TW411508B - Method of forming trench- bottom gate oxide with improved thickness control - Google Patents

Abstract

This invention is about a method of forming trench- bottom gate oxide with controlled thickness. A photoresist unit is put on the area where the trench-bottom gate oxide will reside. This photoresist unit is used as a mask in the succeeding etching procedure to protect the gate oxide, making the effective control of its thickness possible.

Description

411508

This case relates to a method for forming a gate oxide layer at the bottom of a trench, and more particularly to a method that can be used to form the thickness of the gate oxide layer formed at the bottom of the trench. Due to the increase of the accumulation degree, in the traditional process, the method of forming an interlayer oxide layer at the bottom of the trench will cause an etching step due to improper process steps. Easy to control and the gate oxide thickness at the bottom of the trench cannot reach the required value, etc. problem. The problems caused by traditional processes are explained below. Please refer to the first diagrams (a) to (c), which are flow diagrams of the traditional method for forming a gate oxide layer at the bottom of a trench. As shown in Fig. (A), a silicon substrate 1 is first provided, and a pad oxide layer 101 is formed on the silicon substrate 丨, and then a silicon nitride layer is formed on the pad oxide layer 101.丨 〇2. Then, a part of the silicon nitride layer 102, the pad oxide layer 丨 and the silicon substrate 1 are removed by lithography and #etching techniques to form a trench 103. Secondly, as shown in the first figure (b), an oxide layer 10 is deposited in the trench 103 by chemical vapor deposition (CVD). Finally, the oxide layer in the trench 丨 03 is etched by wet etching to form a gate oxide layer 106 at the bottom of the trench as shown in the first figure (c). From the above description, it is known that the conventional method uses traditional chemical vapor deposition to deposit the oxide layer 104, but is limited by the energy limit of the traditional chemical vapor deposition system. For trenches with an aspect ratio greater than 2, a trench such as The first layer (b) shown in FIG. 1 covers the oxide layer 104 of the trench 10 as a whole, and inevitably forms a void 105 (void) in the oxide layer 104. However, the formation of this void 105 will not be easy to control for subsequent etching steps. Because when the etching is performed, once it is etched to the gap 105, it will quickly pass through the gap 105 and further etched to the area where the gate is about to form the gate, so it is difficult for Liang to control the side etching at the same time. Trench and forward etch rate

Page 4 411508 5. Description of the invention (2) Stripping of the pad under the silicon layer of the oxide layer on both sides of the thickness of the oxidized layer on both sides. The problem layer of control is finished. In addition, the thickness is heavily affected by the oxide layer. Therefore, the main purpose of the present chemical layer is to avoid full removal and reach at the same time. Shi Shui recognizes the bottom gate oxygen excavation u S that is required for β 1 It will also cause the bottom of the trench to be etched to a predetermined value before-τ Λ 1, ^ ⑴. Nitriding 101 on both sides of the trench is also etched, and then the charge, # & ^ k becomes the silicon nitride layer 102 to the rear. Sequence of process steps. The invention, in view of the lack of known technology, was the spirit of perseverance and perseverance, and finally created the method of forming a trench in this case. The following is a brief description of the case. The purpose of the present invention is to provide a method for forming gate bottom gate oxide which is not easy due to the formation of a gap (v oid). Another purpose of this case is to provide a method for forming a gate bottom gate oxide layer. Gate oxide thickness at the bottom of the trench. The method provided in this case includes the following steps: (a) providing a substrate, and forming a pad oxide layer on the substrate; (b) forming a silicon nitride layer on the pad oxide layer; (c) Removing the silicon nitride layer, the pad oxide layer and the substrate to form a trench, (d) forming an oxide layer on the bottom and two sidewalls of the trench and extending to cover the surface of the silicon nitride layer on both sides of the trench (E) forming a photoresist unit on the oxide layer at the bottom of the trench, (f) removing the portion of the oxide layer not covered by the photoresist unit, and (g) removing the photoresist unit to Define the gate oxide. According to the idea of the present case, the substrate is a silicon substrate. According to the idea of the case, the method of forming the ditch was formed by lithography and surname engraving techniques. The oxide layer is made of high density plasma chemical gas.

