TW505978B - Residue-free bi-layer lithographic process - Google Patents

Abstract

A residue-free bi-layer lithographic process utilizes an anisotropic O2/SO2 plasma etching process as a dry development process, and further utilizes a fluorocarbon gas/oxygen plasma as a de-residue process to remove residues created during the dry etching process. In the present invention, a first resist layer is coated over a substrate and baked later. Then, a second resist layer is coated over the first resist layer. The second resist layer is imagewise exposed and developed to expose a predetermined area within the first resist layer. An anisotropic O2/SO2 plasma dry etching process is performed to remove the predetermined area within the first resist layer. Finally, a de-residue process is performed to remove residues created during the dry etching process.

Description

505978,, ΎΦ Fei ._ " j: Mx90122203_Car Moon Day—Modification__ V. Description of the Invention (1) Field of the Invention The present invention provides a bi-layer lithography method, especially a residue-free ( residue free). Background note

Lithography and etching are the most important steps in the semiconductor manufacturing process to form the structures required for contact windows, metal interconnects, and semiconductor components. The conventional single-layer photoresist is usually used in a sub-micron process with a line width of about 0.25 microns (V m), and the surface of the silicon wafer substrate must be flat and not easily reflective, because when a single-layer photoresist is applied, When placed on a substrate that is easily reflective and locally uneven, photoresist with different thicknesses cannot be easily lithographed and etched to obtain the line width required for the process, and may cause notching effects.

In the trend of shrinking semiconductor device manufacturing and increasing the accumulated capacity, multi-layer photoresists can be used instead of single-layer photoresists to improve the resolution of lithography. Multilayer photoresists are currently used on optically absorbing organic polymers, such as a flat antireflective layer, and spin-coating-an imaging layer on the surface of a flat antireflective layer, using spin coating The cloth method can improve the problem of uneven thickness of the imaging layer and control its critical dimension (CD) well. In addition, the use of a thinner imaging layer can improve the focal length tolerance of lithography.

505978 V. Description of the invention (2) One (focu = latitude). However, the disadvantages of using a photolithography process with multiple photoresists are that the process is more complicated and it is prone to the problem of residues. Please refer to FIGS. 1 to 3, which are schematic diagrams of a conventional double-layer lithography method. First, as shown in FIG. 1, a flattened photoresist layer 14 is coated on a partially uneven silicon substrate 12 on a semiconductor wafer 10, and soft baking is performed for several seconds. After soft baking, the solvent content in the photoresist layer η will decrease and the thickness of the photoresist layer 14 will also decrease. Then, a thin silicon-containing photoresist layer 16 ′ or other material containing a silicon-containing photoresist layer 16 ′ can be formed on the photoresist layer 14 after being etched by an oxygen (0 2) plasma. Thing. The thickness of the planarized photoresist layer 4 is about 500 nm, and the thickness of the silicon-containing photoresist layer 16 is about 2 3 5 nm. The flattened photoresist layer 14 has an absorption of South, and can suppress the reflection of the Shixi substrate 12. As shown in FIG. 2, the photoresist layer 16 containing silicon is exposed through a photomask 15 ′ to transfer the pattern on the photomask 15 to the photoresist layer 16 containing silicon. At this time, the exposed silicon-containing photoresist layer 16 has an exposed area 11 and an unexposed area 13. As shown in FIG. 3, a dry development is performed, for example, plasma etch, and unexposed area 13 is etched to transfer the pattern of the photoresist-containing layer 16 to the photoresist layer 1 4 To form a pattern with openings 18.

