Plasma processing method and plasma processing apparatus

Abstract

The present invention provides a plasma processing method which is capable of achieving the effects of (1) reduction of a copper layer, (2) high-speed ashing of a photoresist and (3) hydrophilization of the inner surface of a via during plasma processing of a substrate for electronic devices, in said plasma processing a semiconductor substrate that has a copper layer in the surface being etched with use of a photoresist and being subjected to plating. A plasma processing method for plating of a substrate for electronic devices according to the present invention is characterized by comprising: (a) a step in which a substrate for electronic devices such as a semiconductor substrate, a lead frame or the like is arranged in a processing chamber; (b) a step in which a starting material gas that is composed of hydrogen and water vapor, and is obtained from an apparatus that electrolyzes water is supplied to the processing chamber; and (c) a step in which plasma processing is performed on the substrate for electronic devices by exciting the starting material gas in the processing chamber into a plasma.

Description

Plasma processing method and plasma processing apparatus

[0001] The present invention relates to a plasma processing method and apparatus for cleaning the surfaces of substrates for electronic devices such as semiconductor substrates and lead frames.

[0002] With the advancement of the information society, semiconductor packages are becoming more sophisticated, functional, and smaller. Although flip-chip mounting technology allows semiconductor chips to be connected at high density, microbumps using copper (Cu) posts are widely used to meet electrical performance requirements, increasing I / O counts, and rising gold prices.

[0003] Microbumps are often formed as shown in Figures 1(a) to 1(f) (Non-Patent Document 1). First, a photoresist 13 is applied to a substrate 11 (Figure 1(a)) covered with a copper layer 12, and a via (opening) 14 is formed in the wiring portion (Figure 1(b)). At this point, a pretreatment is performed with plasma 15 to clean the inside and surrounding area of ​​the via 14 (Figure 1(c)). Then, the via 14 is filled with copper 16 by plating (Figure 1(d)). After that, the photoresist 13 is removed (Figure 1(e)), and the copper layer 12 on the substrate 11 is removed (Figure 1(f)).

[0004] JP 06-029254 JP 2018-098353 JP 2015-160192

[0005] "Application of Aqua Plasma(R) to Microbumps", samco NOW Vol. 111, October 2020, Samco Inc.

[0006] When forming copper microbumps, cleaning of the vias is required to achieve the following effects: (1) preventing or reducing oxidation of the copper layer at the bottom (on the substrate), (2) ashing photoresist residue, and (3) making the inner surface of the via hydrophilic to facilitate penetration of the plating solution. In conventional semiconductor substrate processing using plasma (e.g., Patent Document 1), hydrogen plasma processing in a specific chamber was effective in (1) preventing or reducing oxidation of the copper layer, but was insufficient in (2) ashing photoresist residue and (3) making the inner surface of the via hydrophilic.

[0007] The effects of (1) to (3) (and (2) achieving a sufficient ashing rate) are required not only for the process of forming microbumps, but also for the pretreatment of etching a semiconductor substrate having a copper layer on its surface using a photoresist and then plating it. Furthermore, in the conventional mounting technology that connects the lead portion (lead frame) and the electrode portion (hereinafter referred to as the metal portion) of the semiconductor substrate with a metal wire, it is also necessary to prevent or reduce oxidation of the lead portion and the electrode portion.

[0008] The present invention has been made to solve such problems of the prior art, and its object is to provide a plasma processing method that can obtain the effects (1) to (3) described above when processing such semiconductor substrates and substrates for electronic devices that include metal parts, lead parts, etc.

[0009] The present invention provides a plasma processing method for a substrate for an electronic device, which has been made to solve the above-mentioned problems, and is characterized by comprising the steps of: a) placing a substrate for an electronic device in a processing chamber; b) supplying a raw material gas consisting of hydrogen and water vapor obtained from a water electrolysis device into the processing chamber; and c) subjecting the substrate for an electronic device to plasma processing by converting the raw material gas in the processing chamber into plasma.

[0010] Here, the electronic device substrate includes not only the semiconductor substrate but also its metal parts such as electrodes and peripheral lead parts such as lead frames. It is also desirable that the amount of water vapor in the source gas as a whole is equal to or greater than the saturated water content in the source gas. For example, at 27°C, this is approximately 3.3% pressure or more. Furthermore, a pressure of 10 to 40% pressure is desirable.

[0011] In addition, the present invention provides a plasma processing apparatus for plating substrates for electronic devices, which has been made to solve the above problems, and is characterized by comprising: a) a plasma processing chamber provided with a mounting table for the substrate for the electronic device to be processed; b) a water electrolysis device connected to the processing chamber, which is a supply source of raw material gas consisting of hydrogen and water vapor; and c) a plasma generation unit that converts the raw material gas introduced into the processing chamber into plasma.