Page 5 5. Description of the invention (3) Formed by phase deposition technology. According to the idea of this case, the step (e) further includes the following steps: (el) covering a photoresist layer on the oxide layer 'and (e2) partially removing the photoresist layer for the oxidation at the bottom of the trench The photoresist unit is formed on a layer. Wherein, the step (e2) is formed by removing the photoresist layer outside the bottom of the trench by microwave technology. The thickness of the photoresist unit is about the same as that of the oxide layer formed on both sides of the trench. According to the idea of the present case, the step (f) is formed by removing the portion of the oxide layer not covered by the photoresist unit by using the photoresist unit as a mask. Wherein, the oxide layer is removed by wet etching. Of course, the best one is that the wet etching is a buffer oxide etching solution of a mixed solution of hydrofluoric acid (HF) and helium fluoride (NILF). According to the idea of the present case, the gate oxide layer preferably has a thickness of 2000 angstroms. The depth of the trench from the surface of the substrate is preferably 1.5 to 3.0 mm, and the diameter is preferably 0.5 / zm. This case further provides a method for forming an open-oxide layer at the bottom of a trench. The method includes the following steps: (a) forming a trench on a semiconductor substrate, and (b) forming an oxide layer on the bottom and two sidewalls of the trench. (C) forming a photoresist unit on the oxide layer at the bottom of the trench; (d) removing the portion of the oxide layer not covered by the photoresist unit, and (e) removing the photoresist unit to define The gate oxide layer. According to the idea of the present case, the step (a) further includes the following steps: (al) forming a pad oxide layer on the semiconductor substrate, (a2) forming a silicon nitride layer on the pad oxide layer, and (A3) Partially remove the nitride

411508 5. Description of the invention (4) The silicon layer, the oxide layer, and the semiconductor substrate form the trench. In this case, you can gain a deeper understanding through the following diagrams and detailed descriptions: Figures (a) to (C) are schematic flowcharts of the traditional method for forming a gate oxide layer at the bottom of a trench; and the first figure (a) to (F) is a schematic flowchart of a preferred embodiment of a method for forming a gate oxide layer at the bottom of a trench according to the present case. The main components and their symbols in the above figure are explained as follows:

1 * IY 102 104 106 201 201 203 205 206 Dream substrate nitride nitride layer oxide layer gate oxide layer pad oxide layer trench photoresistor gate oxide layer 1 〇1: pad oxide layer 103: trench 1 〇5: Gap 2: Silicon substrate 2 〇 2: Silicon nitride layer 2 0 4: Oxidation layer 2051 · Photoresist unit pulls two β donors-a method of forming a polar oxide layer between trench bottoms' Using this, This method can avoid problems such as the formation of gaps and the difficulty in controlling the etching. Moreover, it is easier to control the thickness of the gate oxide layer formed at the bottom of the trench. See "(a) to ({) '" in the second figure, which is a preferred embodiment of the method for forming an electrical emulsified layer in a trench according to the present case. Process flow diagram. The detailed steps of the method in this case are described below. As shown in Fig. 2 (a), the silicon substrate 2 is first provided, and the silicon substrate is provided here.

411508 5. Description of the invention (5) A pad rolling layer 201 is formed on the material 2, and then a silicon nitride layer 202 is formed on the pad oxide layer 201. Then, a part of the silicon nitride layer 202, the pad oxide layer 201 and the silicon substrate 2 are removed by lithography and etching techniques to form a trench 203. Wherein, the depth of the trench 203 measured from the surface of the Shixi substrate 1 is about 1.5 to 3.0 μm, and the diameter is about 0.5 μm. Secondly, as shown in the second figure (b), an oxide layer 2 0 4 is deposited on the bottom and two side walls of the trench 20 by high-density plasma chemical vapor deposition and extends to cover both sides of the trench. The surface of the silicon nitride layer 002. As the high-density plasma chemical vapor deposition system can control the formation of an oxide layer 204 covering the surface of the trench as shown in the second figure (b), the formation of an oxide layer 204 in the trench can be controlled, thereby preventing the formation of gaps in the trench. Moreover, the thickness of the oxide layer can be controlled by a high-density plasma chemical vapor deposition system at different deposition speeds, making it easier to control the thickness of the gate to be formed in subsequent steps. Of course, at this time, the thickness of the oxide layer formed at the bottom of the trench is equal to the thickness of the gate oxide layer to be formed, which is about 2000 Angstroms, I′1, and a non-resistive layer ZUb is formed on the oxide layer 04. Then, a part of the photoresist layer is removed by microwave technology to form a photoresist element 2051 on the oxide layer 204 at the bottom of the trench 203 as shown in the second figure (1). Then, as shown in the second figure, using the photoresist unit 2051 as a mask, the portion of the vaporization layer 204 that is not covered by the photoresist unit 2051 is removed by wet etching. . The wet-type remaining etching method used in the Benthodon + tea example uses a buffer oxide layer etching solution A,,-our horse, this buffer rolling layer # 刻 液 一

It is generally composed of a mixed solution of fluoric acid (HF) and fluorinated fluorinated ^ μH paper U F). In addition, in order to control the thickness of the gate oxide layer formed at the bottom of the trench, the thickness of the gate oxide layer is low.