505978 V. Description of the invention (3) It may cause the lateral etching of the photoresist layer and cause a critical dimension loss; (2) Etching with a plasma plasma may cause spontaneous etching and etching of the photoresist layer Selectivity; (3) The ion bombardment energy of plasma etching is related to the oxygen atomic degree, which is difficult to control. C) It is known that in order to protect the side wall of the etched layer from excessive side etching, there are CS and CS〆Η 2 plasma engraving are used to replace the 0 2 plasma remaining etch, but the disadvantage is that too many residues (residua 1) 1 9 are generated on the side. SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a bi-layer lithography method which can well control the critical dimension (CD) and residue free, so as to improve the resolution of the lithography in the semiconductor process. In order to achieve the above purpose, the preferred embodiment of the present invention includes the following steps: (1) coating a first photoresist layer on a substrate, (2) baking the first resist layer (3) coating a The second photoresist layer is on the surface of the first photoresist layer, and (ii) develops the second photoresist layer, (5) uses an anisotropic 〇2 / S02 to cross the A-12 gas, and etches the first in the predetermined area. A photoresist layer, and (: de-res i dua 1) procedure, using a mountain line special / 0 2 plasma, at a pre, radio frequency electrode work compound | under pressure, Removal of dry etch and pre-projections within a predetermined time.

505978 V. Description of the invention (4) The method of the present invention combines the #isotropic 〇2 / S〇2 plasma dry development step, and adds a dry residue removal process, which only needs to obfuscate the mixed gas of compound gas and oxygen. The residue left on the slurry impacting the opening for several seconds can be used to remove the residue generated in the double-layer photoresist lithography. The method of the present invention can solve the problem of the residue in the conventional dry development process and the short rhyme time. It will not cause the semiconductor process to be lowered at all. Detailed description of the invention 4 Refer to FIG. 4 to FIG. 6, which are not intended for the double-layer lithography method of the present invention. As shown in FIG. 4 'the double layer of the method of the present invention The photoresist structure 21 is composed of a photoresist layer 24 and a silicon negative photoresist (siHcon-containing negative resist (SNR)) layer 26. The silicon negative photoresist layer 26 contains a weight percent of about 2% To 12% of the element of the stone eve. The method of forming the double-layered photoresist structure 21 is to first apply a photoresist layer (planarized photoresist layer) 24 on the surface of a partially uneven stone eve substrate 22 on a semiconductor wafer 20 . Then with temperature ^ ^, proceed Bake for about 60 seconds. After soft baking, the solvent content in the photoresist layer 2 4 will decrease and the thickness will also decrease. Then, the photoresist layer 24 will be coated with _thickness, ', spoon from 0 · 4 to 0 · 5 micron silicon-containing photoresist 2 6 where the 'flattened photoresist layer 2 4 may also be an organic planarized underlayer, such as an anti-reflection layer with high absorption, ^ To suppress the silicon substrate 2 2 reflection.

505978

The layered region is shorter as shown in Figure 5, and then passes through a photomask Γ 248nm (such as KrF laser) UV ^ I Hexianbu) at a wavelength of 26. At this time, the exposed barrier [n: domain 29] and an unexposed area 27 after exposure. However, an ultraviolet light having a wavelength of 248 nm and a wavelength of j 广,, short, eXCimer laser radiation, or a short-wavelength light source is also suitable for the present invention.

As shown in FIG. 6, a dry development process is then performed, using an anisotropic plasma as an etching gas, and transferring the silicon-containing photoresist layer 26 pattern to the photoresist layer at room temperature. In 24, a pattern having an opening 28 is formed. 〇2 / s〇2 Plasma etching has good anisotropy, and can suppress the lateral etching of the photoresist layer 24 under the silicon-containing photoresist layer 26. Sodium oxide composition in the etching gas accounts for about 50% to 100%. When the so concentration increases, both the vertical etch rate and the lateral etch rate of the etched layer decrease, and the optimal ratio of s0 is about 80%. Among them, the power of the upper electrode of the dry development process is about 150 to 600 watts. The power of the electrode at the radio frequency (RF) is about 30 to 2000 watts. The oxygen flow rate is about 50 to 300 sccm ( standard cubic cent i me per per minute), the sulfur dioxide flow is about 50 to 300 seem, and the pressure is about 5 to i 00 millitorr. Although the use of 0 2 / so 2 plasma etching can improve the critical dimension control problem

