CN103632949B - The forming method of the hot oxygen medium layer of the inter polysilicon of groove type double-layer grid MOS - Google Patents

Abstract

The invention discloses a method for forming a thermal oxygen dielectric layer between polysilicon of trench-type double-layer gate MOS, comprising the steps of: 1) growing a first nitride film; 2) trench etching; 3) growing a dielectric layer; 4) Growth of the first layer of polysilicon; 5) The first step of reverse etching of the first layer of polysilicon; 6) Photolithography of the first layer of polysilicon and second step of reverse etching, and removal of the trench sidewall dielectric above the first layer of polysilicon 7) After depositing the second nitride film, etch to expose the first layer of polysilicon; 8) Growing the thermal oxygen dielectric layer; 9) Removing the nitride film; 10) Growth of the gate oxide layer; 11) The second layer Polysilicon deposition and reverse etching; 12) Formation of base and source; 13) Formation of contact holes, metal and passivation layers. The invention can solve the problem that the thickness of the dielectric layer between the two layers of polysilicon is difficult to control, and improve the performance stability of the MOS device; at the same time, it can prevent the gate-source breakdown voltage from being weakened by the strong electric field generated at the two ends of the polysilicon tip.

Description

Formation method of thermal oxygen dielectric layer between polysilicon in trench type double-layer gate MOS

technical field

The invention relates to a method for forming a thermal oxygen dielectric layer in the field of semiconductors, in particular to a method for forming a thermal oxygen dielectric layer between polysilicon in a trench-type double-layer gate MOS.

Background technique

Among power devices, trench double-layer gate power MOS devices have the characteristics of high breakdown voltage, low on-resistance, high conversion efficiency and fast switching speed. Usually, the polysilicon electrode of the first layer is used as a shielding electrode and is short-circuited with the source or drawn out separately, and the polysilicon electrode of the second layer is used as a gate. The thickness of the oxide layer between the two polysilicon electrodes needs to be strictly controlled, otherwise leakage or lower breakdown voltage will occur.

At present, the preparation method of the oxide layer between two layers of polysilicon electrodes in the existing process is to grow a high-density plasma (HDP) oxide film after the first layer of polysilicon is etched back, and the grown HDP oxide film must be thick enough to Fill the trench (Trench), and then perform CMP (Chemical Mechanical Polishing), photolithography, HDP oxide film reverse etching, and finally leave 2500 Angstroms of HDP on the first layer of polysilicon as the dielectric layer between the two layers of polysilicon. Among them, the specific process is as follows:

1) Before trench etching, grow an oxide layer as a barrier layer, and then perform trench etching;

2) Dielectric layer growth in the trench;

3) The first layer of polysilicon growth;

4) The first step of reverse etching of the first layer of polysilicon;

5) The first layer of polysilicon photolithography and the second step of reverse etching;

6) High-density plasma (HDP) oxide film deposition;

7) HDP oxide film CMP (chemical mechanical polishing) to the remaining 3000 Angstroms;

8) Wet etching, so that 2500 Angstrom HDP oxide film remains on the first layer of polysilicon in the trench;

9) Growth of gate oxide layer;

10) The second layer of polysilicon deposition and reverse etching;

11) Form the base (BODY) and source (Source);

12) Form contact holes, metal and passivation layers.

Among them, the cross-sectional view of the cell (the original cell of MOSFET) in which an oxide layer is grown as a barrier layer before trench etching in the existing process is shown in Figure 1; the first layer of polysilicon in the existing process is etched twice The cross-sectional view of the cell area after etching and removing the sidewall oxide layer is shown in Figure 2; the cross-sectional view of the cell area after the growth of the HDP oxide film in the existing process is shown in Figure 3; the HDP oxide film in the existing process The cross-sectional view of the cell area after wet etching is shown in FIG. 4 .

For the existing process, when the second etching depth of the first layer of polysilicon is 1.15 μm below the silicon surface, the HDP silicon oxide deposition thickness is about 1.5 μm, and the HDP silicon oxide CMP grinding amount is about 1.2 μm. Due to the HDP oxide film growth thickness and The thickness of the CMP grinding is very large, so the residual film thickness after CMP fluctuates greatly. In addition, there are differences in the CMP polishing rate between different positions in the silicon wafer and among silicon wafers, which also leads to poor uniformity of the residual film thickness after CMP. The above two points lead to poor uniformity and stability of the thickness of the dielectric film between the two polycrystalline layers.