$ 8Page 5 'Invention Description (6) ----------- The thickness of the photoresist unit 2 0 5 1 is controlled to be about the same as the thickness of the middle layer, so that it can be etched ^' formed on both sides of the trench When the oxidized layer is completely removed, the oxide layer between the gaps on the two sides of the trench can be rolled at the same time from the thickness of the photoresist unit 20 51 and the trench 203 in the forward direction. ° At the end of the gate formed by the engraving, the oxide layer on the bottom of the trench is moved as shown in the second figure (f): ^ The photoresist unit, and at this time ... was previously formed on the bottom of the trench = required The thickness of the oxide layer is about the same as the thickness of the exposed layer. Therefore, the oxidation of the bottom of the photoresist sheet can be easily used to avoid the area during the step. As a result, the thickness of the gate oxide layer to be formed can be more effectively controlled. Therefore, 'from the above description and illustration, the f method provided in this case can not only avoid the formation of holes and solve the etching. The problem is not easy to control, and the silicon nitride can be prevented from being etched by the pad oxide layer during the etching step. Furthermore, the thickness of the gate gasification layer formed at the bottom of the trench can be controlled. The method provided in this case has real industrial value. "This case can be modified by people who are familiar with the art, but they can be modified as desired by the scope of patent application.

Claims (1)

(g) Remove the photoresist unit to define the gate. 2. The method for forming a gate at the bottom of a trench as described in item 1 of the scope of patent application, wherein the substrate is a silicon substrate. 3 _ The method for forming a gate at the bottom of a trench as described in item 1 of the scope of the patent application, wherein the method for forming the trench in the step (C) is formed by lithography and etching techniques. 4 · The method for forming a gate at the bottom of a trench as described in item 1 of the scope of the patent application ', wherein the oxide layer is formed by a high-density plasma chemical vapor deposition technique. 5. The method for forming a gate at the bottom of a trench according to item 1 of the scope of patent application, wherein step (e) further includes the following steps: (el) covering a photoresist layer on the oxide layer; and (e 2) The photoresist layer is partially removed so that the oxide layer at the bottom of the trench is formed into the photoresist unit. Page 10 411508 6. Application for patent scope 6 · The method for forming a gate at the bottom of a trench as described in item 5 of the scope of patent application, wherein the step (e 2) is to remove the light outside the bottom of the trench by microwave technology Barrier layer. '7. The method for forming a gate at the bottom of a trench as described in item 6 of the scope of the patent application, wherein the thickness of the photoresist unit is approximately equal to the thickness of the oxide layer formed on both sides of the trench. 8. The method for forming a gate at the bottom of a trench as described in item 1 of the scope of patent application, wherein step (f) is to use the photoresist unit as a screen and remove the oxide layer that is not covered by the photoresist unit. Partly formed. 9. The method for forming a gate at the bottom of a trench as described in item 8 of the scope of patent application, wherein the oxide layer is removed by a wet etching method. 10. The method for forming a gate at the bottom of a trench as described in item 9 of the scope of the patent application, wherein the wet etching is a buffer oxide etching solution using a mixed solution of hydrofluoric acid (HF) and ammonia fluoride (NH4F) as Of it. 1 1. The method for forming a gate at the bottom of a trench as described in item 1 of the scope of patent application, wherein the thickness of the gate is 2000 angstroms. 1 2. The method for forming a gate at the bottom of a trench as described in item 1 of the scope of the patent application, wherein the depth of the trench from the surface of the substrate is 1.5 to 3.0 / z m, and the diameter is 0.5 μm. 1 3. A method for forming a gate electrode at the bottom of a trench, the method including at least the following steps: (a) forming a trench on a semiconductor substrate; (b) forming an oxide layer on the bottom of the trench and on two sidewalls; c) forming a photoresist unit on the oxide layer at the bottom of the trench; Page 11 411508__ VI. Scope of patent application (d) Remove the part of the oxide layer that is not covered by the photoresist unit; and the bottom gate of the square gate. The ditch pole is in the shape of a gate, so the meaning of item 13 is to block the light, and to remove it, please remove e) Γν ο oxygen (a 塾 step into the shape), its cal method is listed below The material guide of the upper substrate should be the layered substrate guide and the electrode layer, and the upper layer of the oxide layer is oxidized, the pad is oxygenated, and the layer is siliconized, and the nitrogen is removed. The nitrogen is removed. The forming material 2 3 Page 12