Page 9 505978 V. Description of the invention (6) 2: ^::: f Engraved edge of the silicon-containing photoresist layer 26 of the mask: Two residues " Do not. Therefore, after the method of the present invention is completed, the electro-hydraulic dry method is completed. After that, the dry-type residue removal procedure must be performed immediately to remove a small amount of remaining residue. This dry-type residue removal procedure is performed at room temperature. If the electrode is used at a predetermined radio frequency, the electrode power and Under a predetermined pressure, the residue generated during the dry plasma etching process is removed within a predetermined time, and the production of the double-layer lithography method without residue is completed. Among them, the radio frequency (RF) lower electrode power of the dry residue removal process is between 5 and 30 watts, and the upper electrode power is between about 15 and 6 watts, and its pressure is about 5 to 100 ¾ Torr ( fflTrr), the predetermined time is less than 60 seconds, and the fluorocarbon gas can be CF 4, c 疋 6, CHF3, CH2F2, CHF, CF3H, C2F2H2, C2F5H, and C2F3H3, and the gas flow rate is about 30 Between 150 and 150 sccm, and the oxygen flow rate is between 10 and 50 sccm. The dry development process in the present invention uses 〇2 / SO 2 plasma etching. Due to the dissociation of SO molecules, sulfur atoms and oxygen atoms are A competitive adsorption reaction occurs on the surface of the etching layer. At room temperature, sulfur atoms do not react spontaneously with carbon atoms. Only when the temperature is higher than 15 ° C, carbon disulfide (CS 〇) is generated spontaneously, so sulfur atoms can block the photoresist layer 24 in the etching process. Spontaneous etching of the sidewalls, sulfur atoms slow down the on-i nduced chemical etching rate at the bottom of the opening 28, reducing the lateral #etching rate. Then in order to remove a small amount of remaining residue

Page 10 505978 V. Description of the invention (7), and then use the etching gas composed of fluorocarbon gas and 0 to carry out the process of removing residues, it only takes a few seconds, containing fluorine atoms, carbon atoms and oxygen atoms The etching gas will react with the residue, thereby achieving the effect of removing the residue. Compared with the conventional technology, the present invention is characterized by replacing the conventional oxygen plasma or CS2 / Η 2 plasma etching with 0 2 / sulfur dioxide (S0 2) plasma etching with good anisotropy, and increasing In a dry-type residue removal process, only a mixed gas of fluorocarbon gas and oxygen plasma is required to strike the remaining residue at the opening for a few seconds, and the residue generated in the double-layer photoresist lithography can be removed. In this way, the 0 2 / S0 dry development technology can be truly applied to mass production. The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the scope of the patent application for the present invention shall fall within the scope of the invention patent.

Page 11 505978 Simple illustration of the diagrams Simple illustration of the diagrams Figures 1 to 3 are schematic diagrams of the conventional double-layer lithography method. FIG. 4 to FIG. 6 are schematic diagrams of a double-layer lithography method according to the present invention. Symbol description

Page 12 10 Semiconductor wafer 11 Exposed area 12 Silicon substrate 13 Unexposed area 14 Photoresist layer (bottom layer) 15 Photomask 16 Silicon-containing photoresist layer 18 Slit 19 Residue 20 Semiconductor wafer 21 Double-layer photoresist structure 22 Silicon substrate 24 Photoresist layer 26 Silicon-containing photoresist layer 27 Unexposed area 28 On Π 29 Exposed area

Claims (2)