Since the residual thickness of the HDP oxide film after CMP fluctuates and fluctuates, it is difficult to control the residual thickness of the HDP oxide film after etching back, which will make the performance of the device very unstable. Therefore, it is necessary to solve the problem that the thickness of the dielectric layer between the two layers of polysilicon is difficult to control, so as to improve the performance stability of the trench type double-layer gate power MOS device.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for forming a thermal oxygen dielectric layer between polysilicon in a trench-type double-layer gate MOS. Through this method, the problem of difficulty in controlling the thickness of the dielectric layer between the two layers of polysilicon can be solved, and the stability of the performance of the MOS device can be improved; at the same time, the strong electric field generated at the two ends of the polysilicon tip can prevent the gate-source breakdown voltage from being weakened.

In order to solve the above-mentioned technical problems, the method for forming the thermal oxygen dielectric layer between the polysilicon in the trench type double-layer gate MOS of the present invention comprises steps:

1) On the silicon substrate, grow the first nitride film;

2) On the silicon substrate, trench etching is performed;

3) In the trench, grow a dielectric layer;

4) On the dielectric layer, grow the first layer of polysilicon;

5) Perform the first step of reverse etching on the first layer of polysilicon;

6) Perform photolithography and the second step of reverse etching on the first layer of polysilicon, and remove the trench sidewall dielectric layer above the first layer of polysilicon;

7) After depositing the second nitride film on the bottom and side walls of the trench and the surface of the silicon substrate, etch and remove the second nitride film at the bottom of the trench to expose the first layer of polysilicon;

8) On the first layer of polysilicon, grow a thermal oxygen dielectric layer;

9) removing the second nitride film on the side wall of the trench and the first and second nitride films on the surface of the silicon substrate;

10) Growth of gate oxide layer;

11) The second layer of polysilicon deposition and reverse etching;

12) Form the base (BODY) and source (Source);

13) Form contact holes, metal and passivation layers.

In the step 1), the method for growing the first nitride film includes: low-pressure chemical vapor deposition or plasma-enhanced chemical vapor deposition; the material of the first nitride film includes: silicon nitride; the thickness of the first nitride film It is 500-3000 Angstroms.

In the step 3), the dielectric layer is an oxide film with a thickness of 500-3000 angstroms; the growth method of the dielectric layer includes: thermal oxygen or low pressure chemical vapor deposition.

In the step 4), the method for growing the first layer of polysilicon includes: low pressure chemical vapor deposition; the thickness of the first layer of polysilicon is sufficient to fill the inside of the trench.

In the step 5), in the first step of reverse etching, until the silicon surface is etched.

In the step 6) of performing photolithography on the first layer of polysilicon and the second step of reverse etching, photoetching is performed on the first layer of polysilicon to protect the position where the source polysilicon needs to be connected, and the remaining position of the first layer of polysilicon The second step of polysilicon back etching is carried out until the desired depth below the silicon surface is etched.

In the step 7), the second nitride film deposition method includes: low pressure chemical vapor deposition or plasma enhanced chemical vapor deposition; the material of the second nitride film includes: silicon nitride; the second nitride film The thickness is 500-3000 Angstroms; the etching method is dry etching.

In the step 8), the method of growing the thermal oxygen medium layer is to grow the thermal oxygen medium layer by means of thermal oxygen; wherein, the process temperature in the thermal oxygen mode is higher than 950°C; the thickness of the thermal oxygen medium layer is 500- 3000 Angstroms.

In the step 9), the removal method includes: wet etching.

The present invention grows a layer of nitride layer before etching the trench, and retains it until the first layer of polysilicon electrode is etched below the silicon surface, grows a layer of nitride film on the surface of the groove, and then uses dry etching The principle of anisotropy forms the sidewall of silicon nitride and connects it with the silicon nitride layer previously retained on the surface of the silicon substrate to form a protective layer on the sidewall and top. Thermal oxidation is used to generate a thermal oxide layer on the polysilicon surface at the bottom of the polysilicon trench, and then the sidewall and top silicon nitride are removed to form a thermal oxygen dielectric layer between two layers of polysilicon in a trench-type double-layer gate MOS structure. Since the present invention utilizes the nitride film as the protective layer of the long two-layer inter-polysilicon heat-oxygen isolation dielectric layer, the process of forming the silicon oxide dielectric layer is greatly simplified compared with the existing process of forming the silicon oxide dielectric layer under the same isolation performance, and multiple HDP and CMP are omitted. High-cost process flow, and there is no risk of difficult control of HDP oxide film, which greatly simplifies the difficulty of process control, that is, the present invention solves the problem of difficult control of the thickness of the dielectric layer between two layers of polysilicon, and improves the stability of device performance. More importantly, because this method uses a thermal oxidation process as the dielectric layer, the shape of the underlying source polysilicon (the first layer of polysilicon) changes from a concave shape with sharp ends to a convex shape with round ends, thereby avoiding the The strong electric field generated at both ends of the polysilicon tip weakens the gate-source breakdown voltage.