[0012] The method of the present invention can reliably achieve the following effects in plasma treatment of substrates for electronic devices: (1) prevention or reduction of oxidation of the copper layer on the substrate, (2) rapid ashing of photoresist residue, and (3) hydrophilization of the surface, making it easier for the plating solution to penetrate into narrow spaces.

[0013] 1 is an explanatory diagram showing a procedure for forming microbumps; 2 is a diagram showing a sample set in which a copper oxide chip and a silicon chip are placed on a dummy substrate; 3 is a schematic diagram of a plasma processing apparatus used in a test conducted to confirm the effects of the present invention; 4 is an emission intensity graph showing the results of an emission spectroscopic analysis of plasma conducted during plasma processing; 5 is a table showing the contents of each test conducted to confirm the effects of the present invention; 6 is a table showing the results of test 1 and test 2; 7 is a table showing the results of test 3;

[0014] The methods and results of tests conducted to confirm the effects of the present invention will be described below with reference to the drawings.

[0015] [Samples] The following two types of samples were used in the test. (1) Copper oxide chip: A copper plate measuring 10 × 20 × 0.3 mm with the surface oxidized. The oxide layer was 40 nm thick. (2) Silicon chip: A silicon (Si) plate measuring 15 × 15 × 0.5 ± 0.025 mm with a photoresist (PR) applied to its surface. The PR was a Tokyo Ohka Kogyo THMR-IP3250 product baked at 110°C for 5 minutes, with a coating thickness of 1 μm. In Test 3, described below, these chips were placed on the following dummy substrate: (3) Dummy substrate: A pure copper plate measuring 200 × 150 × 0.3 mm. This substrate simulates a 300 mm (φ8) wafer. Figure 2 shows sample set 20, consisting of a copper oxide chip 22 and a silicon chip 23 mounted on a dummy substrate 21.

[0016] The plasma processing apparatus used was a parallel plate type plasma processing apparatus (PD-220) 30 manufactured by Samco Corporation. As shown in Figures 3(a) to 3(c), in this plasma processing apparatus 30, the lower electrode 32 was grounded, and the upper electrode 33 (with an area of ​​452 m) 2 ) was connected to a high-frequency power supply 34 (PE mode). The processing chamber 31 was connected to a vacuum pump (DRP) 35, which was then connected to a plasma gas source via a flow meter (FM) 36. Different plasma gas sources were used depending on the test. The details are shown in the table in Figure 5. The processing chamber 31 was made of metal (stainless steel).

[0017] The methods and results of each test are as follows: The methods are shown in FIG. 5, and the results are shown in FIGS.

[0018] <Test 1> In Test 1, as shown in Figure 3(a), an electrolyzer 37 was used as the plasma gas source. Using a high-pressure hydrogen cylinder as the plasma gas source would require installation and maintenance under the High-Pressure Gas Safety Act, so the present invention uses an electrolyzer 37. The electrolyzer 37 generates and outputs hydrogen by electrolyzing water, but at the same time, water (water vapor) is also output. Because water is output at nearly saturated water vapor pressure, it is contained in the output gas at approximately 3.3 pressure % at room temperature (27°C).

[0019] When generating hydrogen in the electrolyzer 37, pure water can be used as the raw material, as well as water containing a small amount of sodium hydroxide (NaOH). This allows for more efficient water electrolysis. However, when using water containing a small amount of sodium hydroxide, a raw material gas containing a trace amount of Na may be supplied to the processing chamber, potentially contaminating the interior of the processing chamber and the substrate surface with Na. For this reason, it is preferable to use pure water as the raw material, and in this respect, an electrolyzer equipped with a solid electrolyte cell is desirable.

[0020] The copper oxide chip 22 and the silicon chip 23 were placed on the lower electrode 32, and the processing chamber 31 was evacuated with the vacuum pump 35. Then, hydrogen containing water vapor was supplied from the electrolyzer 37 into the processing chamber 31, and the pressure was set to 5 Pa. At a flow rate of 20 SCCM, a plasma raw material gas (hydrogen and water vapor) was supplied, and high-frequency power was applied from the high-frequency power supply 34. The applied high-frequency power was 100 W, and the processing time was 3 minutes.