505978 6. Scope of patent application 1. A residue free bilayer lithography method, the method includes the following steps: coating a first photoresist layer on a substrate; baking Baking the first photoresist layer; coating a second photoresist layer on the surface of the first photoresist layer; exposing and developing the second photoresist layer to expose the first photoresist layer in a predetermined area ; Performing a dry type engraving, using an anisotropic (anis 0tr 0pic) oxygen (02) / sulfur dioxide (SO0 plasma) as an etching gas to etch the first photoresist layer in the predetermined area; And performing a dry de-residue procedure using a fluorocarbon gas / oxygen plasma at a predetermined radio frequency (RF) electrode power and a predetermined pressure for a predetermined time Residues generated during the dry etching process are removed. 2. The method according to item 1 of the patent application scope, wherein the second photoresist layer is a photoresist-containing layer. 3. The method according to item 2 of the patent application scope square , Wherein the second photoresist layer contains a silicon element with a weight percentage of about 2% -12%. 4. If the method of the third item of the patent application is applied, wherein the thickness of the second photoresist layer is about 0.4 to 0. . 5 micro i. P. 13 / younger month / Z s repair, supplement M 90122203 said in the correction of mi special? Nm where the exposure of the second light 5. As in the method of applying for the scope of the first item of the patent application, the resist layer uses a 2 4 8 nm UV light. 6. The method according to item 1 of the patent application, wherein the exposing the second photoresist layer uses a 193 nm light. 7. The method according to item 1 of the patent application range, wherein the electrode power at the predetermined radio frequency (RF) of the dry-type residue removal procedure is between about 5-30 Watts (W a 11 s). 8. The method according to item 1 of the scope of patent application, wherein the predetermined pressure of the dry residue removal process is between about 5-100 millitorr (m T 0 r r). 9. The method according to item 1 of the patent application range, wherein the predetermined time is less than 60 seconds. 10. The method of claim 1 in the scope of patent application, wherein the fluorocarbon gas in the dry residue removal process comprises CF4, C2F6, CHF3, CH2F2, CHF, CF3H, C2F2H2, C2F5H, and C2F3H3. 11. A residue-free image transfer method, comprising the following steps: forming a bilayer film on a substrate, wherein the bilayer film is composed of a planarized bottom layer and a silicon-containing photoresist layer And the silicon-containing photoresist layer and the bottom layer have different Page 14 505978 90122203 Correction VI. Lili Absorptivity; Expose the broken photoresist layer to form an exposed area in the chopped photoresist layer; develop the stone-containing photoresist layer so that Forming a developing region in the stone-containing photoresist layer; performing a dry etching, anisotropic dry etching the underlying layer of the developing region; and after the anisotropic dry etching, using a fluorocarbon gas plasma, Residues generated during the anisotropic dry etching process are removed. 1 2. The method according to item 11 of the scope of patent application, wherein the dry etching uses a 0 2 / S 0 2 plasma. 13. The method according to item 12 of the patent application range, wherein the 02 / S02 plasma is formed under the following conditions: 1. Power of the upper electrode (13.56MHz): 150-600 watts; 2. Radio frequency (RF) lower electrode power: 30 to 200 watts; 3 · oxygen flow: 50-3 0 0 sccm; 4. S0 crazy amount: 50-300 sccm; 5 · pressure: 5-10 0 millitorr (mTorr ). 1 4. The method according to item 11 of the scope of patent application, wherein the fluorocarbon gas plasma is formed under the following conditions: 1. Power of the upper electrode (13.56MHz): 1 50-600 watts; 2. Radio frequency Page 15 505978 j_4) case: Thailand, 90122203 _ year, month and month amendment _ 6, the scope of patent application (RF) electrode power: 5-30 Watts; 3. CF ammonia body flow: 30-150 sccm; 4 · Oxygen flow: 10-50 0 s c c m; 5. Pressure: 5-10 0 millitorr (mTorr). 15. The method according to item 11 of the patent application scope, wherein the bottom layer is an anti-reflection layer. 16. The method according to item 11 of the scope of patent application, wherein the silicon-containing photoresist layer contains a silicon element in an amount of about 6% to 8% by weight. 1 7. The method according to item 11 of the scope of patent application, wherein the thickness of the silicon-containing photoresist layer is about 0.4 to 0.5 microns. 18. The method according to item 11 of the scope of patent application, wherein the fluorocarbon gas includes CF4, C2F6, CHF3, CH2F2, CHF, CF3H, C2F2H2, C2F5H, and C 2F 3H 3. Page 16