Description of drawings

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

FIG. 1 is a cross-sectional view of a cell region in which an oxide layer is grown as a barrier layer before trench etching in the prior art;

Figure 2 is a cross-sectional view of the cell area after two-step reverse etching of the first layer of polysilicon and removal of the sidewall oxide layer in the prior art;

Fig. 3 is a cross-sectional view of the cell area after the growth of the HDP oxide film in the prior art;

Fig. 4 is a cross-sectional view of the cell area after wet etching of the HDP oxide film in the prior art;

Fig. 5 is a cross-sectional view of a cell region in which a layer of nitride layer is grown as a barrier layer before trench etching of the present invention;

Fig. 6 is a cross-sectional view of the cell area after two-step reverse etching of the first layer of polysilicon and removal of the sidewall oxide layer of the present invention;

Fig. 7 is a sectional view of the cell area after growing a nitride film of the present invention;

Fig. 8 is a cross-sectional view of the cell area where the sidewall nitride film protection layer is formed by etching in the present invention;

Fig. 9 is a cross-sectional view of the cell region after growing a thermal oxygen dielectric layer on the first layer of polysilicon in the present invention;

10 is a cross-sectional view of the cell region after removing the trench sidewall and the nitride film on the surface of the silicon substrate according to the present invention.

The reference signs in the figure are explained as follows:

1 is the silicon substrate, 2 is the oxide layer, 3 is the first nitride film, 4 is the dielectric layer, 5 is the first polysilicon layer, 6 is the second nitride film, and 7 is the thermal oxygen dielectric layer.

detailed description

The method for forming the thermal oxygen dielectric layer between the polysilicon in the trench type double-layer gate MOS of the present invention, its steps are as follows:

1) On the silicon substrate 1, grow the first nitride film 3, that is, the silicon nitride layer, by low-pressure chemical vapor deposition or plasma-enhanced chemical vapor deposition, and the thickness of the first nitride film 3 is 500-3000 angstroms (as shown in Figure 5);

The first nitride film 3 in this step can be used as a protective layer on the top of the trench in subsequent processes;

2) performing trench etching on the silicon substrate 1;

3) On the sidewall and bottom of the trench, grow a dielectric layer 4 (i.e., silicon oxide) with a thickness of 500-3000 angstroms by means of thermal oxygen or low-pressure chemical vapor deposition;

4) On the dielectric layer 4, a first layer of polysilicon 5 is grown by low-pressure chemical vapor deposition, and the thickness of the first layer of polysilicon 5 is sufficient to fill the inside of the trench;

5) Perform the first step of reverse etching on the first layer of polysilicon 5 until it is etched to the silicon surface;

6) Perform photolithography and second step reverse etching on the first layer of polysilicon 5, and remove the trench sidewall dielectric layer 4 above the first layer of polysilicon 5 by wet etching (as shown in Figure 6);

Wherein, the first layer of polysilicon 5 is photolithographically protected to protect the position where the source polysilicon needs to be connected, and the remaining first layer of polysilicon is subjected to the second step of polysilicon reverse etching until it is etched to the desired depth below the silicon surface ( specific depth);

The first nitride film 3 in FIG. 6 serves as a surface protection layer for the subsequent thermal oxygen dielectric layer 7;

7) By low-pressure chemical vapor deposition or plasma-enhanced chemical vapor deposition, deposit a second nitride film (that is, silicon nitride film) on the bottom and side walls of the trench and the surface of the silicon substrate 1 (the surface of the first nitride film 3 ). ) 6 (as shown in FIG. 7 ), dry etching removes the second nitride film 6 at the bottom of the trench, exposing the first layer of polysilicon 5 (as shown in FIG. 8 ); wherein, the second nitride film 6 The thickness is 500-3000 Angstroms;

8) On the first layer of polysilicon 5, grow a thermal oxygen dielectric layer 7 (as shown in FIG. 9 ), that is, a silicon oxide layer, with a thickness of 500-3000 angstroms by means of thermal oxygen (temperature higher than 950°C);

9) Wet etching, removing the second nitride film 6 on the side wall of the trench, and the first nitride film 3 and the second nitride film 6 on the surface of the silicon substrate 1 (as shown in FIG. 10 ), leaving A thermal oxygen dielectric layer 7 exists on the first layer of polysilicon 5 at the bottom of the trench, thereby forming a thermal oxygen dielectric layer between two layers of polysilicon in the trench type double-layer gate MOS structure;

10) According to the existing process, use thermal oxidation to grow the gate oxide layer;

11) According to the existing process, the second layer of polysilicon deposition and reverse etching is carried out, that is, the second layer of polysilicon is grown by low-pressure chemical vapor deposition, and etched to the silicon surface;

12) According to the existing process, form the base (BODY) and source (Source) by ion implantation;

13) According to the existing process, form the contact hole, metal and passivation layer, that is, use the mask plate to etch to form the contact hole, deposit the metal layer and etch to form the contact electrode, deposit and etch to form the passivation layer.

