radicals, ions, and electrons are generated from the SF ₆ gas as in the isotropic etching process. In this state, when high-frequency power is supplied to the lower electrode 12 from the first high-frequency power supply 18, electrons in the plasma jump into the lower electrode 12 following changes in the electric field formed by the high frequency. Since the blocking capacitor 16 is connected to the lower electrode 12, a negative bias voltage (self-bias) due to the electrons is applied to the lower electrode 12, and ions are accelerated toward the lower electrode 12. In this step, these ions contribute to etching.

  The ions are linearly accelerated toward the lower electrode 12 and are incident on the bottom surface of the etching hole 33. The protective film 34 formed on the bottom surface of the etching hole 33 is sputtered and etched by the incidence of ions. In this step, ions are incident on the Si substrate 30 with directionality, so that the protective film 34 is selectively removed from the bottom surface (FIG. 2 (c)).

By repeating the above three steps, an etching hole 33 having a high aspect ratio can be formed in the Si substrate 30 in the Bosch process (FIG. 2D). The plasma etching end point detection method of this embodiment measures the change in the intensity of light emission caused by the reaction between plasma and SiF _x (x = 1 to 4) in the bottom surface etching process among these three processes. Thus, the end point of etching is detected.

As described above, in the bottom surface etching step, the protective film 34 formed on the bottom surface of the etching hole 33 is removed by the incidence of ions. When the protective film 34 formed on the bottom surface is removed, the ions sputter the exposed Si. The sputtered Si reacts with F-based radicals generated from SF ₆ gas together with ions, and SiF _x (x = 1 to 4) is generated as in the isotropic etching process. In the plasma etching end point detection method of the present embodiment, the light detection unit 28 acquires the emission intensity of the wavelength at which light emission by SiF _x occurs from the start to the end of the bottom surface etching process, and the data is transmitted to the control unit. 29. During the bottom surface etching process, the control unit 29 continues to determine whether or not the light emission intensity is greater than or equal to a preset threshold value.

In the plasma etching end point detection method of the present embodiment, the reason for detecting the end point of etching in the bottom surface etching step is as follows. As described above, in the bottom surface etching process, the flow rate of SF ₆ gas and the pressure in the reaction chamber 10 are lower than those in the isotropic etching process. This is because if the amount of other floating particles such as radicals other than ions is large, the ions collide with them and do not enter the bottom surface of the etching hole 33 linearly. If it does so, the anisotropy of the etching of the protective film 34 will fall, and the aspect ratio of the final etching hole 33 will also fall in connection with it. Therefore, the bottom surface etching process is originally performed in a state where the supply amount of SF ₆ gas is small and the pressure is low (that is, the degree of vacuum is high) as compared with the isotropic etching process.

When the degree of vacuum in the reaction chamber 10 is high, SiF _x generated by ions etching Si after removing the protective film 34 on the bottom surface easily reaches the plasma. Therefore, in the bottom surface etching process, light emission is likely to occur due to the reaction between plasma and SiF _x . Therefore, in the bottom surface etching process, if the light emission at the wavelength at which light emission is caused by the reaction between the plasma and SiF _x is observed, the etching end point can be accurately detected without reducing the speed of any of the above three processes. It becomes.

FIG. 3 is a graph plotting the maximum light emission intensity in each bottom surface etching step in the plasma etching end point detection method of this example. This data was obtained by repeating the isotropic etching process for 4 seconds, the protective film forming process for 2 seconds, and the bottom surface etching process for 2 seconds in order (ie, 8 seconds per cycle). Further, the workpiece 11 used was a Si substrate 30 of 450 μm and a SiO ₂ layer of 1 μm. The setting conditions in each step of this example are summarized in the table of FIG. In the table, ICP corresponds to the high-frequency power input from the second high-frequency power source 21, and BIAS corresponds to the high-frequency power input from the first high-frequency power source 18.

As shown in the graph of FIG. 3, it can be seen that in the plasma etching end point detection method of this example, the change in emission intensity can be clearly distinguished even in the bottom surface etching process. In this data, the etching is etching the emission intensity after reaching the SiO ₂ layer becomes luminous intensity ratio of about 1.2 before reaching the SiO ₂ layer. Therefore, for example, if the threshold value for detecting the end point is set to about 1.1 times the emission intensity before the etching reaches the SiO ₂ layer, the end point of the etching can be detected with high accuracy.

As comparative examples, the results of plasma etching and end point detection under the conditions shown in the table of FIG. 4 are shown in FIGS. The table of FIG. 9 shows the emission intensity ratio of this example and Comparative Examples 1 to 4 and the time required for the etching to reach the SiO ₂ layer.

