Double terminal detecting method for silicon nitride thickness stability in STI CMP technology

Abstract

Shallow tank insulating (STI) technique is a rising field region insulating technique coming into being with the development of deep submicron IC technique. It has the characters of small characteristic size, high integrity and good insulating effect. But, at the same time there are the problems of complex process and control difficulty, where the more prominent problem is the problems of Dishing and Erosion in CMP process, which has an effect on the important index 'Overhead' of STI, and in order to control 'Overhead' in a certain range, it needs stable SiN thickness after CMP process. The invention adopts a control method using two-step terminal detecting system, solving the problems of mis-detection and maximum time automatic termination caused by grinding speed and film thickness change between batches when using an one-step terminal detecting system only.

Description

technical field [0001] The invention belongs to the technical field of integrated circuit technology, and in particular relates to a method for controlling the thickness stability of a silicon nitride residual film after chemical mechanical polishing in a shallow groove isolation process. Background technique [0002] In the process of semiconductor integrated circuits, the traditional isolation technology is self-aligned field oxidation isolation technology, that is, the active area is covered with a hard mask, the substrate silicon in the field area is exposed, and then the isolation area is oxidized by thermal oxidation. silicon. This method is simple, highly productive, and the production process used is mature. The disadvantage is that a 'bird's beak' area will be formed at the boundary of the active area, such as figure 1 Shown becomes a bottleneck in the development of deep submicron technology to increase the degree of integration. [0003] In practice, it is diffi...

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Problems solved by technology

[0004] STI silicon oxide over-grinding (Disching) problem: Due to the influence of pattern density, the grinding rate of CMP process is different in different pattern areas. In the area with higher pattern density in the active area, the grinding speed lower

[0012] However, affected by the actual situation in production, the end point detection system may have the following problems: 1. False detection, that is, the normal detection waveform does not arrive during the process, and the end point detection system is triggered by detecting similar waveforms. Commonly used The method is to fix the grinding in the previous step to grind through the thickness that may have similar waveforms; 2. In order to prevent missed detection due to accidental factors, set the maximum detection time in the end point detection system to automatically terminate the process, but sometimes due to grinding The rate is low and the detection point is not reached within the maximum detection time

[0014] 1. The CMP machine is affected by factors such as working hours, consumables replacement and machine conditions, resulting in instability of the grinding rate between batches, which is the main reason for the occurrence of false detection points and the exhaustion of the maximum process time

However, if the process control specifications are tightened, the process cost will increase;

[0015] 2. In a batch, due to continuous grinding of silicon wafers, the grinding rate is unstable due to changes in the condition of the grinding pad, because the range of change is small and can be controlled by the end point detection section;

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