According to the above steps, after the photolithography of the first layer of polysilicon 5 and the second step of reverse etching, it is necessary to grow a second layer of nitride film 6 and use dry etching to anisotropic features, so that the bottom of the trench is nitrided. The silicon is etched clean to expose the underlying first layer of polysilicon 5, while the sidewall silicon nitride protection layer remains (that is, the sidewall protection layer of the second nitride film 6) and is formed together with the silicon nitride on the surface of the silicon substrate 1. Forming a protective layer, that is, the sidewall of the trench is connected with the first nitride film 3 previously grown on the surface of the silicon substrate 1 to form a protective layer, so that the subsequent thermal oxygen dielectric layer 7 is only grown on the first layer of polysilicon 5; then , by removing the trench sidewalls and the nitride film on the surface of the silicon substrate 1, the thermal oxygen isolation layer (that is, the thermal oxygen dielectric layer) is formed, that is, the trench type double-layer gate MOS structure is formed by using silicon nitride as a shielding layer The thermal oxygen dielectric layer between the two layers of polysilicon. Therefore, the present invention can solve the problem that the thickness of the dielectric layer between two layers of polysilicon is difficult to control, and the trench type double-layer gate MOS that is finally prepared has high performance stability; at the same time, the present invention can also avoid The strong electric field generated at both ends weakens the gate-source breakdown voltage.

Claims (7)

1. a method for forming a thermal oxygen dielectric layer between polysilicon in trench type double-layer gate MOS, is characterized in that, comprises steps: 1) growing a first nitride film on a silicon substrate; 2) performing trench etching on the silicon substrate; 3) growing a dielectric layer in the trench; 4) On the dielectric layer, grow the first layer of polysilicon; 5) Carry out the first step of reverse etching on the first layer of polysilicon until it is etched to the silicon surface; 6) Perform photolithography on the first layer of polysilicon and the second step of reverse etching, and remove the trench sidewall dielectric layer above the first layer of polysilicon, in which photolithography is performed on the first layer of polysilicon to protect the source that needs to be connected The position of polysilicon, the remaining polysilicon position of the first layer is subjected to the second step of polysilicon reverse etching until it is etched to the required depth below the silicon surface; 7) After depositing a second nitride film on the bottom and side walls of the trench and on the surface of the silicon substrate, etch and remove the second nitride film at the bottom of the trench to expose the first layer of polysilicon; 8) On the first layer of polysilicon, grow a thermal oxygen dielectric layer; 9) removing the second nitride film on the sidewall of the trench and the first and second nitride films on the surface of the silicon substrate; 10) Gate oxide layer growth; 11) The second layer of polysilicon deposition and reverse etching; 12) Form the base and source; 13) Form contact holes, metal and passivation layers. 2. The method according to claim 1, characterized in that: in said step 1), the method for growing the first nitride film comprises: low pressure chemical vapor deposition or plasma enhanced chemical vapor deposition; the first nitride film The material includes: silicon nitride; the thickness of the first nitride film is 500-3000 Angstroms. 3. The method according to claim 1, characterized in that: in said step 3), the dielectric layer is an oxide film with a thickness of 500 to 3000 angstroms; the growth method of the dielectric layer includes: thermal oxygen or low pressure chemical vapor deposition . 4. The method according to claim 1, characterized in that: in step 4), the method for growing the first layer of polysilicon comprises: low pressure chemical vapor deposition; the thickness of the first layer of polysilicon is sufficient to fill the inside of the trench. 5. The method according to claim 1, characterized in that: in the step 7), the second nitride film deposition method comprises: low pressure chemical vapor deposition or plasma enhanced chemical vapor deposition; The material of the second nitride film includes: silicon nitride; the thickness of the second nitride film is 500-3000 angstroms; The etching method is dry etching. 6. The method according to claim 1, characterized in that: in said step 8), the method for growing the thermal oxygen dielectric layer is to grow the thermal oxygen dielectric layer by the thermal oxygen mode; wherein, the process temperature in the thermal oxygen mode is higher than 950°C; The thickness of the thermal oxygen medium layer is 500-3000 angstroms. 7. The method according to claim 1, characterized in that: in the step 9), the removal method comprises: wet etching.