  Comparative Examples 1 and 2 in FIG. 4 are cases in which plasma etching is repeatedly performed in the order of an isotropic etching process, an endpoint detection etching process, and a protective film forming process. In Comparative Examples 1 and 2, the bottom surface etching process is not performed. Further, Comparative Examples 3 and 4 in FIG. 4 are cases in which plasma etching is repeatedly performed in the order of an isotropic etching process, an endpoint detection etching process, a protective film forming process, and a bottom surface etching process. In Comparative Examples 1 to 4, the emission intensity of plasma is measured in the etching process for detecting the end point (the process surrounded by a thick line). Moreover, in order to compare the etching arrival time in the plasma etching of an Example and Comparative Examples 1-4, the time required per cycle was 8 seconds in any example.

In Comparative Example 1, the isotropic etching step and the end point detection etching step are performed under the same conditions. In this case, as shown in FIG. 5, the emission intensity hardly changed, and it was not possible to detect whether or not the etching reached the SiO ₂ layer. This is presumably because the degree of vacuum in the etching process for detecting the end point was low, and the etching product could hardly reach the plasma.

Comparative Example 2 is a case where the supply amount of SF ₆ gas in the etching process for detecting the end point is reduced as compared with that in the isotropic etching process. This Comparative Example 2 corresponds to the Bosch process described in Patent Document 1 in which the etching process and the protective film forming process are provided with a small amount supply process for end point detection. In this example, a change in emission intensity was observed as shown in FIG. The emission intensity ratio in this example was about 1.1, which was lower than the emission intensity ratio of this example. The etching arrival time to the SiO ₂ layer was almost the same as in this example.

  In Comparative Example 3 and Comparative Example 4, the end point is detected in the isotropic etching step of the Bosch process described in Non-Patent Document 1, which includes the three steps of the isotropic etching step, the protective film forming step, and the bottom surface etching step. Corresponding to those with a small amount of supply process. In Comparative Example 3, the end point detection etching step is performed under the same condition as that of the bottom surface etching step of the present embodiment (high frequency power is supplied from the first high frequency power supply 18). This is a case where no high frequency power is supplied from the first high frequency power source 18 in the etching process for detecting the end point.

In Comparative Examples 3 and 4 as well, a change in emission intensity was observed as shown in FIGS . 7 and 8 , but the emission intensity ratio was about 1.1, which was lower than the emission intensity ratio of this example. Further, the etching arrival time to the SiO ₂ layer was 230 seconds longer in Comparative Example 3 and 240 seconds longer in Comparative Example 4 than in this example (FIG. 9) .

In Comparative Examples 3 and 4, the time required to reach the SiO ₂ layer was longer than in this example because the gas flow rate was reduced because a part of the Si etching process was used for light emission observation. Further, the emission intensity ratio of this example was higher than that of Comparative Example 3 where the conditions at the time of end point detection were the same. In the plasma etching end point detection method of this example, before the bottom surface etching step for performing end point detection, Since there is a protective film forming step with a low gas flow rate and a low degree of vacuum as in the bottom surface etching step, the amount of suspended particles that inhibit the etching product from reaching the plasma is smaller than in Comparative Example 3. It is thought that.

DESCRIPTION OF SYMBOLS 10 ... Reaction chamber 11 ... Work 12 ... Lower electrode 13 ... Dielectric window 14 ... Gas introduction port 15 ... Gas exhaust port 16 ... Blocking capacitor 17 ... 1st matching device 18 ... 1st high frequency power supply 19 ... Coil 20 ... 2nd matching 21 ... second high frequency power supply 22 ... first gas supply source 23 ... second gas supply source 24 ... first MFC
25 ... 2nd MFC
26 ... Vacuum pump 27 ... Observation window 28 ... Light detection unit 29 ... Control unit 30 ... Si substrate (etched layer)
31 ... SiO ₂ layer (lower layer)
32 ... Mask 33 ... Etching hole 34 ... Protective film

Claims (1)

An isotropic etching step for performing isotropic etching on the etching target layer of a workpiece having a layer to be etched and a lower layer film provided on the lower surface of the layer to be etched, and a portion etched in the isotropic etching step ions and the protective film forming step, while a higher degree of vacuum than the isotropic etching process, the protective film which the protective film is formed on the formed surface sac Chi bottom surface of the surface forming a protective film In the plasma etching having a bottom surface etching process selectively removed by irradiation of
Intensity of said intensity of the light generated by the at the bottom surface etching step etching products formed by etching the etching target layer from reacting with the plasma was measured in the bottom etching step, the light measured at the bottom surface etching step A method for detecting an end point of etching in plasma etching, wherein it is determined whether or not etching has reached the lower layer film from the change in.

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