JPH05160125A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make the surface of an insulating film as flat as possible by forming the P-containing hot-melt insulating film so that the P density on the surface may be lower than that inside the film and by allowing the insulating film to reflow and then by etching back the insulating film to the specified thickness. CONSTITUTION:A film 6 is formed which is formed of high-density P-containing PSG and which is 300nm in thickness. After that, the film is allowed to reflow at 900 deg.C for 60 minutes in N2 and just then the surface region of a BPSG film, where the P density is relatively low and the B density is relatively high, flows. As a result, a region 5 which has a relatively low P density and relatively high B density is formed thick in a recessed part of the BPSG film 4. Nextly, the reflowed insulating films 6 and 4 are etched using deluted HF or deluted NH4F. Since an etch rate is high when the P density is high and the B density is low, a protruding part is etched more rapidly than the recessed part. Consequently, the insulating film 4 having as flat a surface as possible is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art Generally, when manufacturing a semiconductor device, an insulating film is coated on the element to form a metal wiring after the element such as a MOS transistor is formed. As the insulating film, SiO ₂ not doped with impurities, and BPSG (borophosphosilicate glass) or PSG doped with P or B
Although (phosphosilicate glass) is used as its material, the surface of these insulating films has irregularities due to the steep step shape of the lower layer. These irregularities cause uneven thickness of photoresist and uneven resolution during exposure due to lithography for fine contact openings and metal wiring that will be performed in the next manufacturing process, and the accuracy of the resist pattern will be increased. Becomes worse. Further, there is a problem that the metal wiring is not smoothly performed due to the unevenness of the surface of the insulating film.

Therefore, a flattening technique is required for smooth metal wiring. Conventional flattening technology
A reflow technique is used in which a PSG or BPSG film containing P or B at a high concentration is exposed to a high temperature atmosphere to increase the fluidity of the surface of the film for planarization. When this reflow technique is used, the surface of the insulating film becomes flat to some extent with respect to the steep steps of the underlayer, but it is not completely flat. It is possible to use a BPSG insulating film having a higher concentration of P and B in order to improve the flatness, but in this case, there is a problem that the compound of P and B is deposited on the surface. In order to solve this problem, a PSG insulating film containing P at a high concentration is coated on the BPSG insulating film and reflowed. However, even when the P and B concentrations are further increased, the surface of the insulating film is flattened to some extent by reflowing, but there is a problem that the surface is not flattened because the time spent for the reflowing process is limited. .. Further, it is becoming more and more necessary to flatten the surface of the insulating film in order to achieve high integration of elements and multilayer wiring. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a semiconductor device in which the surface of an insulating film can be made as flat as possible.

[0004]

According to a method of manufacturing a semiconductor device according to the present invention, a heat-fluidic insulating film containing P is formed on a semiconductor substrate on which an element is formed, and a P concentration at the surface portion is within the film. The method is characterized by including a step of forming the insulating film to have a lower concentration than the P concentration, and a step of reflowing the insulating film and then etching back until the insulating film has a predetermined film thickness.

[0005]

According to the manufacturing method of the present invention having such a structure, the heat-fluidic insulating film containing P is formed on the semiconductor substrate on which the element is formed. The surface portion of this insulating film has a lower P concentration than the inside, and the surface portion flows due to the reflow in the next step, the portion having a relatively low P concentration is relatively thick in the concave portion, and the P concentration in the convex portion is compared. The lower part is thinly formed. Since the etching rate of the portion having a low P concentration is slower than that of the portion having a high P concentration, by etching the insulating film after the reflow, the convex portions are swiftly etched and the concave portions are slowly etched to obtain an insulating film as flat as possible. You can

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a manufacturing process of a semiconductor device manufactured by a manufacturing method according to the present invention. First, silicon substrate 1
A polysilicon film 2 having a film thickness of 800 nm is formed thereon by using, for example, a hot wall type CVD method (see FIG. 1A). At this time, the gas source is SiH ₄ and is formed under the condition of 600 ° C. Then, the polysilicon film 2 is patterned. Then, a steep step is formed (see FIG. 1A). After that, an insulating film 3 made of, for example, SiO ₂ and having a film thickness of 100 nm is formed by using the hot wall type CVD method (see FIG. 1A). At this time, TEOS (tetraethoxy orthosilicate (Si (OC ₂ H ₅ ) ₄ )), which has good coverage, is used as a gas source, and the film is formed at about 700 ° C.