[0021] The results of optical emission spectroscopy of the plasma during processing are shown in Figure 4(a) (solid line). In addition to the presence of a high H (hydrogen) peak at 656 nm, the OH (hydroxyl radical) peak at 309 nm, which is due to water vapor, was observed to be twice as high as in Test 2 described below, and the O (oxygen) peak at 777 nm was observed to be 1.5 times higher than in Test 2 (Figures 4(b) and (c)). OH (hydroxyl radicals) contribute to improving the hydrophilicity of the surface, and O (oxygen) contributes to improving the ashing rate of PR.

[0022] After this plasma treatment, when the surface of the copper oxide chip 22 was observed, it was found that the copper oxide had been completely reduced and the pure copper surface was exposed (upper middle column of FIG. 6).

[0023] Next, the ashing rate was calculated by dividing the thickness (1 μm) of the photoresist (PR) on the surface of the silicon chip 23 by the processing time, resulting in 19 nm / min (middle column in Figure 6). Furthermore, the water contact angle of the surface (photoresist layer) of the silicon chip 23 after plasma processing was measured. A water contact angle of 90° or less is defined as hydrophilic, and a water contact angle of 10° or 5° or less is defined as superhydrophilic. The measurement results showed a water contact angle of 3°, indicating superhydrophilicity (bottom middle column in Figure 6).

[0024] In Test 2, instead of using an electrolyzer, a high-pressure hydrogen cylinder 38 containing high-purity hydrogen was used as the plasma gas source, as shown in Figure 3(b). The purity of the hydrogen supplied from the high-pressure hydrogen cylinder 38 was 99.9999% or higher.

[0025] As in Test 1, copper oxide chip 22 and silicon chip 23 were placed on lower electrode 32, and processing chamber 31 was evacuated with vacuum pump 35. High-purity hydrogen was then supplied from high-pressure hydrogen cylinder 38 into processing chamber 31, and high-frequency power was applied from high-frequency power supply 34 while plasma raw material gas (hydrogen) was flowed at a pressure of 5 Pa and a flow rate of 20 SCCM, as in Test 1. As in Test 1, the applied high-frequency power was 100 W, and the processing time was 3 minutes.

[0026] The results of optical emission spectroscopy of the plasma during processing are shown by the dashed line in Figure 4(a). No clear peaks were observed for OH at 309 nm or O at 777 nm, which are due to water vapor (Figures 4(b) and (c)).

[0027] After this plasma treatment, when the surface of the copper oxide chip 22 was observed, it was found that the copper oxide had been completely reduced and the pure copper surface was exposed (upper right column of FIG. 6).

[0028] In Test 2, the ashing rate was 6 nm / min (center of the right column in FIG. 6), and the water contact angle was 20° (bottom of the right column in FIG. 6).

[0029] 3(c), a hydrogen gas source and a water vapor source were used together as the plasma gas source, with the hydrogen gas source being an electrolyzer 37 with a water vapor trap device (H2O-TRAP) attached (electrolyzer 39 with H2O-TRAP) and the water vapor source being a thermal vaporization type water vapor generator 40. The flow rates of the hydrogen gas and water vapor were adjusted using flow meters 36a and 36b, respectively, and plasma treatment was performed while the mixture ratio of the two was changed in 10% increments from 0% to 100% water vapor.

[0030] In Test 3, in order to approximate the actual processing environment of the wafer, a copper oxide chip 22 and a silicon chip 23 were placed on a pure copper dummy substrate 21 as a sample set 20 and set on the lower electrode 32 as shown in Figure 2. The plasma processing conditions were the same as in Tests 1 and 2.

[0031] When the surface of the copper oxide chip 22 was observed after plasma treatment at hydrogen / water vapor mixture ratios of 100 / 0 to 0 / 100, as shown in the second row of Figure 7, the copper oxide on the surface was completely reduced and the pure copper surface was exposed under conditions of hydrogen / water vapor ratios of 100 / 0 to 60 / 40, but the surface was not completely reduced under conditions of hydrogen / water vapor ratios of 50 / 50 to 0 / 100 (the results for hydrogen / water vapor ratios of 40 / 60, 20 / 80, and 30 / 90 are omitted from Figure 7).

[0032] The ashing rate of the photoresist layer under each condition is shown in the third row of Figure 7. The ashing rate was slightly low when the hydrogen / water vapor ratio was 100 / 0, but the photoresist layer was removed at a sufficiently high rate when the hydrogen / water vapor ratio was 90 / 10 to 0 / 100.

[0033] The water contact angles of the photoresist layer after treatment under each condition are shown in the fourth row of Figure 7. Here too, when the hydrogen / water vapor ratio is 100 / 0, the water contact angle is somewhat large at 20°, but when the hydrogen / water vapor ratio is 90 / 10 to 0 / 100, the water contact angle is 5 to 3°, indicating superhydrophilicity.