Next, TEOS, TMB (trimethoxyboron (B (OCH ₃ ) ₃ )), PH ₃ and O are added to the reactive gas.
Substrate 1 by the hot wall type LPCVD method using ₂
A film 24 made of BPSG and having a film thickness of 500 nm is formed on the entire surface (see FIG. 1B). At this time, TEOS, TMB
Is vaporized using a liquid material vaporization control device, the flow rate is adjusted directly by a flow rate control means (not shown), and is introduced into the reaction furnace through a pipe heated by a heater. As film forming conditions, the furnace temperature is about 600 ° C. and the furnace pressure is 0.8.
TEOS is 200 sccm (2 ° C at 20 ° C and 1 atm)
00 cc / min), TMB 0 to 50 sccm, 10% PH ₃ diluted with He 0 to 1000 sccm, O ₂ 0 to 1
Approximately 000scm is introduced into the reaction furnace, for example, as shown in FIG.
As shown in (a) and (b), PH ₃ ,
The flow rates of O ₂ and TMB are changed. That is, PH ₃ , O
₂ increases the flow rate from the start of film formation to the middle of film formation,
After that, the flow rate is decreased so that the flow rate is almost the same as the flow rate at the start of film formation immediately before the end of film formation. Further, the flow rate of TMB is decreased from the start of film formation to the middle of film formation, and then increased so that the flow rate immediately before the end of film formation becomes substantially the same as the flow rate at the start of film formation. Then, the concentrations of P and B in the BPSG film from the bottom surface to the surface of the BPSG film 4 change as shown in FIG. That is, the P concentration near the surface of the BPSG film 4 is lower than the P concentration inside the film 4, and the B concentration near the surface 4a of the film 4 is higher than the B concentration inside the film 4. Get higher The surface of the BPSG film 4 has irregularities according to the steep steps.

Next, in order to prevent the precipitation of P and B compounds on the surface due to the heat treatment performed in the next step, TEOS and PH are added.
₃ , using a gas source of O ₂ , a high concentration of P, for example, 5
A film 6 made of PSG containing P of about 10 ²¹ atm / cm ^{3 and} having a film thickness of 300 nm is formed (see FIG. 1B).
Then, reflow is performed at 900 ° C. for 60 minutes in N ₂ . Then, the surface region of the BPSG film 4, that is, the region having a relatively low P concentration and a relatively high B concentration flows, and as a result, the P concentration is relatively low and the B concentration is relatively high in the concave portion of the BPSG film 4. The region 5 is formed thick (see FIG. 1C).

Next, the reflowed insulating films 6 and 4 are etched with diluted HF or diluted NH ₄ F. Then, since the higher the P concentration and the lower the B concentration, the faster the etching rate,
As the convex portion is etched earlier than the concave portion,
It is possible to obtain the insulating film 4 having a surface as flat as possible as shown in (d). In addition, as shown in FIG.
Even if the B concentration in the PSG film 4 is kept constant and the P concentration in the vicinity of the surface is made relatively lower than the P concentration inside the film 4, the same effect as described above can be obtained. Also, B
Instead of the PSG film 4, it is possible to obtain the same effect as in the above case by using a PSG film which is not doped with B and whose P concentration becomes low near the surface as shown in FIG.
At this time, it is necessary to raise the reflow temperature.

[0010]

As described above, according to the present invention, an insulating film as flat as possible can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor device manufactured by the present invention.

FIG. 2 is a graph showing a concentration distribution in the depth direction of an insulating film according to the present invention.

FIG. 3 is a graph showing gas flow rate characteristics used for forming an insulating film according to the present invention.

FIG. 4 is a graph showing the concentration distribution in the depth direction of the BPSG film according to the present invention.

FIG. 5 is a graph showing the concentration distribution in the depth direction of the insulating film according to the present invention.

[Explanation of symbols]

1 Silicon substrate 2 Polysilicon film 3 SiO ₂ film 4 BPSG film 5 BPSG film with high B concentration and low P concentration 6 PSG film

Claims (1)

[Claims] 1. A step of forming a heat-fluidic insulating film containing phosphorus on a semiconductor substrate on which an element is formed so that the phosphorus concentration at the surface portion is lower than the phosphorus concentration inside the film. After the reflow of the insulating film, a step of etching back until the insulating film has a predetermined film thickness is provided, and a method of manufacturing a semiconductor device.