[0034] Summary: Comparing Test 1, in which the plasma source gas was hydrogen and water vapor, with Test 2, in which only hydrogen was used (Figures 3(a) and 3(b) and Figure 5), we found no difference in the copper oxide reduction effect (Figure 6, second row). However, Test 1, which used hydrogen and water vapor as the source gas, achieved a higher photoresist layer removal rate (ashing rate) than Test 2, which used hydrogen only (Figure 6, third row). Furthermore, Test 1, which used hydrogen and water vapor as the source gas, achieved a high degree of hydrophilization of the photoresist layer surface (Figure 6, fourth row). These results demonstrate that plasma treatment using a source gas consisting of hydrogen and water as a pretreatment for etching a semiconductor substrate with a copper layer on its surface using photoresist followed by plating can (1) prevent or reduce oxidation of the copper layer, (2) ash photoresist residue, and (3) hydrophilize the photoresist layer surface, such as inside vias, to facilitate the penetration of plating solutions. Such plasma treatment is also effective when it is necessary to prevent or reduce oxidation of metal parts such as lead parts (lead frames) and electrodes in mounting technology that connects lead parts and electrode parts of a semiconductor substrate with metal wires.

[0035] When hydrogen and water vapor are used as source gases in plasma processing of substrates, the water vapor that inevitably gets mixed in with the hydrogen gas produced by the electrolyzer can be used as is by using an electrolyzer as in Test 1. When a high-pressure hydrogen cylinder is used as the hydrogen gas source, it is necessary to prepare the required facilities and assign qualified personnel in accordance with laws and regulations such as the High-Pressure Gas Safety Act, which presents a high practical hurdle, but using an electrolyzer makes it possible to avoid such problems.

[0036] When the source gas is hydrogen and water vapor, the water vapor ratio is preferably 10 to 40%, according to the results of Test 3. Thus, when the water vapor ratio in the source gas is 10% or more (more precisely, when the pressure is above 3.3%, which is the saturated vapor pressure of water), the hydrogen gas (including water vapor at saturated vapor pressure) generated by the electrolysis device described above is insufficient, so a water vapor generator separate from the hydrogen gas source must be prepared and the generated water vapor must be added.

[0037] The inventors have proposed a plasma treatment method in which a mixed gas of water vapor and oxygen or a mixed gas of oxygen and hydrogen is converted into plasma to reduce copper oxide or silver oxide (Patent Documents 2 and 3), but it is also possible to use an electrolysis device as a source of these mixed gases.

[0038] REFERENCE SIGNS LIST 11...Substrate 12...Copper layer 13...Photoresist 14...Via 15...Plasma 16...Copper 20...Sample set 21...Dummy substrate 22...Copper oxide chip 23...Silicon chip 30...Plasma processing apparatus 31...Processing chamber 32...Lower electrode 33...Upper electrode 34...High frequency power supply 35...Vacuum pump 36, 36a, 36b...Flow meter 37...Electrolyzer 38...High pressure hydrogen cylinder 39...Electrolyzer with water vapor trap device 40...Water vapor generator

Claims

1. a) placing an electronic device substrate within a process chamber; b) supplying a source gas consisting of hydrogen and water vapor obtained from a water electrolysis device to the treatment chamber; c) supplying water vapor into the processing chamber so that the mixture ratio of the source gas is hydrogen / water vapor=90 / 10 to 60 / 40; d) subjecting the electronic device substrate to a plasma treatment by converting the source gas in the treatment chamber into a plasma; 1. A plasma processing method for a substrate for an electronic device, comprising:

2. 2. The method for plasma processing a substrate for an electronic device according to claim 1, wherein the device for electrolyzing water does not include a water vapor trap device.

3. The plasma treatment method for a substrate for an electronic device as described in claim 1, characterized in that the substrate for an electronic device has a photoresist layer and a copper layer on a surface thereof.

4. a) a plasma processing chamber provided with a stage for placing a substrate for an electronic device to be processed; b) a water electrolysis device, which is connected to the treatment chamber and serves as a source of a raw gas comprising hydrogen and water vapor, and which does not include a water vapor trap device; c) a water vapor generator for supplying water vapor into the treatment chamber; d) a plasma generating unit that converts the gas introduced into the processing chamber into plasma; A plasma processing apparatus comprising:

5. The plasma processing apparatus of claim 4, further comprising a flow meter for adjusting the mixture ratio of hydrogen and water vapor in the gas introduced into the processing chamber.